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Too much air, not enough gas?

hje_326

CB750 Enthusiast
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Location
Crawfordsville, IN
1977 CB750K

I was finally able to get all four cylinders firing the other day but when it's running I notice the the pipes for 1 and 2 aren't getting nearly as hot as 3 and 4, which get very hot and very quickly. One and two aren't nearly as vocal as 3 and 4 and unless I'm accelerating they don't seem to speak at all. When I have the bike at idle it doesn't like to keep running without the choke at least 1/4 out.

I have the airbox for a 750F on with a K&N filter, and my exhaust is a 4 into 2. I'm not sure of the brand name of the exhaust.

Will I need to adjust the jets? How can I tell jet sizes without any special tools?

We've adjusted the idle circuit screws to about 2 1/2 turns out from all in on one and two and 3 turns on 3 and 4.

I know this information is very scattered and I apologize. I haven't been sleeping well so my thoughts are a little scattered.

If there is any more information that could be useful please ask. I am eager to learn how to get my bike in top shape and keep it that way.
 
Your idle screws are way to far out, never over 2 turns. You need to remove the jets to read the number stamped on them. Sounds more like dirty carbs and a couple plugged/restricted jets. Your mods wont make much of a jet change, 1 size larger at the most but again you have to jet for your bike...way to many things affect jetting for a one size fits all answer to what size jets a bike needs. Get the carbs cleaned, verify what jets you have for reference then do a carb sync. Then proceed with determining what jets you need to change.
 
Thanks Dirtdigger!

Clearing the crud out of the carbs/jets with a paper clip is how we were able to get the bike to start, but I'll check again because there is no telling what was hiding in the works that can get caught in there.

The idle screws for the 77 K, is it out to rich in to thin? I haven't been able to find something that says "go this way to do this".

Is there a better manual than Clymer?
 
If all you did was use a paper clip then I am sure you have plugged passages inside. The paper clip then isn't that good of an idea as it is easy to damage the hole in the jets which is a fairly precise hole, it doesn't take much of a nick to affect fuel flow rates through the jet.

Start with 1 3/4 turns on the mixture screw.

Best manual out there is the factory manual, they are hard to find and expensive but there is no comparison.
 
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