Topic: 73 CB500 cuts out at hot idle

[tvg]

The bike runs great, but once it's good and hot it will die at idle.  The idle adjust screw won't give me a stable idle until 2000+ rpm, when hot.  Before fully hot it idles just fine at 1400 or so.  I can feather the throttle to keep it running but left alone the idle falls gradually until it coughs then dies.  The plugs are new, the points were adjusted but are not new, the carbs were thoroughly cleaned recently and the mix set to 1 turn out.  Any ideas?
Thanks,
Tom

[eldar]

You would need to check your plugs after it dies from idle.  You can then see if you are too rich or lean. How much choke you need when you start can also provide a clue. If you do NOT need choke, I would almost say you are running to rich.

[TwoTired]

What other changes from stock have been made to the bike?
Are all the head pipe temps equally hot?
Is the air filter clean?
Adjust the tappets yet?

Make the carbs the last thing to adjust.

You cleaned the carbs, but what of the fuel tank?  It only takes a bit of crud larger than .016 inch to clog up the pilot jets.  You might drain each carb bowl into a clean catch pan to see if what's in the carbs is still clean.

It ought to idle lower than 1400.   Mine are set between 1000 and 1100 RPM.   
Are you absolutely certain the slow jets and the passageways behind them are really clear?

Have you checked the spark advancer?

Really seems like carb slow jets, though.

[eldar]

yeah I have my 78K about 1100 or so. The best thing is to make sure all basic tuning is covered. Once you have that, then you have a base to go from.

[Philly550K1]

if it idles cold but not hot, you could try outening the air screws a turn and see what you get.

plus my new favorite -- once it's acting up, run it with the points cover off and gently squeeze or prod the points.  (this has to have happened to somebody else, right?  i'm afraid i may bring it up until i get some sign that i wasn't crazy.  points that seem okay but aren't...     )

by all means, use it as an excuse to get all the basics in order.

-jon

[tvg]

Thanks for all the replies!  I'll try to answer a few of the questions brought up. As far as I know it's stock, the valve clearances have been adjusted, all 4 head pipes get hot, the tank is clean and I'm running a couple inline filters to the carbs, of course I want the bike to idle at 1000 - 1300 rpm as speced in the manual, but once it's hot my choices seem to be 0 or 2000+, I did adjust the points with a dwell meter and timed it and checked advance, and I choke it but I reduce choke almost immediately to keep it running.  Now that I think about it I think I accidentally richened the mix when I meant to lean it slightly when changing plugs.  I'll play with the mix and see how that works.  Thanks again - I'll let you know how things go,
Tom

[normalguy]

Any update on this?  I have a similar problem on my 400F.

[number13]

Did you synch the carbs? If not, try it!

[pmpski_1]

I'm having the same problem right now. Running rich, after about 10 miles it won't run at all. I'm going to do all the basics this weekend, timing, new points, recheck valves. Clean the plugs - they're new but carbon fouled.

I have a new airfilter and the pipes are not stock. I rebuilt the carbs once and cleaned them again this past weekend. The exhaust is not stock - it's a 4-2 system. I noticed the slow jets are 38s while I was cleaning them. The manual says they should be 40.

Hopefully I'll get everything set up straight and get to ride this weekend!