Left cylinder fouling/popping/backfiring - all of the above

[habib]

Ok so here is the situation. my 73 cb350 twin was running great, I was on my way home from work and the left cylinder (#1) stopped firing. I took it too my buddy because prior i had some issues with it stalling when coming to a stop. he adjust the carbs and got the the bike to idle at 1000 RPMS and it stopped it from stalling. After a fe days of riding my left cylinder craps out again. I figure maybe since the old plug was so carbon fouled I should just change it out, so I do that and I am off. Last night I am riding and it does it again. This morning I pull the plug out expecting to see a black fluffy mess, instead it smells heavily like gas and looks to me like an oil foul. It is black and wet, and it makes me sad. Where do I go from here?

EDIT: Also I pulled the plug put the cap on and started the bike while holding it near the cooling fins and i was getting good spark. I am new to MC mechanics and I am at a loss.

Other info:
Mikuni VM30 carbs
NGK B8ES plugs
what else would be helpful?


Here is a picture...

 

[habib]

Re: Let cylinder fouling/popping/backfiring - all of the above

Bump/Question.. Could it be the valves are loose or not sealing? And if I run a hotter plug to temporarily skirt the issue are they any negative repercussions to that?

 

[HerrDeacon]

Re: Let cylinder fouling/popping/backfiring - all of the above

If its wet and smells of gas, you're running real rich. Could possibly be the float level is too high, did you check it? How's your compression? Valve clearances?

Also, do you have any performance related engine work done? The reason I ask is that the VM32's are pretty big for the 350 and could be causing it to run really rich.

 

[GLENNWOOD55CAMEO]

Re: Let cylinder fouling/popping/backfiring - all of the above

This is probably unrelated to your problem but is worth mentioning. If your CB350 is stock then sorry to say that the VM32 Mikuni's are way too big for your bike.

 

[habib]

Re: Let cylinder fouling/popping/backfiring - all of the above

So I bought the bike from a guy who rebuilt. I had my local honda/vintage mechanic run through and tune everything. I thought I was told they are the vm32's but i could have misconstrued it in my mind and they might the 30's. I cant seem to see where it would say that on the actual carb.


So when I was having the issue of my bike dying when coming to a stop i took it to my mechanic at doomtown motorworks. He adjusted everything with me and we got it idling at 1000 rpm's and the stalling stopped. But not I am gett this issue. The plug when pulled is not wet as in soaked but it does smell like gas.


I checked the valve clearance and they bothed seemed good. exhaust at .10mm and intake at .05mm. It seems running the hotter plugs (B7ES rather than the B8ES) has skirted the issue for now.


I am pretty new to all this and I have done very little carb work (single carb on a moped only). I would not mind trying to adjust the carbs but I am confused on with screws are what. There should be an idle adjust and air mixture. The rest would have to be done through jet size right?

 

[habib]

I am still trying to 100% identify with what size the carbs are. Unfortunately the only numbers i see stamped on the carb is G 7 and X 1. So I dont know... Where should I be looking. I want to measure the float height but I needs to know what I am measuring for. I feel stupid, so thanks for the help and dont give up on me!


EDIT. I measured the engine side of the carb and got 30mm, additionally the clamp says 30 so I am gonna guess they are the VM30's. If I am right my float height it approximately 22-24mm. So I think We are good there.

 

[JohnnyB450]

Im having the same issue with my 1970 cb450. left side fires up but as soon as i try to rev it up it sputters, bogs and eventually dies. Did you ever find a permanent solution?

 

[habib]

not really. I have since been running a hotter plug (B7ES in stead of the B8ES). That has solved my problem. Sort of....