Carb sync does matter above idle speeds!

[BonS]

I've fielded quite a few questions about carburetor synchronization and its effect on performance. Our carburetors are a constant velocity (CV) type and these perform differently than the older carbs with just a slider or butterfly controlling everything. I have read opinions that say synchronization is only applicable at idle with CV carburetors so I wanted to see this for myself.

Previously I mentioned a test that I did in my driveway. I synched my carbs and then deliberately set one of the carbs 10 counts higher than the others. I then ran the engine rpm up to about 3,500 RPM. In that test the carburetor that was 10 points higher at idle stayed 10 points higher than the others at all RPM's.

I know that things are different when an engine is under load versus simply running up the RPM's so I strapped a Digi Sync onto my Interstate gas tank today and went for a ride. I had plans to video tape the ride but it turned out not to not really be necessary.

I once again set one of my carbs out of sync by 10 counts and strapped the Digi Sync to my gas tank. One of the nice things about the Digi Sync is that the backlit LCD display is more visible in sunlight than otherwise.

The test results show that carburetor synchronization matters most at idle as that's where I had set the 10 point difference. At a steady 40 mph the difference shrinks to about 6-7 points. At 50-55 mph the difference is about 4-5 points. At 70 mph the cylinders are running about the same - except - for when I back off the throttle a tiny little and the 10 point difference comes right back.

In summary, at high loads and 70+ mph sync doesn't matter much but when cruising at at 60 mph and slower there remains a difference in engine performance due to carburetor linkage synchronization settings. A good way to look at it is that you have 40%-60% of whatever sync error you have at idle affecting your engine performance when cruising at 40 to 60 mph. WOT performance with a CV carburetor is not affected by synchronization.

BonS

[Ricky-D]

If there is a large difference in the sync. it will affect the upper ranges a bit

but the sync is only effective for the idle characteristics.

***

[BonS]

If there is a large difference in the sync. it will affect the upper ranges a bit

but the sync is only effective for the idle characteristics.

***

Hi Ricky, did you read what I said in this post? Synching affects our Valkyrie engine's performance from idle to around 70 mph. Only in diminishing amounts. The sync settings aren't like an idle screw setting that turns off as soon as we crack the throttle. The vacuum levels in the cylinders tell the story quiet clearly. If the vacuum reads high then that cylinder isn't contributing to the power output of the engine like the other cylinders. If a cylinders vacuum reading is low then it's providing more power than the other cylinders for any given load.

[Patrick]

I  agree.
But, what RPM did you sync at ?  I'm assuming idle speed or a slightly high idle speed if I read your post correctly.



Years ago there were some that insisted this should be done at high engine speed [and that they did it at those engine speeds] to which I disagreed.

So, I'm interested.

[BonS]

I synch at 900 rpm. I've read about doing it at high-idle speed but they went on to say that it's just to keep the engine from dying while turning the sync screws. My experience has been that some of the sync screws will dramatically lower the rpm while the screwdriver is pressed against them while turning and if the idle is set at a minimum i suppose that the engine can die. Our Valks are darn resistant to dying at any idle.

[Patrick]

I synch at 900 rpm. I've read about doing it at high-idle speed but they went on to say that it's just to keep the engine from dying while turning the sync screws. My experience has been that some of the sync screws will dramatically lower the rpm while the screwdriver is pressed against them while turning and if the idle is set at a minimum i suppose that the engine can die. Our Valks are darn resistant to dying at any idle.

I experience the same, they are sensitive critters.  I blip the throttle quite often and go over them several times to make sure they stay the same before I button them up.

[sandy]

How does the DigiSync measure RPMs?

[BonS]

It looks at the vacuum intakes pulses and times the intervals. Each cylinder is timed separately and then they're averaged together. It also looks for outliers in the data and throws them out. Finally just a touch of smoothing is applied. All this to remove jitter and still be responsive and precise as possible.

[Rio Wil]

I haven't paid much attention to this tool......but what do the numbers represent (192-193)......mm of mercury or ????

Question is, does a difference of "10" or "20" at moderate speed (or any speed) make any significant difference in the amount of fuel drawn into the air stream......enough to make a discernible difference in performance? Wonder what a dyno would say?

