Would 105 vs 100 main jets affect mpg much?

[rekit]

When I got this 99 IS a few months ago, 8000 miles on her, she was stock with dirty carbs. Have had good luck with Sigma 6 carb kits on some other bikes, so I put one in which consisted of 38 slow jets, air screws 2 1/4 out, and I put the 105 mains in, also did the needle shim. Bottom line--runs great, gas mileage sucks (28-34). I ride mostly 50-70 mph solo with a throttle grip that's trying to save for my retirement vs giving to the local tax coffers. Stock air filter, stock exhausts. Brakes don't drag, etc. I just think this mpg could be better. Would jetting from the stock 100s and the shims make that much difference? I am going to go to 1 3/4 on the air screws and change the jets to the 100's, leave the shims, pending comments. Thanks.

[sandy]

38's set at 2 1/4 is way too rich. Yes, go back to 1 3/4. I have no experience but have heard 105's costs you in the MPG area. I'm an old conservative guy. I have dynajet needles set to the 2nd notch down which leans it a bit. I get 36+ most of the time.

[98valk]

use the 35 PJs for better mpg. any PJ is good for adjustment out to 4 turns out some bikes/carbs will alllow 4 1/2. if needed that many turns out then next size larger PJ is called for.
cruising down a hwy throttle should only be about 1/8 throttle whereas u are mainly on the PJ range of the carb. main jet is 3/4 throttle to WOT.
if stock airbox and exhaust all u need is 100 MJs.
for a little air flow boost remove the metal screen from the oem air filter. shim the front two carb needles only with one additional washer, the others should be stock.

[Bighead]

Mine is bone stock and I only get about 34 on my 97 standard and about 33 on my Interstate. But I do likes to twist tha wrist

[Patrick]

I'm surprised it doesn't look like an old diesel running down the road. I'd recommend what the fellas said.
100 mains
1.5 to 1.75 pilot setting[38s] or install the 35s and set them at 2.25.
original needle setting

[rekit]

Yeah, I thought the spark plugs might be a little on the "dark side", but they looked perfectly tan-grey. We have some bad weather coming, time to get to it. I'll report back.

[signart]

38's in the slows will cost you nothing, (right, 1 3/4 turns out). If anything you will gain because of easier starting, faster warm ups, smoother and easier every time you take off from dead stop, on and on. IMOP the single best performance mod you can make on a Valkyrie with no downsides.
I don't know how you would gain anything by running 105's but maybe someone could enlighten.

[98valk]

38's in the slows will cost you nothing, (right, 1 3/4 turns out). If anything you will gain because of easier starting, faster warm ups, smoother and easier every time you take off from dead stop, on and on. IMOP the single best performance mod you can make on a Valkyrie with no downsides.
I don't know how you would gain anything by running 105's but maybe someone could enlighten.

hogwash, would get the same result and little better mpg and a crisper throttle response using the oem 35s and opening up the mixture screw to 2.5 - 3.5 turns out.
this is basic 101 carb tuning.

[signart]

38's in the slows will cost you nothing, (right, 1 3/4 turns out). If anything you will gain because of easier starting, faster warm ups, smoother and easier every time you take off from dead stop, on and on. IMOP the single best performance mod you can make on a Valkyrie with no downsides.
I don't know how you would gain anything by running 105's but maybe someone could enlighten.

hogwash, would get the same result and little better mpg and a crisper throttle response using the oem 35s and opening up the mixture screw to 2.5 - 3.5 turns out.
this is basic 101 carb tuning.

Hog hocky, I check every tankful on my two valks. No worse, and more times better. Throttle action very noticeably better in all situations and starts way better in cold and extreme cold temperatures. Take offs, roll on throttle out of turns, parking lots, you name it, all around better performance. In warm temperatures no choke needed n cold engne. Just start and drop the clutch, no wasting fuel waiting for warm up.  You'll be hard pressed to find anybody running 38's that would switch back to 35's. Some say their harder to clog with the corn,  I can't say but mine hasn't clogged a 38. I wish everyone's Valk ran as good as mine.

