SOHC.co.uk Forums > CB500/550

CB500 Four - engine cuts off in idle

<< < (5/7) > >>

Siloxious:

--- Quote from: deltarider on November 02, 2023, 04:57:32 PM ---
--- 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.

--- End quote ---

Thanks for your valuable input!
Today I've managed to get the engine to idle at 1000 rpm by simply turning the thumb screw. I've made 3 videos that explain some concerns.

Video 1: https://youtube.com/shorts/sF54YTm3NVY?feature=share
After starting the engine with choke closed, the engine idles at 3000 rpm with choke open. When I close the choke again, the engine instantly stalls. Is this normal?

Video 2: https://youtube.com/shorts/Bz4SHuQANso?feature=share
I turned the thumb screw and managed to get the engine to idle at 1500 rpm. But when I use the throttle, the engine got stuck in a high idle at 3000 rpm.

Video 3: https://youtube.com/shorts/NGVH7g6JEZg?feature=share
By further turning of the thumb screw, the engine idles around 1100 rpm. However, there is a sound coming from the engine that doesn't sound that good. Also, after throttling the engine almost stalls.

How do I proceed from here?

Cheers!

K2-K6:
This is characteristic of impaired low speed/idle circuits, they should take responsibility for this very rpm range but when limited in their delivery the carburettor needs you to open the throttle more to get fuel from the main jets and needle delivery.

Classically, you'll ordinarily just go round and round again and again by adjusting the "thumb" screw to reposition the main slides, but never get anywhere conclusive.

The poor sound when running lower rpm is because all of tge cylinders are not firing (no fuel from idle on some) that just rattles the chains and components inside.

peterengland:
Just use the fast idle screw, can do it with your gloves on. Never understood the 'race to the bottom' with idle speeds myself

deltarider:

--- Quote from: peterengland on November 03, 2023, 07:06:28 PM ---[...] Never understood the 'race to the bottom' with idle speeds myself

--- End quote ---
Neither do I.
Here's a fine CB550 from Honda's Collection Hall which seems to idle at 2000 rpm. I am used to raise the idle to 2000 rpm myself after a cold start to reduce it to say 1150 a km further on. I am with the legendary Carl Hertweck, who was in favor of fast idling.
Mine shifts just as easy @ 2000 as @ 1100.
https://www.youtube.com/watch?v=Z4GYMDP7Jtk&t=90s
Just don't rev to 8000 as in the vid.

deltarider:
Siloxious, here's a simple check for the idle circuits.
Have the engine 'idle' at a rpm, where it's steady. Then turn with a screwdriver the airscrew of carb #1 all the way in (gently!) and wait 15 seconds and then to three turns out and wait again. There should be a change in rpm. This change can be a minor one, so listen carefully. Reset the airscrew to its former position.
Repeat this for carb #2, and then #3 and finally #4. The carb that does not give a change in rpm, has an issue in the idle circuit. Don't forget to wait some 15 seconds after each change.

Navigation

[0] Message Index

[#] Next page

[*] Previous page