I been havin a carb kit from SETX Performance, Great help and product!!, but when i run at 80% throttle it runs great and strong... once i squeeze the rest of it, at wfot, it spits and sputters and looses rpm till i let off the gas. any ideas as to why this is goin on... ive tried messin with the air/fuel screw but nothing helps.
thanks

at what rpms is this happening at. valve lash fuel deliverey.need more info.

with a new mb wheel it runs great at 3850-3900 and with a worn gt wheel it runs great at 4150-4250.
its just when i want that extra tiny bit of power that you get from 3/4 throttle to wide open.
am i making sense?

do you have a rev limiter installed

What main jet is installed on what motor/mods? If you have spark, its either fuel or air.

If you have a primer bulb installed, pump it when you get to WOT and see if it goes away. Maybe you are not getting fuel, or too large a main jet and you are getting too much at the very top end. Another thing to check is to take the air filter off and see if it improves the full throttle performance. Both those checks will give you clues.

too much fuel from the main jet.

I've got heads and a stock gutted ehxaust.
What size main jet should I be running?
I'll check on what I have after I get home from work

What size carb 42 Mikuni? If so you can just adjust where the clip is on the main jet pin to lean it out. That is if it is running rich. Install new plugs and do a full throttle blast then read the plugs for rich or lean. Adjust accordingly.

Russ

Let me take a step back if your running rich at full throttle then it may be the main jet not the pilot jet. The main thing you need to do is determine if this is a running rich issue. Have you pulled the plugs after a couple hard full throttle runs? If not I'd say install new plugs, go out and do a could hard full throttle runs, pull the plugs. Are they wet or black. If so then you likely are rich and need a smaller main jet. Another thing is make sure your choke is fully open. If not it could cause a rich condition.

Here is a good PDF of how to tune a Mikuni HSR 42. It is for a Harley. http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf The application may be different but the concept is the thing. This discusses tuning each of the fuel delivery systems in the 42. Where it references the throttle position that should apply equaly here also.

One other thing to consider, you are running an airfilter arent you? If not air could be blowing acros the carb and causing issues.

Hope this helps,

Russ

I appreciate all the input, where can i get a new main jet from?

Harley shop or on-line (JetsRus)

Also check your slide to make sure its not opening to much, If you look down the throat of the carb and lift the slide, you'll see an arch made into the bottom of it that should be flush with the top the throat at WOT and no more or it will do exactly what your experiencing now. You can set it by the throttle cable or on the carb it self ( theres a small set screw with a back up nut on the top left side the carb.

Ok, another question.
when im idiling around froggin or bowfishing my exhaust spits a flame every once in a while. btw i have a gutted stock exhaust.
and it still bogs down a little even after adjusting the screw so my slide is even with the carb arch

i took the air filter, pre filter, and rain cover i made off the carb last night and it ran like a champ

your main is to big for the filter or get a new filter