Test your troubleshooting skills

[randy]

I'd go to the coils next. The plug caps may have corroded at the wire ends. Unscrew them and clip 1/2" off the end of the wire. Screw the caps back on, then test through the coil secondaries. Look up the specs, I can't remember them, but the spec are posted here somewhere. Also the specs are in your shop manual.

No power, but idles like a dream is a classic weak spark symptom.

HTH

Randy

[randy]

I'd go to the coils next. The plug caps may have corroded at the wire ends. Unscrew them and clip 1/2" off the end of the wire. Screw the caps back on, then test through the coil secondaries. Look up the specs, I can't remember them, but the spec are posted here somewhere. Also the specs are in your shop manual.

No power, but idles like a dream is a classic weak spark symptom.

HTH

Randy

[fredintoon]

My own sad tale.

90% of carb problems are iggy problems you ain't found yet sayeth the Mantra. Yeah, right.
My XS11SG started running like crap and guzzling gas and the #1 & #4 plugs were all sooty. The old wet finger on the exhaustpipe trick showed #4 was dead. I'd just fixed a broken pickup wire but WTF. I wasted an entire week checking, double & triple checking the iggy to no avail. Even with the coils swapped over #4 was still dead.
After I borrowed a compression tester and all 4 cylinders blew +150 I removed #4 carb & soak cleaned it. Fired right up and runs like a train.
I'd bet that for $130 the dealer didn't remove & soak clean your carbs, they just blew spraycan carb cleaner through them.
I'd say take all 4 carbs completely apart and soak the bodies overnight in the water-soluble carb cleaning solution that comes in gallon cans. (Not the rubber bits, that stuff dissolves rubber too.)
Fred Hill, S'toon.

[Hawkins]

Solved!

Took it to another shop owned by ex-Yamaha mechanic. He checked the carbs, they were fine, checked the timing and it was 80-90 deg out! I can't remember all the bits in the advance system, but he said there was a 10mm nut that had backed off and allowed the spark advance to change.

Doesn't add up to me - as I recall, the reluctor assy can only fit on the crank in one position, the coils screw on the plate in one position, and advance is changed by rotating the whole advance assy.

oh well, as long as it's fixed. $110 isn't bad. Total cost will be $350 includiong gas to get back there and get it. The worst part is 2 weeks lost from an already short season and 3 or 4 frustrating days in a hot shed trying to diagnose the trouble myself.

Thanks to all who replied. This forum makes having an old bike acceptable.

I'll buy a beer for any of you who ride to St. John's, but f*ck the Screech!

[TopCatGr58]

Hey there Hawkins,

There is a large bolt that goes thru the center of it all, holding the #2 timing plate and all in position, that could have come loose? Also, the 80 models were the only ones that used a special sheer off bolt to secure the base timing plate in position! They made it that way so you couldn't adjust it! They went 1 step further in 81 and locked the base plate down, aside from the vacuum advance module being able to move it, so we can't even tweak the timing on our 81 machines. At least with the sheered off bolt, you could remove/drill it out, and replace it with a regular bolt/nut combo if you wanted to!

Sorry to hear it's going to hit your wallet so hard, hope you get a few more weeks or more riding in before the cold white stuff arrives!!??
T.C.

[Hawkins]

TopCat

I think you're right. I looked at an old engine and if it was running with that bolt loose, the centifugal force could throw the reluctor assy out past the guide pin. It could then rotate freely and continually throw the timing off more and more (retarding it because of the direction of rotation) with each revolution. Before it went way off, the only point at which the timing would be sensible again was at full advance, which I'm thinking occurs pretty much at the 4000 RPM mark (that's where it felt as if a switch was thrown and she would run fine). That's certainly consistent with the symptoms anyway.

It seemed like a timing problem all along, but I couldn't think of a way that spark timing could change mid-ride. That's why I wondered if the cam chain had stretched and jumped a tooth or two, but then that wasn't consistent with running well above 4000. So, I had ruled timing out.

The upside of all this is that I've gained a better knowledge of what keeps the yammy ticking. I'm sure that'll come in handy at some point!

later guys.

[RS Thornton]

You found something else that is valuable. That second shop sounds like it has a mechanic that knows something about bikes. The first one seems more like the ones we all have horror stories on.