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Discussion Starter #1
Last november my XS starting to pop thru the carbs. When the motor was cold. Just a little worse each time I started it and it stopped when it warmed up. Then it became almost unrideable from the popping. Since I had lots of little oil leaks, I figured it was time to clean out the carbs and install new top end gaskets and seals. Got all the seals and gaskets replaced and put in a new cam chain ( timing chain ?? ) I had a couple of those orange boxed Keyster carb kits and cleaned out the carbs and put in the new parts. The parts in the kit matched what was in the carbs, except the slide needle and it's jet, so I reused the originals. All the passages seemed nice and clear. With the little pipe on the Gumout can, all the ports and passages flowed well, or at least I thought.

Got it all back together and it still poped out the carbs, not one, but both. If the choke was on, no popping and it ran great. Turn off the choke and it started poping just over idle about 2000rpm. It idles perfect, I mean one kick starts and perfect glass smooth idle. Took everything apart again, rechecked cam timing, ignition, points and anything else I could think of. Blew the carbs out with compressed air. And more carb spray. Put it back together and it still pops out the carbs with the choke off, put it on and run it around town and all is well, turn off choke, it is unrideable with the popping out the carbs. Pulled the carbs again, tied the carb body and the float bowl to the railing behind the shop, hit them with steam at high pressure. Thru all the passages and all the ports. I didnt miss anything I could think of, New carb holders and diaphragms from JBM. A neighbor says it is the spark plugs …........ huh ??

I ran this thing all summer with no problems, now the choke has to be on just to run it around the block.

Any thoughts are welcome..................

Thanks

John:(
 

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Are your air filters plugged up? I had that problem with a Honda CB360-basiclly same symtoms (can't spell that word, but you now what I mean). Ended up running without filters and sold it quick.
 

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Doesn't sound like spark plugs. The facts are: popping (on decel? accel? always?), fixed when choke used. Sounds like it's running lean. Have you made any changes to intake or exhaust? That would account for a lean situation, and indicate a need to rejet your carbs.

The perplexing facts that complicate this diagnosis is the slow onset you describe and the fact that when warm the issue is less offensive. That would suggest to me a different problem, possibly seal-related, compression, ignition, or leaky carb boots.

One question: does it have any problems with the choke on? If it idles well, has good mid-range, and runs well at WOT without fouling plugs or running hot, then why not ride with it choked?

Finally, is it an XS650, 400, 750, or what?
 

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Discussion Starter #4
OOPS, 1975 XS650..... with the choke on there is a good idle and fair mid range, pretty good top end. turn the choke off and it starts popping about 2000 rpm and it'll die if you let it just keep popping. The stock air boxes were eaten up by battery dripage, so am running the pod filters MikesXS sell for around $ 20.each.
http://www.mikesxs.net/products-40.html#products
I agree with the running lean idea, just after almost killing these carbs with cleaning and re-cleaning, I do not see how there could be a blockage.

What do I know ...............
 

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I bet leaky manifolds. Did you re-seal the head-manifold surfaces?
Perhaps the carb clamps are stretched, and along with the Yamaha shroud thingy that goes over the manifolds, not allowing full clamping action.
1194 is your friend.
With it idleing and a can of start fluid in hand, with red tube, give a squirt around the manifolds in localized areas and listen for engine speed change.

NE
 

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+1 on manifolds. Sounds like an air leak. I had KZ1000 with VM29's drive me crazy until I re-sealed the intake manifolds to the head.
 

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Discussion Starter #7
I replaced the manifolds/mount thingies, and used a good quality sealer. then I replaced the slide diaphragms since I was in there. Like I said this is getting damn annoying and fairly expensive. I am starting to run circles !! This evening, we pulled the carbs and re-re-cleaned the things. Gave the passages a serious hoseing with an old Sears pressure washer. Then blew them dry with compressed air. Probably wasnt needed, but it acts like a carb passage blockage. Ran great all summer, then this creped in and things got silly ....

Wonder what this thing is worth ???

Maybe sell it and buy a Chinese scooter, atleast then I would expect things to go wrong !!
 

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Discussion Starter #9
Looking at some exploded views of these carbs, could the seals on the butterfly shafts be causing all this tail chaseing I am doing on this damn bike ?????
 

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One more thing to think about. The same gas wasn't sitting in the tank since last fall, right? New gas in the tank after the carb rebuild? Letting the ethanol gas sit for that long could cause a lot of these symptoms.

Craig
 

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There are tiny little pin holes you may need to clean out with thin gauged guitar wire or something similar. I believe they are the "mix screw outlet" and the 3 "bypass holes", they are very easily dismissed as clean.
 

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I'm in accord with what has been said above and will add the following to the mix: sometimes a back fire through the carb is a result of a too tight intake valve. adjust the valves next. good luck, cheers, bcr
 

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My XS popped until I tore apart the to end to find a sticky valve. Just sayin'. You could be chasing something that isn't a carburetor/electrical problem.
 
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