I have posted on this journey for quite some time now and I would like to again say, THANK YOU to all that have offered advice and encouragement.
I finally found an old retired Yamaha mechanic that would take a look at my 350. He rode the bike and double checked the adjustments. The bike didn't run right but all the adjustments were good.
After checking the usual adjustments, he did a simple test: He disconnected a spark plug, started the bike and raised the carb slide on the cylinder that he had disconnected the plug. The engine revved up. That was his test for the labyrinth seal.
I wished I had known of that simple test a year or so ago. Since I had checked, changed, swapped, bypassed, measured, double checked and checked again everything I could possibly think of.
So, I guess the engine has to come apart. I would like some guidance on how to approach changing the seal. I think I can get the crank out. I haven't done this kind of thing in decades and that was on single cylinder Enduros but I plan to try to split the RD's cases.
Who do I send the crank to? I can't change it myself, can I? I have other engines, but I don't know what condition the bottom ends are in and this is the original engine for this bike and everything works good if I can just get the engine to run right.
Thoughts, opinions, and suggestions would be appreciated.
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To replace the lab seal you have to break the crank down... you'll need a press. I think the hardest part of that will be finding a replacement seal.
If you have an "original", never serviced RD350 crank, it's time to do something with the crank. Bearings DO NOT last 50 years, even in a box on the shelf.
Send it here https://www.billbune.com/
what intakes are on the bike? does it have a crossover tube? pic would help
I don't know what kind of pricing you are getting/expecting for a rebuild, but brand-new cranks are very reasonable. Last year I bought a VITO's modern updated crank off eBay and they are still selling there now for $479.00 and there is a limited time coupon for $20.00 off right now. Free shipping & no core exchange. Uses KOYO mains + Silver caged Upper & lower rod bearings.
I also bought 2 from HPR on eBay and they are currently $399.00 and they also have a $20.00 off coupon. They charge $32.00 for shipping. No core exchange either. Mains are TPI (Taiwan) and also uses the Silver caged upper & lower rod bearings.
Have not run mine yet but quality is top notch and lots of positive reviews on eBay.
they come from the same factory i was told.
that being said, agree, i run a few vitos cranks. just replace it. however i am really dubious on that test. the only way a labyrinth seal will fail is of the inner main bearings failed, badly. if that happened, they would have to be so far out of whack it would sound like a concrete mixer running.
Keep in mind, i have rebuilt my own cranks numerous times in various bikes. i've -never- had to replace a ( edit) labyrinth seal.
I don't know this guy, but just because somebody did something for a long time, doesn't mean they were particularly good at it. Just take it with a grain of salt.
++ to m in sc
I am very open to any and all suggestions.
The intakes are stock and there is no cross over.
What else should I be looking for on this? Both he and I have checked, adjusted, rechecked and readjusted everything we can think of. Rodney was a Yamaha mechanic for decades. Has rebuilt dozens and dozens over the years. Doesn't make him perfect, but he absolutely knows his stuff.
Again, I am open to thoughts and suggestions.
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i find it hard to believe, but we learn every day. Me, id get a new crank and dump it in. after parts and labor, its not worth the aggravation of rebuilding a stocker. Like said, i can rebuild my own and its just not worth it anymore.
If that truly is it, then we learned something new. a new crank is a good preventative if nothing else
If it comes to that, YES it will be a new crank.
Rodney is looking for his pressure testing pieces. He hasn't used them in years.
I'll keep posting as this moves along. After a couple of years, I am not getting in a hurry.
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if the seals have never been replaced, the crank needs out come out anyway, just to change the outer ones.
From your previous post, is the problem that the left plug keeps fouling? Is that the only problem?
It doesn't seem to be fouling nearly as much as it was. The Iridium plugs seemed to help a lot. But now the right cylinder is a bit weak. Comp is good on both; 100 or so. The big problem now is that the bike just doesn't run as good as it should SOMETIMES. And sometimes it runs good. It always starts good; two or no more than three kicks cold and first kick hot. And I can't find anything that changes. It is the most aggravating thing I have ever encountered.
