Spark from side of cylinder on '66 YDS3

I have problem I have never run into before. Still trying to get the burbble out of the top end of my '66 Yamaha and when I came in tonight the bike went to about 6k rpm when I put it into neutral and when I shut off the key it had no effect. Had to drop it into 1st and pop the clutch to kill it. On restart it idled just fine but I noticed a spark jumping between the jug and the choke linkage. When I put a screwdriver close to the jug the spark would jump to the screwdriver even though it was not touching anything for a ground.

Don't know if the two are related but it sure was strange.

Bob

 

"shut the key off..." something in the combustion chamber is getting hot enough to light the fuel when it gets compressed
are the right plugs in it, some bikes used to have two plug holes, only put a sparkplug in one, the other is like a pipe plug
if it's breaking up on top end that might be lean that runs hot that seems to follow what you have
spark from choke linkage to the jug...thats strange, but the jug has to be ground, so somehow the linkage is getting energized, is a plug wire laying on it or close to it, i'd consider the plug wires shot

 

I believe conditions inside your motor are causing the fuel air mixture to autoignite. Honda built a two-stroke back in the 90's that would actually run without a spark plug firing, using this phenomenon, called active radical combustion.

Honda makes lemonade from lemons once again.

 

I seem to remember the electrical system in an old Jap bike long ago (60's mighta been an X6) that was "live" all the time like a lawn mower and the key dropped it to ground. Not sure this would be the situation here, but with sparks jumping where they shouldn't something goofy is going on with the electrics. I would start methodically going over all the electrical connections involving the ignition system, and I'll bet you find it.

 

You folks are absolutely amazing how you can diagnose my problems here in Oregon from Mich, Ottawa and PA. I opened the timing case and the first thing I saw was the timing indicator touching the edge of one of the point mounting bolts. Upon looking a little more I found one of the condensers slightly crushed and egg shaped. Pulled the condenser and it tested OK but will try to pick up a new pair tomorrow. May as well get new points and plugs at the same time as these are the originals. Hope I can find parts this old at the local dealer.
Could the run-on be caused by the timing being too far advanced? I thought I had it set at 1.8 mm BTDC but my dial indicater isn't the best.

 

not directly but timing effects running temp
the problems you found in the timing case don't explain the sparks jumping to the jugs though, if those plugs are original i guess the wires are too, chacal has plug wire splices and caps, a set of those might be in order
what kind of oil are you using, and what ratio?
remember more oil causes leaner running
you might check for vacuum leaks at the intakes and around the lower end cases

 

Trust me, Bob, it is more experience than anything else. Learned the "something touching something it shouldn't in the distributor" lesson a long time ago on a 500 Triumph. Believe it or not, a lot of stuff for your bike is still available from Yamaha, and here are a couple of real good NOS sources: http://216.168.60.165/speedandsportinc/index.tpl
or http://www.nwvintagecycleparts.com/search-parts.php You will need to be armed with a Yamaha part number to search their stock.

 

Just got back from the local Yamaha dealer and when I told him what I needed he laughed at me. According to his microfish Yamaha didn't make a YDS3 in '66. The parts I wanted - you have to be kidding. Thanks bigfitz52 for the info on where to try for parts. Now I just need to find a part number.

 

Replaced the plugs, points and condensers, found the clutch boss nut loose and retorqued it, took it out and ran it in the rain. Still have a high rev miss and tonight it seemed to run out of fuel at about 7000 rpm. Nearly died then came out of it and shot to about 9000. When I slowed down it again seemed to starve and wouldn"t hardly run above an idle. I'm miles from home, its all uphill, no phone and its raining. You can imagine my thoughts. After chugging for about 30 seconds it came back to life and got me home. I had already taken the petcock apart and cleaned it so I don't think thats the problem. I thought it might be running lean so put the choke on slightly without any noticable change. Any Ideas?

 

Don't ride in the rain. Seriously though, sounds like crud in the tank sloshing about plugging/unplugging your fuel source. I had a LEAF in the Triumph's gas tank once drove me CRAZY with the symptoms... Or it could just have been wet electricals. I'd dry it out and see what happens on a sunny day, and have a look in the tank with a flashlight. Could also have a big "glob" of water slithering about on the bottom of the tank. I would suggest Sea Foam but don't know what effect it might have on a 2-stroke.

