SOHC.co.uk Forums > CB500/550

Black smoke and hanging idle after a full rebuild

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Trigger:
Why would a main jet fall out, it is held in by the spring and compressed by the float bowl  ;)

Once upon a time i built a 550 motor,  the bores were with in spec so, i just put new rings in with a light X hatch. The carbs were fully rebuilt but, the bike smelt very rich and had a small amount of black smoke. After 3000 miles and forgot how many times i had the carbs off, i decided to strip the engine back down again and check the head and barrels. Everything was with in spec and as i had a set of 0.50 pistons and bores sitting on the shelf, i decided to fit them.

Now that bike has never smelt rich or given any black smoke since and Julie is still knocking up the mileage on it  ;)

A bike is many components and not just a bank of carbs  ::)

thomaspigeon:
So this CB has been rebored at +0.5mm with new pistons fitted, new valve seals, valve have been  lapped too. I’ve done a compression check and it has 145psi (everything is new I assume the compression will raise after the run-in period).

Hard to believe I have a leak somewhere. I had the valve play inspected by a specialist, he said it was ok.  Unless I forgot some lapping paste on a valve (I also cleaned everything with cotton buds and petrol) I doubt it’s possible I have any leak.

Trigger:
145PSI is too low if you have had the top end done.  Running pods will never help you as, these old girls don't like them  ;)

royhall:
Agree with Trig. Hands up anyone who has got these bikes perfect with pods fitted. They usually end up as some sort of compromise.

hairygit:

--- Quote from: Trigger on July 14, 2021, 12:01:01 PM ---145PSI is too low if you have had the top end done.  Running pods will never help you as, these old girls don't like them  ;)

--- End quote ---
Running pods, especially some of the ones I've seen have appalling filtration, basically they can knacker a rebuilt motor in a 1,000 miles as abrasive dust, grit etc gets dragged straight into the motor. All very well assuming that because racers use them they must be a good bet, but most engines are rebuilt after every race!

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