Bike Has Spark, Won’t Start

[MiffedFan]

We have an 80cc motorized bike kit that doesn’t seem to have any obvious issues, has spark, clutch engages and disengages nicely, new carb, we have changed the gas and mixed the oil to the right ratio, tested the CDI and the magneto with a multi meter, tested again and again, the bike will just not start. At one time the muffler was lose and tightening seemed to allow it to start but has since stopped starting again. We are running out of ideas as nothing seems obviously wrong here.

Based on what I have given above, can anyone provide any new suggestions for me?

 

[Venice Motor Bikes]

what is the gas /oil ratio you are using?

 

[MiffedFan]

1 gallon of gas to 6.4oz of oil. I don’t recall the exact ratio but this was what is came out to for the break in period.

 

[Venice Motor Bikes]

That's too much oil... Try 3.5-oz oil / 1-gallon of gas... (32:1)

Next... How did you test for spark?

 

[MiffedFan]

Held spark plug against the cylinder head while connected to the CDI and cranked the wheel. We have visible spark.

 

[Venice Motor Bikes]

Held spark plug against the cylinder head while connected to the CDI and cranked the wheel. We have visible spark.

That's the best way

 

[Greg58]

Two things I can think of, is fuel getting to the cylinder? You should see unburned fuel on the plug. Is the head leaking? A leak will make it real hard to start. What a lot of us do is true the head with sandpaper taped to a flat surface like a piece of glass, sand the sealing surface in a circular motion then check for high or low spots. I have found some that were not flat.

 

[Greg58]

Have you removed the magnet? If so it could be on backwards. The keyway should be at 1 o'clock at top dead center with the flat side of the magnet horizontal. It's easy to do, I've done it myself.

 

[MiffedFan]

Thanks for the suggestions! I don’t think gas is getting to the cylinder. Spark plug and piston are always dry it seems whenever we have opened it up. Not sure why. My suspicion is gas is not getting there for some reason. Have also put some gas in the cylinder directly under the spark plug, for a time this started it but it would not stay running. Now it doesn’t start at all even with that. I will also mention that I believe there were gaskets under the intake manifold and the muffler connections, but those have deteriorated and are gone. Could this be a source of air leaks even if the connections are tight? Magnet has never been removed or adjusted.

 

[Venice Motor Bikes]

How long have you had the bike (& has it ever been running properly)? I'm trying to figure out if this is a 'new bike' problem, or if it's something that recently broke.

 

[MiffedFan]

Bike was built in July. Ran fine for a while. Issues started in Sept I believe. was able to start off and on. At one point we got the muffler tightened and it started, then suddenly stopped again.

 

[Venice Motor Bikes]

Replace the intake & exhaust gaskets (& make sure they're sealed correctly)... a intake air leak can easily cause the lack of fuel that you're seeing.

Also... if you've removed the head?, you should sand the surface of the head (as Greg detailed), & install a new head gasket & torque the head to 12 ft/lbs. ( these heads warp very easy & have compression leaks if over torqued).

 

[MiffedFan]

Will do and will report back afterwards.

 

[MiffedFan]

New gaskets on intake manifold and muffler. No change. Will work if the cylinder head and the head gasket next.

 

[Greg58]

Any oily areas around the base of the cylinder? I've blown a base gasket, that will keep it from starting, there's a template in the instructions section.

 

[Greg58]

Does the compression seem to be the same? If not the head gasket or a broke ring could cause it. Don't give up we're here to help.

 

[MiffedFan]

No oil around the base. That all seems sealed up well. Compression feel, I’ll have to check. My son is testing riding it, it’s his bike, but I have tested as well. I will try tomorrow. I will be working on the cylinder head and gasket tomorrow. Where would the seal be, if one was blown?

 

[Greg58]

While you’re working on it remove both side covers, there’s a seal on each end of the crankshaft, look for fuel, especially the left side behind with the magneto. That seal is thinner than the one on the right, I’ve had problems with that seal on one of mine. If you don’t find fuel it would be hard to see if those seals were leaking.

 

[MiffedFan]

So I was able to test the bike tonight. The compression does seem better now that the gaskets are there, but no ignition. Work on the head gasket and cylinder head will go ahead tomorrow as well as checking those seals.

 

[MiffedFan]

A couple of updates. Sanded cylinder head, replaced and torqued to 12 foot lbs. Not able to replace the head gasket right now, but will if it could still be the issue. No ignition, but with the spark plug out, I definitely smelled more gas than I had previously coming out of the cylinder. We also put some gas under the spark plug, no ignition. Haven’t checked those seals yet, but I will. Also checked for spark again, we still have spark.