[pancho]

I have noticed this, and I will check into it further in the future. When I am making power (getting into the throttle) with the carbs closely synced, there will be very little or no vibration at any RPM noticeable in the mirrors, when one or more carbs are out of sync,, there is,, the further out, the wider the RPM band where this is noticeable..   I know this is not a measurable indicator, but I have used the mirror vibration as a notice that I need to connect up the manometer and do some adjusting. 

[BonS]

I haven't paid much attention to this tool......but what do the numbers represent (192-193)......mm of mercury or ????

Question is, does a difference of "10" or "20" at moderate speed (or any speed) make any significant difference in the amount of fuel drawn into the air stream......enough to make a discernible difference in performance? Wonder what a dyno would say?

The number are approximately 1/10" of mercury. But drawing a simple analogy between a mercury column or gauge and the peak-vacuum technology used here is not appropriate. You can take a look here at a few annotated oscilloscope graphs. It's my best effort to show the difference. http://thedigisync.com/why-the-digi-sync-is-simply-better.html

A dyno really doesn't fit into this discussion as dyno's are all about WOT and this is not the where the payback of having properly balanced carburetor linkage is realized . With CV carbs and running at WOT it's not much about the low and mid range carburetor performance. At idle and cruise speeds (apparently <=60 mph on an Interstate according to my test run today) is where proper synchronization pays off.

Proper balance means that all cylinders are pulling their load. A lazy cylinder that not running at the same power output level does several things: It means that the other cylinders have to put out a disproportionate share of power to make the necessary horsepower to push you down the road. The lazy cylinder runs cooler and leaner (so I'm told). Some additional roughness and uneven idle as can be seen here in a video that I took before synching and after. The video was taken parked at idle. A close friends Valkyrie was badly out of sync and after we worked on it he reported much better driveability around town, standing starts, and a smoother running engine overall. He's very pleased. As he rides every day he was really, really  surprised.

In short, properly synched carburetors is mostly felt as a crispness in response at part throttle as well as smoothness at moderate cruising speeds and idle which is a range where we spend a most of our riding time.


http://youtu.be/ZsvRixLb7Y0

[Rio Wil]

On a bike that is "badly out of sync", what would be typical variation between cycliners.....+- 5 points....+- 50 points?

[Bigwolf]

This thread is very interesting to me.  I built a carb syncing tool to sync my carbs and usually sync them at 3k rpm.  Reason, I spend most of my run time around 3k.  This has led to a big disagreement  with a friend of mine who insists they must be synced at idle.

My home made sync tool is extremely sensitive.  10.88 inch difference on my sync tool is equal to 1 inches difference of mercury.  If I set the carbs equal at 900 rpm, then bring the rpm up to 3k,  the carbs will spread out about 1 inch (0.092 in of HG).  If I set the carbs equal at 3k, and then let the engine back to idle, the carbs spread out about 1 inch (0.092 in of HG) in the reverse direction.  Either way, cyls 1 and 2 remain equal, 3 and 4 remain equal, and 5 and 6 remain equal.  That is with the stock headers.  There was no such difference ever when running the cobra 6x6.

I believe carb sync is important at most normal riding speeds.  But that may just be me.  Few people would bother to sync their carbs as closely as I do mine.

BTW, great sync tool you have there BonS

Bigwolf

[BonS]

This thread is very interesting to me.  I built a carb syncing tool to sync my carbs and usually sync them at 3k rpm.  Reason, I spend most of my run time around 3k.  This has led to a big disagreement  with a friend of mine who insists they must be synced at idle.

My home made sync tool is extremely sensitive.  10.88 inch difference on my sync tool is equal to 1 inches difference of mercury.  If I set the carbs equal at 900 rpm, then bring the rpm up to 3k,  the carbs will spread out about 1 inch (0.092 in of HG).  If I set the carbs equal at 3k, and then let the engine back to idle, the carbs spread out about 1 inch (0.092 in of HG) in the reverse direction.  Either way, cyls 1 and 2 remain equal, 3 and 4 remain equal, and 5 and 6 remain equal.  That is with the stock headers.  There was no such difference ever when running the cobra 6x6.

