Question about my holley carb..Bogs when I hit the gas..

Hello there.. Well, engine is rebuilt in my vette and the rear is now in..Runs well, except with the quick snap of the gas to the floor.. It falls on it's face, and sometimes just stalls. If I ease into it normal it is okay.

This is where I am at so far...350 w/rv cam HEI
Set the idle at 800 rpms.. Set base timing at 8-10 btdc w/advance line disconnected. Installed advance vacume line and it advanced...good..
Took a vacume guage and started with 1 1/2 turns out on each mixture screw until reached highest vacume..Floats as well if the sight plugs are removed and you bump the car a litttle, gas comes out.

Turn the car off and looked down the carb, and slowly moved the throtle..The squirt starts the instant I move the throtle, and seems to be fine.

I tried the adjusting the acc. pump, and I even went from one extreme to the other adjusting too much just to see if for some reason it might correct the problem..

Thought the power valve was maybe blown out since I fired through the carb because I installed 2 wires incorrectly..duhh.

I turned the mixture screws in until they seated, and the car stalled, so I would think the power valve is okay, which is a 6.5 which came in the rebuild kit.

Any more input to where I might be going wrong here?? I work at a Lexus dealer, so any techs feel free to chime in.. If the damn thing had a computer I could get this right, but it has been awhile since I tuned a holley on a 350..ha ha...Oh, and it is a 750 cfm dual feed, single pump carb #3310 if that helps at all. I am sure all the jets, ect are stock in it.

Like I said, seems to be fine if I ease into it, but If I just stomp on it, blaaaaa.
Any input would be nice..Thanks.

Hows your timing at idle look with the vac advance hooked up? You shouldn't have any vacuum advance at idle.

That 750 carb is big for that motor. A hesitation off idle is a fact of life with big carbs on small motors. When you open the throttle fast, it takes time to build vacuum in the venturi. The carb can't pull fuel from the main circuit without a vacuum in the venturi. The solution is to run it richer, it will help the low rpm response but may be too rich up top. Without lots of expensive tools, you've just got to experiment around a little bit with different jet sizes and accelerator pump shots.

if you have a buddy that has a 650 ask him if you can test it out on ur setup... i have a mildly built 350 with a holley 650 dual feed... car is quite responsive at a quick snap of the throttle and performs well all the way up through 600rpm

Hey guys.. Called a place called "The Carb Shop" out in CA..I am from outside Philadelphia Pa, but this place is suppose to be known for good work on carbs.. His take was since it is on a 350 that is mild ect, that a 750 is just plain to big, and that for top end a 750 would be good, but since I want just a street car that is a little fast(gets out of it's own way) that I should go with an electric choke Q-jet from about 1978. Says the small primarys are great for better milage, and when you need the power the secondarys as we all know are much better..All in all a better more responsive carb for the street.. The guy makes sense to me, and he does own a well known carb shop. What do you think??

man just get an edelbrock and solve all your problems ;)

:LOL: :LOL: :LOL:

Quote:

---

Originally Posted by #1firebird

man just get an edelbrock and solve all your problems ;)

---

I've got the older generation 4MV Qjet for 1975 and earlier cars as well as some new trucks. It's a little simpler to operate, tune, and rebuild. Parts are harder to get, nobody makes metering rods anymore. Edelbrock uses the slightly newer M4M carburetor. The 4MV doesn't work particularly well with an electric choke. The throttle response is excellent if you get your vacuum advance hooked up right. The milage is also excellent. I get 18-20 mpg. and sometimes more, from a mild 350 in my 1976 GMC 1500 pickup with a TH350 transmission and 3.07 gears. Ran a 15.37 and 90.5 mph in the quarter, which is faster than most Hondas, so it can get out of its way even with the Quadrabog. Unless you make major engine modifications, the Qjet is somewhat self-tuning. It sets the fuel air mixture based on throttle position and manifold pressure so it can adust itself for small changes n valve timing and athmospheric conditions.

ive seen q-jets on 11-12 second cars its all in the tuning you just need to have LOTSA patience or the know-how to tune a q-jet, hell my friend jade knows how to build a q-ket and smack in on my car and it'd run just as good with it as it does with the holley. like i said its all in the tuning. i had a q-jet on a 79 malibu wagon hey it got 23 mpg to seattle:D

750 is a bit big for a mild 350, I'd suggest a vacuum secondary 600 or 650.... I'll chime in with some of the others on a Q-Jet, set correctly they work great, set up wrong they're a POS....

oKAY, SO i AGRE THAT THE CARB IS TOO BIG. I wonder if the q-jet bought new will be pretty much a bolt on situation. I am sure that maybe some fine tuning with mixture and idle. I wonder about the holley 600...What about these edelbrock carbs. Anyone else??

