Carb Jetting

rhinoevans

rhinoevans

Active Member
Moved from Vintage:



How about you go out and drop the float bowl and tell us what jets are in the bike. You should be the 29.5/31 - 74/76 area. If they are larger than these then you can go from there but you need to know where you are at right now. Adjusting the fuel/air is only for idle. Accelerator pump is for starting and quick throttle motions.

OK, I pulled it. 70 and 31. Now help me under stand this. Smaller numbers = less fuel. The Large numder is the main jet which is higher RPM. So it looke like that jet is not right, but is that causing the over rich. Looks like the intermediate jet is in the ballpark, or does the difference of 31 to29.5 make that big of a difference????


The more I read the more confused on these numbers. I have a rich condition, but if I go with a 74/76 would that be a more rich jet? Maybe the answer is the 29.5 which would give me a more lean condition from the 31 intermediate jet.

Also Indiana 500 MSL Las Vegas 2200 MSL which I think means Vegas would be a more RICH condition from Indiana.

Did not mean to hijack this thread, but I also havea 2002 Pitbul. Hope this knowledge helps your issue also.

After some thought, I think a 29.5 is a significant change from a 31. Am i correct on this? Still do not know what to think on the 70 main

Rhino
 
Raywood

Raywood

The Pirate
Staff member
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Troop Supporter
Glad you are trying to learn but do yourself a favor and read the S&S .pdf on turing a carb so you have an understanding of what the jets are doing.
Here is an illistration of how the intermediate and main jets work and about what rpm they come into play. This illistration also has a thunderjet just ignore that for how. It's at the bottom right of the page.

There is very little difference between the 29.5 and 31 jets. S&S tells you that when you are tuning to go 4 points at a time!!!
When I had my 107 I ran 31/76 and you should be able to also or there abouts.
Why do you think it's running rich? Are you seeing black smoke or do your buddies that ride behind you tell you you are smoking? 70 is awful lean for that motor if you ask me. I think the 31 or 29.5 is right for the intermediate but you need to change them and play with them to get a feel for it. Not all bikes are the same due to different air intakes and exhaust and riding styles. So, get you a bag of jets and see what happens.
I would first bump up the main jet to a 74 and see what happens.

:2thumbs:


http://www.bigdogbiker.com/forums/performance/3822-carb-issues-what-2.html#post63537



 
Raywood

Raywood

The Pirate
Staff member
Calendar Participant
Troop Supporter
Also, you shouldn't be running rich with these jets. If your plugs are fouling then ensure that your enrichener is fully closed. Do not us it as it fouls plug real quick.
And tell us where your accelerator pump is set to. Turn it in till it touchs the pump arm then back it back out to where you had it. Tell us how many turns it was. It shoud be about 1 1/2 to 2 full turns.
Have you tuned the fuel/air mixture screw, is it set right?
Tell us if you have a strong odor of fuel around the carb!

We can go from there.

:cheers:
 
rhinoevans

rhinoevans

Active Member
I am fouling plugs very quickly and some black smoke, but mainly the plugs. No time next couple of day to check the accelerator pump, but will check as soon as I get a chance. Never use the enricher. Thanks for all the help. I will say that other than fouled plugs, the bike runs and idles great. I would say yes on the strong odor.

And yep found this in the S&S instruction sheet:

Set pump travel screw at point where best throttle
response is noted with minimum pump travel.
Minimum pump travel is recommended to conserve
fuel, prevent spark plug fouling, and curtail black
smoke from pipes when “blipping” throttle. Black
smoke from pipes is usually an indication of a rich
condition or excessive accelerator pump travel.
 
Last edited:
rhinoevans

rhinoevans

Active Member
Raywood and Gas MAn, Thanks for all the help. Learned alot on this venture, however, I have decided to just let the local wrench DYNO the bike which should retune my carb. RIGHT?
 
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