Bicycle Engine Sputter

When I first installed my engine, it ran out great. As time and a few miles went by, it started missing at higher RPM's. I noticed oil coming from the exhaust gasket around this time as well. My question is, would a blown exhaust gasket effect high speed RPM? I have not torn into one of these engines yet and do not know what the reed valves look like (any pic's of valves?).

bicycle engine total tear down

Go here, Norman did a complete tear down and took lots of photos...................

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There are no reed valves in these engines....they are piston ported.

Have you tried a new plug?

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Go for the wire change as well. Not much will make one of these things sputter except the electical. At least that is my thinking. Before you do replace things check to be absolutely sure the plug wire it firmly attached at both ends.

I don't know about the exhaust manifold oil though I'm not sure unless the oil which migrates down the cylinder walls as a lube, just ran out the exhaust gasket. I know the bottom of my exhaust pipe looks like crud so maybe that is normal.

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An exhaust leak will make it run a bit leaner, as will breaking in. I'll bet it's with the crappy carb, but go ahead and do the new plug and wire upgrade. After that go one notch richer on the needle.......

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Yea, I changed the wire and cap. Used 7mm wire. I tried all settings on the carb needle and then just replaced the whole carb. It still does not run like it did the first week after assembly. I will replace the exhaust gasket this weekend and let you know if that improved the running. Seems if there are no reeds, the blown gasket may effect vacuum and cause problems. Since two different carbs did the same, I think I have eliminated that as the cause. I shut the fuel valve off while riding and once it started running out of gas (leaned up) the sputter went away.

I don't know what to say about it running better with the fuel shut off.....how is the carb/manifold seal?

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Intake is sealed good. Used blue silicone on it. The engine seems to be running very rich. I took off the air filter and when I revved the engine there was fuel blowing from the carb. I may try a smaller jet.

Definitely sounds too rich then. What elevation are you at?
Where is the clip set?
What pre-mix ratio are you running?
Is it possible that you've run it rich/long enough to have partially plugged up the exhaust baffle?

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Hey Joe, the clip is on the second notch. That's where it was when it ran as it should. Pre-mix is 7 oz per gal. The baffle has been cut so it's not clogged . I think the problem is going to have something to do with the blown gasket. I'll work it over this weekend and get back with you guys and let you know what I find. It will probably be something simple and make me feel dumb.