Topic: #2 cylinder hot, 1973 CB500

[docoffey]

Finally have no 4 carbs dumping gas out the overflow tube.  Started it up, Real high RPM, 7000, #2 exhaust pipe turned cherry red, finally got the rpms down to 1100, running rough, backfiring, uneven idle, finally just shut down.  I'm thinking #2 is too rich, if so, how do I fix it? I've cleaned and put in 3 carb. kits,  The plugs are new.  What else should I check?
thanks.

[calj737]

Cherry red is a sign of way too lean, not rich!

Verify that all 4 pipes do get hot. Have you bench synch'ed the carbs? Vacuum synch after install?
Is the idle adjustment screw turned up way too high? Can you verify fuel is flowing to all 4 carbs equally? Did you set the float heights correctly?

Sorry, lots of questions, little info provided.


Understand this principle: this is an air-cooled engine. Do not let it sit on the stand idling, or over-revving for a lengthy period of time. It needs air circulating over the cooling fins to help with heat dispersion. If you must tune it in the garage, get a fan and blow it directly at the front of the motor with outside air as much as possible.

[goldarrow]

First check to make sure you have fuel flowing through both sides of carbs

[docoffey]

Thanks for replying.  All four carbs are getting fuel. I used a 1/8 drill bit as a spacer to set the spacing on the each carb. I do have the idle down to about 1100 hundred rpm now but it is still backfiring after it's warmed up and not running smoothly  the idle speed is not steady.
I do not know how to sync.  the carbs, nor do I have the vacuum gauge setup for that.  And yes I'm afraid I am running on the stand.  Not sure I have another option.  How do I make is less lean?

thanks

[docoffey]

Also the floats were set a 21 mm. on the bench.  #1 was not shutting and dumping fuel so I "tweaked " that float a bit and it stopped dumping.

[docoffey]

Not sure how to tell if all four are getting fuel equally but all are getting fuel.

[calj737]

1. When you say you used a 1/8" drill bit to set the spacing, was that for the slides? If so, that would be "bench synch". This synchronizes all 4 carbs to open and close at the same time, the same amount. You can find plenty of YouTube videos on how to bench synch.

2. If you are running on huge stand, use a floor fan to blow some air across the front of the engine.

3. If the float was not shutting off at 21mm, it may be installed upside down?

4. There's a few methods to verify fuel level. One is the "Clear Tube" method. It's basically the same water level technique used for thousands of year. Another good test is open the petcock and allow the bowls to fill, then drain each individually into a small jar. Time and measure how much fuel comes of each. This won't guarantee your float levels, but it will get you close and confirm "how much" fuel is getting to each carb.

5. Backfiring at idle can easily be associated with ignition issues, plug wires/caps, points and condensers. It could also easily be a vacuum leak. Have you checked around the boots for a leak?

6. You should find, build or buy some vacuum synch gauges. Or, take your bike to a shop to have that done. Getting them properly tuned to each other is paramount for best operation.

[docoffey]

Sounds like some good ideas that I think I can do. Thanks for the help and advice. It's Sunday so I won't mess it today, but hopefully can get started Monday. Wife wants to go fishing so it might be later. Anyway I sure appreciate all the advice you folks provide on this forum.
doyle

[docoffey]

And yes, the 1/8 bit was the spacing for the slides, they do all move equally.  I'm pretty sure all floats are installed correctly, but I will recheck. 
thanks