Okay, carburetor gurus. Got one for ya.

Well, today I replaced the Zener diode that looked funky along with the 4 diodes associated with the pickup wiring, seems they are known to have problems as they age. It runs exactly the same.

Ouch, that sucks.

You still think the ignition is failing or are you back to the carbs.

I'm at the point where I need to swap a known good TCI box on it; if it runs right with another box I know where my problem is. I put the call out on xs650.com to see if anybody around here might have one I can plug in to test with.

Did some more fiddling and testing. I replaced the output transistor in the TCI box, no change. So I went through and ohmed/voltage tested everything in the ignition system; the TCI box has clean full battery voltage and a good ground, the pickups ohm to specs, the kill switch has no resistance, everything looks good. I ohmed the ignition coil primary and secondary windings, they are within spec. I have previously checked for spark but why not do it again, right?

Now, this next part involves knowing how this ignition system is designed. It's a waste spark, both plugs fire at the same time but one will always fire on the exhaust stroke. That means that both the spark plug leads share the secondary winding. So I put a spark plug on the left side cylinder lead and started it up, the idea being to see if the spark quits when the engine dies. The spark on that plug was reddish and weak, I didn't see the hot blue spark with a 'snap' that we like to see. It continued to spark even as the engine began to die, though. So I did the same test with the right side cylinder using the same spark plug I used for the left and I had the same reddish spark but with the occasional hot blue snapper. As I increased the engine speed, the right cylinder spark went away. Huh. Why would it do that if both spark plugs share the same secondary winding? I have an ignition coil on order.

Check fuel flow?

Fuel flow is excellent for a gravity feed system. I took every piece of the fuel delivery system apart and made real sure the passages etc were all clear, still the same damn problem. The coil is due soon, keeping my fingers crossed. '90% of carburetion problems are ignition....'

Be aware that because you have stock dual output coil that's one less thing you'd have to buy if you went to a PAMCO setup.

Really, for $300 you can get a PAMCO and used-parts PMA and have an electrical system that's probably more advanced than most bikes from the 90's, and more reliable as well.

I love the peace of mind my PMA gives me. I can finally cross "battery or charging problems" off my troubleshoot list.

Yeah, I've thought about that. That's not in the cards at the moment.

Anyway, got the new coil today. It cleaned up the spark (it's now blue instead of reddish) but it still runs like a bag of ass. Pull the choke out all the way and it's rideable. There's another set of BS34's in all my crap that's ~100 miles away, I guess that's the next step.

In reply to Curmudgeon:

You want me to send them to you?

If things go like you and I were talking about, I was going to make a consolidated trip to do paperwork, get tools, carbs, all kinds of stuff. Lets give it a few days. Thanks, though.

Pulling the choke and it runs well? That makes me think there is some type of clog in the air idle circuit. Maybe use an ultrasonic cleaner from a jeweler on the carbs?

You've got pod air filters on it right? I had an RD350 and pod filters F'ed up the jetting bad. It would jet one way at low speeds and then at high speeds the pod filters would cause a secondary and completely different jetting. I don't know if this applies to XS motors or not. Just throwing it out there for consideration.

I'll bet you've sorted the the electrics and now are dealing with a carb issue.

The whole thing is weird because the bike ran GREAT at first, pods existing jetting and all. I haven't changed a thing. I am at the point where I think that the POR15 tank liner has sloughed off a little bit that is now stuck in a part of the carb that I can't get to. POR15 is supposed to be ethanol proof and if I stick a screwdriver through the cap opening and try to scratch it nothing comes off. But that doesn't mean maybe there was a tiny bit somewhere that wasn't completely cured. If that's the case, a set of carbs is in order along with something to keep it from happening again, like one of those fuel filters made of sintered bronze instead of plastic mesh.

