76 xs650 right cylinder problems

[Jacob Canada]

First time posting. Ive searched far and wide and cant find anything that pertains to my issue. I have a 76 xs650 that was running great. Then broke down one day after riding about 10 mi. After a few min the bike would fire up then die. Thought it was the coils, changed them and the bike seemed to be fine for a day. Went on a ride and about 2mi in the exhaust note from the right cylinder totally changed and power wasn't as great. Made it home and have tried everything with no avail. Here is what ive done/ parts im running.

New plugs
New coils
New points and condenser
Rebuilt carbs [stock bs38s]
Uni foam air filters
Straight pipes
Checked valves
Checked timing
All fuses look good
All grounds and wires seem in place
Compression is at 115 on both sides.

Bike will fire on first kick and idle great but when I rev it up the right exhaust is considerably louder then the left. Has a very brappy type sound to it. When riding it doesn't get up go like it used to and back fires a lot. Plug on said side looks wet when pulled and cylinder is warm. What am I missing? What would make one side way louder then the other? Have any of you experienced this before? Im hitting a wall. Any help would be greatly appreciated! Thanks in advance.

 

[Paul Sutton]

The difference in noise could be just down to very poor firing on the one side - hence the reason for it being warm rather than hot.

Check the wiring continuity from ignition power all the way through to the points just in case there is a bad connector or broken wire.

Does the wet plug dry in the sun? If so then it is wet with fuel rather than oil.
Is there any evidence of fuel soaking the Uni foam on the problem side, or fuel leaking from the foam when engine is off and fuel on?
Check the fuel level using a plastic tube on the carburetor bowl. Is the carburetor a bit sooty from backfiring?

If you have a strobe light you could quickly check the timing to make sure one set of points hasn't shifted badly. An irregular reading may indicate capacitor issues. Do you have another capacitor to swap in just in case?

Have you checked the gap on the exhaust valve/lash screw just in case some thing is wrong there i.e. badly chipped lash screw? If you turn the engine over slowly using a socket on the alternator and measure the gap you may get an indication of the valve sticking, but this may only show up a engine speeds because your compression values are OK.

I realize you have checked a couple of these already.

Best of luck.

 

[Jacob Canada]

Hey Paul, Thanks for the reply! I will go through the wiring and see what I come up with I am going to swap my bs38's tonight and try some bs34's that have been gone through to see if it is a carb issue as well.

All the valves seem to be spot on but I will check them again.

I do know with the bs38's that are on the bike now, yes fuel will leak out of the left carb when the bike is on the kickstand and fuel is left on but not the right side which is the side I have the problem with. I will tear into those when they are off and see what I find. I'm thinking its a weak spark for some reason but cant figure out why?

Thanks again

 

[grizld1]

Good troubleshooting list from Paul. In addition, do this. With lights off and keyswitch on, check battery voltage and compare to voltage at the coils (R/W wire). If there's more than 0.5V difference, you have a dirty/defective contact at the key switch (check brown wire in headlight shell), kill switch (check R/W wire in headlight shell), and/or connectors between kill switch and coils. And check your oil for fuel contamination if you've let the bike sit with the petcocks on.

Good luck!

 

[Jacob Canada]

Grizld1 thanks for the input I will be checking all of the above when I get home from work tonight. If I get any head way or some numbers I will post my findings. I really appreciate the help guys!

 

[gggGary]

yeah I'd be charging the battery and checking that the bike's charging system is working.

 

[Jacob Canada]

Hey Gary, the battery says its charged but who knows could have a bad cell. Might be time to change it and see if it makes a difference.

 

[gggGary]

watch a volt meter off, at idle, and revved up.

 

[Jacob Canada]

So I am pretty sure its an electrical issue. I checked the ignition switch and everything was good there. I put another set of carbs on last night to see if that makes any difference. It feels like im getting a weak spark on the right side. I have a friend coming over tomorrow that knows a little about electrical. I will post my findings to keep you all updated on my progress with this issue. Could be a bad battery even though my charger is saying its charged just might not have enough juice pumping through the system. We'll see..

 

[Jacob Canada]

I've attached a link with the sound its making. From what I can tell everything seems in order except the brappy loud sound from the right exhaust. Any thoughts?

 

[5twins]

I don't think there's anything wrong. I think that's just normal sounding for that rather open exhaust.

 

[Jacob Canada]

It didn't sound like that before? It sounded like the other side which isn't as loud? I was riding one day and It sounded like something gave way and it started running like crap and the exhaust note was totally different on the right side? At idle they sound the same but when revved up the right pipe is noticeably louder then the left? What you are hearing is the right pipe mostly. I also noticed the right pipe feels like more pressure coming out of it when I put my hand over it compared to the left. But the left cylinder seems to get hotter quicker then the right? Im so baffled with this.

 

[5twins]

Well, my first check would be carb sync. It shouldn't change radically and abruptly like that, but you never know.

 

[Jacob Canada]

How would one go about syncing these carbs? I don't see any ports on them that the vacuum lines go to? I'm running stock Bs38's. I have tried some Bs34's and it ran worse but ran and the sound was still there. I also tried a buddy's vm 34's and it ran fine but still had the sound. That's why I ruled out carb issue. But if I can sync the ones I have Ill try anything at this point! Thank you for the reply's I can use all the help I can get. You guys rock!

 

[Jim]

Im so baffled with this.

Your description is almost textbook for a baffle coming loose and blocking the exhaust.... It's abrupt, restricts pressure and reduces noise. Try taking the muffies off and see what happens.

 

[Jacob Canada]

I took the right side off and it was clear. Let me do the left tonight and see whats in there. From what I can see down in there with a flash light, and from what the guy said I bought it off of the baffles were not in there to begin with. Ill let you know what I find later today when I get the chance to take the left pipe off. Thanks Jim!

 

[5twins]

Since you don't have vacuum barbs in your manifolds, there are a couple other ways you can go about this. There are vacuum ports in the sides of your carbs, capped by big flat head screws. You can temporarily replace the screws with hose barbs for the sync gauge .....

Your other option is to remove the carbs and do what's called a "bench sync". With that, you simply look in the engine end of the carbs, at the butterfly plates, and make sure they are both cracked open the same amount. It's pretty hard to judge those small opening just by looking at them so here's what I do ..... first, back the idle adjustment screw out enough so it's not touching the cable arm anymore. This allows the butterfly plates to fully close. Now hold the air filter end of the carbs up to a good light and look in the other end at the butterfly plates. If the carbs are in sync, both plates will be fully closed and you will see little, if any, light coming through around the edges. If out of sync, one plate will be closed and the other will be showing (more) light around the edges. Adjust the sync screw on the linkage between the carbs until the open plate closes up and both are closed. It helps to remove or prop open the slides so the light comes through better. Once "synced", turn the idle speed screw back in until it just cracks both plates open a hair. This should get you "in the ball park" for idle speed. Final idle speed adjustment will have to wait until you fire it up again.

 

[Jacob Canada]

Awesome thanks 5twins! If I were to use syncing gauges where would I pick up the correct hose barbs and do you happen to know the size?
Thanks again!

 

[5twins]

The thread size is a standard M6. A few on-line places sell them, like 650Central, but what would probably be the easiest would be to get some M6 grease nipples, drill the ends a little to get the ball and spring to pop out, then use them as "nipples". Save the balls and springs by the way. They make perfect replacements for those parts as used on the BS34 choke rod.

 

[Jacob Canada]

Great! I'm going to do a couple more things tonight and update you all on my progress as I figure things out. I ordered the electronic ignition from Mikes XS so I should have that next week maybe that will help as well. Talk to you gents soon!