I went ahead and changed the left crank seal just because it wasn't difficult and I was just not wanting to leave any stone unturned.
I also have a '73 250 Enduro that had running problems when I got it. I found it's issue straight away (the lobe for the points was dry and pitted causing the points to wear very quickly) and now it is a joy to ride. Starts and runs good and the same every time I throw a leg over it.
Rodney is going to try and find his testing equipment to test the lab seal before we do anything major. Meanwhile, we will test ride it and continue to check and recheck everything we can think of.
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"SOMETIMES" sounds intermittent? If it was lab seal, wouldn't you expect it to be all the time?
it absolutely would be every time. also a pressure test wont tell you anything on a lab seal. its not sealing unless the motor is actually running, and over 1000 rpm.
sounds electrical to me
I can't remember everything that Dave has tried so far, but if you haven't checked the reed cages to see if petals are sealing properly that could mimic some of what you are seeing with running good sometimes and excess fuel symptoms at other times.
Mark is absolutely correct about the lab seal. It is not a seal as we know them but has clearance to the crank. It has nothing to wear unless the main bearings are so worn that the crank is rubbing on the seal and crankwheels would probably be rubbing on the cases.
100psi is a bit low for compression. Not so low it won't run, but it won't exactly be perky.
If the motor hasn't been apart since Pontius was a pilot, it's probably a good time to strip and rebuild the motor with new pistons in a fresh bore and a new crank with all new motor and transmission seal.
With the motor out, it's time to clean the carbs meticulously. The outsides are just for appearances, it's the insides that have to be clean. And a great opportunity to clean out the fuel tank and filter.
Okay then, the lab seal is not the problem. The engine is quiet. No bottom end noise.
I have repeatedly tried the above suggestions. Original cylinders had about 100lbs compression on std bore. As part of the 'no stone unturned' path, I have new ebay cylinders sets on. Again, with about 100lbs comp.
I have completely disassembled the carbs including the emulsion tubes and have put on other carbs that I have.
Every single piece of the ignition system has been changed, swapped side to side, and changed again. I have even bypassed the bike's wiring harness and jumpered the ignition directly from the battery. I have the ignition on a relay as I was losing just over a volt through the harness. I can pull the carbs AGAIN and either inspect or swap the reed blocks, but they look fine.
I have done just about everything I can imagine multiple times. We will spend some more time with it. I don't know how I feel about it not being the lab seal; On the one hand, I wasn't looking forward to spending the time and money to tear down the engine. But I sure would have been happy to put this saga behind me.
Oh well.............................
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for the same money spent on that, you can put a cdi on it .testing good and actually being good especially w old ignition components can be totally different
I was an Evinrude mechanic years ago and I can attest to what you are saying. Using factory test equipment, many times I have seen ignition components that were in spec but wouldn't work and vice versa. The ONLY true test was with known good components.
If it were the ignition on my bike, I just don't understand how every piece that tests good from my stash would do the exact same thing on my bike. And I have tried several different pieces at each juncture. Now I don't have a way to run the pieces on another bike to test, but still, the same problem with different parts?
I am stumped. And have been for some time. But with this guy's help, I will keep trying different things.
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my 72 t500 was like that. i chased it forever. like, a few years. then just put a cdi on it. been perfect for the past 5-6 years.
the 71 got a regular points replacement elec ignition. all i'm saying is, it sounds like ignition/electrical.
i chased this on an rd years ago, and on my buddies GT550 as well, both turned out to be intermittent charging issues.
an HPI is a more cost friendly option vs the vape. both replace charging and ignition system on the bike. just my 0.02
As always; Thank you.
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I have read through some of the ignition threads. But I didn't find what the Vape does over the HPI given it's higher cost.
Are there recent threads with more details on each and maybe why one over the other?
I have worked on my fair share of ignitions both points and electronic and just cannot grasp how changing every single part of the system still leaves me with the same symptoms.
BUT! I greatly respect the experience here. So, i am seriously thinking about dropping the coin for an electronic system. Frankly, the biggest down side is the cost. Seems exorbitant to me given what I am used to spending for car ignition systems. If it weren't the cost AND the possibility that it won't fix my issue, I would be all over it. But, it is what it is.