A friend of mine has a '69 Stang. He took off the old Holley and bought a Qjet and the engine don't like it. He is now buying a new Holley. I think stories like this abound on both sides, and products can be good or not so good ......

As for me it's Holley or Demon ..................

BTW before you change carbs, and I agree your 750 is too big, make sure the idle system is set correctly. Are the plates within the idle circuit transition slots when at idle? Does she respond when you tweak the mixture screws? Running way rich? Power valve stuck/blown due to backfiring? The idle circuit can have a dramatic effect on how she responds to stabbing ...........

Regards, Kitz

I have to take my vacume guage home from work tonight. It just dawned on me that I have the vacume advance hooked up to the port on the side of the metering block. I know it has advance, but I forgot that the holley has a port just above the throtle plate as well. I never checked which port to use with a vacume guage.. Maybe that is my problem.(No I an not talking about manifod vacume either.) It has been about 10 years since I played with a holley, so maybe it is as simple as that I have the advanced hooked to the wrong port.

Well, after work tonight I took my vacume guage to the engine.. In drive, while foot is on the brake, I have 14inch of vacume.. I know I put a 6.5 power valve in the carb.. I first unplugged the vacume advance from the port where I had it on the metering block on the holley and checked the vacume.With the guage hooked up, and a quick snap of the throtle the vacume dropped, then went up..The same thing happened on the port below that on the throtle plate..Hummm So which port is it suppose to be connected to? I am not refering to the large manifold vacume port in the rear, I know better than that, but I can't remember which front port to use, the one at the block or the throtle plate.. Tech Inspector, you are good at this kind of stuff, what do you think..

Connect the vacumn to the metering block and take the main jets down to 64's

Why 64? I am not sure what it came with stock, guess I will have to pull it apart. How did you come to this conclusion?? Just trying to learn.

a mild 350 for street cruzin only needs about 450 cfm. a 600 holley will work fine if leaned out 2 steps down from out of the box. i change to the 50cc acc pump and use 62 to 64 primaries.
personaly for my sbc i like the 390 holley.

What shine said. A 750 is way too much carb for a mild 350 on the street. A 650 is bordering on too big and I ran a 650 DP on a fairly milld 400 and had to jet it down to 64's so it wouldn't run so rich.

14 inches at idle was the one above the throttle plate? What was the one below? The vaccum port below the throttle plate is exposed to manifold vacuum. It should be high at idle and low at full throttle. The one just above the throttle plate should be low at idle, high at slight throttle opening, and low again at full throttle. This is the one you want for vac advance. It may not be really low, it just has to be low enough not to actuate the vacuum advance. 14 inches low enough.

Okay, after thinking about this, do you think it might make the most sense to remove the over sized carb, and go with either a holley 600 electric choke, or a Q-jet new (from say a 75-75 model car with electric choke?? The original carb was an electronic q-jet, but I removed all the computer stuff, ect..I guess I could always sell the holley on ebay, as it does work, just a little too much so for my engine. If I installed the 64 jets, would that solve my problem? What about the shooter size?? I called Holley and they told me I need a BIGGER shooter.. I dunno about that. I sometimes hate calling the tech lines.. I called Comp cams 4 different times, and got 3 different suggestions for the same aplication..I sometimes wonder who is on the other end..

Check for a vacume leak, If that is all tight and it still bogs then try a list 1850 holley 600 cfm vac sec

damn and to think i need 750 cfm's :LOL:

I like the crisp low-end response of a spreadbore on mild engines, because of the small primaries, and a used Q-jet is the cheapest way to test this. Then, if you want chrome you can upgrade to an equivalent Edelbrock (Carter AFB replica).

Holley used to make a spreadbore 650 double-pumper if you want that look and intend to run 8000 RPMs. If you want to simply romp the pedal without an finesse, you won't want a double-pumper, but one with vacuum secondaries.

i had a 67 stang with a mild 302 and a holly 650 dp.if i eased on the gas it was fine.if i dumped it it would hesitate its butt off.I figured iw was dumping to much fuel on the hard stomp so i chenged the shot squirter to a smaller size and i almost bulled e wheelie on me lol.problem was solved.

Quote:

---

Originally Posted by jchrisd

Why 64? I am not sure what it came with stock, guess I will have to pull it apart. How did you come to this conclusion?? Just trying to learn.

---

3310 750cfm should have come with 72's up front and a 6.5 PV.

I run a holley 750 DP on my mild 350 and have no hesitation. Its all in the tunning. MY bud runs a proform body and front metering block reworked body to ~850cfm on his ford NA 302, radical cam and head setup and runs mid 11's all day long and as crisp as you can get. If you have some one local who can tune it for you Id stick with it. Bud thats just me. :)