aDotInTime

XS650 Kook
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Hey everyone. I finally decided to get out from under my own fear of not knowing a god damned thing and ask for help.

I have a '71 with a 750 big bore kit, HHB PMA, and Boyer's ignition. I bought it from a fellow last week and over the weekend dropped the engine into my bobber frame. I cut all the wiring and rewired a new and healthy loom. I fried the reg/reg when I was putting everything back and the bike wouldn't start. I disconnected the reg/rec and the bike fired up, and ran for about 2 seconds before dying. There after I went to kick the bike again but received MINIMAL compression. The kick through was spongy and didn't build any back pressure. I took the kick assembly out as I read that it might be an issue of a slipped spring. I replaced the assembly and went to kick again only to find the same issue.

Is this a cam chain issue? Is this a clutch issue? I don't know where to begin and am willing to do what needs to be done as I'm broke as joke and want to ride thing as soon as possible. I'd love any help. Thank you!
 
It could be a clutch adjustment issue. The kicker works through the clutch to get to the crank and turn the motor over. If the clutch is adjusted too tight and, in effect, disengaged, the kicker won't work.
 
Thanks 5twins! So would you reccomend backtracing through the clutch to determine the issue? Could it be the clutch rod, or something in the entire clutch assembly?


Edit: And just to be clear: The kicker is pushing through its throw range. So the kick lever is definitely working. It's NOT stuck.

(Thank you again!)


Edit 2: I also don't know if this makes a difference, but the clutch engages and has the proper tension from the handle bar. I don't know if that makes a difference. I haven't taken the case off yet to take a look inside... Not that what I'm looking at will make all that much sense.
 
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Go down to the clutch adjuster screw on the worm gear, on the left side cover, and re-set that. It might be too tight. You need a small amount of freeplay between the adjuster screw and the pushrod.
 
5twins,

So I gave some play in clutch line with the clutch adjuster screw. Nothing. Could it be that the cam chain tensioners are shot?
 
The cam chain tensioner shouldn't have anything to do with what you're experiencing. You have to determine whether or not the kicker is connecting with and spinning the motor over. Easiest way would probably be to observe the cam or rotor while you kick it over. That would only involve taking a few little covers off. If the cam and rotor are spinning then the motor is, and it sounds like you may have lost compression. That could be caused by something as simple as tight valves and require a valve adjustment, or it could be worse, like a holed piston, broken rings, or bent valve.
 
If it worked properly before you took the cover off my guess would be that you've somehow caused an issue with the clutch worm assembly or the clutch cable adjustment as 2M says which is causing your clutch to be constantly engaged or your kick start assembly is incorrectly fitted
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With the ignition switch off and the spark plugs out, kick the engine over... You should hear the whoosh as compression is created at TDC on each cylinder alternately. Put your finger over the spark plug holes and you'll feel the compression building.

Make sure you have the kick start properly engaged before the cover goes back on........ its easy to let the kickstart assembly get out of position if you don't maintain pressure on the assembly when replacing the cover
.
 
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Rear tire is moving when kicked. Does that indicate that the kick assembly is working and meshed properly? I actually used that video to reinstall The kick assembly. I didn't get a chance to pull anything today, yet. Is there some way to diagnose the worm issue? I fully relieved it so there was no tension in the clutch lever and I screwed it all the way in and then set it to spec with nothing. I haven’t over tightened or over loosened anything. I think?

Could it be a matter of the clutch being engaged for another reason? Why am I not getting any consistent building compression?

Thank you for taking the time. I truly appreciate all input.
 
if your kickstart is not engaging the crank then your engine won't turn over but you say that it is...
Try removing the plugs as I suggested and see if compression is building in the cylinders . Make sure you keep the ignition switch off when the spark plugs are not grounded or you could damage your Boyer ignition
 
I’ve been tracking this thread. So. You got the bike a week or so ago. You have zero history on the bike. Brought it home. Kicked it over and it ran for 2 seconds then quit. Then seemed to have no compression with the Kickstarter. Am I right so far? My first thought was..A. Trash in the chambers were blocking the valves. B. Camchain broke. That would be bad but I don’t think that happened. If it were me. I’d pull the left case cover off. Take off the left points inspection cover. Pull the plugs. Put a 17mm socket on the nut at the dyno and rotate the crankshaft. See if the cam is turning. If it is? Check compression by any means you have. Sometimes if trash is hanging up on a valve it can be blown out with compressed air at a little below TDC on intake stroke or exhaust stroke through the plug hole. That happened to me once with a helicoil because a plug was seized and stripped the threads in the head coming out. I got lucky. If that doesn’t get you back, and you’re sure the clutch is right,and you’re sure the kicker is in right, then you gotta spin that motor by the nut on the Dyno and get a compression reading. I’m by no means a guru. I’m not even a mechanic. It just seems weird that you lost compression all at once. Good luck. Gary, 5 twins, 2M, Peanut, Scull, MaxPete, Mailman and all the others here are awesome. They’ve helped me out many times. Again. Good luck.
 
Need to do some diagnostics and some maintenance to eliminate some issues...........

As 5t suggests, set, and or, check the valve settings........ If they are to tight the valves aren't seating properly, causing loss of compression..........

Take the chrome cam cover cap off and slowly turn the engine over, (by hand on the kick start or a socket on the rotor nut, by taking the plate on the left engine cover, that has Yamaha stamped on it), and see if the cam is rotating..........or the boyer back plate/magnets........

Assuming the engine turns over and still no compression.....Take the spark plug out and get the piston up near the top and shine a light in on the top of the piston............look for a hole............also check to see if the bores look scratched, (maybe a broken ring), would think if one piston had damaged rings the other would still have compression..........
 
5twins, peanut, Gator xs2, 650Skull, I just want to thank all of you immediately for being INCREDIBLY helpful and informative. I didn't get a chance to hit the garage tonight. I'll be there tomorrow morning. I can honestly say that this is the most responsive and supportive community I've ever been a part of. It makes owning an XS650 worth more than just the art of repair and the pleasure of riding it.
 
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Just a quick reply to how good these guys are. When Roland Stuart built my motor...And this is a guy who built the world record holding top fuel nitro bike...Told me “ your camchains too short” The guys in this forum said to compress the head. They were right. When I picked up my stuff I asked Roland if he’d ever seen that. He said “never”. “ I’d have bet you a thousand dollars. And Chuck would have bet you a thousand dollars that it would still be too short”. You gotta torque the head to get a new chain on. That’s how good these guys are. They beat this guy.
 
So I must be a flat out idiot. I checked the piston head and there is no holes or damage. The bores are healthy and smooth. Cleaned out with some compressed air. I am now getting about 80 psi in both cylinders. The clutch is working. The kick is working. The car is rotating on kick. The Boyer plate is rotating.

I’m confounded and am sorry if I’m not expressing my situation with clarity. This is really and truly my first time doing mechanical repair.

I thinks it’s important to note that despite having that bit of compression, it’s not building. Before this happen and I wasn’t working to get the bike started, I couldn’t build back pressure and the kick start arm would become increasingly harder to throw and that’s when I’d kick through. Now the arm won’t build any resistance outside of the minimal compression. No pressure build and ability to kick through with the appropriate level of compression.
 
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I am now getting about 80 psi in both cylinders
80 is quite a bit low. Squirt a teaspoon of oil in each cylinder and check it again. Make sure you are holding the throttle wide open and kick hard and fast until the compression quits going up. Any idea how many miles are on the 750 kit and how long did it set before you bought it?
 
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