Concern: "Pop" and smoke from carburetor

[VCPatel]

Recently purchased a 79 Special which was in running order, though not all too reliable.

When I first had it running, it was popping quite a lot, which I attributed to old fuel in the tank [previous owner had it sitting for several months] and/or the carburetors asking for a cleaning. The carburetors were also leaking fuel. The PO also had K&N filters installed; I assume the carbs weren't tuned properly for these either.

I put some fresh fuel in her and decided to give her a go. I tried the starter but it was a no go-- I expected this. Decided to kick it-- and it seemed to come close to starting on several occasions. Then, during the last kick there was a loud "pop" and I saw some smoke coming from under the bike. I didn't think much of it until I looked down at the carbs. They seemed to have come loose-- very scary. I don't think the previous owner had them securely attached after switching to the K&N filters.

I ended up pulling the carburetors that day and bringing them in to clean them out and rebuild. I noticed that both carburetors were varnished, BUT, the right side carb seems to have some black residue on the filter end. There is some black residue on the "engine-end" of both carburetors, but only black residue on the filter end of the right-side carburetor.

I am rebuilding the carbs tomorrow, but I am now worried if the pop/smoke/black-residue might point to some larger issues of concern that I should look into. I just really hope that I haven't done some permanent damage to the engine by being a bit overzealous in my attempts to get her started when she didn't want to.

Please, let me know if anyone has any ideas about this. I'm also replacing the spark-plugs [just in case].

Sincerely,

VCP

Also-- attached a photograph of the rust-bucket



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[xjwmx]

Nice looking bike! I put handlebars from a 1980 cb750k on mine to keep the height but save my shoulders from rotator cuff disorder of the buckhorn bars. The Honda bars make the palm face down rather than to the side.

I doubt you damaged anything. The residue should come off the carbs with carb cleaner. If I had a points bike like you I would put a Pamco on it, but I would modify it so that I could leave the ignition on with the bike off and not fry anything. I don't like that aspect of it. But it's got to be better than points. The blast out the intake is probably timing related. Easily addressed. Clean out your tank and put in a lawnmower style inline gas filter to keep the clean carbs clean.

 

[OakBehringer]

Yeah man, timing. Sounds like you had detonation when the intake valve was open.

XJWMX, why would you mod the bike so that you can turn the bike off, but leave the ignition on? (to me that would be leaving the bike on)

 

[xjwmx]

I don't have one so I haven't followed it thoroughly, but there's an issue where if you leave the ignition on with the motor stopped it can fry either the coil or the output transistor of the pamco, I forget which. I think Pete says points are the same way. It might be ok for most, but I know I would fry it and at the worst possible time.

 

[VCPatel]

Thanks very much, friends. At least I can rest assured that, if something is still wrong after I have rebuilt and reinstalled the carbs, it is not a serious engine issue.

Thanks for the compliments xjwmx: I also did not like the stock handlebars and replaced them with black powdercoat drag bars. Here's a picture of the new, but unfinished, assembly:


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I can see this is a timing issue. This would just require adjustment of the carburetors, correct? I have plenty of guides for carburetor adjustment, so I'm not too worried if that is the problem.

 

[weekendrider]

Get the carbs clean. Adjust the cam chain tension, the valves, the points,the timing (with a light), then tune your carbs. You will probably want a shorter clutch cable with the short bars.
Too bad she didn't fire up. The bike looked better than some I ride.
And welcome to the site.