1980 sportster trouble

I have a 1980 sportster with a problem I can't figure out. Hoping someone can help. Bike has new jugs and pistons. Heads have been professionally done. Bike won't fire on front cylinder. Have tried everything I can think of. Short of rolling bike off cliff. Lol. Can anyone give me some suggestions as to what could be wrong? And bty thanks for letting me join your forum

Thanks for the welcome , hope to meet lots of new people. I tried all your suggestions. Great ideas but front cylinder still won't fire. Only has 50 lbs compression, back cylinder has 120. I am perplexed. I have never seen anything like it. if you or anyone else has any more ideas I would love too hear them. I'm ready to try anything to get this beast running. Thanks again.

Performed leak down test , held 100 lbs for over 20 minutes, never lost a pound. Pushrods are all the same. They are new and adjusted perfectly. I'm starting to hate this bike.

Already done. Rings are spaced 120 degrees. Ring end gap was machine shop set.

New gaskets and heads bench tested. I,m just gonna roll it off cliff! No, not really. I will eventually get it figured out, just not tonight. Thanks for the ideas.

If it won't fire on front cylinder, try another plug? Sometimes new ones don't work at all. All connections tight between the coil and plug wires? Hopefully it's something simple. Is your coil single or double fire? If you have EI, make sure you have matching coil. Make sure your EI is calibrated correctly. If running points/condensor, make sure you have the correct coil.

I take it you did the leak down at TDC ...0% is pretty awesome ....Did you try it a couple more times with the piston farther down the hole each time to see what you get...or add some oil in the cylinder to see if pressure came up....You're loosing pressure somewhere, an out of round or egg shaped jug is what I'm thinking since head gasket, rings and valves are holding perfect seal at TDC ...Good luck....keep us posted


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Wouldn't his problem be electric in nature? Not firing tells me he's getting no spark to front cylinder. He has compression and fuel.

But when he did his compression test he only had 50psi on the front cylinder. I wonder if rings that weren't gapped right would cause that? Too big of gap?

Rerunning leak test. Holding steady 100 psi no leaks. Still no fire. Tested at various piston position. I'm missing something just don't know what:witsend:

I'm not understanding why low compression would cause the cylinder not to fire. My cylinders were 60 and 65 lbs. respectively after my so-called rebuild LOL, but they both FIRED and I ran it that way till I got the heads redone last winter.

just checking, you say 120 rear and only 50 front cranking comp but both cylinder leakdown good? Does that have hyd. or solid lifters? to leakdown good seems like valves, rings and gaskets are ok at TDC. Are the cams and lifters still the same or changed ? Never had a sportster, you have 4 cams correct ? If you changed cams could you have the cam timming off in the front cyl. , that would change cranking compresion . or possibly a valve hanging in a guide.

Stupid question maybe, on a bike I know almost nothing about, but is it easy to swap the front and rear ignition coils to see if you can at least establish secondary ignition fire on the front cylinder? It may be a failed coil. Can't help with the compression issue. Sounds like all have good possibilities.

Check the schrader valve in your compression tester and retest with a new one before you disassemble engine. Might have a bad reading due to testing equipment.

do you know there is no spark or are you guessing because exhaust pipe is cool, if you crank engine with both plugs out setting on heads do they spark?