Does this sound like a carb problem?

I'm trying to figure out why my bike runs like ass, and not really getting anywhere. Here's the story:

Couple weeks ago, was riding home, bike started running really awful. Sounded like it was running on one cylinder.

I decided to rebuild the carbs, found out the throttle stop bolt was missing and the idle adjustment was adjusted all the way in. I put a standard rebuilt kit in both carbs (did not separate them). Tried to balance the carbs as best I could with a feeler gauge, and put a new bolt on for a throttle stop (and by the way, what sort of gap am I supposed to have between the butterflies and carb bore when they're closed all the way?). Everything went pretty smoothly.

After reinstalling the carbs I was having a hard time getting the bike to start. I found out I had a weak spark on the left cylinder, so I went ahead and bought a Dyna 3.0 ohm coil and 7mm copper core plug wires, and new plugs. I also replaced the points & condenser while I was in there. I put the points back exactly as they were and made sure the gap was about .35 mm.

Well, now it fires up quick, but it's running awful. It's puffing black smoke out of the exhaust and running really rough. To be honest, it sounds like it's only firing every other revolution, and according to the tach it's running at a little under 1000 RPM. The throttle is very unresponsive. It runs for about 20-30 seconds and shuts off. I can usually get it to start again after that, it will run for less time and shut off again, then just cranks and won't start. If you pull the plugs after this, they're always black and smell like raw gas, so it looks like I'm fouling them out. I know I'm getting good spark because I checked it.

So, what did I screw up? I'm really feeling pretty clueless about this thing at the moment.

If the pipes are belching out black that is a sign the fuel mixture is to rich(blue smoke is oil). just need to lean out the mixture on the bottom end. also check the floats make sure they are set and also check the seat, is it closing off, you can pressure test easily with a peice of fuels line that hasnt been used and just blow int it then close the seat,,should hold pressure

#1 How do I lean out the fuel mixture?

#2 How do I check the floats?

#3...huh? Can you explain this pressure testing the seat thing, because you lost me.

This is the twin...right? Are you sure you don't have the advancer/rotor on 180* out? I think you mentioned you didn't remove it, in another thread, but it could be a bit hard changing the points and condenser, w/o removal. I know a couple of people think it won't run, at all, but I've had my CSR running just like that. Kinda like it's hittin' on each cyl, every other rev? I screwed up and had it 180 out, turned it around and started and idled fine...I have a stock IE and not points. Never have to screw w/points:woohoo:

Well, like I said I didn't actually remove the stator or anything else intially...I just removed the old contact breaker and condenser, and installed the new ones. I tried to remove the advancer but I don't have a thin enough wrench.

So when you say "turn it around"...exactly how do you do that? What do you "turn around," the stator? I'm definitely up for giving it a try, at this point...

Well, if the bike was runnin' good and you've never had it off, that can't be it. You do need a thin wrench to hold the shaft. FYI, the advancer has 2 parts, the horizontal piece, the advancer, w/the springs and the rotor, the "tube" in the center. The rotor has a high point, that raises the points and is held in place, basically by the spring tention of the advancer and will just pull/twist out. The rotor has 2 slots in the bottom that fit in 2 tabs, directly across from each other, on the advancer. So it's possible to install the rotor 180* out and still have the advancers timing marks line up w/the timing pip, but it's firing 180* off time.

You said "I put the points back exactly as they were and made sure the gap was about .35 mm."
What do you mean by that? Did you set the points/timing per the manual specs/instructions or did you just replace 'em and kinda eyeball the placement?


I believe you have the BS38 carbs and I don't have any experience w/them. Other than the possibility that if you got a lot of tank gunk in the carbs, you may not have got them really clean. IMO a total disassembly and sonic clean, is the only way to be sure they are clean, I got nothin'.

I suspect ignition coil breakdown or low voltage at the coil.

Do this,with the gas tank removed and the ignition on you should get the same voltage as the battery at the primary side of the coil(small wires),if not then you should do the "wired George" relay mod bypassing the aged wiring on your bike causing current drop and low spark voltage.

His website is www.wgcarbs.com and he lists parts and how to do the mod.
Many guys here have done the mod and it makes their bikes run like they should.

I already did the coil mod, as noted in my signature.

And I also stated that I have a good spark, because I already checked that. I checked both sides. I really don't think that's a problem.

I have a bit of an update (well, sort of). I just started the bike a couple minutes ago and pretty much got it to run for the longest time that it has run so far.

It was still running rough and blowing black smoke and there was a lot of vibration. If I revved it up, it was blowing a bit of white smoke from the left cylinder.

Anyway it actually stayed running although it was running very poorly. I shut it off and pulled the plug from the right side cylinder and it was BLACK.

Agh, I just don't know anymore. I'm wondering if this is a combination of problems. Maybe I should just take it to a shop.

Alrighty then.

I guess I'll just take the carbs off again, take them apart, and soak them in carb cleaner, since I don't know what else to do.

ronjones wrote:

...You said "I put the points back exactly as they were and made sure the gap was about .35 mm."
What do you mean by that? Did you set the points/timing per the manual specs/instructions or did you just replace 'em and kinda eyeball the placement?

...the possibility that if you got a lot of tank gunk in the carbs, you may not have got them really clean. IMO a total disassembly and sonic clean, is the only way to be sure they are clean,...

Did you see this post above, or did I spend a lot of time, writing it, for no reason?

I had another thought. When you were using carb cleaner, before, did you remove the diaphrams? Nothing will screw up the diaphrams more than carb cleaner. It will turn them into worthless pieces of rubber and metal. I ruined 2 pairs of diaphrams w/carb cleaner, because I didn't know what I was doing.
Do you have a manual/specs?

I set the points according to how the maintenance manual that I have says to do it.

Which is to turn the motor until the breaker is open, measure the gap...and adjust it until you get .3-.4mm.

It also describes a procedure for setting static timing with an ohmmeter, except that it says to put the ohmmeter on the 1K setting and when you do, it pegs the ohmmeter and it never moves (and I have a cheapo multimeter that I got just for this, that only has the 1K setting on it).

And yes I removed the diaphragms. I completely disassembled both carbs before spraying any carb cleaner into them. The diaphragms are good and I checked their operation after reassembling the carbs.

Cool;) OK, I'm sorry if I'm asking simple questions, but it really doesn't sound like the carb. It sounds to me as if the timing is way out and it's been a long time since I've had to mess w/points. When you set the points gap was the correct timing mark, on the advancer, lined up w/the timing pip on the case? Again, sorry if I'm asking another D'oh question. I know how frustrating it can be to be close and not think of that one little thing that has slipped your mind.