Yet another carb question

[mac65]

Hey all working on 81 gs 1000 gl,bike has pods & 4 in 1 kerker has 40 pilots and 120 mains air mix screws at about 2 turns,starts easy, idles great but has a nasty stumble about 3 grand,past about 3500 it goes like stink so question is what else needs to be done to get smooth throttle throughout rpm range? Needle not adjustable,Carbs are clean, valves in spec, boots good any advice would be great thanks Mac

[tkent02]

idles great but has a nasty stumble about 3 grand,past about 3500 it goes like stink

At which throttle position does it stumble?

[mac65]

Throttle position? Maybe quarter to half,thanks

[tkent02]

So if you go wide open it will blast right on through 3,000?
How about if you just barely crack the throttle in first gear, will it go smoothly through 3,000?
If so it sounds like you may benefit from shimming the jet needles or getting adjustable aftermarket jet needles.

[mac65]

Cant really say it wil blast through does do better if you ease into it,how would I go about shimming stock needle has one thin flat washer between spring and clip,maybe put in two?I have extra set of parts carbs could rob parts from

[twr1776]

Are you getting any decell pop? I have a stock box and V & H header on the same bike and am running 42.5 pilots, 120 main, and shimmed needles. I think Basscliffs site has info on shimming stock needles. I am no carb expert but I would think you need a bigger pilot for sure and to shim the needles. Have you done plug chops?

[tkent02]

how would I go about shimming stock needle has one thin flat washer between spring and clip,

It's the spacer above the clip that positions the needle, remove the fat nylon spacer and put in a couple thin washers. This lets the spring push the needle up farther. You might try putting the thick spacer underneath the clip and the thin washer above, but this is probably too big a change. Thin washers of the correct size are available at Radio Shack, in a small washer assortment.

[mac65]

Are you getting any decell pop? I have a stock box and V & H header on the same bike and am running 42.5 pilots, 120 main, and shimmed needles. I think Basscliffs site has info on shimming stock needles. I am no carb expert but I would think you need a bigger pilot for sure and to shim the needles. Have you done plug chops?

None to very little pop on decell ,bike had 50s and 130s when I got it WAY,WAY to rich =black sooty,gas soaked actually just put in smaller jets and is much better will go check plugs now see how their looking.

[mac65]

It's the spacer above the clip that positions the needle, remove the fat nylon spacer and put in a couple thin washers. This lets the spring push the needle up farther. You might try putting the thick spacer underneath the clip and the thin washer above, but this is probably too big a change. Thin washers of the correct size are available at Radio Shack, in a small washer assortment.

Thank you,headed back to the garage to see what happens thanks again Mac

[doctorgonzo]

None to very little pop on decell ,bike had 50s and 130s when I got it WAY,WAY to rich =black sooty,gas soaked actually just put in smaller jets and is much better will go check plugs now see how their looking.

To really dial it in you have to do a true "plug chop". My just rebuilt engine is very lean on the needle (same symptoms as yours, breaks up badly betweem 1/3 and 2/3 throttle), pulling my carbs to raise the needle tonight. However, when I finished that initial ride and pulled the plugs they were sooty. Probably because I'm rich on the pilot (what it was one as I slow putted up the driveway and parked it).

[mac65]

O.K. definitly headed in the right direction used washers about half thickness of plastic spacer now revs smooth stationary still has some stutter under power but is better,still need to go thinner yet?also do I need thicker washer between spring and clip?Plugs are losing black turning dark gray any comments?Thanks,Mac

[tkent02]

O.K. definitly headed in the right direction used washers about half thickness of plastic spacer now revs smooth stationary still has some stutter under power but is better,still need to go thinner yet?also do I need thicker washer between spring and clip?Plugs are losing black turning dark gray any comments?Thanks,Mac

Sounds like the right direction, go a little bit further. Go thinner. The washers under the clip do not matter as long as the spring maintains some tension pushing up.

Raising the needle makes it richer, you say the plugs are turning less black? That's backwards, if they are black they are rich.

I suspect you are not doing correct plug chops.

It can easily be too lean in one throttle opening and too rich somewhere else.

Plug chopping will tell you what is going on.

[mac65]

Sounds like the right direction, go a little bit further. Go thinner. The washers under the clip do not matter as long as the spring maintains some tension pushing up.

Raising the needle makes it richer, you say the plugs are turning less black? That's backwards, if they are black they are rich.

I suspect you are not doing correct plug chops.

It can easily be too lean in one throttle opening and too rich somewhere else.

Plug chopping will tell you what is going on.

Plugs were black when I started it did have 50 pilot and 130 mains way to rich now they are turning a dark gray with 40 pilot and 120 mains will go play more later time for granddaughters 4th birthday dinnerthey just got here will check back later.