What about the rr on the HPI? Other than MORE money. This is a street bike. Is there a recent thread that details? I guess I would stay with DC, right? So, I also need a rectifier?
And there are several threads on HPI failures. Is that a product problem or operator error?
I would very much prefer to just stay with the points. I understand what electronic ignition brings, but unless my point system is broken, for the cost, the electronic just doesn't bring enough to the party. But, if it is the ONLY way to resolve my bike's issue, then I have to go that route.
Thanks again for putting up with me.
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i have extensive experience with both, for years. the vape is the stronger unit as far as charging. however, the hpi is half the money and can be great on a street bike. i have an hpi w a rr on my lightweight rd. bern working for years, documented well in that thread in the haus of projects.
what about the Dyna S from Economy Cycle? Seems like the most cost-effective solution to eliminate the 50 years old points system entirely for sanity check here. Also, the solid-state r/r are available multiple places- I think I paid $45 for mine off eBay. If you added those 2 parts and still doesn't fix problem I would go new IGN coils if not already done. OEM here can create open circuit condition when hot, then repair itself when they cool. Last thing I would do is replace original main wire harness. Those wires often turn brittle over time and create intermittent failures. I hate shot gunning for solutions, but I'm a much better parts switcher than debugger on electrical Gremlins :twocents:
https://www.economycycle.com/product-category/yamaha-rd250350400r5ds6ds7-parts/electrical-ignitions-lighting/ignition/dyna-s-ignitions/
i would concur w above for the most part.
look in the supertune section he goes over installing both cdis.
as far as coils, i have a poat in the tech library? about using sv650 cpils
Converted to the SV coils last year. And have tested with the bike's wiring harness completely bypassed by using jumper wires.
I currently use a relay to power the coils. That way I have bypassed that part of the harness and keep full battery voltage to the coils. Before, I was losing just over a volt through the harness.
Now, one thing that I haven't done is to monitor the voltage to the coils ALL the time. The battery is new and the lights are bright so I don't think I am dealing with low voltage. It runs the same with the lights off as it does with them on.
Keep the ideas coming. I MUST be missing something.
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Quote from: RDDave on July 22, 2026, 08:47:41 AMI have read through some of the ignition threads. But I didn't find what the Vape does over the HPI given it's higher cost.
Are there recent threads with more details on each and maybe why one over the other?
I have worked on my fair share of ignitions both points and electronic and just cannot grasp how changing every single part of the system still leaves me with the same symptoms.
BUT! I greatly respect the experience here. So, i am seriously thinking about dropping the coin for an electronic system. Frankly, the biggest down side is the cost. Seems exorbitant to me given what I am used to spending for car ignition systems. If it weren't the cost AND the possibility that it won't fix my issue, I would be all over it. But, it is what it is.
What about the rr on the HPI? Other than MORE money. This is a street bike. Is there a recent thread that details? I guess I would stay with DC, right? So, I also need a rectifier?
And there are several threads on HPI failures. Is that a product problem or operator error?
I would very much prefer to just stay with the points. I understand what electronic ignition brings, but unless my point system is broken, for the cost, the electronic just doesn't bring enough to the party. But, if it is the ONLY way to resolve my bike's issue, then I have to go that route.
Thanks again for putting up with me.
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Unless you had a known good complete OEM ignition to swap on there to confirm, I'm leaning towards your ignition is the source of failure. I had a Gremlin like this back in the 1970's - IIRC it was my 1975 RD250B. I ended up buying an aftermarket tune-up kit (Rocky I think) and that cured the problem. Pretty sure it was bad condenser. I think you have reached the point as you detailed above I bolded. If you haven't replaced points & condenser 1st as cheapest option- try that, otherwise if it was me it would be new ignition time. The time spent on this is worth more than the couple hundred $ at my stage of life.
I have a lot of spare parts and have changed the points and condenser (more than once) and have also swapped the points between cylinders. I have tried probably 6 or 8 different combinations of points and condenser. I also test the ignition components. The point resistance is very low. I file and clean them, then check for resistance until I get it as low as I can. And the different condensers all hold a charge. But I haven't tried new ones, and I don't have a way to test run them on another bike.
