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
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
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.
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.
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.
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
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.
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.
.
I saw no reference to it - Did you replace the spark plug wires?
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.
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.
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.
Dave: Check your grounding points and try without the relay. You might also want to check the resistance of both coils with a DMM.
I will do that.
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?
Quote from: m in sc on August 09, 2025, 09:55:03 PMthese 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?
Dang! 15 bikes! Are they all 2 stroke Yammies?
I second that! Your RD would thank you immensely. Once converted to CDI ignition, your engine will run cooler and smoother. CB points if not timed properly, quality of the points, wear of cam etc. are many factors that aid in timing not being optimum and with age they worsen, with symptoms of improper combustion and heat build up etc.....Also, if you have a spare carb, try swapping out the left carb to narrow down the issue.
Dave
Not to be rude but let my suggestion sink in. Points are outdated technology plus the mechanics/electrics are 50y+ already. They fail and are hard to get back to original condition without spending a fortune and you still end up with suboptimal performance and reliability.
I know its not what you want to hear but if you want to enjoy these bikes without too many worries it is the best option.
Been there done that, after many hours and replacing almost the entire system I chickened out and bought an electronic ignition. Best decision ever and I put it in all my bikes once the points ignition develops issues.
Its not only the points, the charging system is also 50+ y old and bound to fail next, then you can open the next topic wondering why its not charging.
guys, he wants to stick with points. they do work well when set up right. that being said, the structure around it is old, wires do break down and IMHO the issues here become charging voltage and or wire (like in the harness) condition. My 67 C2tr and the LS2 are still on points and both run fine.
I will say the biggest issue w points these days is the quality of the replacements, the heels are almost always too long and need to be filed down so that the gap and timing can eb set within the range of the plate.
I bet you have a corroded wire that's resistance is too high.
Have you read any of my posts? I have removed the ignition system from the bike's wiring harness and jumpered it directly to the battery and points.
How much is a new electronic ignition? It is sheer hypocrisy to say that someone must 'spend a fortune' to maintain an original ignition system when compared to the cost of a new system. Besides, I see more than a few posts here asking for help with their new system. They are NOT perfect. They are often better when right, but are not for me. Not until and unless they come down significantly in price. THAT is my biggest knock on them.
Back on topic; Yesterday, I did the following:
I swapped a different carb on the left.
I again switched the coils and their wires side to side.
Installed new plugs.
Swapped points side to side again.
Changed condensers again.
Wired the left coil directly to the battery removing even the relay. The battery has 12.4v.
Wired the coil directly to the points.
Completely disconnected the ignition from the bike's wiring.
I removed, cleaned, inspected and tested the stator assembly and cleaned and tested the rotor assembly. But haven't reinstalled the stator yet.
I think the left is hitting at idle because I feel good warm pressure out the exhaust, but it basically quits as soon as I twist the throttle. The flash from the timing light is a bit weird at throttle and has an occasional bright flash which corresponds to when the left cylinder hits. But it's just a hit now and then.
I am going to test and adjust the regulator today. As I have said; I have a lot of spare parts and parts bikes as well so I have lots of alternatives.
By going into the charging system this deep, I feel like I am getting into the weeds a bit. If the charging system was the fault, why does the right cylinder ALWAYS run fine while the left will not even with the parts from the right. That is the most confusing part of this for me.
Frankly, I have never had much trouble from the ignitions on my Yamahas. Most certainly NOTHING like this. And to be honest, if it weren't for the cost, I would consider a new electronic ignition. But for now, I really, really want to get to the source of this issue. This is not just about getting the bike running right.
I would have someone else look at this thing at this point to see if I am overlooking something, but there is no one anywhere around here to turn to. So, I am on here. Thank Goodness for this resource. I don't know what I would do without it.
Thank you for the helpful suggestions. And please keep them coming. Because I am nearing a complete impasse.
Gas tank interfering with something on the left side when you put it back on? Crank bearings ok letting the points cam spin true and not wiggle?
there's a lot to read thru to be honest, i didnt catch you had bypassed the points to coul wire.
You never gave what the charging voltage is either. its fairly well documented that w low voltage, one cyl will drop before the other. its common tbh. the cdis work well and they replace the charging system completely. so its 2 birds w one stone. its a hard pill money wise to swallow, thats for sure. but, it is what it is. that being said, points absolutely should work just fine when everything else is in good order. check the health of the charging system 1st. then go from there.
If you really want to stick with points you will have to work through this systematically.
