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Discussion Starter · #1 ·
I'm finding my '80 CB400T hard to start when cold. It takes a minute or two of it stumbling a few times to get it to start, and even then it doesn't sound too confident. The choke doesn't seem to have much of an effect either. So, tonight I tried it again and same issue, so I pulled the plugs and found the plugs looked completely different: one looked either oily or covered in gas, and the other looks lean. Not really sure what is causing the drastic difference in the plugs. Is there a way of determining if its oil or gas on the plug? I smelled it and there was a slight gas smell but not 100%. Once totally warmed up it seems fine.

I gave these carbs a quick clean when I had them off but can't remember too much about them. I'm not real familiar with these Keihen carbs either. Not used to chokes either as my KZ has a enrichener circuit. What jet is used primarily on choke and what purpose is the jet underneath the rubber plug. I don't believe I removed this plug, so now I'm wondering. Before I tore down the bike, the bike would start pretty good.

The floats on these bikes are the plastic type and not really adjustable, so what tuning options do I have. I have the pilot screws out the stock 2 turns. Is turning out leaning it out, or making it richer?

Here's a pic of the plugs. Even the leaner looking one has a wetness at the base.



Thanks for looking.
 

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Looks like too much fuel. Turn your screws all the way in to lean it I believe.
 

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Perry....From the pics, It appears to me that one cyl is running a bit rich and one is a tad lean.. (This is based on the grounded electrodes which 'record' the last mixtures before the engine was "chopped")...What worries me is the combination of what is apparently oil and grit at the ends of the threads......Something is seriously amiss there.....JMHO... Steve
 

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To me they both look rich. The one on the left may also have some oil but it's hard to tell just looking at
pictures. If your choke doesn't help with cold starting that could also indicate a rich condition.

The mixture screws only adjust the mixture at idle (and maybe slightly above). I don't think adjusting them is
going to fix the problem.

I'd suggest starting with a thorough cleaning. Kits for these things are pretty expensive and you really shouldn't
need the metal parts anyway. There's a thread here someplace that lists a place where you can get kits with
just the seals and I think the float needle. Have to be sure you get the right year as they're not all the same.
I've also been able to get individual seals and needles and such from a local one-man motorcycle shop. Cheap.
 

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Discussion Starter · #5 ·
Thanks guys for the responses, appreciate it.

Steve, I believe the grit on the plug is just a bit of paint chips from the engine. It chipped a bit around the plug hole when I installed/removed them. The oil/gas is concerning though. I'm not even sure which it is, could be a combo. I'll take the carbs off tonight for another cleaning and see if that helps.
 

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Discussion Starter · #7 ·
Its amazing what a choke can do when its hooked up correctly :D

When I took the carbs off to loosen the sync lock nut, I notice the spring that controls the right side choke butterfly wasn't hooked up and so the right butterfly wasn't closing when pulling on the choke cable :shock: I know it was setup correctly the last time I had them off, so I'm thinking the spring caught on the intake boot or something and came off. Fixed that up and tried it out this afternoon...started right up :D

I was going to sync the carbs today but ended up breaking the sync adapter that a buddy made :? I'll have to figure something out, as I want to get it sync'd up and on the market soon. Whats the thread size of these taps?
 

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HerrDeacon said:
Its amazing what a choke can do when its hooked up correctly :D

When I took the carbs off to loosen the sync lock nut, I notice the spring that controls the right side choke butterfly wasn't hooked up and so the right butterfly wasn't closing when pulling on the choke cable :shock: I know it was setup correctly the last time I had them off, so I'm thinking the spring caught on the intake boot or something and came off. Fixed that up and tried it out this afternoon...started right up :D

I was going to sync the carbs today but ended up breaking the sync adapter that a buddy made :? I'll have to figure something out, as I want to get it sync'd up and on the market soon. Whats the thread size of these taps?

Ain't it funny eh? Good for you.
 
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