750 twin, no TDC when kickstarting

I have a 80 kz750 twin, kickstart only, no tachometer, runs like a Swiss watch. Since I’m running no tach I plug the tach hole with the cable end and had a cap jb welded to that. I’ve had it like that for 6 years or so until the other day when it backed out and covered me and the bike in a ton of oil haha.

So I changed the oil and found a 18mm fine thread bolt to plug my tach hole. I rode it around last night and everything is back to normal. Tonight I go to kick it and it runs for a split second then shuts off and now I can kick the kicker all the way through the stroke without it stopping at tdc. I have spark. I took the plug out and can see valves and pistons moving. I can hear air going in velocity stacks. Another weird thing is when my clutch is pulled in while I’m gear it rolls very very hard. It rolls fine in neutral.

What the hell happened? Did I break a kicker gear?

I would be surprised if you broke the kicker gear unless you are doing the "tough guy" kickstart. It sounds like the clutch is not engaging/disengaging correctly, which will not allow the kicker to turn the engine. I would adjust your clutch. If that doesn't fix it its time to drop the oil pan and see whats going on in there.

I got around to adjusting the clutch and that didn’t do anything. I also dropped the oil pan and it’s clean as a whistle. Guess I’ll pop off the right side case cover and see if there is anything.

Rotate the engine by hand and see if you have resistance as you approach tdc.
Use a ratchet just in case the engine suddenly rotates..you won't bust your hand open.

You may do a compression test as well..I'm thinking you may have a valve train issue.

I have very little resistance at tdc when rotating by hand.
Compression is 90psi in both cylinders after adding a cap of oil. Full throttle, choke closed.

gregm wrote: I have very little resistance at tdc when rotating by hand.
Compression is 90psi in both cylinders after adding a cap of oil. Full throttle, choke closed.

You need to have all the plugs out, throttle full open and choke “off”. Not sure if that’s what you mean with “choke closed”. You need to allow as much air into the engine as possible. There is quite a diverse appinion about adding oil or not. I’m in the not corner. Unless you using it to diagnose. Kick the engine as many time as needed to get highest pressure reading on the gauge. Ideally the engine should be warm it’s a more real life test.

With both plugs out I’m at 60psi in both cylinders with choke off. I can’t help but feel something went to hell in the trans.

I don't think you can kick over this engine fast enough to get an accurate compression reading. When you have the oil pan off stick your head under there and look at the gears. move through the gears by hand and check everything out. the inability to disengage the clutch is a sign of a problem there.

DoctoRot replied as I was typing...

The compression tester needs to have a valve in the tip. Otherwise it will read lower than actual. I've always heard that if the cylinders have even compression (within like 10%) then it should run. It might be barely though at 60 psi. If valve timing jumped or something then it can cause low compression numbers because it won't allow enough air in, or allow it to escape early.

TDC is just a location of the piston. What TDC feels like is the compression of the engine. If it has low compression for any reason then the feeling of TDC won't be as obvious ("no TDC"). I don't see how low compression would be transmission related. Sounds like you have 2 issues. I've never messed with that specific bike so I won't be able to help much beyond general advice.

Good luck with the fix.

I can only offer a little general advice as M_A_T_T mentioned.

An engine needs 3 things to run, fuel, compression, and spark. I’d be thinking the same as Doc. The clutch might not be disengaging the trans and the extra mass is not allowing the engine to kick over fast enough to start. I’d check out the clutch. You have spark and fuel.

The very little resistance at tdc concerns me. Of course "very little resistance" is subjective.
Check your valve clearance at tdc to make sure your valves are completely closed.

The valve clearance comment reminded me of something. My brothers 90 cbr 600 just wouldn't start one day. He went through trouble shooting a bunch of stuff. Changed coils, rebuilt carbs, etc. I had suggested checking valve clearance and he kinda brushed it off at the time. Eventually he checked the clearance, which needed adjusted, and it fired right up. No problems since. (Thanks Nessism and others who regularly suggest checking valve clearance)