1973 rd350 barn find- sitting 25 years. Seems to have a bottom to mid range stumble. Right side is definitely not firing as much as the left. Checked coils, rectifier, regulator, timing, condenser, and points. All are within spec. Spark plugs seem to be a little sooty, and appear about the same. Carbs have been throughly cleaned, and synced, new float valves installed. Unsure about exhaust, (DG expansion chambers) seems to be smokey upon startup. Will check to make sure they are clear. (Plan to have them hot tanked) Removed the light checker unit, it runs much better without it. (Took a while to figure out thst issue) I've gone through everything ad nauseam.. Can anyone put a little meat on the bone?
Super Dave
Maybe try a compression check. Sooty plugs should be replaced. Voltage reading while running? Spark plug cables ok?
if the coils are original, change them. they can test ok but not be. also plug wires and caps.
Cylinders still show cross hatching from a very recent bore before storage. Spark plugs are new, but dirtier than normal."Sooty" was the most accurate means to describe plug condition. Have not tested voltage while running, I am assuming the hot lead on coil? (Both coils have resistance within specs) I have access to some original coils, I used CM 11-50's. (It had some funky coils (cracked) mounted on the frame rails) spark plug wires look new, but appear to be automotive (built in plug caps) Thank you both for the input, I'll be back at it after the holidays.
few things to look at:
charging voltage. its needs to be over 13v over 2k. if not, it can be an issue.
the carbs.. all original brass inside? im assuming so, but if you used a kit and used the supplied slide needles, they are incorrect. also assuming the jet tubes were removed and thoroughly cleaned. if not, can be an issue.
the ignition: use copper core plug wire. If the coils are suspect, i posted a link about using SV650 coils int he tech forum. would recommend. as far as plugs and caps: since non resistor plugs aren't being made by NGK anymore, economy cycle lists non-resistor caps.
since you're saying BOTH are sooty, its more of a macro issue affecting both. In MY experience, and i cant explain why, when battery voltage is low, it seems to affect the RH cyl 1st.
good luck w it. you'll def get is sorted.
Thank you for your advise. Brass is original, the floats are the closed cell plastic type. Both floats weigh 2 grams. The emulsion tubes were checked, no corrosion. Since the plug wires and caps are suspect,I will replace them, (and the coils) before startup. (Will check the charging circuit then) The battery of course, is new, and well charged before the test ride. I felt that the plugs were dirtier than need be for such a short ride, they appeared a little "damp" (25 pilot/150 main) I didn't really get to row thru the gearbox, as the clutch was slipping. Parts are on order.
May not be relevant to your issue, but unleaded gas tends to leave the plugs looking sooty especially if the bike is not run hard enough to get the plugs up to self cleaning load levels.
Update: Installed copper core plug wires and non-resistor caps. Fired bike up, it is now misfiring on the left side instead of the right.(right side is running fine) Rechecked timing, and carb synchronization. I have not replaced the coils. Has anyone out there experienced this type of malady? Any input or information would be appreciated I haven't seen this before. I'm about ready to get some bongos, put on a grass skirt, headdress, and see if I can excise the Gremlins from this bike.
Update: There is 13.4 volts going to the battery while bike is running. Replacing Springs on clutch was inadequate, must replace clutch pack. In spite of misfiring, and the clutch slipping, it feels like the bike is capable of making great power.
timing wont cause a misfire.. but 50 year old coils will. :twocents:
Quote from: Super Dave on January 06, 2025, 06:39:04 PMUpdate: There is 13.4 volts going to the battery while bike is running. Replacing Springs on clutch was inadequate, must replace clutch pack. In spite of misfiring, and the clutch slipping, it feels like the bike is capable of making great power.
SD, I've had my bike for 5 ? months now and haven't made it out of the garage yet. But this community on here is great at helping out. And I'm getting close. But what is the light checker unit and was it shorted out and what were the symptoms if I may ask.
