Engine does not run at all!

nathanb

New Member
Jul 11, 2021
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A few weeks ago me and a buddy of mine put my old cylinder (in good shape) on his bike along with a new nt carburetor. he previously had a zeda-80 dio reed valve cylinder but found it was to complicated for him to work on it. Since the bike ran before we expected it to run perfectly fine with the more stock setup. spoilers, it didn't. first we found a few basic problems such as the piece of metal the float moves was bent from the factory, the clutch wasn't perfectly fully engaging, and the cdi was worn out. We fixed the issues and to our dismay, it didn't run. then we found that the previous owner had stripped the nut holding the magneto on along with the respective threads on the crankshaft. It had 10 to 20 degrees of play. we tapped the crank to the nearest size down (5/16) and reinstalled the magneto. Then with high hopes after fixing some problems with the bike itself it was even worse. Before it was puttering but now, nothing. We tried gapping the plug to get good spark in the high compression head, completely different carbs and new fuel yet still no change. I noticed the magneto had a little play in it when we put it back on. how much does that matter? 1 to 3 degrees only. also the old cylinder had a few bottom gaskets while I only put one on, did he do that for a reason? also it has a windowed piston do those work well with stock carbs? Another idea is maybe a crank case seal isn't seated in right and so the case cant hold enough pressure to push exhaust out or enough gas into the cylinder.

Here's what I know the problem isn't:
-it makes good compression in the cylinder, new rings gasket etc.
-it has fuel, plug always comes out wet
-it has spark, checked while outside the motor

Any suggestions help. I've spent a few days and only have 2 more days left to get this thing running. I could only order parts if I do it tonight.
 

nathanb

New Member
Jul 11, 2021
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so turns out my magneto was on the wrong way. its back to puttering. Now the problem with the motor seems to be the windowed piston. From other forums it seems clear that you need a reed valve to run a windowed piston.
 

Greg58

Well-Known Member
May 1, 2011
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Newnan,Georgia U.S.A.
so turns out my magneto was on the wrong way. its back to puttering. Now the problem with the motor seems to be the windowed piston. From other forums it seems clear that you need a reed valve to run a windowed piston.
Correct, it looks like you figured it out. The windowed piston is for reed valves, otherwise you will get blowback through the carburetor.