BS34 Troubleshooting

OldskoolXS650

OldskoolXS650

Obsessed XS650 Owner
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I just bought a rebuild set of BS34's from a forum member and switched them out I noticed that the left exhaust was cooler than the right. I have Unipods and Pandemonium hot rod pipes. The PO of the carbs said he installed 45 PJ & 137.5 Main jet. I am currently charging the battery and I have been reading the carb guide. Could the battery being low cause the spark not to jump across the head? I was wandering if anyone could shed some light on what might be the problem. I plan on going thru tuning procedure once battery is fully charged. I have a Pamco and Hugh's PMA to install but I don't want to make to many changes at once until carbs are good. Thanks in advance
 
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i guess i'm always a skeptic. just because someone said they were rebuilt i would still crack 'em open and see what you got. making sure the passageways are all clear and floats set correctly is an easy procedure and can save you a lot of headache right off the bat. you said the left exhaust is cooler than the right but does that mean the left side isn't firing at all or just some of the time?
 
Hi, as Deadchef say, treat them like any other set of carbs you'd get hold of - they aren't set up right. Strip them and make sure everything as is as it should be. You're on the right path using the carb guide and definately check you have a spark like you say. Also, just to rule it out - check compression too, then you're left with fueling.
 
Ive actually run into this several times. Before doing all the carb work, do a simple plug check first. The side that is cool will usually be fouled out. Replace both plugs, then check them again. Then go through the carb checks. Both times its happened to me have been fouled out plugs. Starting with a fresh set of plugs can help you tune them in properly. Hope that helps.
 
Nail the basics, then get back to the carbs. Cam chain tension set, valves set, Compression tested. I keep one of those in-line spark testers around. They do two things show spark AND will improve how a fouled plug sparks. A device similar to this was sold in Popular Mechanics ads as a "performance enhancer" for decades LOL.

Has a carb synch which can only be fine set on your engine been done?

Vacuum leak intake manifold, cracks, gasket sealing checked?
 
Ok I checked compression today and it's good. :thumbsup: I have 155 on the left side and 160 on the right. I'm going to order new carb holders mine are a little cracked. I have to go back to work (Oil Field) so I'll keep everyone posted when I get home.
 
I installed new plugs and carb holders today. I also went thru the carbs I found that one mix screw still had the old washer and Oring stuck in it with the new. I'll keep y'all posted.
 
I took the carb apart and cleaned them today. the float level was good. I put on new carb holders and new plugs. The left side is still not idling correct but seem to do better when you blip the throttle. I took it for a test drive on deceleration it back fires. Any ideas?
 
I set both mix screws at 3 turns out and I have not synced carbs yet. I need to build a manometer. Thanks for the help I'll keep at it with fingers crossed.
 
I tried the dead cylinder method and the bike won't even idle on the left carb. I even turned the idle screw all the way in and it dies unless you give it a little throttle. What controls the idle circuit?
 
If your carbs are out of sync, the mix screws provide only very fine adjustment. Its the adjustment screw on the throttle shaft you need. A good way to get them close is to pop them off and look at the gaps on the butterflys. Use the adjustment screw in between the carbs on the throttle shaft to get them as close as you can visually and then use the same screw with balance gauges or a manometer connected up.
 
Paulrxs650 I had the left cylinder idle screw on the shaft all the way in not the mixture. The mixture was at three turns out and right cylinder was dead by means of spark tester. The bike would start but you have to keep the throttle on if you let off the bike would not run or idle. Today I went thru the carbs again and now the right carb has fuel running out of the filter end. :banghead:
 
Sounds like you need to read the carb guide. Did you check the jetting if so was it the 45 and 137.5. You should have synchronize . I think paul told you bench sync. The manometer is a fine tune after. At this point sounds like you need to go back into the carbs and clean them as per the guide. check the o ring for float needle on the leaker and float level.
 
Ok, so, firstly, pull the carbs off the bike. Using the shaft adjustment, get the butterflys equal by sight. Perhaps even use a feeler gauge to get them even closer. Then, pull the bowls and diaphragms and using carb cleaner and a rubber tipped air line, blow all the passages through, making sure they are clear. Next, pull the floats out (careful with the little pin) and check the o ring seal for the float needle is present / in good condition. Next check the floats are solid (the brass ones are prone to leaking). Next, reassemble the floats and check the float height. As Scabber says, read, read and read again the carb guide in the Tech Section (brilliant piece of writing) and reassemble, pop back on the bike and let us know how you get on.
 
Ok so sent the carbs to Oldskool and he rebuild them I put them back on the bike and the left side was back firing. I got the manometer out and synced carb. I get the fluid the same level and bump the throttle the fluid rises on the left side and after idling for a while evens back out. Also the left side is still cool exhaust and doesn't sound like the right side. It seems as if the left isn't firing well until you rev the throttle. I have put in new NGK plugs and checked spark on both cylinders. Any help appreciated
 
cross the spark plug wires to the other plugs. if it still has a dead cylinder on the same side, you have ruled out anything electrical. next, have you adjusted the valves? maybe one isnt opening or closing just right. are your idle mix screws in the right places?

i had hell with mine, must have gone through the carbs 4 times before i found the culprit- a missing washer.

also, I've been to Palestine TX before. Dated a girl that lived there. well, Elkhart, but close enough.
 

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