It has been taking forever to get my parts in. A light Checker unit is simply a 12 volt light bulb connected to a couple of wires, ending in alligator clips. (It's easy to make one,as I did) The bike seemed to idle fine, but when RPMs were applied, one of the sides would misfire. At first it was just the right side, then later it switched to the left. This was pretty damn confusing. I am still using the same coils, they are stock, but they are not original. In the interim, I discovered that the autolight spark plugs I was using were equivalent to a br-9es. I found the champion equivalent to a b-9es, which is an 805. When I fired the bike up, it seemed to be improved running on the bench. Received the fiber plates for the clutch last night. When I took the clutch apart, I discovered there are no rubber dampeners in between the metal and fiber plates. (7) I am now hesitant to reassemble without these parts. The local Yamaha shop wants $21 a piece, which I think is out of hand. Question: are these rubber Parts in between the plates really necessary? Could the source of the misfire malady been caused by using plugs that were too cold of a heat range? My RD has the DG heads (which is why I'm using an ES instead of an HS plug) and expansion chambers.
A light Checker unit on an 73 rd350 is located in front of the coils, behind the steering head. There are three wires coming from the dash that plug into it.
they are not. most people remove them. when you use a FZ600 set of plates they dont even fit anymore. just throw em in the trash.
Thanks for the reply. I had no idea that FZ600 fiber plates would fit. They are probably far superior to the aftermarket reproduction ones I had bought. I am anxious to see how the RD will run. What year FZ? Will the metal plates fit as well? (Most likely I will end up replacing the clutch pack)
Correction: Champion 805 spark plugs are equivalent to a NGK B-8es. This is a non-resistor spark plug, which produces a little bit hotter spark than a NGK Br-8es. (They are available at the local auto parts store) NGK no longer produces the B8-es. I am hopeful that changing to a hotter spark plug than the autolight 4063 will cure the misfire.
might be a bandaid but that's not the cause. look elsewhere. plugs, unless fouled due to bad tune, defective, or worn out will not case a misfire. I've run resistor plugs w resistor caps before (long story) never caused a missfire..you have other causes
You're describing carb issues and looking at way too many variables at once. I mean, you have to have a well functioning ignition, but it's not going to cause what you're describing 99% of the time. I would make no assumptions about a bike that sat for 25 years and do a compression check. How are you syncing the carbs- vacuum gauges, snail sync, grounding the plugs? Is there a crossover tube? Where in the throttle is it misfiring? Does the choke fix it or make it worse? Have you checked for air leaks? Are you running filters and is the tank pristine inside?
I def wouldn't trust the coils or wiring either. are they the big round aftermarket aluminum coils?
The carbs are in really decent shape internally. I have checked every passage with contact cleaner and compressed air. I installed new float valves, I checked the floats, I even weighed them! I checked the pilot and Main Jets to ensure that the numbers were standard, the air screws are out one and a half turns. I don't know what a snail sink is, trust me, they're opening up identically. These are stock carbs, there is a crossover tube. And it does not run better with the choke on. But when running, this seems to happen around mid-range to the upper throttle the symptoms are better described in some of my past posts. The tank is pristine, and I am running filters. It's not entirely a carb issue because it was missing on the right cylinder, and then magically switched to missing on the left cylinder. To me, that is indicative of being an electrical issue. I've almost got it back together, and I'm going to take a test ride tomorrow after fixing the clutch. If it is still missing, then I'm going to replace the coils. The ones that are on it came out of a pile of coils and I absconded with two of them. I verified that the serial numbers on the coils were the proper numbers.
it's just a 3 ohm coil. common saying w rds: most jetting issues are electrical :lol: you'll find it I'm sure :gentleman:
Snail sync
(https://www.merlinmotorsport.co.uk/files/resized/small/S/img/syn001.jpg)
Fired the bike up on the bench. This is the first time that it has ran with the champion 805 non-resistor plugs. It idled fine, and revved cleanly, sounds very crisp. Going to take it out tomorrow for a test ride. Will put a load on the motor and see if it reves cleanly.
Awesome. Hoping for a sorted ride.
Try running without filters...
