TX500 engine trouble

[jake1113]

Recently I aquired a 1974 TX500 from a friend with 3 of them. I had to do a motor swap right away because the plugs on the original motor (with 9800 miles! ) broke off flush with the head. The new motor came out of the third bike (He is building a cafe out of his) and it has 24,000 miles on it. At first, it ran fantastic. After about a week, though, it would start cutting out on the left cylinder intermittently until it eventually would just die if I kept riding. We replaced the condensors, checked the carbs for gunk (found a missing spring in the slide) gapped the points, replaced the battery (it was bad) and the problem is still the same. We cleaned the carbs again today, and it was running great on until I got about 6 blocks from home, then it just died. After it cooled off about fifteen minutes, it started right up, but now there's this grinding/ratcheting noise coming from the kickstart area. And it died again after running for only two blocks.
Long story short, I don't know what's causing this running problem. My buddy says it might be because we never adjusted the valves, but I find it hard to believe the bike would just die like that. It was running great, and now it's not. I'd appreciate any info from someone who knows more about these motors than me.
Thanks guys.

 

[hillsy]

Fuel starvation, perhaps? Is the tank venting properly?

Open up the fuel cap when the problem occurs and see if that changes anything.

 

[two-smoker]

For the record, I'm the guy who gave him the bike, and I've been working on it with him. The problem is not fuel related. When the bike gets hot, it shuts off. We've checked the fuel flow, and it's more than adequate. The problem appears to be internal, but I'm not too knowledgeable about these specific engines other than the "known problems". Just looking for ideas from people who've been inside one of these puppies.

 

[hillsy]

Bad coil(s) can stop working when they get hot.

 

[two-smoker]

Replaced the coils. Problem is not ignition either.

 

[teazer]

could be a bunch of things, so let's start with the easy/cheap ones.

Condensers tend to fail when hot. Try replacing them with a pair from Autozone/PEP boys etc. Do you still have spark when it's hot and failed?

Fuel tank breather may be partially blocked. Fuel; flow would be fine for a while and then it would cut off.

Vapor lock is a possibility. How hot are the carbs getting? Hint: they should stay no more than warm to the touch.

Plugs can break down if they are getting fouled or if they are too hot. What do those look like after it dies?

That noise doesn't augur well for a good outcome regardless of whatever else may be wrong. I'd rain the oil and pull off the right side cover and see what's going on there. It's possible that something in the starter gear train is failing and creating a lot of friction.

 

[two-smoker]

We started with the easy stuff. Condensors were first. Then coils. Then carbs. After some thought, I think the tank not venting properly is the most likely explanation. The carbs never get warm, and at startup, the petcocks don't flow gas until the fuel lines are pulled off and replaced. Never occurred to me. Thanks for the insight, guys! Oh, and the ratcheting noise us because the kicker mechanism is sticking. Shouldn't be too difficult to remedy.