I have a 355 with an edelbrock 750 cfm performer carb. when i go to launch it starts to take off falls on it's face and then rips out of the hole. does anyone know what the prob. might be.

 

Usually that indicates inadequate accelerator pump CAPACITY. The squirter is big enough (the discharge hole size) but the total capacity of the accelerator pump is not enough to get you all the way through the "hole" when you first put your foot in it.

Also, ti could be the secondaries are opening too quickly or too soon. I beleive your carb is a vacuum secondary design. There are, I beleive, adjustments that affect when and how fast the secondaries come in.

THose are the two GENERAL areas you should concentrate on. Edelbrock carbs aren't my strongest subject.

 

Sounds like it thinks it's a Quadrajet

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--Steve S--
1984 Trans Am 305 LG4, 5 speed
Daily Driver, Flowmaster 80 Series

 

ok to imitate a 750 carb step 1.

take off the carb! ok then step 2.

take a funnel and hold it over the intake! step 3.


pour fuel out of jug into funnel!

repeat these steps and you have a 750 edlebrock! any how thw back jets need to go lean a few steps. or the accel pump isnt getting enough volume, just move the pump lever to one of the other holes and see if it stops or continues! also if you have a single plane with the wrong componets that will happen! i have a "no" touquer2 intake by edlebrock and mine does the same thing untill it hits about 2000 to 2500 rpm does yours do this to??? is it have a 700-r4? if so try and readjust the tv cable!

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 160 (882) heads,.447/.447 lift 222@.050 duration speed pro 327/350hp cam 350 .40 over (356) Edlebrock torker2 and a 600 edlebrock manual choke (1405)

Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!

 

just to smooth all out .....edlebrock all have mechanical secondaries!! all of them!! even q-junks! im not dissing you just informing so please dont be offended!



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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 160 (882) heads,.447/.447 lift 222@.050 duration speed pro 327/350hp cam 350 .40 over (356) Edlebrock torker2 and a 600 edlebrock manual choke (1405)

Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!

 

yes, i do have a single plane intake. the torquer 2. here are all the engine mods i can think of. 10.3 .1 compression ratio. edelbrock cam Lift at valve: Intake .488 Exhaust .510 Lobe Separation: 112° world product 67cc heads, 350(.030)i as i siad before the carb is 750cfm edelbrock performer. crank turned .010. the tranny is a 700r4. i have made a few mods to the vale body. the rearend is 373 posi made by aulburn. i hope this helps.

 

Burnout, the secondaries are only mechanical with respect to the trottle blades themselves. The actual flow through the secondaries is controlled by an air valve system. On the q-jet, this is adjustable by changing the spring tension on the air valves. This makes the carb very forgiving with regard to engine vs carb size, and very tunable (along with rods & hanger changes). I'm not as familiar with Edelbrocks, so won't comment further on them.

Killer, I agree with Damon. I doubt the squirter will do much for you, but getting those secondaries to open only when the engine can use it is the key to getting rid of that bog.

Another possibility is that the engine is too warm - try cooling it down a bit more before the run.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/LB9 block, ZZ3 cam and intake, WP 305 heads ported & polished, Hooker headers & y-pipe, hi-flow cat).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, 3.08 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

I would have to say it is most likely the pump... do they have a 50cc one for Edelbrocks?

I wonder if the vacuum is too low with that cam too. What sort of stall converter do you have and what rpm are you doing your launches from?

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

 

Your secondaries are mechanical, however there is another airvalve above them that is weight activated via airflow draw into the carb. I highly doubt that has anything to do with it since I do not even run the airvalve in my carbs.. making them straight mechanical secondary.

Edlebrock makes larger pump-squirter nozzles. I had to step up to a much larger #43 nozzle on my #1407 750cfm carb (out of the box before any mods). I also had to drill an extra hole in the bottom lever of the acell-pump rod assembly to increase stroke length. That necessitated some clearancing at the top (air horn portion) of the carb so the upper pump lever would not hit.
To give you an idea on that nozzle size: Edlebrocks new 800cfm carb comes with only a #35 nozzle.
You may also try some stiffer springs on the metering rods to richen up the transition.
Do not confuse richening up the acellerator pump shot & transition with jet changes. Changing the jets is not the way to tune the transitional response of the carb.

Mustangkiller,
I am not telling you to copy my own adjustments here, just giving you an idea of ways to fix your problem.

"yes, i do have a single plane intake. the torquer 2"

First thing I will suggest to you is to get rid of that singleplane intake. Trust me on this. It is a low-profile low-velocity design that does not work well on the street or the track. That's why you can pick them up at swap-meets for next to nothing. I think you will be very happy with a Performer-RPM intake. It is very likely to fix your stumble without any other tuning changes. Even if the stumble remains after an intake swap, the higher velocity of the dualplane intake will make tuning the carb much easier.
In the end, if you are not happy with a "new" Edlebrock Performer-RPM intake on your chevy smallblock, then I will buy it from you @ Summit's list price.

If you have further questions and do not hear from me here, then try my email.

good luck,
ODB



[This message has been edited by The ODB (edited February 11, 2001).]

 

I was thinking maybe he is going with too much carb. I would think a 350 (or 355) would only need a 650 cfm carb. With too much carb, you will bog off the line, but it will be better at top end.
Does this sound legitimate to anyone?

Phil

 

Thanks for all the suggestions. I think the first thing i'm going to try is to change the springs. thanks again.