With the stock points ignition, a worn LH main bearing will make the timing erratic. Have you checked the timing on a running engine, using a strobe lamp? This was the main issue on my 350A, while my cousin owned it and I was doing the wrenching.New main bearings fixed that problem.
(Still, the first thing I did after buying it from him, was replacing the stock ignition and alternator with a Power dynamo/ Vape. Best mod for old RDs)
Got the clutch working properly. However the bike seems to not be firing mainly on the left cylinder. Up on the bench, I hooked a timing light to the spark plug on the left side to see if the ignition was firing. The light ran like it should have with the cylinder firing properly. When it was not firing, (while running) the light still seem to be firing properly. To me, this indicated that the problem was not with the ignition but carburation. Both spark plugs were wet after the bike ran. The right side seem to be as wet as a left, but there was a slight coat of soot on it. Jetting is stock. Floats have been set properly. Carburetors are very clean inside, all passages are clear. I made the mistake of buying a cheap set of valve needle seat assemblies, the brass was too long so I didn't use them. I have been running the stock assemblies, which looked to be fine, could they be sticking?
if they stick they leak out the drain tube. you sure the choke isnt on? or leaking?
I'm not so sure that just because the light is flashing that the plug is firing. Maybe try taking some old plugs and opening up the gap real big and watch if it has enough zap to jump a big gap.
Quote from: Super Dave on January 25, 2025, 02:31:59 PMIt has been taking forever to get my parts in. A light Checker unit is simply a 12 volt light bulb connected to a couple of wires, ending in alligator clips. (It's easy to make one,as I did) The bike seemed to idle fine, but when RPMs were applied, one of the sides would misfire. At first it was just the right side, then later it switched to the left. This was pretty damn confusing. I am still using the same coils, they are stock, but they are not original. In the interim, I discovered that the autolight spark plugs I was using were equivalent to a br-9es. I found the champion equivalent to a b-9es, which is an 805. When I fired the bike up, it seemed to be improved running on the bench. Received the fiber plates for the clutch last night. When I took the clutch apart, I discovered there are no rubber dampeners in between the metal and fiber plates. (7) I am now hesitant to reassemble without these parts. The local Yamaha shop wants $21 a piece, which I think is out of hand. Question: are these rubber Parts in between the plates really necessary? Could the source of the misfire malady been caused by using plugs that were too cold of a heat range? My RD has the DG heads (which is why I'm using an ES instead of an HS plug) and expansion chambers.
I had a similar issue and had the same autolight spark plugs but one of them(cylinders) would not fire. I bought new NGK BR8s, put them in and now idles like a champ.
yeah. I can't remember who used to always say 'doesn't mean it's firing under compression' might have been quencher or aylor
Chainsaw dealers/ repair shops often have handy ignition testers. Basically a large spark gap inside a transparent housing, with a Crocodile clip for ground connection and a spark plug like thingy that the spark plug cap fits on. These will easily detect a weak spark caused by bad coils, bad points, bad capacitor. Or my absolute favorite. Low voltage on the coil +terminal, caused by voltage drop through the rather convoluted path from battery + to coil +. An easy check would be a direct "jumper" from battery to coil ,with a 10 A fuse just in case.
Perhaps I should be more exacting when describing what the bike is doing when it is running. Instead of calling it a misfire, I'll opt out for a description. When RPMs are applied, one side would cut out. It would not fire at all, or just sometimes on one side. (Seems to mostly idle with both cylinders working) There is no backfire, or popping. It simply would stumble a little bit when applying RPMs, then quit firing. Occasionally when RPMs were applied you would hear the cylinder sometimes fire back up, then stop. It would also switch sides, and exhibit the same symptoms on the other cylinder, but only after restarting.
is it better with the headlight off vs on? have you tried that? im being serious. if its worse w headlight on, electrical. low running voltage to be exact.
I have had the motorcycle running with the headlight on, and with it off. Have not noticed any changes. It has been missing mostly on the left side, I left the gas on, and let it sit for a few minutes. There was gas coming out the Overflow tube of the left carburetor. I have the valve needle seats on order from Mike's XS. Hopefully I'll be able to install them in a few days.