I believe carb sync is important at most normal riding speeds.  But that may just be me.  Few people would bother to sync their carbs as closely as I do mine.

BTW, great sync tool you have there BonS

Bigwolf

I'd say that the reason you're seeing a difference at idle versus 3k rpm is not that the carbs are actually different in balance at those speeds. I strongly recommend that you also take a look at my annotated oscilloscope graphs that I referenced earlier. The issue is that fluid columns have mass, viscosity, and inertia and react sluggishly to the vacuum pulses. In addition they are influenced by the vacuum remaining when the intake valve is actually closed and the incoming air is equalizing the pressure differential. It's for that reason that liquid columns (and gauges with their snubbers) read a kind of average vacuum instead of the vacuum that the cylinder "sees" while the intake valve is open. Capturing the peak vacuum that is present while the intake valve is open is the true measure of the performance of a carburetor/intake manifold.

Based upon my ride today with my Digi Sync running, the cylinders that were balanced at idle were running with exactly the same synchronization at 3k rpm. There was no difference whatsoever. The only difference was with the one cylinder that I deliberately dialed out of balance from the others. I set it to 10 counts higher than the rest, not because there's anything meaningful about the 10 counts, but it was simply easier to see the changes as I was riding (and the results translate into percentages easier as well - it's the engineer in me!).

[BonS]

On a bike that is "badly out of sync", what would be typical variation between cylinders.....+- 5 points....+- 50 points?

I don't have an immense amount of experience with how bad bad is or how bad it can be. But I do know that my friends engine was out of sync, for whatever reason, was symmetric right/left. The three cylinders on one side were all higher than the three on the other side. The difference was around 8-10 counts as I recall. But that's all three cylinders on one side that were about 10 counts off and it ran noticeably rough.

[Bigwolf]

I'd say that the reason you're seeing a difference at idle versus 3k rpm is not that the carbs are actually different in balance at those speeds.

That is true.  The difference is created by the change in exhaust scavenging at the different rpm range.  The OEM headers have different lengths for cyls 1&2, 3&4, and 5&6.  That causes a different exhaust scavenging effect IE: optimum exhaust scavenging rpm for each set of 2 cyls.  Many auto manufacturers do this intentionally because it flattens out the power peak of the engine.  The cobra 6x6 is too large in diameter to scavenge the exhaust on these small engines so that is why the carb sync does not change when running the cobras. 

Note that even with the OEM exhaust the difference is so small.  Less than 1/10 inch of mercury.  2 cyls gain by 0.046 inch mercury and 2 cyls drop by 0.046 inch mercury.
Bigwolf

[pancho]

BonS, Could you tell me what devices are being used for transducers in your tool?? I want to take a look at the spec sheet just to get a better idea of the performance that can be expected,,, specifically, I wonder just how closely the curves of six of these devices can be expected to match each other.  Looking for the tolerances.

Quite an endeavor with all the required calibration, counting and averaging code, engineering, assembly, packaging and shipping.     Nice job bringing it all together,, do you have or work for an engineering outfit?

[DK]

Bon,

DigiSync is the first device I've used which gives precise values for each carb over a wide rpm range.  Over the years, I've  synced SU's, Webers and Holleys, with air flow meters, stethoscopes and vacuum gauges and no matter the carb or the method it amounted to an educated guess  based only on no load rpm most always at idle rpm only.

From all this, the way I have to come to understand it, sync should be done at idle. My reason being is that as you open the throttle butterfly or whatever control any particular carb uses, you are lessening obstruction of airflow to the engine. With the throttle fully open, the air flow regulator plays no role in the function of the carb. At full open, Performance is determined only by the fixed elements of the carb - venturis, jet settings, flow characteristics, engine condition, and so on. As the butterfly opens more and more, it matters less and less how much one butterfly is a little less open or closed than others with the engine running at high rpm.  A slight variance is of no consequence.

However, at idle, a slight variance is of greater consequence which declines in consequence as rpm increases. At lower engine rpm, a small variance in sync of any one carb is responsible for greater part of the total output and behavior of the engine as a whole.

In my mind, this explanation is consistent with your latest DigiSync experiment.