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I think one test that you can do is ride it until it doesn't run right, then install brand new spark plugs that are gapped a bit smaller and see if it improved at all. If so, then it would point towards a weak spark.
50 year old capacitors are typically at end of life or done .
i would source some new auromotive ones and try them if points are the way to go for you.
also, if you havent changed the actual wire from the points to the coils, do so. replace them. ive been bit by that more than once. tests ok, but running, it jumps or breaks down.
lastly , filing points is bad . i know it was common practice, but the surface is coated. you file or sand it, that goes away. while its a quick fix, it is absolutely bad practice that is far too common.
you've thoroughly tested and retested everything. That should have caught whatever it is if it was something obvious, common, or simple. IMO you've reached the limit of what static testing will get you. In a recent post you said it starts easily and consistently and runs good most the time, but not as good as you expect all the time. The fail mode is reduced to "sometimes". Armature windings failing with heat? There's an old saying "too much analysis leads to paralysis". I get you want to stay with points, but what choice is left but to try the most affordable no points option? There's no guarantee it will be THE fix, but if it does you at least will know everything else in your system is operational. If it does make it run the way you expect you have your baseline and can always work on converting back to points system when you have the time and motivation to dig in again.
Good Luck!
so, at deals gap this year, there was a guy w a really pretty modded rd350. he couldnt get it to run for shit. we went down the list of everything and it kept coming back to ihnition, for at least me and Chuck Quenlzler. heres the kicker, it had one of those stupid Indian radjoot cdis on it 'because it was half the money' all week. fired up great, then the longer he ran it the worse it got.
few weeks later he dms me on fb, says he put a cdi on it (hpi i suggested) said it absolutely fixed it. what i had said was id rather run points than that crappy cdi, and we know how i feel about those.
I installed an HPI and it was great until the rotor magnet cracked/separated. I installed the VAPE ignition and my bike runs more smoothly in my opinion. I did a 450 miles early this year in the california desert on route 66 with no issues. since I installed the VAPE, the plugs burn more evenly than with the HPI. the best part is that you can run without a battery on both systems and the spark energy is pretty high. With points ignition I was always chasing issues. I once had the right side points intermittently shorting to ground and causing either plug fouling or missing and backfiring. with any of these modern ignition systems these problems are now a thing of the past.
I guess I would be a happy camper if I got rid of the points and all was good. But if I bit the bullet and that wasn't it, I am not sure I could show my face here again.
Lots of you guys keep telling me that it may well be the ignition and have your own horror stories to back it up.
I guess I am hard headed, but I just have a hard time accepting that the stock ignition on a stock bike just will not work right no matter how well sorted out it may be. But, I highly respect the knowledge and experience here.
IF electronic wasn't so expensive, IF I hadn't read several posts here on their failures, and IF I could test one to see, it would be a much easier decision.
I may look more seriously at the Vape. Seems you all think it is worth the coin over the others.
I will spend some time with the search function and would look at any particular threads that you would recommend.
I appreciate all the input.
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$800 for Vape. OUCH!
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you're missing an important aspect. a 50+ year old harness and ignition parts (not all). one part out = issues.
the cheapest way out going electronic is with one of these:
https://ebay.io/m/LlWVD9
im not a huge fan of the concept of a cheap ignition from china.. but... they have gotten pretty good. i have one on my t500 (the 71) because i did put a vape and a zeel on my 72 + a different coil, well over 1100 in ignition stuff, and that was before they got even more expensive a few yrs ago.
i also bought one for my LS2, they were the only ones making a point replacement and dammit, it works. yes with sv coils as well. (on both actually). :twocents:
Quote from: RDDave on July 23, 2026, 08:37:59 PMI guess I would be a happy camper if I got rid of the points and all was good. But if I bit the bullet and that wasn't it, I am not sure I could show my face here again.
Lots of you guys keep telling me that it may well be the ignition and have your own horror stories to back it up.