Meaning: Make a proper diagnoses before swapping parts.
1. Did it run right before? Y/N
If yes: What changed that caused this behaviour? Perhaps you did some work to the bike and damaged something in the process. If it appeared all of a sudden while the bike always ran fine it's probably due to wear or a faulty part.
2. Check basics first: Compression (you say is OK), check spark: (you are not sure), check air/fuel delivery (you say it's OK), check charging system (you didnt check yet)
If you can eliminate the standard suspects you end up with the culprit.
Unfortunately, as mentioned before, diagnosing these old ignitions can be a real pain. There are many things that can cause your symptons.
- bad spark plugs
- bad spark plug wires
- bad spark plug caps
- bad coils
- bad condensator
- bad points
- bad point vilts
- uneven cam on camshaft/unbalance, but this doesnt happen all of a sudden
- flywheel damage
- rectifier/regulator faulty
- generator faulty
- battery faulty
- bad wiring in/to all of the above
- bad timing
You claim its always the left cylinder and the problem doesnt move to the other cylinder despite swapping points, coils, etc. This makes me believe it's either an ignition wiring problem to the left cylinder or a mechanical problem (cam on crankshaft uneven). As mentioned before, the latter will not happen all of a sudden.
Check your wiring from the point all the way to the ignition coil on the left cyliner, wiggle it a bit while measuring and see if you lose continuity.
Quote from: 1976RD400C on August 11, 2025, 10:46:45 AMGas tank interfering with something on the left side when you put it back on? Crank bearings ok letting the points cam spin true and not wiggle?
I have nothing to add here except that when I first started tuning my RD as I was learning and a steep curve at that I believe looking back on it I know I couldn't trust the stock ignition in regards to the points staying put. I repeatedly checked the gap and it was off after running the bike. Thought the new points were installed and fastened correctly. Who knows but maybe it had something to do with what you suggest,crank not running true. That and other things pointed out like no one of higher knowledge to help locally + making good money at the time, I took the hit and got the Vape and a Vito's crank. All that said I lucked out with the help of all of you on this site...Vape install for dummies like me, couldn't of done it without this board because I still had issues. And well after the Vape install I still had to revise/clean up the wire harness, a simple short behind the headlight bucket prompted that as well as the flasher relay burning out. However I get the OP's intent and really he's right. It's just hard when you are on your own.
Interesting thread, I'm staying tuned to learn even though I may never touch upon this issue knock on wood.
Quote from: m in sc on August 11, 2025, 11:51:11 AMthere's a lot to read thru to be honest, i didnt catch you had bypassed the points to coul wire.
You never gave what the charging voltage is either. its fairly well documented that w low voltage, one cyl will drop before the other. its common tbh. the cdis work well and they replace the charging system completely. so its 2 birds w one stone. its a hard pill money wise to swallow, thats for sure. but, it is what it is. that being said, points absolutely should work just fine when everything else is in good order. check the health of the charging system 1st. then go from there.
This ^ :thumbs:
Also, if you have a spare good battery, swap it out. Or see if running it while on a charger changes anything.
Well, well, well................
First off....I would like to thank almost all who offered the help that I asked for...........THANK YOU!
Second....it wasn't the ignition at all. Which in one way reinforces what I have said all along; the stock ignition for a near stock RD is fine for a driver. In the hands of someone who knows what they are doing, the stock points ignition was good in 1975 and is fine in 2025, just like carburetors on 70s era engines.
Now..................the issue was a sucked reed.
How it had the affect on the timing light that it did is beyond me, but there it is.
I had exhausted ALL efforts to have any impact on the ignition of the left cylinder. EVERYTHING checked good. EVERYTHING. I will spare you the list. Nobody reads it anyway.
So, I was going to tear down that left side in desperation and when I pulled the reed block, out fell a reed set. Someone had changed to fiber reeds probably a long ago and one had failed and had partially blocked the intake tract.
Live and learn. I feel a little sheepish.
So, one more question if you'll allow me; I have plenty of the stock metal reeds and have one in that left cylinder which runs good NOW. Should I just put the metal reeds in both sides.......or is there enough advantage to going with the pricey fiber V Force or fiber replacement reeds. This engine is stock except for Bassani chambers. How much (if any) difference will either of the fiber reeds make and bottom line; are they worth the hundred or so dollars for this basically stock bike?
Thanks once again for the assistance.
.
Congrats :clap: Odd root cause, but OK :umm: Glad you got it sorted out!