All of the above brings me to another question related to this: 

Now that I know all six carbs are precisely synced, I'm still getting a +\- 20 degree difference in header temperature at idle even after riding the Valk long enough to clear itself out and be thoroughly warmed up.

Plugs <1000 miles - NGK Iridium; 15,000 Total Mileage, Valve never reset; .38  low jets.

Is this due to improperly set pilot screws?

What else could cause the variance?

.38 Jets?

Dan

[BonS]

BonS, Could you tell me what devices are being used for transducers in your tool?? I want to take a look at the spec sheet just to get a better idea of the performance that can be expected,,, specifically, I wonder just how closely the curves of six of these devices can be expected to match each other.  Looking for the tolerances.

Quite an endeavor with all the required calibration, counting and averaging code, engineering, assembly, packaging and shipping.     Nice job bringing it all together,, do you have or work for an engineering outfit?

The transducer is a Freescale MPXV6115VC6U. Its absolute accuracy is 1.5% and that's before gain and offset calibration is executed in software. Linearity is not accounted for. I have a test rig that pulls the same vacuum on all six channels simultaneously and the final calibrated output is +/- 1 count out of 200 so relative accuracy is 0.5% and a lot of that is rounding error for whole digits. And it's relative accuracy that is the most important result of calibration.

Thanks for the compliment. I'm an electrical engineer and have been practicing professionally for 35+ years. My day job is for Fike Corporation, as director of research, and we design and manufacture industrial life-safety products such as pressure relief, explosion protection and isolation equipment, fire suppression and fire alarm systems. I've also run my own business for the past 20 years but that's a whole other story!

[BonS]

Bon,

DigiSync is the first device I've used which gives precise values for each carb over a wide rpm range.  Over the years, I've  synced SU's, Webers and Holleys, with air flow meters, stethoscopes and vacuum gauges and no matter the carb or the method it amounted to an educated guess  based only on no load rpm most always at idle rpm only.

From all this, the way I have to come to understand it, sync should be done at idle. My reason being is that as you open the throttle butterfly or whatever control any particular carb uses, you are lessening obstruction of airflow to the engine. With the throttle fully open, the air flow regulator plays no role in the function of the carb. At full open, Performance is determined only by the fixed elements of the carb - venturis, jet settings, flow characteristics, engine condition, and so on. As the butterfly opens more and more, it matters less and less how much one butterfly is a little less open or closed than others with the engine running at high rpm.  A slight variance is of no consequence.

However, at idle, a slight variance is of greater consequence which declines in consequence as rpm increases. At lower engine rpm, a small variance in sync of any one carb is responsible for greater part of the total output and behavior of the engine as a whole.

In my mind, this explanation is consistent with your latest DigiSync experiment.

All of the above brings me to another question related to this: 

Now that I know all six carbs are precisely synced, I'm still getting a +\- 20 degree difference in header temperature at idle even after riding the Valk long enough to clear itself out and be thoroughly warmed up.

Plugs <1000 miles - NGK Iridium; 15,000 Total Mileage, Valve never reset; .38  low jets.

Is this due to improperly set pilot screws?

What else could cause the variance?

.38 Jets?

Dan

How are you getting your header temperature readings; IR or thermocouple? I like using a naked thermocouple that's been wetted with a drop of oil for the most accurate readings. IR devices are subject to variances due to surface emissivity that leads to readout errors or uncertainty. Is there any order such as front-to-back that the temperatures vary?

[pancho]

BonS, Could you tell me what devices are being used for transducers in your tool?? I want to take a look at the spec sheet just to get a better idea of the performance that can be expected,,, specifically, I wonder just how closely the curves of six of these devices can be expected to match each other.  Looking for the tolerances.

Quite an endeavor with all the required calibration, counting and averaging code, engineering, assembly, packaging and shipping.     Nice job bringing it all together,, do you have or work for an engineering outfit?

The transducer is a Freescale MPXV6115VC6U. Its absolute accuracy is 1.5% and that's before gain and offset calibration is executed in software. Linearity is not accounted for. I have a test rig that pulls the same vacuum on all six channels simultaneously and the final calibrated output is +/- 1 count out of 200 so relative accuracy is 0.5% and a lot of that is rounding error for whole digits. And it's relative accuracy that is the most important result of calibration.