Curmudgeon wrote: The whole thing is weird because the bike ran GREAT at first, pods existing jetting and all. I haven't changed a thing. I am at the point where I think that the POR15 tank liner has sloughed off a little bit that is now stuck in a part of the carb that I can't get to. POR15 is supposed to be ethanol proof and if I stick a screwdriver through the cap opening and try to scratch it nothing comes off. But that doesn't mean maybe there was a tiny bit somewhere that wasn't completely cured. If that's the case, a set of carbs is in order along with something to keep it from happening again, like one of those fuel filters made of sintered bronze instead of plastic mesh.

I'll bet this solves your problems. The carbs have some tiny air jets in them for idle, choke, etc. Any bit of trash in there is going to cause some issue. It is strange that it will idle fine at first and then progressively (sounds like) fuel starve itself. But that could be consistent with some small trash being in the carb passages, expanding with heat, then completely sealing off whatever passage it's lodged in. Which leaves us with materials that expand a lot with heat which could include rubber or metal.

Will you let us know how it goes?

Stone filters are where its at. I guess I kinda assumed that's what you'd be using.

Even with stone filters I discovered that debris was still getting into my bowls. I drained the bowls, flushed with fresh gas, and it runs like normal again.

And you've lubed and checked the advanced unit right? Or dont the 80+ models have those?

I will definitely let y'all know what happens. PHeller, I didn't use the stone filters because the new petcock has a super fine plastic mesh inlet filter. D'oh. Mine is a TCI so it doesn't have the mechanical advance, that's all done by the TCI box. Since it revs up good with the enrichment knob pulled all the way out it seems pretty certain my problem lurks in the carbs, which was my first guess.

Ok...so it'll run on the choke, but not with it off?

And we know the air filters aren't blocking anything?

So when its off-choke, its not providing enough fuel.

Can you accelerate out of the bog or stumble or does it just fall flat on its face?

It sounds to me like its debris getting sucked through the jets. Mine was doing the exact same thing. One time it would run good at a certain rpm, the next time it wouldn't, the next time it would be fine again. When I drained the bowls out came all kinds of particles.

Because of where the primary jet is located (off to the side) I think that the main jet pulls up more debris. It also pulls harder.

What I hate is the idea that I can't locate where this debris is from. I may be 150 miles into a road trip through the mountains when it suddenly decides it wants to suck up some debris in the fuel system.

Yeah, I know. I'm probably going to rig up some sort of sediment bowl setup to go between the petcock and stone filter, too. All this makes the idea of converting to FI appealing. Speaking of that, have you seen this vid of the turbocharged/Megasquirted XS650?

http://www.youtube.com/watch?v=s44_EFLTd80

Fuel Injection still requires clean fuel lines.

I think the biggest problem on these bikes are the old tanks.

If you got the carbs ultrasonically cleaned, all new seals, fuel line filters, petcock filter, and new tank I think you'd never have any carb problems.

We were doing good till we got to 'new tank'. It's not evident from my pics of my bike but there is a LOT of custom work under that white paint, did you notice the emblems are missing? Hate to toss all that hard work out. I might pull the petcock and see if it's possible to put a stone filter on the tubes.

Well. Swapped all kinds of carb stuff back and forth, cleaned the bodies to a fare thee well including Berryman dunk, still ran like ass. One set of Mikuni VM34's later, runs like a raped ape again. The old carburetors have been stripped of their brass and the evil bodies are in the recycle, they will go to the great carburetor graveyard and never harm anyone again.

Cool. Was that the parts you picked up the other day or did you end up getting different ones?

Do me a favor, keep it shiny side up.

Different. The bodies I picked up were in nasty shape (worse than my own personal beer bag!) and I wasn't able to cobble together anything that would work. Got the VM's on a deal.

Glad to hear you got it back to running right!

44

Curmudgeon, any pics of your bike?

You want pictures? Unfortunately, I didn't take any pics of it in its 'basketcase under the workbench' stage. It was absolutely beautiful today so I took it out for a snort, put ~70 miles on it, it runs great.