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Subversive
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Discussion Starter #1
Okay well I just figured I'd get some opinions here about this problem if I can... The more ideas and information I have the better the chances are of getting this problem nailed down...

First off my bike is a 1981 CB900C... I've done or had done a ton of work on the bike so far but I have not as of yet tackled any carb or fuel issues, nor have I dealt with the clutch, which appears to be slipping a bit, mainly at high RPMs when power shifting...

Okay so here are the symptoms:

1. Horrible mileage around 22MPG Average.
2. Strong smell of gas when starting her up and in general.
3. When warm (only) there are major fumes (thin misty cloud) from everywhere.
4. As she gets warmer to hot the idle goes up to around 1500
5. Oil is BLACK even though just changed only 300 miles about...


My mechanic said compression was ok...
My mechanic said plugs were ok...
My mechanic said the valve clearances are ok...
There is no observable puddle of gas anywhere...
Motor likes to be warm...when cold she wants to stall

I don't think that the PO did much in the way of any work on the carbs or anything else.. Yet my mechanic doesn't seem to think the carbs are at fault.. But I am bringing it in next week.

That's about it...

Any ideas about this are appreciated.

------------------------------

Jim
 

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Your carbs need to be rebuilt. Once they are off, the job is easy. parts are cheap since all you will be replacing are all small parts and usually they come in a "Carb repair kit."

Every symptom you have can be related to a very RICH condition, basically soaking your combustion chamber with excess gas.

Please check your air cleaner)S) because if they are very dirty or blocked by a rodent or something, the air for the most part will be nonexistent making the fuel/ air mixture very rich.

Valve stem seals are often overlooked and they wipe oil off of the valve so that it doesn't flow into the combustion chamber. This excess oil can foul plugs, burn oil and darken the plugs.

If your exhaust is dark, sooty and smells like gas, then you know a very rich mixture is causing your problems.

A very rich mixture will flow past the piston rings and end up in your oil, turning it dirty or black. This situation can ruin piston rings in just a few miles. It is called "Wash down" in the industry. You should be able to remove the dip-stick and notice the smell of gas in your oil.

There is the chance that the original purchaser or purchasers, were inept and put much to large main jets in the bike.

There could be leaking and worn out needle jets too, that cause a rich condition.

The "Float needle" and floats can be worn out which is common in a bike so old. Floats can develop leaks and this leads to flooding and too much fuel being sucked into the combustion chambers.

Are the carbs the constant velocity type? If so there is a rubber diaphragm that opens the slide when you open the throttle. These are famous for developing cracks and major running issues. They move up and down by vacuum and even a small hole will allow them to leak.

You forgot a very important bit of info: How many miles on the bike?

If you aren't able to do the carb work yourself, look around and fine a shop that knows how to rebuild bike carbs. Once the "Kit's" are in the whole job for the 4 carbs wouldn't take me an hour to do:biggrin:

http://www.google.com/url?sa=t&rct=...B2Whuv26VZCYhcEAQ&sig2=9h56e2jBteu5Ms9yu8MrVw

http://www.google.com/url?sa=t&rct=...oGheP1JhRQaarB6XA&sig2=twbcdUK3X6r50MF1mPQkmw

Sam:coffeescreen:
 

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Thanks Eye!

I came from a poor/ lower middle class, working Family and none of us ever took our cars, trucks, farm equipment, lawn equipment, etc to anyone to fix it. We just couldn't afford it and we learned a lot by having to do it ourselves.

I do like to help others when I can.

Sam:biggrin:
 

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Subversive
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416 Posts
Discussion Starter #5 (Edited)
Okay, that's what I figured....

The miles, yeah, it didn't even occur to me because I am actually not sure what the miles are... When I got the bike the owner said the speedo was not the original and he was fuzzy on the miles... Best guess is between 30K-45K...
And as far as I know the PO (previous owner) did almost nothing in the way of maintenance on the bike, it was a hare's azz away from blowing up when I got it... Now it runs well but with the fuel issues I mention.

Sadly, I don't have the time or place to do the carbs myself.. Dealing with mechanics has been a problem as well... I found one guy who is good and gave me a good price on some other motor work, but made no sense when I talked to him about this carb issue...just warning me that if the mixture is too lean it would cause problems but clearly, at least to me, the mixture seems too rich...

I'll see what he says later this week...Thanks!

Oh EDIT:

Btw: It doesn't seem to be using or burning any oil whatsoever. The exhaust is clear, but when hot or warm this eye burning misty cloud just seems to form around the bike...
 

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Good, then the excessive fuel hasn't WASHED DOWN the Valve guides, onto the pistons and ruined the rings and possibly the cylinders too!

Good luck, once the carbs are fixed you'll have a nice bike.

Sam:coffeescreen:
 

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5,640 Posts
Just to add, the slipping clutch could be oil related, but is more likely the clutch springs. It is well documented in the Suzuki Intruders that these springs take a 'set' and let the clutch start to slip around 30k-40k miles. I don't see any reason this wouldn't be true with yours, and it's an easy, and relatively inexpensive change to find out. Barnett and Vesrah make good springs, BTW.
 

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Subversive
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416 Posts
Discussion Starter #8
Just to add, the slipping clutch could be oil related, but is more likely the clutch springs. It is well documented in the Suzuki Intruders that these springs take a 'set' and let the clutch start to slip around 30k-40k miles. I don't see any reason this wouldn't be true with yours, and it's an easy, and relatively inexpensive change to find out. Barnett and Vesrah make good springs, BTW.
Okay thanks... That and the carbs are the last two main issues with this bike... (knock on wood)
 
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