Thanks for the compliment. I'm an electrical engineer and have been practicing professionally for 35+ years. My day job is for Fike Corporation, as director of research, and we design and manufacture industrial life-safety products such as pressure relief, explosion protection and isolation equipment, fire suppression and fire alarm systems. I've also run my own business for the past 20 years but that's a whole other story!

Appreciate you generously giving the information BonS,, I think it was a little like asking someone what color and size their underwear is, but I'll get a kick out of checking the devices specs and maybe doing a couple of calculations.

[DK]

Bon,

I'm using IR. Never heard of thermocouple & oil.

I've got really high gas consumption even for .38's and can't figure what is causing it. Improperly set pilot screws are now my favorite suspect.

I see some black smoke out the exhausts, mainly from the left side when revving the engine up from idle.

Any suggestions? I've got new plugs, new air filter, and perfectly balanced carbs. I'm about out of things to blame it on.  I reset the pilot screws, I think properly, and thought I had solved the problem until putting the trike on the road.

This is the procedure I followed resetting the pilot screws: 

http://www.valkyrieforum.com/bbs/index.php/topic,78142.msg766010.html#msg766010

I'm not looking forward to stopping at every third gas station between Little Rock and Spearfish.

Any help on this would be appreciated.

Dan

[BonS]

Two thoughts: Have you installed new float needles? The old ones get soft and can lead to a higher bowl fuel level that in turn leads to a richer mixture. The best source seems to be K&L from Amazon.
http://www.amazon.com/Supply-Float-Needle-6pk-18-8955/dp/B001KOD732/ref=au_as_r?_encoding=UTF8&Make=Honda|59&Model=GL1500CF%20Valkyrie%20Interstate|17894&Year=1999|1999&ie=UTF8&n=15684181&s=automotive&vehicleId=7&vehicleType=motorcycle

The second possibility, based upon the smoke could be your valve stem seals. You can do a compression check to eliminate rings but in my recent experience our valve seals are quite old and they have hardened. It certainly fixed my friends Valk since we replaced his, and balanced his carbs the smoking has stopped, period. I've followed him a lot: no smoke. Oil vapor in the fuel mixture can't be good for mileage either.

[Ricky-D]

Those #38 idle jets are the main culprit for your poor gas mileage and if you did that you

may have changed the jet needle which, if you have done that, you should change them back to stock.

The Valkyrie engine normally runs rich to begin with and adding more gas does nothing but

carbon up the engine and reduce gas mileage.

***

[BonS]

By the way DK, how bad is your gas mileage? My Interstate sometimes gets 38-42 highway at speeds around 60'ish . Above 70 I'll see 32 or so. I've gotten as bad as 22-24 mpg against a cross/head wind, with trailer, two up @ 70-75 mph.

[DK]

Bon, Ricky D.,

I've never exceeded 30 mpg at legal highway speeds under ideal conditions. The mileage falls as speed increases, on curves & hills & headwinds all the way down to 18 - 19 when really flogged in twisties. Followers have commented on smoke from my tailpipes; when asked, they say black; gearhead followers say no blue or oil smell or belching off-throttle.

I haven't been into the carbs. The .38's were installed by the PO done by a Dallas area shop. I have the invoice.

All I have done with the carbs is to sync them and adjust the pilot screws using the DigiSync. The trike now runs great without any low-speed unevenness or doing the neat sounding " hit & miss " in first gear with a slack throttle.

Bon, as I told you when we talked, I intend to install .35's and new needle valves. However, being new to Valk carbs, I'm hesitant to do this so near to my impending trip to Spearfish.

I don't think it is intake valve seals. The Valk has only 16,000 miles; I've driven it 6,000 miles in the year I've had it; I changed the oil when I purchased it & in the 6K miles it has burned no oil; I just changed the plugs & the old ones showed no indication of oil fouling, ( pic. attached ); all plugs seem ok except 1 & 3 which seem to be the really rich ones ( incidentally, # 1 was bad out when I synced ); the smoke from the exhaust is definitely black, not blue and does not have oil smell, just gas; the tailpipe soot is not oiley; and finally, it doesn't belch blue or black smoke when throttle is snapped shut from high rpm.