I guess I am hard headed, but I just have a hard time accepting that the stock ignition on a stock bike just will not work right no matter how well sorted out it may be. But, I highly respect the knowledge and experience here.
IF electronic wasn't so expensive, IF I hadn't read several posts here on their failures, and IF I could test one to see, it would be a much easier decision.
I may look more seriously at the Vape. Seems you all think it is worth the coin over the others.
I will spend some time with the search function and would look at any particular threads that you would recommend.
I appreciate all the input.
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I totally understand your frustration and desire to get the stocker to work if you can just verify the fault. Here's the flaw I see in your reasoning and reluctance: you are assuming you are starting with a proper working OEM ignition that just has a problem you haven't found and fixed yet, right? You mentioned you replaced the Left crank seal, so you obviously had the complete stock ignition removed and in your hands. You saw both sections had the copper windings in them. It's a great leap of faith that 51-year-old copper wound components/assemblies are 100% still intact and reliable at all speeds and temps. You don't have access to a known good complete generator assembly. What choice do you have but to buy a new replacement ignition that will confirm yes or no yours is actually good if you find the mysterious fault and fix it?
I'm expecting to face a similar situation soon: I have a 1973 RD250, 2 1974 RD350 and a 1977 RD400 in my shop and NONE are complete! I have spare motors, ignitions, etc. Only the 400 was running when I bought it so I have reasonable expectations that will be a running baseline when I get it back together. The others will get a reasonable effort to get running with OEM ignition. If I get too far into any of them and not running- I'm going straight to another ignition and it's NOT going to be a top-of-the-line performance system either. Can't afford it and don't need it- I just want a basic runner out of all the bikes to start with.
There are some brilliant people on here that live and breathe this stuff who I really admire, but I can't match their passion and enthusiasm with so many bikes to get going and limited time at 68 years old. My wife gave me the ultimatum not to die and leave her with all this "junk" to dispose of so I have to fix what I can reasonably in time available and thin the herd over time. :whistle: I will probably be too embarrassed to broadcast if I choose Newtronics for quick and dirty solution, but will feel Ok if I go Dyna S solution to get these babies back on the road before I die :vroom:
Quote from: m in sc on July 23, 2026, 09:41:51 PMyou're missing an important aspect. a 50+ year old harness and ignition parts (not all). one part out = issues.
the cheapest way out going electronic is with one of these:
https://ebay.io/m/LlWVD9
im not a huge fan of the concept of a cheap ignition from china.. but... they have gotten pretty good. i have one on my t500 (the 71) because i did put a vape and a zeel on my 72 + a different coil, well over 1100 in ignition stuff, and that was before they got even more expensive a few yrs ago.
i also bought one for my LS2, they were the only ones making a point replacement and dammit, it works. yes with sv coils as well. (on both actually). :twocents:
I saw those and they scared me lol. I'm still keeping in mind the Newtronics from Yambits for a low budget fix if needed.
Quote from: 1976RD400C on July 23, 2026, 09:28:44 AMI think one test that you can do is ride it until it doesn't run right, then install brand new spark plugs that are gapped a bit smaller and see if it improved at all. If so, then it would point towards a weak spark.
I agree w this
Outside the box: Petcock flowing good and continues to flow good?
I have had big block and Hemi Mopars all my life. I still have a '70 HemiCuda with a 540" Hemi. And one thing I have always done when I tore something up was to do forensics. I wanted to know what happened. I have learned far more from that than most anything else. That is what I am pulling against in this. I really hate to give up. Wanting to know what is actually wrong is driving me as much as just plain wanting it to run right. Otherwise, I would have moved on last year. Which might have been the smart thing to do.
BUT! Maybe I am whipped on this one and it's time to move on.
Does that Ebay ignition have battery charging? It doesn't look like it.
The Vape would be my preference based on the collective experience here. I guess if I had tore into the engine to change the labyrinth seal, that would have been over half the cost of the new ignition, been a LOT more work, would not have fixed the problem, and it would still have points ignition.
So A HUGE THANK YOU to you guys: THANK YOU!
