Carb question?

[Chargedblack03]

I am running a 750 dominator on my 347, and last year the car would stall out once and a while at the track, and the car always seemed to bog at the line when it didn't stall. Still to date my best 60' times is a 1.75:(, and thats with 4.88s, 33 spline, c-clip, and a weight of only 2640 w/out driver. Around august the car had gotten worse, so I after pulling the carb off, I found the accerlator pump had a small tear in it. So after replacing it the car seems to run and idle allot better, but still bogs off the line....

So does anybody have any ideas or does anybody know a good carb guy who could go thru my carb?

Sorry about my ignorance to carbs before this car, I always had an EFI.

Thanks
Pete

[Chargedblack03]

Also, I forgot to mentioned, I haven't checked the plugs yet, but I am guessing from the car bogging down that they might be fouled out.

I'm not totally sure that there is something wrong with the carb, the car has a high idle, so I don't know if just from idle is fouling out the plugs, hence giving me problems at the track? I do drive the car on the street once and a while...

[Jim]

the bogging could be coming from a few different things. what does your converter stall or flash too? what is your total timing at? what size squirters do you have for primaries and secondaries? if it's idleing real high maybe you have a vacuum leak somewhere? what heads are you running?

i was running a 4150 750 holley on my 347 with a 35 up front and a 37 in the rear. timing was best at 35 total on the dyno, but that could vary on the track in different weather. i'll have to look what jets i had in it.

i was alway chasing a bog when i ran my 308 and the same carb. it got a little better when i changed to the 8" converter but was still somewhat there. not until i added more cubes did it go away. my 60's with the 347 were 1.63-1.62 on a 9" tire. i was running 4.30's with 28X9 tire @ 30xx lbs.

[Chargedblack03]

I am running 36 degrees of totally timing, AFR 205 heads ported by Keith Craft, 4500 precision stall and the jets are 76 in back and 80 in front I think....

[Slow Ride]

maybe the accelerator pump cam? I had a wicked off idle lean stumble and tried all kinds of squirters and even tried a 50cc pump. I changed everything back to stock and advanced the pump cam one hole and it went away.

[1SLO5.0]

Throw the power valve in the garbage and put a plug in. Square the jetting and step up 4 sizes to start with to make up for removing the powervalve. Jets meter fuel alot better than a power toilet does. Make sure the accelerator pumps have a small amount of preload on them from the pump arm. Do you have a transbrake? If so, use it.

[Chargedblack03]

Thanks for everybodys input, I will try the bigger jets, and pitch the power valve, and yeah I do have a transbrake.

Tonight I will check the plugs and go from there.

[1SLO5.0]

Were you using the transbrake and it was bogging?

[Wicked]

Bogging can also be caused by overjetting. A common thing to do it overjet the carb, mostly becasue as the builder of your own drag car, you want to be overly optimistic about what the car makes for power and jet accordingly. I has my mechanical secondaries opening too soon on my previous mustang and this caused a small stumble on launch. Once I figured this out I went from 1.80 60ft times to 1.53 with 4.10's and a 3500 stall running a 26" tall 10.5" ET street.

[4cfed]

well my s10 did the same thing.. still does now and then..my carb loads up the motor at idle or low rpms..and i can clearly see it puke black out of the tail pipes...changed the plugs and it helps.....dont know if that will help you any

[Chargedblack03]

well my s10 did the same thing.. still does now and then..my carb loads up the motor at idle or low rpms..and i can clearly see it puke black out of the tail pipes...changed the plugs and it helps.....dont know if that will help you any

That exactly how my car feels...

I will check out the plugs tonight and depending on what time I leave work I will also get rid of the powervalve.

[4cfed]

with mine its a puss ass 305 with a 650 holly carb so i know its drownding its self but the spark plug change did help it a noticable bit

[Rick Finsta]

In my humble opinion:

1. Check how much of the transfer slot is uncovered - if you have a high idle and no holes in the throttle blades, this can give you a fuel problem going on-throttle. The slot should look about square when viewed from below the blade. If you don't have holes, and can't get the car to idle with the slots square, then holes need to be drilled. I'd have a professional carb guy do it.

2. Power valves on the front side can be great, especially if you street drive in the primaries. If you DO decide to get rid of them, then do the math and figure out what size jet to go to; everyone acts as if there's nothing but a rule of thumb, but it's all simple geometry. The power valve doesn't meter fuel at all, the Power Valve Channel Restrictions do, and they're really no different than a jet: a small hole. The power valves' only job is to determine when the PVCR's are open to the fuel bowl.

3. Tune your pump shot? I use a 50cc pump and smaller squirter (30F/40R). I really have no advice on where to start for tuning yours.

Just my $0.02. I bought a carb from Pro-Systems after dyno'ing my current motor, and had Patrick set me up a nice 4150. He also makes a 3-circuit 4150 that might work very well for you. I'm not knowledgeable enough to play with emulsion and all that, so I just paid a pro builder (which cost me $60 less than the box-stock Holley HP of same configuration, incidentally). He also does updates/tuning on older carbs for a few hundred bucks.

[Kevin Garceau]

In my opinion you will waste alot of time and effort with that carb to yield very little gains. Its not very racer friendly let alone consistent. I would go a different route.

Also if the carb is set up correctly you can run a PV. The carbs were designed to run with it, removing and jetting up is band aid fix. But it can be done as well. I have ran with them and without them. I liked running with them better, much better low end response and driveability, granted my driving was just through the pits etc.

But I still think that 750 dominator is a pile of junk....hence the reason you wont see them on many cars. But they do still have a cool factor to them. I would get something in the Holley HP line-up....them carbs flat work. But I run injection now, although thinking of going with carb on this SBC I got....never ran a SBC before so who know :)

[1SLO5.0]

In my opinion you will waste alot of time and effort with that carb to yield very little gains. Its not very racer friendly let alone consistent. I would go a different route.

Also if the carb is set up correctly you can run a PV. The carbs were designed to run with it, removing and jetting up is band aid fix. But it can be done as well. I have ran with them and without them. I liked running with them better, much better low end response and driveability, granted my driving was just through the pits etc.

But I still think that 750 dominator is a pile of junk....hence the reason you wont see them on many cars. But they do still have a cool factor to them. I would get something in the Holley HP line-up....them carbs flat work. But I run injection now, although thinking of going with carb on this SBC I got....never ran a SBC before so who know :)


That's funny because Pro Systems and Jeff Wick both told me that a power valve meters fuel as good as a toilet does and they have no place in drag racing. I've always been told that you can't run without a power valve on the street which I found to be untrue a couple years ago thanks to some advice from Jeff Wick.