 

bigfitz calls it again. Drained the fuel tank and took apart the petcock a little further and found dog hair!!! in the passages. Cleaned them again. Went back into the carbs and reset the floats, drove out the needle jets and cleaned them. Replace all parts and found the right carb overflowing. Reset the float and cured that. Took a ride and still have the 6000 rpm miss/hesitation with sudden acceleration to 9000. Returned home and now the idle will not go below 2200 rpm. Both idle adjustment screws are down tight. Throttle cable slacked beyond suggested. Mixture screws messed with open and closed with minor variation in rpm. Right cylinder has louder, sharper snap at exhaust than left, also more smoke. Both show 150-160 psi compression. Mains are 120. Air jets .5. Pilots #20. Air screws at 1 1/2. Starter jet #40. Floats at 25 mm. Points .011. Plugs .025. Timing 1.8 mm BTDC. Have not changed jet needle. Could that be it? Am I missing something else?

 

Could be needle position, but I hate to mention this: Go back and re-check your points gaps and timing. Quite often when you move the plate to adjust the timing you inadvertently change the gap. What makes me think it might be ignition related is your comment about one side having a sharper "snap" than the other; if the carbs are even CLOSE I get the gut feeling the timing is off on one side again...OR: You mentioned a "squished" condenser. Did that ever get replaced? When the miss/hesitation occurs, can you tell if it's only one cyl or both? It COULD (and I'm getting a little into left field here, but then again, dog hair?!?) it COULD be a condenser that won't "cycle" at high RPM, or a bad coil. I had a problem with aftermarket condensers on the Nort some years back wherein one of them would just "give up" above about 4000 RPM. You could watch with the timing light the pulses would just start to "splatter" and become one long flutter above 4K. Installed new, proper (read expensive) condensers, it was fine. I would replace the condensers if you haven't, and try swapping coils, especially if you can narrow it down to one cylinder, then see if the problem "moves." I'm beginning to enjoy the challenge of your getting this old monster on the road, unfortunately at the cost of your frustration. My first bike was a '66 Honda, I have a sentimental stake in this too...

 

Once again bigfitz calls it. Checked the gaps and found #2 at about .020 instead of .011. Reset and was ready to try it when I got called back to work. So much for riding on my day off. I'll let you know it this changes the unequal snap. The oval condenser was replaced with an OEM from NWVMCP. I'm still looking for ideas on the high idle speed. Don't have any idea what would cause it unless the carbs are overflowing which doesn't appear to be the case.

 

Well, after tearing down the carbs again and cleaning them again, I put them together and started to sync them. What did I find but that the #1 carb slide wouldn't go all the way down. I tried letting it down with the idle screw without any change. WTH, did I mess up the jets? Took it back apart and tried to slide the needle into the jet. It would go so far and then stop. I recleaned the needle jet again and retried. Still no go. Then I happened to look at the needle itself and it appeared to have some type of coating on it. Is this right? Finally removed the needle from the slider and tried to polish it with steel wool. The coating came off fairly easily and when I tried it into the jet again it slid in easliy and all the way to the bottom. All that cleaning the carbs and I forgot the needle becaust it was attached to the slide hanging on the bike. Fast idle fixed!

 

OK, so with the timing fixed (again) and carbs sync'ed and the idle problem solved, how does it run? One tip: I have sworn off steel wool altogether in favor of ScotchBrite. The stuff comes in different "grades" just like steel wool but DOESN'T leave microscopic bits of steel behind. (Thanks RickCoMatic.)

 

Still had some problems in the mid to high range. Took the carbs back off and rechecked everything. Reset the floats again. Cleaned the needle on the other carb and noticed an extra part that wasn't on the first one. It's called a circlip and serves to hold the needle down in the slider. Made a new one from a washer and put everything back together. Took it out and warmed it up. Set the idle and air screws and was off. She hasn't run like this since I've had her. I'm through farting around and am ready to do some serious riding. Thanks to you bigfitz and the others who have responded I think this thread is closed. Again thanks to all who responded.