thebruce

I'm still in the middle of trying to decipher my carb problems-- I tracked down a vacuum leak under the base of the carb, so I'm one step closer to solving the riddle of the dripping primary while at idle (carb is a Performer 600). I adjusted the float levels, which stopped the leak on one side, so I figure the needle and seat may need to be replaced on the other. Anyway, I went down to start it up after breaking for a bite to eat (engine was still warm), and the engine started immediately and began revving really high with no gas pedal input. I quickly shut the car off, and Ka-Boom!!! It sounded like some of the anti-tank munitions I have sent down range in the Marine Corps. My neighbors thought it was a gunshot. Huge backfire. So, now for the questions:
1. I am pretty sure the timing is set right because it is one of the things I checked right before stopping to eat-- what else causes a backfire like that?

2. What can I do to make sure I don't get a crazy over-revving when I start it again?

3. The exhaust system is brand new. Should I check for damage anywhere?

Thanks. :flag

Ganey

Put the throttle back down on the idle stop & Fire it up. What you described caused it- throttle open good & you shut it off.

:cool:

Rockn-Roll

Did you set the timing with the vacuum advance connected? It is possible that you are now getting a different vacuum signal and your timing is off as a result. A dripping or (spitting) carb at idle is usually due to the idle jets turned off, or idle system plugged, and a mechanic (aka bubba) increased the throttle opening to run off the main jets...the result is the fuel isn't metered well at those low rpms, and the mixture isn't correct due to the lack of fuel from the idle system. If this IS your problem then the only fix is a rebuilt carb, or possibly getting a replacement...or, just live with the drip. Or, another possibility is that you had a big vaccuum leak and fixed it, so now the idle system is working right.

My suggestion is to back off the idle stop screw until it's all the way out so that the throttle plates will close all the way, and have a friend operate the throttle manually at the carb while you turn it over, or get a remote ignition switch to start the car while you are at the carb. Also, have a timing light handy to watch while cranking...just to be sure.

Keep us posted.

thebruce

RocknRoll and Ganey-

Thanks for the info. I'll try to restart it once I can get the neighbors out of their flak jackets and helmets. :D

Two questions:
About the idle mixture- should I be able to see the fuel flow into the venturi from a nozzle somewhere when the carb is operating on the idle circuit alone?

About the floats- if I want to make sure that the floats are functioning correctly, can I adjust the float level to more than the 7/16" that Edelbrock recommends to make sure the fuel flow is being shut off when the bowls are full? I tried blowing throught the fuel inlet (with the air horn off the carb!) when the floats are "up", and it was blocked. When I lowered each of the floats individually, I could blow air through the inlet.

Thanks again.

Top_Notch

The first question should be why the engine was revving.

My thoughts are this: Possible hang-up in the throttle linkage. Possible hang-up in the choke linkage. Improperly adjusted idle stop. You said the engine was warm so I think #3 is out. Check for smooth operation of the throttle with the engine off and make sure the throttle blades return to close all the way. Just a tiny fraction (¼") off can cause the engine to rev to the moon...especially under no load circumstances. I had a similar problem and it turned out that the choke linkage slipped off the eccentric and propped the throttle open. It looked like they were closed, but on start up I nearly ate my heart.