[M Crotty]

I have a 2002 Sr. with the bolt on evo upgrades, the local track is at 4300 feet so we jet a bit lean.

On a 70 degree day I started with a 130 jet and kept stepping down to try and find the pop. At 112 I ran out of jets and never heard the pop, although I seemed to get best revs around 118.

I’m a beginner, so my best revs may have been due to my mood rather than the jet, still too early to tell. It seems to come up to speed faster than it used to, a bit less bogging, but again consider your source.

Do you think one jet above popping is still a valid strategy? Anyone ever achieve popping on an evo?

[M Crotty]

Thanks Walt, I’ll try to find a way to keep a little more fuel in the bowl one way or another.

The low speed jet fix sounds odd, why would it be directional? Maybe you’re barely on a threshold.

I’ve cleaned my carb passages as a first attempt (and the screen filter), if that doesn’t help I’ll try bending the arms. Diaphragm type fuel pump has 4 races since a rebuild, I’m expecting to rebuild each season so that should be OK.

I’m rotax, so my pop-off pressure isn’t controllable, however measuring it would probably teach me something. I can bend the float arms or use heavier floats to increase the amount of fuel in the carb bowl.

My ribs are recovering, I’m hoping to make the next club race July 5th. I’m changing a bunch of stuff during my forced hiatus so it’s going to be difficult to tell what’s working this time around.

[M Crotty]

I’ve been working through something just like this. So far I’ve tried gearing shorter and playing games with the pedal in the problem corner, both of which do help. I’ve checked the frame for twist and it’s slightly twisted the wrong way to cause my issue, it’s lifting the inside rear more in that direction, maybe it drops too soon. Obsessively clean the power valve.

Anyway my scenario matches Walt’s description, a fast S, short straight, then hairpin. What would you do to the carb? My guess is:
Clean passages.
Raise the fuel level in the bowl.
Replace needle valve.

Curious,
mike

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