Help with my VERY puzzling ignition problem

[RDDave]

Stock '75 RD350. The left cylinder has always ran cooler than the right and has fouled plugs. But lately it has gotten worse.  Compression was 95lbs on both cylinders. Chinesium cylinder kit has them at 110 now. When I kick it over with a spark checker, the left has a blue spark... BUT....it is not quite as fat as the right. And, it stops sparking just a little bit sooner than the right as the engine coasts down from a strong kick.

I have tried EVERYTHING that I know of:
Swapped coils side to side.
Have the Suzuki coils recommended here on there now.
Have swapped them side to side.
Have a relay on the power side of the coils, so they are getting a full 12V.
Changed points. More than once. They check good.
Changed condenser. More than once even though they checked good.
Points set to 45* dwell.
Timed with timing light to just after the mark. Have tried different timing.
Jumpered directly to the coils from the points eliminating the harness.

Nothing has helped. The left side is weak to no power. It pops once in while like a whiskered plug does, but not often. I have also pulled the air cleaner out and sprayed some WD40 in the tract just to be sure it is not a fuel problem. But the left plug is black and  oily while the right looks good, so I swap them. And yes, I have had a LOT of different plugs in it, too.

I am out of ideas. I have changed just about the entire ignition system EXCEPT the generator. Could that somehow be the problem? I do have a couple of spares I could try if someone would think that was the issue. But I would be curious how it would cause my issue.

I am sorry for writing an encyclopedia, but if anyone could help, they would need this information.

I would really appreciate some thoughts on this. And NO, I am not going to an aftermarket ignition. I have never had ANYTHING like this before on a Yamaha point ignition. I haven't even looked at the ignition on the Enduro in a couple of years, it starts and runs fine. Just like all the other point ignitions I have ever had. No more than I get to ride anymore, a good set of points will probably outlast me anyway.

Thanks in advance for your thoughts.

Dave

[m in sc]

cha4ging voltage and or harness issue . I ran into this in the past a few times. run new wires from the points to the coils, new connectors, etc. check all that.  I have had the wires in the harness themselves be the issue before.  Just fyi

[RDDave]

As mentioned, I have a relay running voltage directly from the battery to the coils completely bypassing the bike's harness. I have a full 12 volts to the coils. Before, I only had about 10.4 volts going to the coils. That was enough for the right cylinder. It has never gave me any trouble. ONLY the left.

And I temporarily ran a jumper wire from the points to the coil, bypassing the bike's harness. None of that helped.

I guess I could jumper voltage from a separate car battery on the floor to the coils. I can't see where that would be any improvement, but I am up for about anything.

Have I missed something there?

The ONLY thing that I haven't changed is the generator. Is it possible for it to only cause the left cylinder to have problems? The right has never given me a minutes problem even when components from the left are powering it.

As I said, I have checked, changed, tested every single piece in the system multiple times. Nothing has had any affect. Clearly I am missing something. But I simply cannot think of anything else in the system that I haven't changed or bypassed. More than once.

[RDDave]

You know.................When I jumper wired the points to the coil. I only disconnected the coil. I just alligator clamped the jumper wire to the points leaving the harness wire attached.

Maybe I should disconnect the bike's harness from the points. Maybe it is somehow grounded out and confusing the firing. Is something like that even possible?

Obviously, I am grasping at straws here. But I will try that in the morning.

[m in sc]

yes its possible.  that was my point (no pun intended)  , the wires from the points to the coils.

also keep in mind, new parts doesn't guarantee they are good. 

whats it battery voltage after running a few minutes ? does the cylinder pick up when you turn the headlight off? if you havent tried that, try it. if it picks back up even momentarily, it will tell you theres a charging issue.

[BlueR32]

This may not help at all, but I had a mystery charging issue on my RD250:
https://www.2strokeworld.net/forum/index.php?topic=7029.msg57821#msg57821

[RD350NL]

To be honest.. I would just ditch the entire ignition and replace is with a modern VAPE ignition. Yes, its not cheap but the best upgrade for these bikes. I ended up spending way too much time on my historic points ignition. As soon as they give problems imo its better to replace for an electronic ignition.

Oh and ps: ditch the Chinese barrels as well. Get your original cylinders bored to next oversize and put some mitaka pistons in it, they are not expensive. Thank me later.

[RDDave]

Thank you for suggesting EXACTLY what I said that I was opposed to doing.

I have had Yamaha single and twin two strokes for over 55 years and have have ridden many, many miles and hours using only points ignitions. They are not the best thing going, but they are far from junk. Besides, there is no proof yet that the problem is directly related to the points ignition.

I also have a '70 HemiCuda that is carbureted. Lots of guys want to go to a retofit EFI system on those old dinosaurs for the same reasons that some here want to use a modified electronic ignition system on these old two strokes. But I won't insult them. Or you.

I said before that I WILL NOT go to a 'modern' ignition. If the original ignition was so poor, why does the right cylinder run so well? This is a single fault, not a systematic failure.

If I have a flat tire on my car, I am not going to change the wheel bearings. To me, changing the entire ignition system for a single fault would make as much sense. Besides, I learn the most when I diagnose the most difficult problems. To me, throwing the whole system in the trash and replacing it is a cop-out.

Oh, and the Chinese cylinder thing was a last resort. Not at all what I started to do. I will spare everyone the long saga, but I have several sets of STD or first OS original cylinders. And new Yamabits pistons and rings. But don't have a good boring service around here for them. I will eventually get a pair of original cylinders done. But for now, I am concentrating on the left cylinder issue.

Now, getting back to the more helpful responses:

Thanks for the link.

I have been doing all of the testing with the headlight off. But I will check the output again.

I have a good amount of used parts. So I have been using used points and condensers. I file the points till I get good test results and even switch them between the cylinders as a final test.

Nothing seems to have any impact, so I don't believe I am close to the source of the problem.

But, today I will disconnect the harness between the points and the coil which I didn't do before when I ran a jumper lead between them.

Thanks for the suggestions. Please keep the useful ones coming.

.

[Brad-Man]

I saw no reference to it - Did you replace the spark plug wires?

[1976RD400C]

Maybe take an old unfouled spark plug or make some sort of adjustable spark gap thing and open the gap way up to get an idea of how far the spark can jump a gap and compare the 2 sides.

[RDDave]

New wires and plug heads came with the coils. And I have switched them side to side more than once.

I have a very good adjustable spark checker and noted the interesting results earlier.

[SoCal250]

Since you have just about replaced everything in the system and the issue is still present, I would run your test you mentioned with the jumper leads to the points and the harness leads disconnected. Leaving the harness in the circuit will alter your result.
I would also get out your DMM and start going through the entire system checking resistance on all the wire sections and components in the circuit. Note anything that seems high and compare left to right.

[350GUY]

Dave: Check your grounding points and try without the relay. You might also want to check the resistance of both coils with a DMM.

[RDDave]

I will do that.

[m in sc]

these problems are exactly why none of my 15 bikes have points except 2. and thats going to change on both of them eventually .  but I hear where you're coming from. what's charging voltage at 2k?