Idle Speed Variance

[BudMan]

After Stude31 and I synced the carbs the other weekend at Pharmboy’s we adjusted the idle to around 850.
(We had a great time there by the way, but that’s another story!) 
 The engine was up to temp and everything looked normal.  I rode home and found the idle to be around 1500.
I didn’t have a chance to do anything about changing it until this weekend.  When I started the engine, the idle was right back where I wanted it, about 850.  We went for a ride that ended up being about 70 miles or so and at each stop I noticed the idle had increased to around 1500. 
Any ideas why the idle would do this?  Could there be a vacuum leak that only opens up when heated?  I have not been able to get my hands in to the adjustment while it is this hot, but will try that today.
There is no need for choke to keep the engine running, and I would hate to apply choke just to gain an increase in idle speed but that is my initial approach for a fix.
The main question is this: how much change in idle speed is normal for a “warmed” engine to one that is fully “heat soaked”?

[Ricky-D]

Maybe a couple hundred rpm's tops!

Sounds like the synchronization is not good and maybe, just maybe, the idle circuit is too lean on a couple of carbs.

Mainly though I think it's the synchronization.

***

[DFragn]

What kind of sync tool did you use?

With 6 gauges or 6 liquid tubes i.e. mercury or ATF it is completely obvious that adjusting any one carb will throw the rest off. Being able to see all 6 carb vacuums simultaneously is the best way to sync. It takes time as you adjust here it goes off there and so forth. After an hour and a half I quit and settled with them extremely close but not perfect.

That being said. I have always [10 years & 75k] had to set the idle at my preferred 900 rpm only when heat soaked and tolerate the idle decrease at start up until it's heat soaked.

It's been like this since I took new delivery from the dealer. They set it up from the crate for pickup and 8-10 miles into my first ride my idle was just under 2k. It was dark and I had no idea where the idle adjustment was. It took me a week to determine it needed to be set when heat soaked.

It seems inherent with all 5 Valks in the neighborhood here.

[fudgie]

Do you have the ECT mod?

[BudMan]

The gauge set up was one vacuum gauge running through a manifold with 6 individual air switches to select each carburetor for analysis.
I would doubt the ETC mod has been done.  The engine has not been de-smoged,…yet.

[DFragn]

The gauge set up was one vacuum gauge running through a manifold with 6 individual air switches to select each carburetor for analysis.
I would doubt the ETC mod has been done.  The engine has not been de-smoged,…yet.

Yeah, not that thats a bad way you just can't immediately see what's happening to the other 4 carb settings when you adjust one. I don't think that's my cold/heatsoaked varience 'cause I got mine sync'd pretty much perfect and the lines are 5' long making my sync very very sensitive. And everything else is in top condition by way of a fine tooth comb.

The first pic is after going over the carbs about 7 times. As good as it gets.
The second pic is what happened when I only turned the #5 adjustment about 5 degrees. It threw all the carbs off. It's not a specific carb that screws it up. I experimented with all five. They each would individually throw my entire sync out of whack. Even the fixed #3 is affected!

So, I just set my idle when heat soaked and forget about it.
If it's not fuel related, electrical or vacuum lines then I suspect it's just an idiosyncrasy.

BTW I ditched my TwinMax carb sync tool. Kingbee's ATF system is much too accurate not to use.

[Madmike]

If my math is correct.......

Looking at the manual the spec for maximium difference is 1.6" of Hg.

1" of Hg converts to 13.5962" of Water.

Specific gravity of water is 1, specific gravity of ATF is about 0.870


1.6 x 13.5962 / .870 = 25"

.... am I correct in thinking that the 1.6" of Mercury tolerance converts into about 25" of ATF????

[BudMan]

The math looks good to me, but then again as lots of guys have heard me say, “I don’t do math in public.” 
Given the 1.6 inches of Mercury is the accepted deviation in suction, then having the ATF within just a couple of inches would be way more accurate and easier to read than the equivalent minute variance in Hg, I would think. 
All things considered, I feel the one gauge/six valve and manifold set up removes the most potential calibration errors.  Six gauges would be easier, but I have no vacuum source I would trust to calibrate each individual gauge.  I like the potential accuracy of the ATF solution, but can see where a little too much adjustment could pull fluid “over the top” as pointed out in some other threads.

