Topic: CB500 Four - Fouling plugs and running hot

[haydo147]

G'day all,

I've been trying to dial in my CB500 four carburetors over the last few months and I'm still having some issues. It runs well with fresh plugs, however after a short time they foul. I have also checked the temperature of the exhaust headers near the head and it sits around 250C. Which from my research is way too hot at idle.

I'm not sure how to make sense of it. It both seems to run hot (indicating lean) whilst also continually fouling plugs (indicating rich condition). Would anyone know what I should do to fix this?

I'm currently running the following setup:
Carburetor model: 069A
Exhaust: 4 into 1 exhaust with a muffler
Pilot Jet: 40
Main Jet: 105
Needle clip position: Second from top
Intake: UNI pod filters
Ignition: 4into1 ignition coils with kokusan electronic ignition
Battery: Anti-gravity 8-cell battery

[dave500]

check the plug cap resistance.

[TwoTired]

If you are fouling plugs, you are too rich.  Unburned fuel in the exhaust can ignite there, and make the pipes too hot.

The needle taper in 069a carbs were matched to the stock 4to1 and a high pressure muffler.  No matter what position they are in is wrong profile for your way different from stock configuration.

If I was forced to make your configuration run as well as it could:
#100 mains
Needles from 627b or 022a carbs clipped 4th groove from top.
#40 pilot jets.
Air screws at stock setting or fine tuned for correct, predictable, throttle response under full load from low RPM, with a 1/2 throttle snap.

I'd start there and either dyno the machine or do "plug chops" to find proper mixtures for the configuration you have.  (Though it may never run ideally with pod filters of unknown air flow characteristics, even when it looks good while parked.)

Cheers,

[scottly]

Have the emulsion tubes been removed from the carb bodies and thoroughly cleaned, especially the air holes in the sides of the tubes? Have you checked the fuel level in the float bowls using the "clear tube" method? Are the air bleeds in the opening of the carbs clear, and unobstructed by the pod filters? Have the UNI foam filters been over-oiled?

[HondaMan]

Do the mainjets (and their clips) fall out of their holes easily when the carb floats are off the carbs? If so, you've been "stung" with the too-thin O-rings on those mainjets, which come in all the modern rebuild kits. In that case, PM me for a set of correct O-rings instead, I have them.

[haydo147]

I'll check the plug cap resistance, however I imagine they're within spec as they're only about a year old.

The emulsion tubes were included in the rebuild kit I bought, so they were all clean. Though I'll have to check if any of the intake air holes are obstructed. And I haven't completed a clear tube test yet, I'll do that next!

HondaMan, they need a bit of a push for the main jets to go in, however I did use the o-rings from the rebuild kit so that might be an issue. I'll PM you.

I also sanded the inside of the main jet clips a bit so they fit the jets, however now they're quite loose on there. Would it be in my best interest to buy new ones that won't move once placed on the main jets?

[HondaMan]

I'll check the plug cap resistance, however I imagine they're within spec as they're only about a year old.

The emulsion tubes were included in the rebuild kit I bought, so they were all clean. Though I'll have to check if any of the intake air holes are obstructed. And I haven't completed a clear tube test yet, I'll do that next!

HondaMan, they need a bit of a push for the main jets to go in, however I did use the o-rings from the rebuild kit so that might be an issue. I'll PM you.

I also sanded the inside of the main jet clips a bit so they fit the jets, however now they're quite loose on there. Would it be in my best interest to buy new ones that won't move once placed on the main jets?

The clips are probably fine: I also find myself 'deburring' the new clips that I have had lately. They are not as perfectly formed as the old Keihin springs in the area around the jet (they don't look like anyone tumbled them after machining to deburr the parts), but they do the job OK.

I didn't realize you're in AUS: the last time I went to send something there in January they told me there will not be US postal service to AUS or NZ until at least March. Something about the Kung Flu...