Four stroking most of the time?

[danlandberg]

I built a schwinn mb with a GRUBE 66cc engine kit. This is my 4th build. This kit came with a cns carb and worked o.k. during break in. Then it began to run like $#!+, 4 stroking most of the time. At WOT it would pic up speed then run like a 2 stroke is supposed to for about 25-35 feet, then bog like it was out of fuel. I replaced the carb with a stock one I had from a previous build. It now runs consistent but 4 strokes unless under load. I have changed the needle clip up 1 notch to gain Moore air to fuel mixture. (I live at 5500 ft ASL). This worked on previous builds just right. I'm thinking because it might have been running out of fuel and sucking in air making a lean condition it ran better for the 25-35 feet. The small carb works, but not like I would like. Any suggestions or Ideas on a fix for this problem? Besides mounting a "speed" carb on. I have used the "speed" carb before and like it for it's simplicity. Any comments would be helpful! Thanks; Dan

 

[Ghost0]

Your symptoms as well as your altitude suggest too large of a main jet and therefore too much fuel. I would raise the clip lowering the needle. If that does not solve the problem then I would recommend a .68 or .66 jet.

 

[danlandberg]

That was my next plan of action. If the weather permits I'll be able to test ride it between snow drifts.