bryant2482 Posted March 25, 2012 Report Share Posted March 25, 2012 hey everybody ive got an issue with my weber carb and im wondering if anyone else has this issue, sometimes when i go to hit the gas pedal and open it up the carb makes a big "pop", almost like a back fire. other then that it runs very smooth and has lots of power Quote Link to comment
datzenmike Posted March 25, 2012 Report Share Posted March 25, 2012 Probably a lean backfire. Fuel for idle is supplied through it's own circuit which can be adjusted for best running. The problem is that when the throttle is opened to rev the motor up it acts like a huge vacuum leak (even more pronounced if done suddenly) and also at low engine speeds there isn't much air passing through the venturi so there is not much vacuum produced to suck fuel in and the mixture goes very lean. The idle circuit cannot supply enough gas for this either. So until the motor can rev up and start drawing in more fuel it will stumble and often backfire. The fix for this 'dead spot' is to manually squirt in fuel to rich-en up the mixture until the motor can get past this spot. This is what the accelerator pump does. With engine off, look down the carb and pump the throttle several times. You should see a strong spray of fuel into the primary barrel. Weak or none means the accelerator pump needs rebuilding. Quote Link to comment
bryant2482 Posted March 30, 2012 Author Report Share Posted March 30, 2012 the only time it will ever do it is when im crusing down the road or when the engine is under a load Quote Link to comment
datzenmike Posted March 30, 2012 Report Share Posted March 30, 2012 Ah. that's info not in the first post... A burnt or overly tight valve lash can do this. It's harder for the spark plug to fire under load so the spark may find it easier to jump to another wire. There are actually two rotors and a lot of wires crammed together onto that dizzy cap so have a good look at it and the wiring. Quote Link to comment
_chiefjt Posted October 1, 2012 Report Share Posted October 1, 2012 I have this same problem but with the stock carb. for my '86 Nissan 720. It was doing it before i adjusted my valves and is still doing it after I adjusted them. I rebuilt my carb. not too long ago and put in a new accelerator pump. Still does it. Wasn't doing this before I rebuilt it. I don't know how much fuel it puts in the carb after I throttle it in idle. Any other suggestions? Quote Link to comment
datzenmike Posted October 1, 2012 Report Share Posted October 1, 2012 Could be a lean backfire. Partially blocked jet. Not getting enough fuel. Take for a run and check the plugs. If very clean or white porcelain it's running lean. Quote Link to comment
_chiefjt Posted October 6, 2012 Report Share Posted October 6, 2012 So I found out it wasn't spittin' out fuel through the accelerator pump. The pump is getting stuck like a plunger but I got it to squirt something. Quote Link to comment
bryant2482 Posted October 15, 2012 Author Report Share Posted October 15, 2012 i advanced my timing and it stopped Quote Link to comment
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