holley 750 too much for 383? [Archive] - Team Camaro Tech

: holley 750 too much for 383?


MA69CAM
Jan 15th, 06, 08:13 PM
I have a 383 stroker and I had a 750 single pumper holley on it and it ran rich. Now I have a 600 holley single pumper on it. I would like to put the 750 back on. So far the jets are #66 from #72. How small can I go? I felt more power with the 750 just ran poor. The fuel pressure is set at 4.5 to 5 psi. Thanks for any help.

Straight-line-69
Jan 15th, 06, 08:34 PM
A vacuum secondary can work well on most anything. That's their beauty. Heck, a 780 was put on the Z's 302 mills. If that were a 780 with mechanical secondaries it wouldn't have run nearly as well.

A few questions,..
1) I'm assuming you have the 3310 Holley 750?
2) Describe "ruuning poor"
3) Do you know what the stock jetting was?
4) Are the floats set at specs?
5) Is your PV matched to the vacuum you generate?

onedynadad
Jan 15th, 06, 08:35 PM
I had the same problem with my .040 over 350 which has 2.02 heads and Comp .525 solid lift cam. Everyone told me I had too much carb with the 750. I went from one to the other and nothing worked until I had a chance to borrow an 850 double pumper. It's been on ever since. I'm not a whiz at the tech stuff, but I think it just need more air volume. After that I added an MSD and that was probably the best thing I did for the car. It's been that way now for three years and still blows me away when I hammer down, not to mention a few others. Good luck, Gary

camaroman7d
Jan 15th, 06, 09:36 PM
No a 750 is not to big for a 383. You didn't give any engine details at all, so it makes it hard to suggest anything. About the biggest thing I see people do with Holleys is open the primaries too much to set the idle.

When you say it's running rich, what do you mean by that? Is is smelly at idle? Do you leave a cloud of smoke when you jump on it? Where it is running rich will help figure out which circuit of the carb needs adjustment.

More engine specs are needed to figure out what's going on (cam specs, compression, intake, heads, headers or manifolds).

If you had to jet down that much from stock, I think something is off. What is the altitude where you are?

onedynadad
Jan 16th, 06, 04:33 AM
Very good point Royce, I forgot to mention that setting the secondary idle correctly was a huge part of getting mine right. I didn't even know that screw existed back then. The throttle pump cam can also give you hrs. of fun. Gotta love a Holley. Gary

MA69CAM
Jan 16th, 06, 01:35 PM
A vacuum secondary can work well on most anything. That's their beauty. Heck, a 780 was put on the Z's 302 mills. If that were a 780 with mechanical secondaries it wouldn't have run nearly as well.

A few questions,..
1) I'm assuming you have the 3310 Holley 750?
2) Describe "ruuning poor"
3) Do you know what the stock jetting was?
4) Are the floats set at specs?
5) Is your PV matched to the vacuum you generate?

#2 runs like it is flooding. Have to leave it in drive to shut off. Timing is at 12 btdc.
#3 72 was stock jetting.
#4 floats are set.
#5 PV?


The fuel smell at idle, no black smoke
Compression is around 9.23:1
holley street dominator intake from advance auto
1.94 heads
Accel HEI
headers true dual exhaust 2.25"

camaroman7d
Jan 16th, 06, 02:05 PM
The running on is not a sign of running rich. It can actually be a sign of running to lean. Probably caused by your reduced jetting. This can cause hot spots in your chambers that act like glow plugs (hot carbon), this keeps the car running. The idle smell has nothing to do with your jets. They are two different animals. The first thing I would suggest is putting the jets back to factory. After that pull the carb off and turn it over, on the primary side there are two slots in the base plate (one on each side), you need to adjust your throttle blades/butterflies so that that slot looks like a perfect square (looking at the carb from the bottom). This is your transfer slot, if you open the throttle blades too far (trying to increase your idle) you uncover too much of this slot and it starts allowing fuel from your main circuit in at idle, this gives you that gassy smell at idle. If you can't get the idle where you want it, you will need to open up the rear throttle blades a little to gain the rest, you can't just crank open the primary side (common mistake). Once you set the throttle blades then adjust the air mixture screws for either highest vacuum or highest idle (usually the same), then you can adjust your idle scre down from where it was set before (from the bottom), you do not want to have to increase the idle there, if you have to then try doing it with the secondary side.

