[Tim Koyen]

Didn’t watch the whole video, but any chance its something silly like the axle sliding over and dragging the brake in the lefts?

[Dustin McGrew]

Tim, its funny you mentioned that because I had the same exact issue in our 2nd race of the season lol. That was just a case of me being a noob and not checking my bearing set screws. Had a few of them fall out and the axle shifted and rotor started rubbing the brake pads. That was more of a gradual feeling though and it bogged the engine down. This new issue with left turns its like the engine completely shuts off for a split second.

[Gary Lawson]

Check the fuel pickup tube. Make sure its long enough and not old/hard. Also make sure your leg doesnt grt near the holes in the airbox. Your suit can choke the engine slightly.

[Dustin McGrew]

Thanks Gary. You might be right about the airbox. I’ve heard that issue mentioned before and it never even crossed my mind that it could be what my problem is too. Maybe I lay my leg down a bit more after 5 laps. I do know that the airbox holes are pointed towards my leg a bit. Hope that is the problem, simple fix :)

I’ll check on that pickup tube too. It’s been on the kart since I bought it in October.

[Gary Lawson]

Yep no problem. Always angle away and zip tie to the seat so it cant turn. Good luck

[James McMahon]

If its not the airbox, observe the rev counter (or review the data) and see if it behaves oddly when this happens. It does sound like an ignition issue. They tend to crop up when the motor gets some heat into it and disappear when its cold.

[Dustin McGrew]

Mike, another EKN member messaged me today and said that the low speed needle might need to be set richer (maybe an 1/8 turn more). He said the engine can start to run leaner as it heats up so that might by why the problem that I have only occurs after I’ve driven for about 5 minutes. Unfortunately I haven’t been able to get to the track to try different things yet but I should be on track this Friday. I’ll let everyone know if anything works.

[Walt Gifford]

What’s your pop off pressure? Maybe drop it down to 8 psi or raise the arm a little. Have you cleaned the carb screen every track day. Throw in a new pumper.

Gif

[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.

[tony zambos]

Don’t bend the individual float arms. Instead, bend the tap over the needle valve.

[Walt Gifford]

Actually I was speaking more to the OP.

[Dustin McGrew]

Finally got back on the track yesterday. I rotated my airbox so the holes faced outward instead of toward my leg. Made 3 10 lap runs and it never stumbled. So this problem had to have been created by my leg covering the airbox holes.

[Walt Gifford]

That’s a carburetion problem. You don’t see it too often but it happens in a certain series of turns/straights with some set ups. The track empties out the crank case and you open the throttle too fast and no fuel. Usually a long straight tight turn short straight another turn and when you get on it nothing.

Gif

[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

[Author]

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