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Atom Heart Brother
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Discussion Starter #1
Now I am not the person who usually asks for help, but I seem to have found myself in quite the predicament.

I recently bought an old Honda twin bike (cl175) which seemed to run like a a champ when I first purchased it, but alas I found myself tearing into the carburetors knowing that the bike had been sitting in a barn for 20 some years.

However, that was a mistake. Now the bike runs very poorly and by that I mean the right cylinder decides to cut out exceeding anything over 1/4 throttle. I noticed that the right plug was much darker than the one on the left. Correct me if I'm wrong but I presume that indicates a rich air/fuel mixture. I have tried all that my previous knowledge has allowed (raising and lowering the jet needle clip and countless hours adjusting the idle/air bleed screws) so I need some advice from someone with more experience on the issue.

The ignition timing, tappet adjustment and compression are all spot on so that leaves the carbs--or another fluke I am just to blind to see.

At this point I have been pondering and google searching for so long I am on the verge of, well...

...you get the point.
 

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23,911 Posts
Black soot on the plug means a rich condition. The most likely cause is a restriction in the carb not allowing enough air into the mixture.
 

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My first guess, what I would check, is a stuck float in that right side carb. If the bowl level is too high it will cause a rich condition. On the other hand a bad needle valve will also result in a rich condition so it may not be the float or its valve.
 

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Atom Heart Brother
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26 Posts
Discussion Starter #4
My first guess, what I would check, is a stuck float in that right side carb. If the bowl level is too high it will cause a rich condition. On the other hand a bad needle valve will also result in a rich condition so it may not be the float or its valve.
You make a valid point--come to think of it i had purchased a carb rebuild kit a while ago off a website which after a close comparison with all the original parts I realized the kit was a complete piece of crap. Unfortunately i damaged the float bowl gasket in the process of opening the carburators up so I had to replace the old ones with the two that came in the kit which were to my suprise the wrong size. I will see if the right side might be catching the float after work today
 

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Challenged Mechanic
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I would pull the carbs completely apart, taking any rubber bits out, then dunk them in a carb cleaner bath overnight. Next day I would run some nylon fishing line through all the orifices, then rinse with carb cleaner and finally blow compressed air through all the holes, watching to make sure air/fluid spits out on the other end. Then reassemble with needles and everything set identically, including turning the idle screw the same turns out on each carb. Make sure, too, that both float valves are in good shape including their seats and that they close at exactly the same level. Install the carbs, adjust the cables so they start to pull at exactly the same time, and see what you get.

Cheers,

Mike
 

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Atom Heart Brother
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26 Posts
Discussion Starter #6
Heh, well I feel stupid. Yesterday I finally dug into the carburators to check whether the floats were hung up or not and... SUPRISE!! I found the main jet sitting in the bottom of the float bowl. I must not have tightened it down enough--anyway, problem solved.

For now.
 

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Atom Heart Brother
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Discussion Starter #8
So after believing that the issue had been fixed, turns out i was wrong. It did run a bit better than before but now the right cylinder is still cutting out, due to rich fuel mixture

I decided to take LWRider's advice and tear the carbs completely apart and giving them a thorough cleaning after more trial and error. I even took the exhaust off and inspected for blockage and I did notice a lot of buildup in the right exhaust port so i cleaned that.

Put it all back together again, synced the carbs, and even treated the engine with seafoam--still nothing has changed besides the throttle response being greatly improved.

So heres where I am at. Could it be an issue with the ignition coil, cables or sockets? I know its not the plugs themselves as they are brand new and I have tried everything i can on the carburators, besides rejetting
 

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Challenged Mechanic
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2,772 Posts
Coils can sometimes fail intermittently, especially after they get hot. That's a possibility, but you would think it would not idle either. I once chased my tail over a similar problem with my CB350 only to find out that the little lug going to the points had loosened and rotated just enough to touch the backside of the cover and ground out. Of course, when I took the cover off the points checked out fine but once I replaced the cover they failed. I don't know about your bike but the 350 has very little clearance there. Worth checking out with a continuity meter.
 
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