I have a TM 33/34 Mikuni flat slide pumper carb on my 2009 KLX250s, (351 big bore installed). I bogs down starting around 8500 rpm. I am thinking of going to a larger main jet, or raising the jet needle, or both? Do I have to remove the carb to change th main jet, raise the needle ? Any other suggestions, solutions? I had the snorkel off and it was worse, so a bigger jet and snorkel off would be better?
Mick

 

You probably don't want to hear it, but doing two major tweaks to a carb at the same time is not recommended unless it's the initial carb jetting setup based on well established data presented here or elsewhere with fairly well agreed upon numbers. You might want to list the data on all your jets and other carb tuning numbers. You'll get better feedback if people know what you already have in there. There are lots of already successful setups on here with the 351 and such.

 

Agree w/TNC, need more information. If you pull the snorkel the restriction of that tiny thing is gone - leaner running as you observe. Personally I'd take the carb apart to find all the jetting numbers for reference, then I'd raise the needle a notch to see what happens. The main may be fine, but you don't know until you try. Other thing is the needle is easier to get to and if the main is fine you don't want to do all that work if you don't have to.

Another good idea is to list the area where you live, so people have an idea of the climate conditions and such. Don't need to get too specific, town and state/province and country for some. I list the actual town where I live, but could put in Columbus Ohio to be a bit more anonymous, but not too worried about that. It's kind of useless to ask about some things that will vary from place to place, like jetting and shop recommendations.

 

All good advice. I am at sea level,Haverhill MA, 20 miles from the coast most of my riding. The carb came with a P 40 and main 140. It runs better with the snorkel on right now, but starts bucking around 8500 rpm. I have been tuning AMAL carbs for years but never one like this. I was thinking of raising the needle first, as suggested, and I was hoping not to have to remove the carb to do it. It looks like I may be able to rotate it to the side to get to the jet needle? After that, bigger main jet if needed. about 1500 miles on the B&B 351 upgrade. I will probably check the valve clearance while I have the tank off too. The carb came from B&B engineering set up as noted.

Thanks