I would appreciate you guys telling me which parts I should have on hand when in the way of gaskets, seals, etc. when I replace the .38's and the needle valves & also the preferable vendors from whom to purchase same.

I also intend to do a desmog in conjunction with the above and it seems that Red Eye Technical Services is most popular among the forum members.

Also, is there anything else to do while in this far such as the vacuum hose to #6 and the intake O Rings?

I probably will replace the coolant hoses also while in there.

Is there anything else I should consider doing?

Dan
pic attached

I either have the only 12 cylinder Valk in existence or I'm not very good at posting pictures. I'm stopping while I'm ahead.

][URL=http://s277.photobucket.com/user/914911928/media/Mobile%20Uploads/2015-05/F1693E85-4484-4654-A602-8FCE41C2F0DF.jpg.html]


][URL=http://s277.photobucket.com/user/914911928/media/Mobile%20Uploads/2015-05/F78040E4-F621-4499-883A-B98C61E3A07D.jpg.html][/url][/url]

[indybobm]

Bon, is there any interaction between carb sync and adjusting the pilot screws. Lets say that you sync the carbs using the Digi-Sync and then adjust the pilot screws using the Tach function of the Digi-Sync.   Can the carbs be slightly out of sync at that point? If so, which do you do first?

[BonS]

Bon, Ricky D.,

I've never exceeded 30 mpg at legal highway speeds under ideal conditions. The mileage falls as speed increases, on curves & hills & headwinds all the way down to 18 - 19 when really flogged in twisties. Followers have commented on smoke from my tailpipes; when asked, they say black; gearhead followers say no blue or oil smell or belching off-throttle.

I don't have any experience with mpg on a trike so maybe someone else will jump in and help out here.

I haven't been into the carbs. The .38's were installed by the PO done by a Dallas area shop. I have the invoice.

All I have done with the carbs is to sync them and adjust the pilot screws using the DigiSync. The trike now runs great without any low-speed unevenness or doing the neat sounding " hit & miss " in first gear with a slack throttle.

Bon, as I told you when we talked, I intend to install .35's and new needle valves. However, being new to Valk carbs, I'm hesitant to do this so near to my impending trip to Spearfish.

I don't think it is intake valve seals. The Valk has only 16,000 miles; I've driven it 6,000 miles in the year I've had it; I changed the oil when I purchased it & in the 6K miles it has burned no oil; I just changed the plugs & the old ones showed no indication of oil fouling, ( pic. attached ); all plugs seem ok except 1 & 3 which seem to be the really rich ones ( incidentally, # 1 was bad out when I synced ); the smoke from the exhaust is definitely black, not blue and does not have oil smell, just gas; the tailpipe soot is not oiley; and finally, it doesn't belch blue or black smoke when throttle is snapped shut from high rpm.

I don't mind the way 1&3 look so I'd say that 2&4 look a little lean. No speckles or other bad stuff there, just a little lean.

I would appreciate you guys telling me which parts I should have on hand when in the way of gaskets, seals, etc. when I replace the .38's and the needle valves & also the preferable vendors from whom to purchase same.

I also intend to do a desmog in conjunction with the above and it seems that Red Eye Technical Services is most popular among the forum members.

Red Eye has all the miscellaneous parts you'll need for 0-rings and gaskets. Jets-R-Us has the jets and Amazon has the K&L needles as we've discussed.

Also, is there anything else to do while in this far such as the vacuum hose to #6 and the intake O Rings?

You can generally use 5/32" hose to replace the oem petcock hose and Red Eye has good intake o-rings. If you don't see any buildup at the base of the intakes then your o-rings may be just fine. If you're already placing an order with Red Eye you might as well replace them.

I probably will replace the coolant hoses also while in there.

Is there anything else I should consider doing?

Dan
pic attached

I either have the only 12 cylinder Valk in existence or I'm not very good at posting pictures. I'm stopping while I'm ahead.

[BonS]

Bon, is there any interaction between carb sync and adjusting the pilot screws. Lets say that you sync the carbs using the Digi-Sync and then adjust the pilot screws using the Tach function of the Digi-Sync.   Can the carbs be slightly out of sync at that point? If so, which do you do first?

