Bicycle Engine Sputter

Biker Mike · Mar 25, 2008

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?).

Ilikeabikea · Mar 25, 2008

Re: Engine Sputter

http://motorbicycling.com/f30/bicycle-engine-total-tear-down-391.html

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

Bikeguy Joe · Mar 25, 2008

Re: Engine Sputter

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

Have you tried a new plug?

deacon · Mar 25, 2008

Re: Engine Sputter

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.

Pablo · Mar 25, 2008

Re: Engine Sputter

Biker Mike said:
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?).

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.......

Biker Mike · Mar 25, 2008

Re: Engine Sputter

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.

Pablo · Mar 25, 2008

Re: Engine Sputter

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

Biker Mike · Mar 26, 2008

Re: Engine Sputter

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.

Bikeguy Joe · Mar 26, 2008

Re: Engine Sputter

Biker Mike said:
I shut the fuel valve off while riding and once it started running out of gas (leaned up) the sputter went away.

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?

Biker Mike · Mar 27, 2008

Re: Engine Sputter

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. :ride:

paul · Mar 27, 2008

Re: Engine Sputter

that is what ussually happens to me. i got my bike all back togather after remodeling it and went for a test drive. pedaled till i thought i was going to have a heart attack and the bicycle motor just wouldnt start. got back home put it in the garage cursing and looked down and remembered when working on it i disconected all the wires. conected them and zoom off i went. i was like duh

deacon · Mar 27, 2008

Re: Engine Sputter

Left the post office yesterday, forgot to turn the gas back on got about two blocks it died and I cursed. Then of course I found the problem and was so proud of myself lol

nogoodnic · Mar 27, 2008

Re: Engine Sputter

I would deffinatly start with the exhaust gasket. The kit gaskets are crap and I have blown more than I can count, I have started making my own gaskets out of high temp teflon that I hand cut...Kelly

deacon · Mar 27, 2008

I know a leaking exhaust is noisy but I had no idea it could cause an engine to skip. I would think skip was related to the firing of the electrical system. I have always thought of it as a miss fire. I guess I learn something new every day.

Norman · Mar 27, 2008

missing can be caused by a plug that getting dirty or a bad plugwire/connection. A wire that's chafed allowing it to short out. Like wise with the kill switch. or any wiring connection that is not good and tight. Water in the fuel will make your day. Partly plugged filter inside the tank which you all know the tank is spotlessly clean and will never do that.
Then there is the did you hear that thing as well.

deacon · Mar 27, 2008

So you are saying electrical or fuel problem. Yes I have had water in the gas and it did make it run like crap. Again I am reminded of something I had forgotten. For water in the gas, I use alcohol. Water will mix with alcohol and alcohol will mix with gasoline. Or so I have been told.

Norman · Mar 28, 2008

alcohol will not mix with the type of oils we use, has to be castor oil or an syn. oil that will mix with alcohol. a very small shot of alcohol probably won't hurt but no more than a shot. alcohol will do nasty things to your engine if its not done right. Best thing if you think your fuel has water is get rid of it all including the fuel filter and fuel in the float bowl. The inline paper fuel filter that we should be using will absorb some water but then will become water wet and kind of plug off. It can take a lot of dirt but not much water. Deacon is right alcohol will mix with gas and alcohol will mix with water. I still don't like the taste though makes me spit fire.

Venice Motor Bikes · Apr 2, 2008

Biker Mike said:
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?).

Change the plug too, NGK B5HS!... move the carb needle to LEAN (needle down, c-clip at top)Double check all wire connections, I like to use solder,(crimps vibrate loose)!
The exaust leak is NOT the cause, my whole pipe fell off in the street going home once & I lost the nuts, so I rode it home with NO PIPE & the bike never ran faster!!!
Another thing I do is adjust the gaps between the spinning magnet & the mag coil to make them equal. I noticed on a few of the engines that I bought the mag coil was WAY OFF. (almost touching)
I don't know if it helps?... but why not?
Also try a 25:1 mix & then a 30:1, see if that helps?

Bikeguy Joe · Apr 2, 2008

Have you adjusted the mag coil? I was asking about that in another thread.

Steve Crutchfield · Jul 9, 2008

I am having the same problem with my chinese motor. Oil appears to be coming from exaust. It sputters at mid range then it seems to come alive and gets up to 35 mph & runs smooth. Then starts sputtering again. I have checked carb & intake all seems well. ( as well as it can anyway ) I noticed today that my plug wire is coming apart. How do you replace it? Do i have to replace the whole CDI box?

Bicycle Engine Sputter

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