[rekit]

OK, 100's, 38 PJ's at 1.5-1.75. What's the thinking with the shims only on the front two carbs?

[Pappy!]

Have to agree that the 38's adjusted to the 1 3/4 range provides identical fuel air ratio as the 35s out to the 2 1/2 range. Nice thing is that the 38s wont plug up as easily as the 35s will.

[Hoser]

I get 39/40 mpg with no headwind at 3000 rpm.  The faster I go the lower it gets. OEM jets and settings.   Hoser  

[salty1]

Your raised needles and 105 main jets are your problem.      

[heavyd]

Not really related except for all the MPG talk, but my record is burning 17L/h. I forget what the mpg worked out to but I remember my gf was getting upset that she was paying for a talk of gas every 45 minutes. But that was cruising at 160km/h with two on and 4 days worth of luggage.

[MP]

OK, 100's, 38 PJ's at 1.5-1.75. What's the thinking with the shims only on the front two carbs?

Sounds like exactly the same conclusion reached on the VOAI forum, when you posted there earlier!   :cool dude:

MP

[Ricky-D]

CA has it correct and the naysayers are all wet.

And the reasons/results to substantiate the claims

by the larger jet crowd are either pie in the sky

or wishful thinking.

There is no benefit to running a gasoline engine more

richly than necessary and could actually be harmful

to the engine.

***

[Pappy!]

Sorry, don't see it that way!
With both jets you can turn the needle (flow restrictor) in to where neither will flow fuel. Equal, right?
From the closed position either jet will be adjusted to pretty much the exact same flow rate as required by the cylinder. Only difference is that one will be turned to around 1 3/4 turns and the other requires around 2.5 turns to flow the same amount of fuel. Pretty much simple physics here!
Your thinking would be correct if both the 35 and the 38 were adjusted to the same number of turns.
Again, the nice thing is that for the guys that don't want to use the enricher they can up the flow on the 38's a little more easily for cold starts and the 38's do not plug as easily during times where the bike is not run.

[Ricky-D]

Nope, you're wrong to the nth!

You have no concept at all regarding the carburetor's

idle circuit, just incorrect assumptions.

***

[Pappy!]

Well.....I sure don't see you backing up your opinion with fact.....just opinion! Will put my carb knowledge against yours any day of the week!
Guess we can agree to disagree and leave it at that.

[rekit]

99 Interstate-stock. OK I left the 38's in, went with 1 1/2 turns, and put in the stock 100's. Also took out 2 of the 3 shims (1 is stock). Pulled the 152 dan-marc and put in a 1112, and did the desmog. Already put in a new in-tank strainer and petcock cover set. It's running great. I filled the tank while the bike was on the sidestand and went 175 miles before reserve, running solo, mostly 65-75 mph with some headwinds and tailwinds. Worked out to 31.6 mpg on that tank. Better than 28 for sure, although I was hoping for 35 or so, but to be honest I could have done a little better with my--ahem--throttle management. Bike does seem to run better like this though, and it never felt like the low fuel level was starving it like it did with the 152. Thanks to all for the replies.

[salty1]

Glad it came together for you! Did you resynchronize your carbs? It will be the finishing touch for all of your efforts!

[Patrick]

99 Interstate-stock. OK I left the 38's in, went with 1 1/2 turns, and put in the stock 100's. Also took out 2 of the 3 shims (1 is stock). Pulled the 152 dan-marc and put in a 1112, and did the desmog. Already put in a new in-tank strainer and petcock cover set. It's running great. I filled the tank while the bike was on the sidestand and went 175 miles before reserve, running solo, mostly 65-75 mph with some headwinds and tailwinds. Worked out to 31.6 mpg on that tank. Better than 28 for sure, although I was hoping for 35 or so, but to be honest I could have done a little better with my--ahem--throttle management. Bike does seem to run better like this though, and it never felt like the low fuel level was starving it like it did with the 152. Thanks to all for the replies.