I am sure pictures would help, I don't have any, I think there may be a few floating around here if you do a few searches on tuning a Holley or something like that.

If you still have a problem with run on after that, you may want to re-check your timing and adjust as needed, I doubt you will have a problem though. I am surprised your car isn't lean surging when cruising, you took the jet size down quite a bit.

Hopefully I explained this well enough to follow. If not just ask questions. Someone else might be able to draw a picture with words better than I have.

thorpe67RS
Jan 16th, 06, 05:03 PM
I have a 383 stroker and I had a 750 single pumper holley on it and it ran rich. Now I have a 600 holley single pumper on it. I would like to put the 750 back on. So far the jets are #66 from #72. How small can I go? I felt more power with the 750 just ran poor. The fuel pressure is set at 4.5 to 5 psi. Thanks for any help.

As mentioned a 750 is not to big but a 600cfm single pumper is to small

davidpozzi
Jan 16th, 06, 08:05 PM
Unscrew the idle mixture screws and squirt carb cleaner in the holes, also squirt some in the air bleeds. If you can follow with some compressed air, even better.
Clogged air bleeds will cause fuel droplets to enter the engine, droplets are not as burnable as a proper mix. A proper mix is a "froth" which is air and fuel bubbled together.

We have a more engine size sensitive 750 double pumper on our ZZ383/425 and it's nice, not too big. I would use a #68 pri jet on a 750 Holley street car.

The engine should "tell" you if it wants more or less fuel. Tip the choke closed gradually and see if the engine speed goes up, if it does, it needs more fuel. Also if the idle adj screws are out a lot, the engine "wants" more fuel. Now it may need more fuel because the air bleeds or such are plugging up, so make sure all passages are open first.

Make sure the engine is completely warmed up before tuning the carb, this means take it out and drive it 5-10 miles before tuning it, it takes that long for the manifold and carb to warm up.

MA69CAM
Jun 14th, 06, 05:59 PM
After all this time I am going to a 750 quadrajet. Tired of smelling gas out the exhaust. I did all kinds of adjustments with no solution. Is jet performance stag 2 carb equivalent ti SMI stage 2 carb. Same price.

Brian Lewis
Jun 14th, 06, 07:05 PM
Call Sean Murphy at SMI and have him build you a custom dialed in carb. The Jet Performance carb is not going to be jetted exactly for your engine/exhaust/trans/gear specs. Sean will make sure the custom carb he builds you is exactly what you want. I paid $325 for one in person at SMI which is just down the street from JET. Sean use to work for JET before he opened his own shop. I am VERY VERY pleased with the switch for DP 750 Holley to a SMI Stage 2 Quadrajet. I did have to change the intake to accept the spread bore carb but it was well worth it.

Sean Murphy Induction Custom Built Stage 2 750 cfm Quadrajet Main Jet .075, Metering Rods 42K Primary, DA Secondary
Edelbrock Performer 2101 Aluminum Intake
Edelbrock 7201 Intake Manifold Gaskets

MA69CAM
Jun 15th, 06, 02:03 AM
He quoted $359 for the stage 2. Same price as Jet. And 1-2 weeks for build time. Jet is 3 business days to my door.

Brian Lewis
Jun 15th, 06, 11:25 AM
I'd wait the 1-2 weeks if I were you. The unit is an amazing quality piece, well machined, all pieces properly coated, dialed in to your specs. Btw don't forget the fuel pump to carb kit you'll need to hook it up! $49 at summit [AER-FCP0139]

Pictures here:
http://69camaro.nextmill.net/photos/smicarb/

http://69camaro.nextmill.net/photos/smicarb/carb1_web.jpg