Engine Trouble Engine dies over half throttle under load

Discussion in '2-Stroke Engines' started by KaoReal, Sep 28, 2016.

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  1. KaoReal

    KaoReal Guest

    I think I did something silly by changing a whole bunch of things at once. I can't identify the problem now. The problem: The engine starts great, idles great, might be slightly low on power up to 50% throttle, but anything after that is a brick wall. Seems to struggle up hills, and I think the engine runs WOT downhill. on flat, the bike slows right down, no power at all, and if I back off the throttle it kicks back on.

    From a stock setup, I added a Jaguar CDI, Mikuni VM18, RSE Reed valve, custom 1.5" manifold, and modified the piston to accommodate the Reed.

    I didn't make boost ports, just changed the intake side of the piston by drilling it. Maybe this my error. Compression is reading 140 psi. Taking off the air filter doesn't improve the situation, neither does engaging the choke. This carb uses a separate circuit for choke instead of a butterfly. Don't know if that changes anything about using choke for diagnostics.

    Thought it could be jetting, so I took the stock 70 main up to 100 incrementally. Seemed to be helping, but something in the back of my mind tells me that's way too big, and I'm chasing rabbits and not looking in the right direction. Cleaned the carb each time, no leaks on exhaust or intake. I'm stumped! Do I just keep jetting higher? Seems to me that an increase of that magnitude would have solved my problem by now if it was going to work at all, but I've never done a Reed valve conversion, so I don't really know. Oh, I also measured incorrectly when drilling and have slightly obstructrd holes in the piston. Is it very critical to have them all 100% exposed?

    Another thought; I did these mods with the intention of porting for higher revs, based on some Jaguar information I pieced together. I don't know the details of port timing, but maybe this setup is incompatible with stock porting?