Timing issue? Carb issue? Valve issue?

[Jmiller057]

Sorry for the length!!

Alright guys here is a little background info. I bought a 1976 xs650 back in August and totally stripped it down to the frame to rebuild it over the winter. I sent the motor with about 14,000 miles on it to a local motorsports shop near my house for a top end rebuild and carb rebuild (the bike ran great before the tear down, but it needed gaskets for sure, so I figured I might as well rebuild it since it is all gonna be torn apart anyways). The bike is all together now and I keep running into issues.

To start off, the right side carb will spill gas out the overflow tube sometimes while you try to kick the motor (mostly happens with the choke on). Had it back to the guys at the shop to rebuild the carbs 3 times (at no expense of course). This last time they put in all new parts in the carb and pressure tested it. I said to check the float, cause thats what I have read on here, but they said it looks fine and they rarely go bad. So I rebuilt the petcocks thinking that maybe that could be the issue. Never the less, they still leak when trying to kick for a cold start.

But here is the main issue. Like always I start the bike and let it warm up for a minute or so. While sitting on the center stand in my garage, I can rev the bike up to 3000-4000 rpms and never have an issue. The bike sounds great. When I put it in first gear and pull out of the drive way, as soon as I hit 3000-4000rpms the bike sounds like it is missing, or sometimes back firing. While other times, from a stand still to 3rd gear it runs like a charm. But it always seems to act up around that 3000 rpm range. Every once in a while I will get a back kick when trying to start the motor (It f**ked up my knee one time), and I have gotten a backfire out the intake a couple times too. Also I forgot to mention, sometimes on a warm start, at idling rpms, it sounds like the motor isn't all there (I can put my hand at the end of the exhaust and the exhaust pressure doesn't feel as strong), but once you rev it one time, the motor sounds like a raped ape at idling rpms.

This main issue, in my eyes all leads back to a timing issue. The ignition shouldn't be an issue since it was perfect before the tear down right? But why does it run so smooth in neutral? I'm looking for some input before I go back to these guys that the local shop. I'm kinda getting irritated with it. Any input is appreciated.

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[Downeaster]

Rule #1: "If you want things done right, do them yourself" There is simply no way to get around that statement.

Rule #2: "Never believe anything the Previous Owner or Mechanic tells you." I've been a mechanical and electronic troubleshooter for 40+ years, and the first thing I learned is that the previous technician was full of shit. Verify everything.

A number of issues are possible, so I'd start with the standard tuneup progression (tutorials on each step are available via a quick search on this site):

1. Check/Adjust the cam chain.

2. Check/Adjust the valves.

3. Check the action of the mechanical advance.

4. Check the condition of the points and adjust the gap.

5. Set the timing.

6. Check the air cleaner elements. If you're using pods, make sure they're not blocking the ports on the carb bell.

Having verified that all of the above are correct, fire it up and see what you see. If you still have flooding/running rich issues, continue with:

7. Take the carbs off yourself and inspect to see if they were cleaned properly.

8. Check the float condition (they shouldn't slosh or be noticably heavy) and height setting.

9. Check the condition of the inlet valve and valve seat.

Do all of that and get back to us.

 

[Jmiller057]

Thanks Downeaster! I'll get started this evening.

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[5twins]

If a new cam chain was part of the rebuild then that would have changed the timing. A new, tight chain will put the cam in a slightly different position in relation to the crank. Your points, which run off the cam, control your timing. But a competent shop should know that.

 

[Jmiller057]

yes, they installed a new cam chain. So I am thinking that is what caused the issue like you suggested. Will Downeaster's steps solve the issue? I know the proper cam chain, valves, timing, carbs steps as Downeaster stated with a few most steps I need to look into. Or will I have to tear into the motor to re-set the cam chain if it is off one tooth?

Side note: the guy I was dealing with in the service department that was rebuilding my motor no longer works there. They didn't say if he was fired or quit. Just simply said they 'parted' ways. I wish I just did it all myself like Downeaster said, I just figured with school and work I would never get it done, but it seems I would have been better off.

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[5twins]

If the timing is simply off a little then yes, those steps should fix things. If the cam is off a tooth, the top cover at least will need to be removed and that, of course, means pulling the motor. There is a way to check that the cam is installed in time correctly with the motor still together and in the frame. You will need to pull the advance unit off is all. Here's a link .....

http://www.650motorcycles.com/CamTiming2.html