1980 sportster trouble

Yes 4cams. Checked cams and reset them. Thought that might be problem too. Took out all solid lifters checked them they are all good. All valve guides ande springs are new. Had professional shop do them. This bike just hates me.

Already tried that. Its a no go. Thanks for idea though

Yes they both have spark when out setting on heads. But when plugs are in bike and bike is started it only wants to run on back cylinder only.

OK.. So there is fire on both cylinders, and the cylinder passes a leakdown test with no air escaping from valves or into the base, and even though the compression is low,(and I assume you tried different guage for comparison) there should still be enough to ignite the mixture, is it flooding the plug or is the plug dry? Are plugs properly gapped? Is it possible to measure the cylinder and see if the shop bored it out too large as compared with the other? Don't laugh, saw it happen once.

if you have 50 psi on the front and 120 on the rear . an exhaust valve is hung open pull the exhaust push rod and recheck compression should be a **** load high . if it is pull the rocker box . you have a rocker holding the exhaust valve open because its hitting the box . what high lift cams are in this build / also are they adjustable push rods?

Seems like you're chasing 2 problems at the same time...I'd look for what's giving you a 70lb difference in compression first,then look why the candle won't light the fire...What BP said makes sense...when you pump the air in for a leak down, it pushes the valve closed and you get a good reading...when you crank it checking for pressure,the valve sticks open and bleeds off the compression...Fix that and she might just fire off on both cyls....

Not sure about high lift cams or not. Push rods are not adjustable. Will try your idea to pull push rod and recheck compression and let you know if this works. Great idea I never thought of that. Thanks

When I pull front plug it is dry. This made me look at the fuel delivery and carb. Thought maybe fuel was only getting to rear but after checking carb and intake manifold it all checked out ok.

Thanks. for all the great ideas guys. Nothing seems to make this beast run. Taking break from it for few days to clear my head maybe get new perspective. Time to give the love love of my life some tlc. She's a 1973 xlch and really good to me. Needs new fork seals, chain adjustment and push rod gaskets, and still runs like a dream. I love old irons

did you ever find the answer to your woes?

Unfortunately no. Still working on it. I have tried everything I can think of and everything anyone else suggested. Tomorrow I am going to try setting timing on front cylinder tdc and see if that works. Lol. This is just crazy. I refuse to let her be a garage queen! Something's got to work eventually. Right? Glad I am patient person. Thanks for asking.

Did you check the pick up coil ?never mind different bike lol

Did you back off the push rods and recheck compression

I am curious, what cams do you have installed?

Ok I just read a few post back on this thred it states you have ssolid lifters if you have solids how are you setting the push rods? They should be set at zero lash then backed off a half turn . Just like shovel solids if not the valves will never seal on the seat . Also you state in another post that you have zero leak down thats impossible every motor has some sort of leak down a good test would be no more than 6. Percent and that my friend is absolutely percect centric cylinder . Something is not adding up here either we are not getting proper diagnostic info from you or you are not giving us proper information on your diagnostic review it a tractor motor spark fuel compression it has to run . Your cam timing has to be off or your valves are hanging open .

I set pushrods as you described. I agree it has come down to the timing. Will try again to set it tomorrow and see how it goes. Thank you for the help