[XXTi]

I like that carb synch tool.  I can't see the bottom of the board in the pics.  Do you have plans or details of the gauges?  I'd like to build one for myself.  I have a 4 column Motion Pro set, but it really would be nice to see all six carbs at once.

[Sasha47VSSS]

1. IMHO, there might be a leak in the vacuum lines and/or connections.
2. The 850RPM is a bit low. Check the voltage delivered by the alternator, it should be higher as possible.

[fudgie]

I use a single vac gauge and bike runs great. Never had a prob doing 1 at a time.

[DFragn]

I use a single vac gauge and bike runs great. Never had a prob doing 1 at a time.

That works fine. But if you sync'd your way and then hook the ATF tool up I guarantee your shock & awe. You'd see that your not actually fully sync'd. But that method does remain acceptable for Honda spec's.
It can always be better and this is the most sensitive way to adjust and then fine tune the sync it. There are few other ways to see how a single adjustment throws the other five out, including #3 your base reading. It does take time to bring them all within a similar level using the ATF method. It's the only surefire way [that I know of].

Would you like to buy my TwinMax? 

[stude31]

Okay... 

First to address the synch gauge it worked great on my tourer and i/s as well as Pharmboys.  It has one guage and Dfragn I agree it is nice to see all six guages but this works great.  After reading this I went to a buddy's house who has the twin max and to my amazement it was right on the money and when we synch'd the tourer two weeks ago we adjusted a few carbs quite a bit.  So I will not completely rule out the guage but if my memory serves me correctly my carbs on the tourer were right around the 10 or 11 mark and on his i/s they were clear down to 7, so that might or might not play a part in this or not....

What would cause a vacuum to be so low... Only thing that comes to mind would be a leak in one of the lines....  I say desmog that sucker and replace the left over lines with new ones...

 

[DFragn]

Okay...  

First to address the synch gauge it worked great on my tourer and i/s as well as Pharmboys.  It has one guage and Dfragn I agree it is nice to see all six guages but this works great.  After reading this I went to a buddy's house who has the twin max and to my amazement it was right on the money and when we synch'd the tourer two weeks ago we adjusted a few carbs quite a bit.  So I will not completely rule out the guage but if my memory serves me correctly my carbs on the tourer were right around the 10 or 11 mark and on his i/s they were clear down to 7, so that might or might not play a part in this or not....

What would cause a vacuum to be so low... Only thing that comes to mind would be a leak in one of the lines....  I say desmog that sucker and replace the left over lines with new ones...


 

I'm not trying to argue your point. But with a single carb sync display if you go back and recheck all 5 once set you will find variences when you thought it was right on and you most likely will have to go round & round many times to get them all close. I discovered that with my TwinMax. Granted you can fine tune your adjustment with single carb readings, but thats a serious pain in the arse and it will never be as close as viewing all 6 carbs simultaneously.
Even the ever so slight adjustment to one carb will throw all the rest of the mark they were and including #3 no matter what method your using.

If someone wants their sync to be better then minimum Honda spec's then you must be able to see all 6 carbs at once and I believe liquid readings are far more accurate then most vacuum gauges. Too much mechanical room for error between multiple vacuum gauges even when individually fine tuned.

You still have to go round & round with the ATF sync board setup. But, at least it's more sensitive and your not having to switch out vacuum lines for readings. Any adjustment results here are immediately visible among all 6 carbs. It just speeds up a more accurate sync.

[FLATSIX]

I cannot help myself in responding to this synchronisation........

What Dfragn told and described is exactly with I experienced with the synchronisation of my Lady : the vacuum is affected on all 6 carbs when you turn at 1 adjusting screw : so you need to see them all 6 at 1 time, secondly: all carbs are affected by the heat : when they are all 6 almost equal in vacuum, the next moment you can get a whole different picture depending on the heat down there.

So even with the 6 gauges (ATF or round vacuummeters) it is not easy to find the good baance between heat/vacuum of the 6 carburators and when you say : STOP , they are good now.

Without a 6-gauge machine to do the synchronisation I would not even think about synchronising my machine! Even TWIMAX or MORGAN CARBTUNE (4 gauges) are completely useless on our 6-carbs motors.

Try it and you will find a more responsive bike !

[DFragn]

Yup, the engine needs to be thoroughly heat soaked and it will be, as you readjust for the 10th time.

I had mine under fans while it took over an hour and a half. It was heat soaked enough that it warped my alternator cover. There was no other damage related to sync temps at about 205* and my "idiot" temp light never came on.

