Holley 750 trouble
Thread Starter
Burning Brakes
Joined: Apr 1999
Posts: 797
Likes: 1
From: EUNICE, La
Holley 750 trouble
I have a 750 dp-df mc secondaries Holley on my 69 350. When I make a stop that is a little on the fast side the car wants to die, the idel goes way down. But I see no black smoke like it would be getting rich? Any help? Thanks Thad.
Instructor
Joined: Dec 2002
Posts: 117
Likes: 0
From: Haddon Heights NJ
Re: Holley 750 trouble (TNT)
Thad..i don't know what kind of set up you have but the carb my be to big and pumping to much gas and making the car bog down when you step on it. I had the same problem years ago and went to a 650 and was fine.
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Holley 750 trouble (TNT)
Float level needs adjustment maybe. To low it could be starving when the fuel sloshes away from the jets. To high it could be causing flooding. float levels are easy to adjust on that carb. click this link then see section E
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
Le Mans Master
Joined: Jan 2000
Posts: 8,721
Likes: 108
From: Canada
Re: Holley 750 trouble (Mikeb690)
Thad..i don't know what kind of set up you have but the carb my be to big and pumping to much gas and making the car bog down when you step on it. I had the same problem years ago and went to a 650 and was fine.
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Re: Holley 750 trouble (Jvette73)
Float level needs adjustment maybe. To low it could be starving when the fuel sloshes away from the jets. To high it could be causing flooding. float levels are easy to adjust on that carb. click this link then see section E
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
Front float too low or rear too high. If the rear is too high the fuel will be forced through the jets on a hard stop, momentarilly flooding out the engine. You may not notice any black smoke because it lasts only a few seconds and by the time you realize there was a problem, the engine is no longer flooding.
Safety Car
Joined: Jan 2001
Posts: 4,660
Likes: 3
From: South Central Louisiana
St. Jude Contributor
Re: Holley 750 trouble (Vetterodder)
I had the same problem with my 750 dp. Adjusting floats should help. There are some clear sight plugs you can replace the brass plugs with to make adjusting floats alot easier.
I agree a 750 is a bit much for a 350.
I agree a 750 is a bit much for a 350.
Safety Car
Joined: Apr 2002
Posts: 3,551
Likes: 0
From: No link, No dupe
Re: Holley 750 trouble (Jvette73)
Float level needs adjustment maybe. To low it could be starving when the fuel sloshes away from the jets. To high it could be causing flooding. float levels are easy to adjust on that carb. click this link then see section E
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
http://142.179.166.168/manuals/Carbs...lB150_0042.htm
Although a 750 might be a little too big for a 350, the problem here is poor idle during sudden stops. Sounds like the fuel level is too low, and the sloshing of the fuel is uncovering the jets.
Any problem with too large a carburetor would more than likely occur during acceleration, not deceleration.
Just my opinion.
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Drifting
Joined: Nov 2002
Posts: 1,951
Likes: 1
From: Shore NJ
Re: Holley 750 trouble (TNT)
I'm currently experimenting with the same setup, a stock 350 motor with a 750 holley #6239 with vacuum secondaries and installed a winters high rise aluminum manifold. (72 LT1 setup) I found the fuel bowl levels must be correct, check your timing, and get the manifold vacuum reading in idle and driving if possible. You also need to check the power valve rating so it matches the vacuum needed. I also changed the jets from #70 to #66 in the primary bowl. Hope this helps, it's what I'm finding out now
Heel & Toe
Joined: Jan 2003
Posts: 24
Likes: 0
From: Oshkosh WI
Re: Holley 750 trouble (73jst4fun)
I have to agree with vetterodder on this as I believe he may have hit the nail on the head. As far as the 750 carb being to big, I have to disagree especially if the motor has some other goodies on it. Either way should be able to make this carb purr like a kitten no matter what is done to the motor...
Thread Starter
Burning Brakes
Joined: Apr 1999
Posts: 797
Likes: 1
From: EUNICE, La
Re: Holley 750 trouble (ragingbull)
First it was the rear float that was too high! I lowered it and tweeked the front and the stalling during a hard breaking is 95% fixed. Yes the carb is a little too big but I am in the process if gathering the parts to build it into a 383 so I am shaking down the carb so I won't have trouble with the new power plant. Thanks Thad
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,402
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Holley 750 trouble (TNT)
In addition to setting up the float levels just right, the stock 750 Holley-type carbs can also have a problem during hard braking and acceleration with fuel climbing up the wall of the float bowl and spilling over the vent tube into the venturi-area. This will cause the problem you describe, and it is very common. You can install a "whistle" in the float bowls to prevent this. A "whistle" is a short plastic rectangular tube that installs into the rectangular vent opening in the metering block. The tube makes the float bowl vent from the opposite side, preventing fuel from spilling out the vent during hard braking. BG carbs comes stock from BG with "whistles" installed due to this common problem. Holleys must be retro-fitted, and it's a very worth-while thing to do.
Burning Brakes
Joined: Aug 2000
Posts: 805
Likes: 0
From: Vasteras, Sweden
Re: Holley 750 trouble (lars)
acceleration with fuel climbing up the wall of the float bowl and spilling over the vent tube into the venturi-area.
I think that tip maybe will solve my problem too, with stumbling on hard acceleration. I have notice some fuel on top of the carb, around the vent tube.
Or is stumbling only a lean condition symptom?
[Modified by Lasse, 3:33 PM 5/29/2003]
Safety Car
Joined: Jan 2001
Posts: 4,660
Likes: 3
From: South Central Louisiana
St. Jude Contributor
Re: Holley 750 trouble (Lasse)
I looked at my old 750 last night and noticed it had those square tubes Lars refered to, they look to me like hollow claranet reeds. But my old holley still had that flooding on two wheels syndrom. I am sure it was due to high float levels.