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CB500 runs lean and doesn't want to pull through

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RBoss:
Hi All,

Recently I have rebuilt my engine by putting in a new primary and cam chain. After reinstalling it into my frame I went for a test drive. All went pretty smooth, the engine is nice and quiet, but it doesn't want to "pull through" at higher rpm. It holds power in when I want go above around 6/7000rpm. Spark plugs are also very white so it appears to be running lean. How I don't know... Before the engine rebuild I rebuilt the carbs and had them cleaned.

My setup:
- jet size 100
- stock airfilter
- airscrews 1 full turn outward
- electronic ignition
- new rubber inlets
- new spark plugs NGK D7EA
- 4 into 1 exhaust

Anyone have an idea what could be it?

K2-K6:
If you need to keep running it like that initially,  then change the plugs to #8 as it'll give you more safety margin. This won't fix anything but with the plug tips getting very hot (white colour on #7) then it risks making pre-ignition which will lead to melted pistons if you're not careful.

Do you know the needle position and what size the idle jets are ?

Oddjob:
Did you remove the inlet manifolds? always replace the o-rings in them if you did as they grow hard and won't reseal after removal. It's the heat cycle which does for them. I'd imagine that the engine is sucking air in from somewhere causing the weak mixture.

RBoss:

--- Quote from: K2-K6 on February 23, 2022, 05:30:00 PM ---If you need to keep running it like that initially,  then change the plugs to #8 as it'll give you more safety margin. This won't fix anything but with the plug tips getting very hot (white colour on #7) then it risks making pre-ignition which will lead to melted pistons if you're not careful.

Do you know the needle position and what size the idle jets are ?

--- End quote ---

Yes needle position is in the middle. Idle screw I don’t know for sure but I figure that is stock either.


--- Quote from: Oddjob on February 23, 2022, 05:39:43 PM ---
Did you remove the inlet manifolds? always replace the o-rings in them if you did as they grow hard and won't reseal after removal. It's the heat cycle which does for them. I'd imagine that the engine is sucking air in from somewhere causing the weak mixture.

--- End quote ---

I did replace all those o-rings… really can’t think of a place where it sucks extra air from… the air mixture screws should not be twisted in any further right?

Oddjob:
Check the carb sync screws on the inlet mainfolds to make sure they aren't loose. You could try the carb cleaner trick , run the engine and spray around the carbs to see if the revs increase, if it does, you've got an air leak. Any splits in the manifold rubbers?. Did you remove the cylinder head?

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