1983 TT600 TT-600 pops sputters backfires

I'll try to explain the symptoms as best I can:

I have a 1983 TT600 that was sitting for several years. It sputters and pops and won't rev very high. It sometimes back fires when letting off of the throttle, and sometimes dies. First I cleaned the carbs, and nothing changed. I then did a top notch rebuild, replacing every replaceable part in it with new ones. I know they are in good shape now, but it still does the same thing. It seems to idle okay, and is torquey at low RPM unless twisting the throttle all the way and it will backfire and die. When it dies while coasting in gear, the engine won't light back up and it will coast to a stop while in gear. It will then start right back up idling just fine. Slowly advancing the throttle in neutral, and it won't die but won't rev very high either.

I am looking for some advice here. I suspect jetting, or possibly some kind of ignition problem. Maybe Trolls or something? Has anyone experienced this with their TT600 and know what the problem was? I want to get this thing running so I can sell it! Running bikes sell better than non running bikes!



I just went through a nightmarish battle with that exact same model. It would idle and not accelerate. After completely ruling out the electronics. I found the carbs to be at fault.What I had found out was this bike was an old desert racer and running on a nitro or alcohol mix and set to run full rich in the carbs.To get it to run on gas I reset both carb needle clips to 2nd from the top,replaced the 136 main jet that was installed 2 previous owners ago with the proper 135 it came with stock(big differance between the two).Resynched the primary and secondary carbs by opening the primary carb 7mm from closed and adjusting the secondary to start opening at the point. It will do more idle now and runs really well. Other things to check would be valve clearances and float level and or wiring connections and spark plug. You could ohm out all the electronics if you have a meter and the schematics to work from. I hope this gives some kind of a jumping off point as information on these is sparse at best I can understand any frustration you might be having.Good luck with it.

Thanks Beezerjoe

I learned a long time ago that ignition is almost never the problem. I actually went through all of the wiring and it looks like there wasn't a problem. Only a few slightly dirty connections and everything is less than an ohm. I did notice however that it has an after market Yamaha wiring harness add on to make it street legal. I unplugged it and I'll try to run it in the morning and see if there is an improvement.

If that isn't it, I'll re sync the carbs and check the needle position as you suggest. Since I'm at 5000 feet, I'll confirm the right main jet is in it too (usually we go one smaller at this altitude). I know this history of this bike, and I don't believe the jetting was fooled with, but anything's possible I suppose. Guess I should check the plug, duh, to see if rich or lean is indicated. Compression is solid, no leak down, so I don't suspect valves at this point...yet.

I'm not frustrated yet! I asked this post in order to avoid the frustration in advanced... I'll report back if I get it to work - or not.

Nothing affected it. Changed the plug, checked the needle position and sync. Everything is right. It runs for a few minutes, then dies.

I removed the plastic center plug from the left side cover of the engine, and I noticed that there is oil in there.

Is there supposed to be oil in there?

On most motorcycles, the magneto/ignition pick up area should be dry. If there is not supposed to be oil in there, then I think I found the problem - a leaking crankshaft seal. Maybe there is supposed to be oil in there, I dunno. Does anyone else know? I'll post separately on this subject if I cannot find a discussion on it already.


Yes those do run the mag in engine oil as the cam chain runs behind it so you get oil run off from the head. It almost sounds to me like a fuel restiction since you know your carbs and such are alright check your in tank fuel filter and petcock to see if the screen is fouled with varnish or water.Also check your fuel cap to make sure the vent is clear and not holding a vacuum in the tank.

One of the first things I did was check the tank and cap. Not the problem.

Here is the history:

The carb was in bad shape when I got this bike. It wouldn't start. I cleaned all the gunk and varnish out, and it then started. It had the same symptoms that it does now, the popping, backfiring, and intermittent running. Since the float neadle was old and brittle rubber, gas leaked out of the carbs. I figured this carbs were causing the problem, so I rebuilt them with all new parts. The carbs are like new now, set up properly and jetted right. But nothing changed from when I first got it running as I expected it would. It still runs intermittently. When it is running, it won't rev without popping and backfiring (big time backfire). It will shut down if the engine is under a load or over revved. I'm sure the fuel system isn't the problem now, as I've completely gone through it and everything is perfect.

So I just got done checking for spark. I was getting spark. I hooked the lead up to the spark plug, and the bike fired right up first kick. Good idle. I let it warm up, then shut the choke off. Good, smooth idle. Then I cracked open the throttle. Starts to rev, then pop pop, shreiking backfire, then the engine coasted to a stop. I then pulled the plug wire off and checked it. NO SPARK! I let it sit for 20 minutes, and the spark came back!

So I have intermittent ignition problems. I've ohmed out the wiring and it is good. So there is one of three things wrong with it:

1) Bad coil

2) Bad pickup/stator

3) Bad CDI

I've never actually seen a bad coil in real life, and I've owned over 30 cars and 30 motorcycles. But maybe. The backfiring leads me to think "nope."

Could the pickup/stator cause my symptoms? The backfiring? Seams like nope.

Could the CDI cause it? I don't know, maybe. Anyone ever had these syptoms and fixed it by putting on a known good CDI? I'd feel better about hunting down a good one if someone could confirm it for me! As far as I know, there's no way to test a CDI. Does someone know of a way to test it?



You can test the CDI. You just need the service manual to do it. It'll give you all the values and which wires to put your probes in for testing the CDI box, coil and stator. Worst part about these bikes is the CDI is a problem from what I'm told as well as with the XT550. The replacement from Yamaha is about $350. Electronics Research and Design sells a replacement called HYPERPAK for about $150 on EBAY. I have one of these on mine and it works good. The only other thing I can think of would a sheared key on the on the flywheel and it might have slipped time but I kind of doubt it. As far as bad coils I've only ever seen one go bad on my dad's Triumph.It's rare but it does happen. Hope you get it figured out:thumbsup:

I've just experienced something very similar on a bike that sat non-operational for a long time. I put a new top end on a good engine, and when it did this same thing I supected carb problems. Went through the carb again and tried to start: nothing. I just ordered a new coil as it was not getting spark!

A fella on one of the forums explained in detail why these coils break down when sitting unused but I can't remember the reason, sorry. The possible electrical reason for the symptoms are that the plug requires more spark to fire under full throttle. At low speeds the compression doesn't have so much of an effect, but at high speeds there's less time for the coil to charge up and there's more resistance against the spark's travel. For some reason the coils get tired and can't produce enough juice under full acceleration but spit out enough to keep it running at lower speeds. At least it's worth checking before you pull out the Master Card for a CDI.

Does anyone have the values for testing the CDI, Pickup, coil, and stator for this bike? If so, please post!


Did the bike make shrieking -and I mean shrieking- backfires when revving around in neutral? Or just loss of power under load?

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