I replaced the left coil. It had 4.4 ohms before I installed it. After installation, I rechecked it. The coil showed showed only 2.8 ohms. I checked the other side, 4.4 Ohms on the right side. Then I unhooked the orange wire on the left side coil, it showed 4.4 ohms. I then turned the ignition on, and checked the left side coil again. This time it showed -1. The coil was getting voltage from the battery on the left side. The right side was fine, it showed 4.4 ohms. I was checking the connections by the battery, and happened to put my hand on the left coil. It was noticeably warm! The left coil is getting voltage from the battery, and going through the system and heating up the coil. I'm surprised it occasionally fired at all on the left side. Has anyone ever experienced anything like this? The problem must lie with the rectifier, the voltage regulator, or somehow the generator.
they get power from the same single wire lead, so no, none of those things. it should be a 2 pin female bullet connector that basically sits on the frame tube.
if the ignition is left on, one will heat up if the points on that side are closed... or the condensor is shorted. it can even do it on a dyna system but will eventually burn out the pickup.
the orange coil wire is the points lead, the brown wire is the power lead. check coil resistance completely unplugged. anything else is a crap shoot. it IS a good idea to check them after being run and warmed up though, but still unplugged. 0.02
Did you try a new condensor and while you are in there, double check for frayed wires or wires rubbing on the frame or engine cases.
The condensers are new. With no wires connected, the left coil reads 4.4 ohms. Fully connected, for some reason it jumps down to 2.8 ohms. That reading is with the key off. The right coil, reads 4.4 ohms connected or not
I recently fought a similar gremlin. I can make 2 points on this:
First, once the engine is 'loaded up', it needs to be run warmed up under load long enough to clean it out. No amount of run time without load will clear it out. Getting there may take multiple plug changes till it gets warm and pulled through a few gears, but is the only way.
Second thing I learned is that the NGKs won't take being fouled and cleaned more than a time or two. After a lot of experimenting, I ended up with the NGK Iridiums. Not much more money on Amazon, but they resisted fouling much better than the standard plugs. AND I could clean them many more times as I was trying to figure out what was going on. They ran longer allowing me more time to try different things.
Often I had to put a clean set in, run till one fouled, change it, run some more until anther one fouled. And kept doing that until I was able to get it warm enough to pull through a few gears.
During that time, I checked and rechecked pretty much everything. Eventually, it stopped fouling the plugs. It may have just been so 'loaded up' from the previous owner's mistakes that it took a while to get fully cleared out. Lots of adjustments weren't quite right, but I never found any one thing that I can say was 'it'.
Quote from: Super Dave on February 19, 2025, 04:26:27 PMThe condensers are new. With no wires connected, the left coil reads 4.4 ohms. Fully connected, for some reason it jumps down to 2.8 ohms. That reading is with the key off. The right coil, reads 4.4 ohms connected or not
If a coil reads low resistance with power on, than there is a short present in the primary winding.
new condesors arent nec good ones.
try new coils.
these are suspiciously cheap but work awesome on rds, and the bolt holes line up. just need a spacer, and a bullet to blade adapter to be made, easy stuff. IF it still does it with these, its not the coils.
as far as ngks... ive run sets for years w out fouling them. the ones in the 70 r5 are i -know- 5 years old. 0.02
Right now, the recommended Suzuki coils are available on ebag for less that $14 a pair including shipping. There is a 10% discount code available for a short time.
www.ebay.com/itm/291264625288
i forgot to ad the link. lol. ^ thanks for that. https://www.ebay.com/itm/275850575096?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=5r9H0_TZSJq&sssrc=2047675&ssuid=9DXeqLNdSLW&widget_ver=artemis&media=COPY
I think the 2.8 ohm reading is caused by, when having the wires all connected, you are actually getting a reading of 2 coils, that are connected in parallel, due to the +12 leads on the coils being connected together.