The radiator fan ran constantly creating no need to try and make adjustments when it cycles off. The only issue that may cause would be a slightly higher idle rpm that is easily remedied after the sync is complete. You still need to make idle adjustments though as you continue to level the readings, but that slows down as you get closer to 6 carb level readings.

I recommend removing the alt. cover temporarily for this type of syncing.

[Ricky-D]

I find with all the carburetors synchronized that they end up at about @ 12 inches Hg.



Have to choke down individual hoses to stifle pulsation.

Adjusting one carburetor changes at least two other carburetor settings.

It is a very frustrating exercise and keeping the motor from heating to the point the fan comes on
has always been a problem which is now solved with an auxiliary fan that attaches to the radiator.

***

[FLATSIX]

DFragn, are you convinced that the best synchronisation is done on a heatsoaked engine?

When all the iron under the tank has become hot and does not expand anymore, then it is possible to turn the screws till all 6 are at the same level with our very accurate ATF-machine. I experienced this too, but the best result that I had was to adjust the best possible just before the fan comes on.

When fan comes on twice or 3 times (with ventilators before radiator) then I shut off engine, wait for 20 minutes, start up again and then follow the heating of the motor again with synchronisation till operating temperature ( 80°C +/-) this is just before fans comes in. Then I stop it - when I do like this she is smoother and sitts on the throttle.

This is also more the situation when you ride - it is then that all 6 should be as close as possible - not when the iron bars that operate the carbs are fully heated, in practice they are not superheated as driving wind will cool them.

That is my experience and theory........

[DFragn]

DFragn, are you convinced that the best synchronisation is done on a heatsoaked engine?

No, not really. I'm not convinced of anything when it comes to sync'n 6 carbs. I doubt any single process is the best, but the ATF method affords the best chance.
But I'm happy with it. It's a just a little rough on cold idle.
But, once it reaches 175* she purrs at idle [like never before] and accelerated & decelerates much more smoothly and sounds better too.
Way better then sync'n with my TwinMax gitup.

[BudMan]

Stude,
You are correct.  My vacuum pressures were in fact in the 7 range.  Given that and the idle speed change situation, I strongly suspect a vacuum leak.  De-smog and recalibration sounds like the ticket. 

[Rocketman]

I had a similar problem after synching, and found that I had synched mine with one of my gauge lines a little loose, giving me a false reading, effectively synching with an artificial vacuum leak.  I redid the synch, and everything was good.

[BudMan]

Rickey-D,
Do you have any method to calibrate your six gauges? Is that even an issue?  It looks to me that you need to make sure 7” Hg on one gauge is the same on all the others.
Just wondering out loud here:  could you parallel all the gauges to one vacuum source and check they all read the same, or would that have too many internal installation errors?
By the way, that’s a great looking set up!  What was your parts source?

[Ricky-D]

Rickey-D,
Do you have any method to calibrate your six gauges? Is that even an issue?  It looks to me that you need to make sure 7” Hg on one gauge is the same on all the others.
Just wondering out loud here:  could you parallel all the gauges to one vacuum source and check they all read the same, or would that have too many internal installation errors?
By the way, that’s a great looking set up!  What was your parts source?

You are correct. I bought six gauges at the outset, hooked them to a manifold and found 3 were identical, 2 were different but identical and 1 was different again. I purchased four more gauges and finally ended up with six that are very, very close together.

The gauges were very inexpensive, $3.40 apiece.

Here's the link:
http://cgi.ebay.com/NOSHOK-2-Dial-1-4-NPT-30-inHg-Vacuum-Gauge-NIB_W0QQitemZ330357346654QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item4cead5115e&_trksid=p4634.c0.m14.l1262

I simply screwed clear plastic tubing that I purchased at Lowes over the fitting on back of the gauge and sealed it with vinyl plastic sealer on the threads.

***

[BudMan]

Karen and I will be riding down to Pharmboy and Linda’s tomorrow and we are going to de-smog the Valk.  We think that will be the starting point for finding out where my missing vacuum pressure is!  I’ll report our results.

[fudgie]

Stude,
You are correct.  My vacuum pressures were in fact in the 7 range.  Given that and the idle speed change situation, I strongly suspect a vacuum leak.  De-smog and recalibration sounds like the ticket. 

Mine were about 8 mm/Hg.