Well, good, at least its running as it should. Everyone seems to get different fuel milage results. I think most of that is engine speed, road speed, and the right hand.
These monsters tend to start to use more fuel above 3K rpm. My cruise speeds are around that range and consistently get 40+ mpg, but, for my kind of riding I don't care about fuel consumption.

[uturn]

not sure anyone rides a valk to save gas...i get 30-35 smiles per gallon...

[98valk]

Sorry, don't see it that way!
With both jets you can turn the needle (flow restrictor) in to where neither will flow fuel. Equal, right?
From the closed position either jet will be adjusted to pretty much the exact same flow rate as required by the cylinder. Only difference is that one will be turned to around 1 3/4 turns and the other requires around 2.5 turns to flow the same amount of fuel. Pretty much simple physics here!
Your thinking would be correct if both the 35 and the 38 were adjusted to the same number of turns.
Again, the nice thing is that for the guys that don't want to use the enricher they can up the flow on the 38's a little more easily for cold starts and the 38's do not plug as easily during times where the bike is not run.

your partially correct u forgot about the 3-4 other holes which these carbs PJs have. and yes there are PJs without holes there u would be correct. the small difference btwn hole Diameters is nothing when it comes to clogging. a 38 will clog just as readily as a 35, most forget that now they use carb cleaners all of the time after putting the 38s in whereas with the 35s they most likely didn't

   the other 3-4 holes are bigger in 38s vs 35s, = worst mpg. its mostly only 1 to 2 mpg difference. most will not notice unless really, keeping great records, on same ride course for a full tank. since I mainly commute on my bike, I can tell u there is a difference esp with my air box and exhaust mods. colder temps I actually need to partially block airflow into the air box. a larger pj would cure the problem but then way too rich on the 3-4 holes during the warmer months.

http://factorypro.com/

"As far as the pilot... Look at it this way...

There are 4 outlet holes for the pilot mixture. ~3-4 at the butterfly and one "downstream" of that (for 75% of the idle mixture).

1 hole is controlled by the mixture screw and with the other 3 or 4, max flow is limited by the size of the pilot jet.

At idle, 1 hole (metered by the fuel screw) and 1 un metered hole are open.

At cruise, when the "butterfly" is just "cracked", all 3-4 unmetered holes + the 1 metered one are uncovered -

So.....

At cruise, you get those 3 unmetered holes + the metered hole... So, at least 75% of the fuel delivered at cruise is limited by the size of the pilot jet.

At idle, you get 100% of the trimmed 1  hole + a butterfly valve-trimmed amount of the other 3-4 metered holes.

Rule of thumb....
If you go 1 size larger or smaller on the size of the pilot jet, you will change the fuel screw ~1.5x richer or leaner to retain the original idle mixture -

Example:
You have a #40 pilot jet installed (with the proper main, needle height and fuel  level already done)  and to get best idle, you are 4.0 turns out (from lightly bottomed out).
Cruise seems lean....

So, I'd expect that I could richen the cruise with 1 size larger (42) pilot jet (size of pj is 75% of cruise mixture) and the "trim" the fuel screw "in" for best mixture for best idle (size of pilot is 25% of idle mixture).

To go back to ~ the same idle mixture, after going from 40 pj/4.0x to the 42........ try 2.5x

40 pj / 4.0x = our reference idle mixture
42 pj / 2.5x = ~ same idle mixture
38 pj /5.5x = ~ same idle mixture (this is a "stretch - after 4.5x, not much changes)

(Using another "rule of thumb", if you have the correct pilot jet, the fuel screw will end up at between 1.5x and 3.0x when set for best idle.)

Marc"  http://factorypro.com/