Help carb tunning

[bro.betterley]

I have a 1992 mostly stock vmax, i have a drop in K&N air filter, i have cleaned the carbs adjusted the floats wet measurment is about 16.5mm average in all 4 bowls. Jets are all stock, the A/F screw is 3 3/4 turns out the needle has a 24 thousands shim. Exhaust is stock.

Problem is my plugs are VERY WHITE, and bike seems to have a lean spot most noticable in the 3500-4500 rpm range

 

[Rusty McNeil]

I have a 1992 mostly stock vmax, i have a drop in K&N air filter, i have cleaned the carbs adjusted the floats wet measurment is about 16.5mm average in all 4 bowls. Jets are all stock, the A/F screw is 3 3/4 turns out the needle has a 24 thousands shim. Exhaust is stock.

Problem is my plugs are VERY WHITE, and bike seems to have a lean spot most noticable in the 3500-4500 rpm range

I don't know the exact answer to your question, but I will say 3 and 3/4 turns out on the screws sounds like a lot for a stock max, so is .024 shims.

Other than the plug condition how does it run in normal to sprited riding?

 

[naughtyG]

When you say mostly stock, what other mods do you have?

Also, what's your elevation?

Have you checked that your plugs are the exact ones recommended by Yamaha?

When you cleaned your carbs, did you take them completely apart? Have you checked all your diaphragms for holes or tears, and also your costing enricheners for the same?

 

[bro.betterley]

everything is stock except shims and k&N, plugs are NGK DPR8EA-9 as recomended by the clymer manual, no tears or holes in diaphrams. I didnt start with 3 3/4 turns, but turn it out 1/4 at a time from 3. I dont know what to say about how it runs its my first vmax, it is running much better than when i got it.

Still feels lean when cruiseing at 1/8-1/4 throtle at 4000 rpms, and when you go WOT from around 4000 rpms

 

[bro.betterley]

Im 500 ft above sea level

 

[naughtyG]

It all sounds like it should be alright, but obviously it's not. When you cleaned your carbs, did you completely take 'em apart, or just did shotgun/peashooter?

Also, you could try two things:

- add another shim to your needles
or
- set your floats richer, maybe 17.5 might work better than 16.5mm for you..

 

[bro.betterley]

I tore them completley apart, all went well, 17.5 would be leaner than 16.5:ummm:

 

[bro.betterley]

took out the k&n and runs much better, will run it a day and check plugs

 

[naughtyG]

did I get the floats wrong? woops lol.. Either way, they may help you richen it up a bit.

The K&N sounds like you're onto something - they do allow for more air so maybe that's your problem. I have a K&N too though, and no other mods, and usually run fine with my A/F screws just 2 5/8 turns out. Since fitting Supertrapps slip-ons tho, I've been running very rich..

 

[gamorg02]

when u took the k&N out, did u have another filter in its place?

 

[bro.betterley]

i took the K&N out wet with a high flo paper filter, and its not near as lean now

 

[vmax626]

I have a 01` max and I just went back to stock from a stage one kit cause the "PO" didn`t put a header system on it but now, I get popping on deceleration although I no longer have the 15- 25 mph. stutter when I accelerate from thse speeds anymore I have a firecracker type pop,pop,pop when down shifting when comming to a light or off a fwy. off ramp.
My mains are 147.5
pilot jet #1 is #90
pilot jet #2 is #170
A/F screws are 3 1/2 turns out
Needles are stock (no shims)
I have denso cop`s
and got rid of the crimp
.I live in So. Cal so i`m pretty close to sea level.
<<Dave>>unk:

 

[naughtyG]

I believe that a little popping is normal - do you have slip-ons on?

The OEM exhaust just does a great job at removing those pops with the collector box, IMHO.

Since putting the Supertrapps on, I also noticed a little popping I never heard before. Having said that, the most common culprit for popping is air leaks in the exhaust - check all your header connections too!

 

[vmax626]

Yeah I do,
I have Dale Walker hole shot cans on it.
but I have stock headers.
<<Dave>>unk:

 

[bro.betterley]

I would think at sea level you could use a larger main and a shim, hows your plugs look, also hows fuel level?

 

[RagingMain]

I would think at sea level you could use a larger main and a shim, hows your plugs look, also hows fuel level?

Shimming might be our next step. One thing I found on my bike when I was popping was one of my coasting enricheners had a pin hole in the diaphragm. When I got that fixed the popping went away.

 

[vmax626]

Shimming might be our next step. One thing I found on my bike when I was popping was one of my coasting enricheners had a pin hole in the diaphragm. When I got that fixed the popping went away.

Hey Fargo,
Does shimming the needle kinda lock it in place (all the way down?):ummm:
I know it moves a little with that little spring in there.
I think I have that little diaphram from the old carb some where.
<<Dave>>:confused2:

 

[one2dmax]

One shim still leaves some flexibility, two shims makes it not quite rigid but close.

Sean