wpgrexx

brand new rebuilt 12a(no problems here), car is a 79 limited edition. Carb has been thouroughly cleaned, all the jets are clear, the needles and floats all cleaned up, little screens on the fuel line on top of the carb were cleaned out, replaced the diaphram with a solid used one since the original had holes in it. Fuel filter is brand new. vacuum is great, timing is bang on and spark is nice and strong.

Car starts great all the time even with only like 40kms on it. it idles great, drives fine until gas pedal is depressed past about 1/4 of the way. once it hits that level the car starts bucking and backfiring a little. So I double checked the timing cuz of the backfiring its all good, the dizzy is advancing also(already tested that). If I hold the gas pedal down while it is bucking I can see gas get fired back out the top of the carb. I have removed the cat thinking it was clogged and being the culprit, it resulted in a marginal improvement but the problem is still there.

The fuel pump is stock, so it shouldnt be giving too high of pressure. Havent checked the actual pressure yet, left my guage at someone else house unfortunately, but it seems to be flowing adequatley.

Does anyone have any ideas on whats going on. It seems like it is almost running too rich? Why though? Could I have to much pressure building up in the tank causing increaed fuel pressure to the carb? But that doesnt really make sense cuz it runs great on just the primaries.

any ideas would be greatly appreciated.

txredneckmedic

Sounds like a vacumn leak. check all your hoses

wpgrexx

I have -17 of vacuum. I dont think it gets much better than that. Sorry I didnt mention, all new gaskets also when I rebuilt it. Any hose that looked suspect in the least has been replaced.

Sterling

Is it possible you have your secondary and primary fuel jets reversed?

txredneckmedic

Maybe take the carb apart again and try again? ive had that happen on other vehicles....and for some reason that works sometimes.

wpgrexx

not likely I took them out and cleaned them one at a time and than replaced it before taking out another one.

Sterling

Please explain/elaborate on this.

Your secondaries are not opening in the driveway if the carb is still using the vacuum diaphragm to operate them.
If your primary fuel circuit is in fact being metered properly by the fuel jets (ie, you have the correct size installed), then the problem of too much fuel would (to my knowledge) be attributed either to too high a fuel pump pressure, or a blockage in one or both of your primary emulsion tubes.
High pressure is problematic at idle, and you state that yours is fine. (Plus the stock pump can only put out about 5 psi max.)

I suspect that there is a blockage in the emulsion system. If the emulsion system is blocked or even impeded the signal to the main circuit cannot be bled off and it becomes too strong at high air5 flow, effectively siphoning the fuel out of the bowls due to the pressure differential.

wpgrexx

with the car in the garage, I would hold the gas pedal down to the floor as it is bucking, when I did so the rpm didnt move and little blasts of fuel started shooting out of the top of the carb.

The jets I took out one at a time and replaced them before I took out the next one, so they are in the original spots from 79. I have a carb rebuild kit on the way for it also.

But I will check for blockages. I just dont havethe car here right now.