The mixture screws won't mess up your balance but they will change your idle speed. Honestly, I haven't done both at the same time yet so maybe someone that has done them back-to-back will chime in here.

[WintrSol]

While the pilot circuit does add an amount of rich fuel/air mix to the air flowing past the throttle plates, and, theoretically they will change the vacuum some, the total contribution is small enough that even the DigiSync may not be able to resolve the change, even if the pilot screws were turned to fully closed, much less the small amount of turns used to tune. In my experience, tuning the pilot circuit always goes better if the carburetors are in close sync to start.

[BonS]

Using the Digi Sync to set the fuel/air mixture is done by observing the engine idle rpm. The factory manual calls for a 50 rpm drop and 50 rpm is easily seen with the Digi Sync tachometer.

[BonS]

Some folks learn visually so I graphed what I learned with my on-the-road testing with the Digi Sync operating.

This graph shows that carburetor balancing at idle doesn't have any effect at wide open throttle with the engine under load.  Simply revving the engine while standing still is more like the second graph than this one.



This graph shows the engine at cruising throttle. At slower speeds any carburetor synchronization imbalance that exists at idle still exists while cruising. As cruising speeds increase the high speed carburetor circuits gradually dominate and when cruising at 70 mph any imbalance seen at idle is gone - until you slow down again. Once again, this data was collected, real time, during actual road tests on my Interstate.




My next test will be with a single carburetor with a pinhole or tear in its diaphragm. If anyone has, for whatever reason, kept a defective CV diaphragm I'd love to test with it. I'll pay the postage, or better yet, bring it with you to InZane and I'll trade you something for it. I'm hoping that I can see the effect of the tear using the Digi Sync as a diagnostic tool. Now that would be cool!

[Dak44312]

So, I've been procrastinating, but I'm ready to buy now. All of the banners are gone and the website is down. Is this just because of IZ, I hope?

[Dak44312]

OK, guess I jumped the gun...website working now. Order placed!  

[indybobm]

Using the Digi Sync to set the fuel/air mixture is done by observing the engine idle rpm. The factory manual calls for a 50 rpm drop and 50 rpm is easily seen with the Digi Sync tachometer.

When using the Digi Sync RPM function to set the pilot screws, what tool are you using to adjust them while the engine is running? Seems like the hi-dollar Honda tool would be good but I do not have that. I have the stubby brass tool which is sometimes difficult to use with the engine off, let alone running with everything hooked up.

[BonS]

I use this stubby thing. I also use thin gloves to avoid burning the crap out of my hands! It's certainly no picnic. I do like the feel that this tool gives me when I'm feeling for the alignment with the "D".

[RGM]

Where did you get that tool?

[Avanti]

Craftsman Tool

http://www.sears.com/craftsman-3-pc-screwdriver-set-finger-bit/p-00941390000P

Motion Pro Tool

https://www.amazon.com/gp/product/B003CMWC4U/ref=ox_sc_sfl_title_144?ie=UTF8&psc=1&smid=AUNMX34AEN231

[Bagger John - #3785]

Those #38 idle jets are the main culprit for your poor gas mileage and if you did that you

may have changed the jet needle which, if you have done that, you should change them back to stock.

The Valkyrie engine normally runs rich to begin with and adding more gas does nothing but

carbon up the engine and reduce gas mileage.

***

#38 pilots and DynoJet or Cobra adjustable needles in both my bikes. Pilot screws ~1 1/4 turns out from lightly seated and jet needle clips in 2nd groove from top.

Intake and exhaust are stock. Tourer has I/S carb springs and ICM.

Tuning was done so that the plugs are just a little more tan than the darn-near bone white of "stock". Dark brown is too rich.

My I/S gets about 30-31MPG in this state of tune and will definitely out-accelerate a stock GL1500CF. The Tourer (a CA-model) pulls almost as hard and routinely sees mileage in the 40+ area when ridden at moderate freeway speeds.

I'd start checking the air screws and jet type/position before throwing the baby out with the bath water.

[Bugslayer]

Very interesting thread.