Totally Stumped!

I can start my brand new engine but it barley runs and doesn’t respond to the twist of the throttle. I ordered this engine because after replacing the plug, plug wire, CDI, magneto, etc. on my other engine and finally threw in the towel on it. It’s a 66cc Grubee ( motor only) that has a few upgrades like a sick bike parts shift kit and expansion chamber exhaust. I couldn’t get it to fire with my old CNS carb so I switched back to the factory carb.

After many frustrating attempts with both carbs I found a working CDI and was able to get it to turn over. I removed the chain that drives the rear wheel and can get it to run by pedaling. The problem is that is it is running at a weak idle. Goosing the throttle makes it louder but does not increase the rpm’s. The slide does move up and down inside the carburetor. I have tried all for settings by moving the E clip on the needle to no effect. (Although with the lowest setting it stalls.) I bought a brand new factory carb and played with the needle setting with exactly the same result. Tried filter and no filter- so I don’t think it’s the carb. I don’t think it can be the plug because it runs the same with the new 3 pronged plug or an old one gaped at .025. The CDI gives enough juice to the spark plug to start it and the wire is a SBP upgrade so I don’t think the problem is there. I replaced the intake gasket with a new one and smeared bearing grease around the joint where the carb mates to the intake as a quick check for leaks. No change. Removed the muffler and blew thru it, no dead mouse. Fuel is brand new and mixed about 25 to 1 and seems to flow freely. I have checked to make sure the the head bolts are tight. I can get it to idle at , oh I’m guessing, 800 rpm but that is it. No power and twisting the throttle must be doing something because the slide moves and the motor gets louder but does not go any faster.

The weather has been fantastic here in Missouri for mid October and I am dying to ride before it starts the steady decline in to winter. If I could just get this little booger to start. Any ideas?

corgi1 said:

Is the kill switch conected?,,plug wire?good conection at top of the plug?,,,have you pedaled fast checking for spark(w/plug out)at higher speeds?

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Hmmm. I hadn't thought of taking the kill switch out of the equation. I figured that it either run or not run. I am going to go clip the wires and see if I get lucky.

Well, that didn’t work. I kinda knew it wouldn’t be that easy. I also made sure that the plug was screwed in tight and the wire was secure to the plug.

Corgi1- about pulling the plug and checking the spark while pedaling fast... do you mean the spark might weaken as the revolutions increase? I haven’t heard that before. I will check that later tonight.

bairdco said:

the only thing i can offer to that extensive list is something that worked for me when i had a bike that wouldn't want to start anymore...

i unsoldered the wires from the magneto, then rewired it with new wires. after that, it fired right up. it was like a new bike.

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bairdco- I might as well give that a try. I really can't think of any thing else.
Geeez, i bought this new motor to avoid doing all this crap. It's going to rain in 2 days! I gotta get some rides in!

It Runs!

Thanks to all that offered advice. I went to Wally world and bought a soldering iron and some 16 gauge wire and rewired the magneto. Took it out back and tried to start …zilch, same problem.
It was dark out by then and I was working under a bright light hanging on the deck. Running a fuel mix 25 to 1 there was a lot of smoke and I noticed that there looked like smoke was coming from the cylinder head, I grabbed a bright flash light and discovered that the even with the exhaust screwed on tight there was smoke leaking out where it was bolted to the cylinder. I unbolted the exhaust, cranked it over and TA DA!
It screamed like a bat outa ****. I don’t think my neighbors were happy but I was. I had pulled the muffler before but I suspect at that time I had a bad CDI hooked up.

The SBP expansion exhaust couldn’t have 30 miles on it and I never would have thought that it was the culprit. I don’t think the expansion part has any baffling in it so I drilled out the rivets on the very end and pulled out some tightly packed fiberglass material. That must have been it. I am going to lightly pack in some copper or steel scrubbing pad material to cut down the noise of a straight pipe. Anybody have an opinion on which is better?

PS My daughter heard the motor start and asked if I would be up early. “Well yes, as a matter of fact I will. I’ve got the day off work and will be home only for gas and maybe food. Maybe not. See you at dark.”

Found the real problem.

I ran a stiff barbed wire through the exhaust and pulled out a bit of oil soaked paper. It must have been in there since it was manufactured. The shape was as if you took a piece of paper and twisted it and cut it with a pair of scissors and then unraveled it. It was a thin strip with a jagged mountain range edge to it and was about 3 inches long. Maybe it was the edge of a cutting or welding template. The whole thing if puzzle pieced together wouldn’t cover half a playing card. But it was just big enough to block the exit tube on the exhaust. Go figure. Off to ride!