Quote from: 1976RD400C on February 20, 2025, 07:22:43 AMI think the 2.8 ohm reading is caused by, when having the wires all connected, you are actually getting a reading of 2 coils, that are connected in parallel, due to the +12 leads on the coils being connected together.
Your meter is measuring the circuit between the two leads, which in this case is the primary coil of one coil. It doesn't matter what's going on behind the leads.
Quote from: Super Dave on February 18, 2025, 07:20:42 PMI replaced the left coil. It had 4.4 ohms before I installed it. After installation, I rechecked it. The coil showed showed only 2.8 ohms. I checked the other side, 4.4 Ohms on the right side. Then I unhooked the orange wire on the left side coil, it showed 4.4 ohms. I then turned the ignition on, and checked the left side coil again. This time it showed -1. The coil was getting voltage from the battery on the left side. The right side was fine, it showed 4.4 ohms. I was checking the connections by the battery, and happened to put my hand on the left coil. It was noticeably warm! The left coil is getting voltage from the battery, and going through the system and heating up the coil. I'm surprised it occasionally fired at all on the left side. Has anyone ever experienced anything like this? The problem must lie with the rectifier, the voltage regulator, or somehow the generator.
The change in measured resistance is because when connected, more circuitry is involved. So that 2.8 ohm value is irrelevant or misleading. What IS relevant, however, is the condition of wiring, connectors and switches between battery and coil +. AND the condition of wiring, connectors and breaker points on the coil negative side. Basically, with the condenser/capacitor disconnected, everything else connected, ignition and kill switch on and the points closed, there should be minimal voltage drop from battery to coil +, and minimal voltage drop from coil negative to ground. Or put differently, very close to 12.6V between coil + and coil negative. This is a very basic but important check for all battery powered points ignition systems.
And one more thing. With a healthy and fully charger battery, the bike shold run fine for at least half an hour even without an alternator. So forget about the charging system until it runs like it should. Many roadrace bikes ran "total loss ignition" back in the day, without problems. They just fitted a fully charged battery before practice, then swapped it for another before the race.
The image in my next post is the basic circuit for one coil/ set of points. I have tried to indicate where to measure voltage, with points closed and ignition+ kill switch on. This relates to my earlier post on checking for good continuity and minimal voltage drop.
(https://i.postimg.cc/67zryLQC/20250223-111759.jpg) (https://postimg.cc/67zryLQC)
I have found the best way to clear out a bike that is loaded up is to remove the plugs, ground them on the head, turn the gas off, choke off, and ignition off. Put the bike at the top of an incline, put it in first gear, and push it with the throttle wide open. 100 or 150 ft should do it. Sometimes you can see the gas spraying out in a mist. Put the plugs back in, and it'll usually fire up. The reason I was getting 2.8 ohms on the left coil, was because the points were closed. If I opened up the points, (with the ignition on) it would jump back up to 4.4 ohms. I bought some B7ES spark plugs, they are the only ones that the bike will not foul. It was still running mostly on the right cylinder. I then took the generator off, to check the wires. Everything seemed to be fine until I spied a condenser wire (for the left cylinder) that appeared to possibly be rubbing against the generator housing. The insulation looked to be somewhat flattened (on one side) almost as if it was abraded or possibly partially melted. There was no indication of arcing on the generator housing. It didn't look too bad, but enough to be suspicious. So I insulated the wire, and put the bike back together. On the bench when I fired it up it sounded fine, so I took it on the road to put a load on it. I rode it for about 10 minutes, the left side didn't cut out at all. Other than the carbs being somewhat out of sync, it ran gangbusters! So hopefully it looks like with some minor adjustments and I'll be good. I am kind of concerned about using B7's, as it is a hotter plug. I also turned the oil pump as lean as I could get it, I'll do a plug check later when I get some time on it. Is anyone out there using B7's?? In addition, I would like to thank all of you for your time and advice. With a little luck I'll be race ready for this spring.
that def sounds like it. side note dont run 'E' series (3/4") reach plugs on a 350, the need to be b8hs or similar, 1/2" reach. and.. good job on finding it