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Post by andy on Feb 10, 2008 13:02:08 GMT -5
Hi all,hopefully somebody can help my bottom end running problems.i'm running a mikuni vm34 carb.when underway it runs great and i'm sure is set about right as the plug colour is spot on.however from closed throttle to just off throttle it feels fluffy and flat.also occasionally when rolling off the throttle coming upto a stop it sometimes cuts out.heres the interesting bit,when checking the plug colour after running at these small throttle positions it is sooty.i have played with the airscrew and tried all manner of settings but i cant get rid of the problem area.i think i'm right in saying that the carb runs via the pilot jet at the bottom end so would a smaller pilot jet be worth a shot.i recently did a top end rebuild including re-bore new piston head and valves cleaned up thouroghly,so i'm happy all is well there[similar problem did exist before].as always your comments are most appreciated.
Andy
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Post by StewRoss on Feb 10, 2008 14:52:12 GMT -5
Do you get any response to screwing the air screw adjustment in or out rev wise...? The air screw adjusts the amount of air supplied to the pilot jet. Warm up the engine and set the idle with the idle (slide) screw. Screw the auir screw in or out and try getting the highest idle point and seeing if this makes a difference to response. If it affects the idle nearly all the way out then go for a smaller size and try again. Change the jet one size at a time. Should idle highest at around 1.5 turns out if properly adjusted as a rough guide. You might also try a more expensive solution for a test and go for a higher slide cutaway than the one you have currently fitted as well. That introduces a lot more air from the 'off' and may address your problems. A good dyno check is not a bad idea also. I am not even really going to bother with playing around with my CRS carby much on the new bike I'm building when the time comes. I'm going straight to a dyno. SR  |
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Post by StewRoss on Feb 21, 2008 6:38:46 GMT -5
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Post by andy on Feb 21, 2008 11:12:03 GMT -5
Stew,That is an excellent article,so simple to understand.gonna try a smaller pilot first,i'm a bit reluctant to remove metal of the slide cos you cant put back once its gone! I'll get there.
Andy
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Post by StewRoss on Feb 21, 2008 15:10:23 GMT -5
Hi Andy, No worries...the brass slides are not real cheap either...it can make a dramatic difference though. SR |
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Post by caferacercarl on Mar 5, 2008 2:25:39 GMT -5
There's those two stroke carbs again, pilot and emulsion tube are critical, PM curly and ask him for his data, he keeps good records on those horrid carbs! Carl. PS, running that rich will ruin your new engine quick, Stew [as always] is right, Dyno time with someone who cares is amazing in its results [unleaded can't be tuned on plug colour]
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