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CB500 Four - engine cuts off in idle

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Siloxious:
Hello everyone!

I had an awesome weekend, I was finally able to get my CB500 Four running! After a year and a half of work on the bike, it came to life. While wrestling with the ignition, I noticed that the previous owner had installed the cam of the ignition advance 180 degrees wrong. After fixing this, the engine came to life with only one kick with the kickstarter. Now, another chapter of the restoration begins!

The engine starts brilliantly, no problems with starting and runs on all four cylinders (the exhausts become hot). However, it cuts off when idling. When I use the throttle, the engine reacts. But beneath 2000 rpm, it begins to sputter and beneath 1000 rpm, it cuts off. It just doesn’t idle at all. I noticed that cylinders 2 and 3 are hotter than 1 and 4. Would anyone know what the problem could be?

The next thing on my list is doing a compression test of the cylinders as I’ve not gotten around to it yet. And if I can manage to get the engine to idle, I’d like to do a carburetor synchronisation.

Overall, it was a good weekend!
Cheers!

Oddjob:
Sounds like some of the idle jets or slow jets as they are sometimes called are blocked. Maybe some of the passageways that supply them with air as well. I presume you've tried using the thumb screw on the carbs to keep them going?

Siloxious:
Just so we're talking about the same screw: if you say thumb screw, do you mean screw number 42? I've put these in and gave them 1 and 1/8 turns from when they're seated all the way (as the shop manual mentions an air screw opening of 1 and +- 1/8).

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deltarider:
First things first. Compression test and synchronisation can wait.
For how long has bike been inactive and during that period, were the carbbowls empty or did they contain fuel? In case of the latter, inspection and cleaning of the slow jets is almost inevitable. On a CB500 you can leave the carbs where they are and just remove the floatbowls. Slow jets can then be removed by sliding a  small screwdriver sideways into the slit to loosen them a bit. From there your fingers can unscrew them. Carb #1 can be a bit difficult because of the nearby clutch cable.
But I'd first begin with the ignition.
When you have the engine running, have a close look at the sparkplugcaps and see if you can detect any intermittent (!) arcing from the cap or its wire to the head. This is best seen in the dark.
Does the advancer move freely? Do you have a stoboscopic timinglight to verify a good functioning of the advancer and to check the timing?
The thumb screw is #58. You can reach it from the right side under the tank an adjust the general idle rpm with it.
#42 Are the airscrews. Don't touch them! At least not now!
#73 are the slow jets aka idle jets. They may need cleaning. May. First check and doublecheck the ignition.

Siloxious:
Thanks for the answer!

1) The bike (apparently) stood still for 2.5 years.

2) The carb bowls were dirty and there was a lot of gunk inside, so I would think they contained fuel.

3) I have already rebuilt the carbs by the instructions of Classic Octane a year ago. I've used a kit, so the jets are new. This is the video I followed: https://www.youtube.com/watch?v=JFTOfYl5BSc&ab_channel=ClassicOctane.

4) Half a year ago, I was ready to start the bike. I used a secondary fuel tank and no exhaust. I had a little accident with some leaked fuel :(. Nothing broke but I definitely learned that I should work safer. I then decided to first fully restore the fuel tank and fit the exhausts, so there would be a small chance of fuel leaking.

5) Now, with a clean fuel tank and exhausts, I started the bike again and it worked. Because I tried starting it half a year ago, some fuel ran through the carbs. So, it could be possible the jets are clogged. Would you suggest that I clean the bowls again?

6) The ignition advancer moves freely. When I noticed the cam was turned 180 degrees wrong, I decided to clean the advancer while I had to take it apart. I've lubricated it sufficiently.

7) Tomorrow, I can work on the bike. I'll check for that ark that you're talking about. I sadly don't have a stoboscopic timinglight, so I'll have to do with a static timing. I'll check the static timing tomorrow (I use a multimeter to test it, since I don't have a static timing light).

8) I've not touched the thumb screw in any way since I've bought the bike. So I guess I'll try it tomorrow.

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