I am not on any kind of a budget. But it is difficult for me to spend $800 on an ignition for a $4,000 +/- bike. But then, compared to Hemi stuff, that is pennies on dollars.
So, I guess I am going to tinker with this a little bit more. The bike is still with Rodney who looks at it a little here and there as his energy and time allows. Maybe something will show up.
Meanwhile, I am going to review the threads here and the youtube videos on the Vape install.
:thumbs:
that ebay ignition is strictly a points replacemen. it should run on battery alone. its the cheapest way to go imho, and one ive used.
I thought so. Not something that would work for me on my street bike.
Although, if I could rent someone's as a test to see if it cured my problem, I would LOVE to do that.
It would just be a waste to buy one as a test knowing that it would not get me where I want to be.
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why wouldnt it work? sure it would. isn't your charging system working? since you know automotive, its basically like a petronix ignition, but for bikes.
So, it ONLY replaces the points while retaining the charging coils?
I wasn't aware of that. Then that would fly for me.
I understand the value of being able to build a curve, but the stock ignition doesn't and I am happy with the level of performance the bike has with the Bassanis when it runs right. I can live with leaving those extra ponies on the table for the cost difference.
The cost per horsepower does come into the equation for me with systems like the Vape.
Thank you once again for the insight.
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so the tytronic, dyna etc just replaces the points. the cdi does both. the hoi has a curve built in,the vape does not, you have to add a component for that. my 70 r5 has a vape cdi. it is otherwise dead bone stock down to the bore and it runs great, and im def not chasing hp. reliability was my goal. 0.02
Well, if reliability is questionable with the Tytronic, then that WOULD be an issue.
But the Tytronic is available for a lot of different bikes and I don't read about any more failures than I do with some of the other conversions. If I am missing something, please let me know.
One more question please; I don't like the throttle cables that someone put on the bike and plan to replace them. I would appreciate recommendations on whose to get.
Thanks...............AGAIN!
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i run 2 of the tytronics. one on the ls2, one on the 2nd t500. money isn't an issue/concern with parts for me, so, that should tell you they are worth it. i currently run 5 vape cdis, an hpi, a dyna, and 2 tytronics. im all over the place. lol. just, simple. zero reliability issues with any, and thats the primary reason i run them. some its performance, but honeslty, just on 2.
as far as cables, if they are stock reach out to economy cycle.
Quote from: m in sc on July 25, 2026, 12:35:23 PMi run 2 of the tytronics. one on the ls2, one on the 2nd t500. money isn't an issue/concern with parts for me, so, that should tell you they are worth it. i currently run 5 vape cdis, an hpi, a dyna, and 2 tytronics. im all over the place. lol. just, simple. zero reliability issues with any, and thats the primary reason i run them. some its performance, but honeslty, just on 2.
as far as cables, if they are stock reach out to economy cycle.
I take it the Tyronics can't cause the motor to run backwards like my old Dyna does? The damn thing has been sitting there idling, lets out a cough, and it's going backwards.
they do not. i suspect they figured out you need longer dwell, and that was the issue with using a 4 stroke dyna trigger on an rd.
almost 20 years ago i guess, i modified an Allison ignition to use on an rd, single coil, ran into same issue and when i pie cut trigger wheel the issue went away. the tytronic & and nicks dyna, employ a similar system but use multiple trigger magnets in the rotor to get the dwell needed. even the vape cdi, early mzb ones, didnt have a ramped trigger on a cdi and could start backwards. ask how i know... :eek: :boom:
1st pic was the 1st attempt i did, from 2006. the later ones were cut on a lathe and had a big pie cut. this was #1 :)
Well crap! I went to order the high top throttle cables from Economy and they are out of them. Crap!
Of course, my '75 had the tall caps on the carbs. Because they are so tall and difficult to get out when working on the carbs, I switched to low tops with the curved adjusters.
I have the low tops with straight adjusters as well. Would you go ahead and order the new cables that they have and change to the straight adjusters? Or would you just wait until the others come in and keep the curved adjusters?
The ones on there now work, I just don't care for them and the amount of adjustments they have left.
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me? id order the short tops cables and revert back to short top carbs if you gave the tops and slides to match