Regarding your question on reeds, I would replace them all at the same time unless you know that brand of the ones in there now. Of course, replacing just one will bring up the question; "when will the others fail?" Also, by replacing just one you may end up with a performance difference between the new one and the older 3 pieces, especially if it's not the same brand and type. An upgrade over stock metal OE would be OE Yamaha YZ "55Y" reeds with one petal trimmed off. Or you could do TDR fiber reeds.
EDIT: In my notes I found the following comments that I saved from 2T guru Ed Erlenbach:
Stock/Unmodified Reedcage
Even on stock bikes I recommend replacing the factory steel reeds with fiber reeds. With the money you spend when you have to rebuild one of these engines to me worrying if one of those steel petals is going to break off and ruin my engine just isn't even worth it.
So there's "basically" three options:
-Some guys like using YZ125 petals part # 55Y-13613-00-00 because the reedcage they come off of is a 6 petal cage, they come as three individual petal joined at the bottom, so you buy 4 of these and cut one petal off of each reed.
- I like to use YZ85 reed petals part # 4ES-13613-00-00 they are a single petal so you buy 4, they bolt right on but you do have to trim the front edges to narrow them just a bit at the front easy peasy.
-Here in the US, TDR makes a racing petal for the RD's, they are a single petal reed that bolt right on but are a little thicker than stock YZ85 or YZ125 petals so they bias topend performance a bit.
(There are of course other brands and materials but these are 3 great options)
thats weird. let time i had a reed issue it ran well up top but showed its ass down low. thats super weird but glad you found it. I'd second the yz reeds. i'll be honest, I was never a fan of old school fiberglass reeds and would rather run stockers given the choice. but the yz reeds are a solid option as well.
Weird is the word. I have never has a reed break and act that way either. And it impacted the way the timing light acted. Weird again.
So let me ask this again; how much (if any) noticeable difference in my near stock bike would a hundred dollar's worth of fiber reeds make? I have to change the other one back to metal at this point anyway (or both with a change to new fibers) so this is a 'bang for the buck' question.
And just as an FYI; I have personally NEVER broken a metal reed in any of the bikes I have owned and nearly all have had the original metal reeds. So, one breaking like this fiber one did is not a real concern to me. Should it be?
Well, it doesn't sound implausible that if the reed breaks the seal for any reason, that the fuel/oil/air mix simply slows or stops moving for that split second. That would change the amount of fuel that goes kaboom in the boombox, and thus change the burn rate. Burn rate changes, timing appears off, because the engine is running out of sync? Though, the light reads the spark signal, so that leads you back to some other ignition fault. Meh.
Fiberglass reeds, being lighter change the opening, dwell, and closing speed of the reed petal as compared to stock ones. The theory being, the faster you get the fuel in, and reed shut, the more efficient the port timing is. Does it make a difference? Only if you are asking for performance along with most other engine mods.
But, I don't really see the point since I can't reed, metal/fiberglass.
in my experience, the only really notable difference in reeds has been going to genuine v force, or much larger banshee/rz/tz ones. I never liked cutting cyls to fit huge cages, but back 'in the day' it was the only real feasible option IF you wanted more reed tip area, which is really what matters.
nowadays, with the rm100 v force reeds as a virtual bolt in, IMHO there's no benefit in going huge unless you are going to like 38+mm carbs.
I have also never broken a stock metal reed, and they work quite well overall. as lomg as the guide plates are used and the screws are tight they will be fine, especially on a stock motor w bassanis. 0.02
Way back when, we used to put Boyesen Reeds in our Enduros because EVERYONE else was doing it. But I honestly don't remember any gain, only going with the crowd. And back then, EVERYONE said that the fiber reeds wouldn't hurt the engine in case they failed like the metal reeds would. But, I remember fiber reeds failing, but don't really remember any metal reeds failing. Certainly, I have never had a metal reed fail.
So, I will replace the fiber reeds in the right cylinder with some O.E. reeds I have.
And thank you AGAIN for the help and guidance.
.
I would strongly recommend changing both sets out together back to sto k, not just 1 side
Of course. I have already changed out the left side fibers that had failed with the only thing I had which were original metal reeds. So, what I meant was the the right side would get the metal ones too.
:olaf: good deal!
Quote from: RDDave on August 12, 2025, 03:21:00 PMOf course. I have already changed out the left side fibers that had failed with the only thing I had which were original metal reeds. So, what I meant was the the right side would get the metal ones too.
:thumbs: