SOHC.co.uk Forums > CB500/550
CB500 Four - engine cuts off in idle
Bryanj:
Get the original brass ultrasonic cleaned and refit as the kit parts are notorious for not being to Honda spec especially the needles and needle jets.
If it has points use a points file to clear oxidation and a SMALL amount of lube on the pivots
deltarider:
--- Quote from: Siloxious on November 02, 2023, 03:56:19 PM ---[...]This is the video I followed: https://www.youtube.com/watch?v=JFTOfYl5BSc&ab_channel=ClassicOctane.
--- End quote ---
The best on the subject is Motormac. On Youtube: Motormac Honda CB500 four Vergaser. You don't have to see all of them. Language is German. But he's the best.
[...]
--- Quote from: Siloxious on November 02, 2023, 03:56:19 PM --- Would you suggest that I clean the bowls again?
--- End quote ---
Personally I'd refit the original parts. Mine ran 140.000 km and still don't wear.
--- Quote from: Siloxious on November 02, 2023, 03:56:19 PM --- I've not touched the thumb screw in any way since I've bought the bike. So I guess I'll try it tomorrow.
--- End quote ---
That should be the first step. Who kniws? Aim at an idle of 1150-1200 rpm.
Oddjob:
The Honda recommended idle is 950-1050rpm for the 500, check the workshop manual if you are in doubt. If the engine is in fettle, as in good condition, it should quite happily tickover at that speed. Increasing the idle speed is like turning the radio up in a car to disguise engine noise. You really want to hear the noises, not mask them, if you can hear it you can work out wants wearing or what's going on inside the engine. An engine is top notch condition will tickover at less than 600rpm with little noise.
The thumb screw or number 58 lifts ALL the throttle slides on the carbs, if it's too low the engine will NOT tickover, almost an instant stall.
As Bryan says, put the original jets/needles etc back in, aftermarket jets are quite frankly awful, poorly made, lack of precision etc. Especially the float seat parts, they leak for fun as a rule.
deltarider:
--- Quote from: Oddjob on November 02, 2023, 05:33:27 PM ---The Honda recommended idle is 950-1050rpm for the 500, check the workshop manual if you are in doubt. If the engine is in fettle, as in good condition, it should quite happily tickover at that speed. Increasing the idle speed is like turning the radio up in a car to disguise engine noise. You really want to hear the noises, not mask them, if you can hear it you can work out wants wearing or what's going on inside the engine. An engine is top notch condition will tickover at less than 600rpm with little noise.
--- End quote ---
Oddjob, with all due respect, what you suggest, is for much, much later.
Let's stay on the safe side and first have it idle at around 1100 rpm.
Oh and I'd welcome a video where a CB500 will tickover at less than 600 rpm. When I had everything top notch, I managed to get at an acceptable idle of 800 rpm. A Honda mec persuaded me to have it idle at around 1100 rpm. Allthough he didn't explain in depth, he said camshafts wear most at idle.
Oddjob:
Mine used to tickover quite easily at 600rpm DR, it would go as low as 400-500 before the engine started to knock a little, at no point did the oil light flicker.
Once it's rebuilt I'll gladly take another vid of the engine idling at very low speeds, it's just the sign of a really good engine IMO.
I'd agree, set a faster idle until it's actually running right, then lower it until it runs smoothly without too much noise.
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