Sea level carb setup

[Diablotin]

hi guys,

what setup would you advise as a base line at sea level with a stock engine, air box (K&N) and with a 4-2-1 exhaust (Over racing, I guess I'm the only one with that exhaust :rofl_200 ?
I check the carb sections, but I don't see anybody at sea level with no carb kit.

The bike is currently running all stock, A/F 3.5 turns and 147.5 main jet.
My mileage is between 28 (usual) to 37 (highway only) MPG.

Does somebody know the size of the carb hoses (vacuum and drain)?
I have a drain one missing and broke a vacuum one during the last sync, so I'm thinking about replacing but maybe not with OEM.

 

[grimmie]

Hey Michael,

There really isn't a base line to tell you the truth. Each bike, engine, exhaust, carb, airbox combination is unique.

I would check your plugs first with a WOT plug chop using brand new plugs. You want your plugs to be a lighter grey or light tan color.

Is the bike not running well?

 

[Diablotin]

The bike is running ok but not as sharp as it used to be.
I changed the exhaust but didnt do much on tuning the carbs.
You know you get used to how the bike runs until you discover it could work much better

I have the feeling I could get more from the exhaust.
I remember seeing different size of jet depending on elevation and exhaust, so I started wondering
No dyno here, maybe planning to get an AFR with a friend for accurate tuning.

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[misiek93]

I have very similar setup (stock carbs, 147.5, K&N filter, 4-2-1 header, IXIL muffler) and from what I was able to find on this site, 147.5 and A/F 3 turns out is a good starting point. Not sure that the stock A/F screws are set to but when I changed to smaller jets I started to get a little of popping on deceleration. I have to drill out the brass caps and mess with A/F now.

My fuel light did go on at 110 miles instead of 99 though.

I did sync my carbs at idle and someone suggested I do it at 3K rpms. I'll give that a try as well and see what happens. This is where I really wish newer Gen I's came with fuel injection :damn angry:

 

[misiek93]

Give this a try, a lot of different setups here.

http://www.vmaxforum.net/showthread.php?t=16981

 

[Diablotin]

Yep I saw it and noticed bigger main at low elevation.
I'm rich with a light smell of gas but I'm losing power with lower A/F.

Dammit I really cant wait to get an O2 sensor

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[SpecOps13]

I'm probably the one who suggested 3,000 RPM for Sync.

I'm running a similar setup on my 89. 147.5's with the stock needles shimmed ??? 25 thousandths or so. AF out 3.5 to 4. Kerker 4-1 with a 12" Mark's Can. My dyno run showed that it was a little lean at Idle and almost a flat line at 11.80 ish throughout the RPM Range. Kinda Rich if the numbers are real....Not real sure how accurate that is but I'm doing some plug testing right now. 126.02 HP, 83.63 Torque...The Air Fuel from the dyno didn't look to me like the Vboost was opening..:confused2::ummm:

 

[Diablotin]

I'm thinking about reducing the AF a bit since i'm rich and shim the needles a bit to compensate the mid range, good idea ?

 

[SpecOps13]

From an experimental view I agree with your plan..... Then Go from there. Mine is possibly too rich with the needles shimmed. The Jury is still out on that....

Good Luck,
Dave

 

[grimmie]

One thing to keep in mind too, is that these are carburetors and it's hard to get them perfect throughout the entire throttle range. Sometimes you have to hit a happy medium between the lower and upper crossover points.

Shane

 

[Diablotin]

I agree with u guys. Ill be happy with a good and strong mid range with an acceptable mileage already.
I was originally thinking the 147.5 was a bit small at sea level. But base on Dave feedback it's no prob.
Experiment is the key

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[SpecOps13]

I felt the same way because my 94 is running Mark's 4-2 with larger jets but the 4-1 wants the main jets smaller for whatever reason... I'd post some comments about how my 89 runs but everyone'd think I was full of crap. Trying to figure a way to do a real time video with one of my cameras of just how fast this thing really is... 4-1 Rocks...