I just had my motor dynoed with a 22mm mikuni and it gets up to about 4000rpm then stops. The guy says it is too rich with a 130 main and 12.5 pilot so we went down to 98 main and it does the same thing. Carb bad?? Cleaning?? I don't know what is wrong but I need to get this thing working so as much imput as quick as possible would be greatly appreciated. :smile:
That huge of a jump between main jet sizes is a bad idea. You could have went from too rich to too lean easily. You need a selection of jets to even begin to tune these, or you're wasting dyno time. Add a 15 and 17 pilot jet to the mix, because at WOT, these jets are additive.
Where is your needle set at? Try for the center position, get the jets close, then lean or rich on that needle.
You also need to look at, and describe your plug appearance.
Where is your needle set at? Try for the center position, get the jets close, then lean or rich on that needle.
You also need to look at, and describe your plug appearance.
Ignition can cause what looks like rich running (ask me how I know). When you say it stops at 4000 is is misfiring? Is it smoking black out of the pipe? I once tried to put the float bowl on backwards and then realized what I was doing and put it on correctly. What I did not see was that I pushed the float up and bent the adjustment tang. It ran super rich after that and it took a while to figure out what I did. For the Chi-Mikuni carbs we use if you hold the carb upside down the float seam should be level if the adjustment is close.
What cam is in the motor and what is the length of the manifold? The only reason gas would spray out the carb is a reversion issue which would make me think maybe cam is out a tooth or maybe carb is flooding and he meant gas was dripping out. Reversion will cause a rich indication because fuel/air mix is blown out the carb and sucked in again picking up more fuel so mixture is very rich.
No they are pretty problem free unless you screw them up like I did. The 130 jet + or - 10 seem to work good and pilots usually 15 or 17.5. Did you measure the seat pressus of the
valve springs? The 26lb springs are speced at that rate at a installed height of .850, if you are greater than that the seat pressure will be less. A 308 cam with 1.3 rockers will need at least 26lbs of seat pressure to work at higher RPM's but 4000 seems low even with a bit less than 26 lbs. First check the float height that's easy.
valve springs? The 26lb springs are speced at that rate at a installed height of .850, if you are greater than that the seat pressure will be less. A 308 cam with 1.3 rockers will need at least 26lbs of seat pressure to work at higher RPM's but 4000 seems low even with a bit less than 26 lbs. First check the float height that's easy.