Right cylinder firing less than left

[Super Dave]

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.

[m in sc]

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

[irk_miller]

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? 

[m in sc]

I def wouldn't trust the coils or wiring either. are they the big round aftermarket aluminum coils?

[Super Dave]

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.

[m in sc]

it's just a 3 ohm coil.  common saying w rds: most jetting issues are electrical    you'll find it I'm sure 

[irk_miller]

Snail sync

[Super Dave]

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.

[irk_miller]

Awesome.  Hoping for a sorted ride.

[Brad-Man]

Try running without filters...

[Dvsrd]

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)

[Super Dave]

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?

[m in sc]

if they stick they leak out the drain tube. you sure the choke isnt on? or leaking? 

[1976RD400C]

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.

[lowandslow]

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.

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.