Fuel Height

[Steris]

The vents and over flows are all clear. The advance retard seems ok, with a strobe it sits on the F mark on tick over and starts to advance about 1200-1500 rpm full advance about 3000rpm
Its driving me nuts

[Charliecharlcomb]

I know that feeling. At least you are getting lots of practice removing and refitting the carbs. If you manage to fix it, do let us know. 

[K2-K6]

Have you tried spraying the intake rubbers from carb to head with something like wd 40 while running to check for air leaks?

[murdock]

Check that the tips of the mixing screws are fine, they must have a conical tip, you turn until reaching the stop without forcing it, and then in a counterclockwise direction unscrew about 2 turns, the 4 equal, with rolling 100 meters You will notice if it drowns or lack of gasoline, if when placing the carburetors they lose their blows, a float may be hooked and not cut the valve, what jets do you have? You say that the needles are at their maximum height, that will only influence after 1 / 2 throttle up to the wot. mark the stroke of the fist in 1/8, 1/4, 1/2 and 3/4 and check how the motorcycle behaves in each position

[murdock]

guidelines

[Steris]

Would low compression cause slow running issues? I'm struggling to think of anything else that's causing my problem. It runs lovely over 3000rpm sits at 60 70 mph great, it also ticks over at 900rpm when cold, but once hot either dies or revs itself up to 3500 rpm. 🤔🤔🤔

[murdock]

http://www.sohc.co.uk/index.php/topic,25429.0.html

[K2-K6]

Would low compression cause slow running issues? I'm struggling to think of anything else that's causing my problem. It runs lovely over 3000rpm sits at 60 70 mph great, it also ticks over at 900rpm when cold, but once hot either dies or revs itself up to 3500 rpm. 🤔🤔🤔

Have you any compression readings for it?

Runaway idle speed is always excess air however it gets the supply to the combustion chamber.

[murdock]

That the air screw rotates 3 turns and there are no changes in idle is not the right thing to do, I think you have the problem in the slow jets, I think you should reduce, which jets do you have at 38, 40?

[JezzaPeach]

I had the same with a hanging idle and found one or two carbs needed balancing.

[Steris]

Hi Merdoc
Everything in the carbs are original  so 40 pilot jets. I'm going to  remove the carbs again this weekend and drill out all the brass plugs in the pilot passage ways and make sure they are 100% clear..

[deltarider]

I wouldn't drill out anything. If yours is a CB500, realise that a common mistake is trying to achieve a highest possible idle rpm by turning out the airscrews. No doubt the engine will idle nicely and pur like a kitten, but it comes at a price: driveability is gone and you'll experience a poor acceleration. Once the engine is hot, rpm will not drop. Realise these are quite simple carbs that lack acceleration jets. Therefore airscrews need to be set as is specified in the manual, even when you need to adjust the big idle knob to arrive at an acceptable idle rpm. Mixture will be quite rich and I wouldn't be surprised an exhaust gas meter would show 5% CO. I recommend an idle rpm of about 1100-1150. Also realise that after a cold start, you will need to maintain a raised idle to prevent stalling. Some do it by keeping the throttle grip twisted a bit (as described in the Owner's Manual), others use the big idle adjuster knob, which they will reset at a traffic light, once the engine has warmed up sufficiently.
Verify fuel supply is constant without hesitations. Abstain from 'extra' inline fuel filters; I had nothing but trouble with them. If float valves and needles are somewhat sticky, a fuel additive like Redex may help.
Realise that todays gas is not the same as in the 70s.

[murdock]

Tell us more, what air filters do you carry?
Have you checked the choke?

[murdock]

http://forums.sohc4.net/index.php/topic,5410.0.html

I hope you find the answer here, don't give up !!!

[Steris]

Thanks for the link Murdoc lots of good info on here, I'm running a standard air filter. I'll read through all this and try again. I'm not going to give up 🤣🤣