Bike Has Spark, Won’t Start

MiffedFan

Member
Nov 8, 2021
51
1
8
46
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?
 

MiffedFan

Member
Nov 8, 2021
51
1
8
46
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.
 

Greg58

Well-Known Member
May 1, 2011
4,602
1,378
113
63
Newnan,Georgia U.S.A.
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.
 

MiffedFan

Member
Nov 8, 2021
51
1
8
46
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

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,816
737
113
Los Angeles, CA.
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

Member
Nov 8, 2021
51
1
8
46
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

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,816
737
113
Los Angeles, CA.
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

Member
Nov 8, 2021
51
1
8
46
New gaskets on intake manifold and muffler. No change. Will work if the cylinder head and the head gasket next.
 

Greg58

Well-Known Member
May 1, 2011
4,602
1,378
113
63
Newnan,Georgia U.S.A.
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.
 

MiffedFan

Member
Nov 8, 2021
51
1
8
46
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

Well-Known Member
May 1, 2011
4,602
1,378
113
63
Newnan,Georgia U.S.A.
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

Member
Nov 8, 2021
51
1
8
46
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

Member
Nov 8, 2021
51
1
8
46
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.