Chevy 350 Jerks/Sputters PLZ HELP!

[inforcer958]

Hey guys i need some help i am absolutely stumped.

Ok i have a 1985 Chevy El Camino, I swapped a chevy 350 into it replacing the old 305. It does not run a computer. The Engine has an Edelbrock Intake and Carb (600CFM) and runs an HEI with a vacuum adv (with the hose on the throttle side of the vacuum port)

I have been running this setup for over 3 years and have never had a problem like this before.

Basically, the car starts just fine, goes in reverse no sounds no problems, goes in drive no sounds no problems. Lately it has been roughly 62 deg in the morning where i live. Now when i take it to work the car seems to drive fine. But around 45mph if you are accelerating decently. (In passing gear I believe its called) the car will jerk violently. The RPM's will go from normal to almost -1,000rpm. And if i keep my foot in the exact spot when it starts it wont stop. Then i let off, and try accelerating again. Sometimes it will do it again. Sometimes not. After i give it a decent drive... 15 min - if i shut it off or not. the problem seems to go away.

If i really give the car the foot it gets on it, shifts like normal, races through all the gears...

I have read through the forums and by listening to others problems i have checked through the list.

I have new:

Plugs
Wires
Dist cap + Rotor
new air filter
Have a new pump to carb hard line and -6AN fuel filter, with a fuel pressure guage inline.

Also have checked for:
Vacuum Line leaks
Leaks around base of carb
Accelerator pump seems to be working (sprays fuel into carb with engine off)
Tranny fluid at correct level and is clean.
Fuel pressure is looking good.


The problem has not gone away with any of the new parts... Can anyone help me out?

[maxwedge]

Key to this is what is the deal with the flakey tach when this happens? I'd start looking at all the electrical connections in the ign circuit,

[inforcer958]

The tach isnt bad... The engine starts bogging down... and its dropping 1,000 rpm in the process. back and forth... thats how bad the JERK/ SPUTTER is...

[maxwedge]

10,000 rpms?!

[inforcer958]

i edited it... i meant 1,000. idk why i kept putting 10,000 HAHA. sry.

[maxwedge]

Obviously you need to determine whether this is a fuel or ign problem. Try and see what the fuel pressure is when this happens.

[inforcer958]

Well I am not quite sure how to check what the fuel pressure is when this happens... its random kinda... and only when its in a kickdown situation and under some decent acceleration... If i give it the foot it just shift straight through no problem. And when everything warms up it doesnt seem to do it anymore...

However i did notice today that when i started the engine after about a 15 min drive. I started it to check the tranny fluid again. ( just in case ) and the fuel pressure gauge i put inline between the pump and the carb is basically at "0" with the needle twitching just a lil... the gauge is fluid filled... idk if that has anyhting to do with it.... When i put it in it seemed to work ok.... But is the engine is running normal... should it read the 5-7 psi that it has read in the past.... i dont understand... could this be the problem?....

Just so you know. This problem with the jerking was going on before i installed the new pump to carb hard line and filter and fuel pressure gauge.... but could the gauge be telling me what is wrong?

[maxwedge]

Hmm, 0 fuel presssure, if accurate this must be fixed no matter what, no way to tell if the gage is bad without testing with another one. Keep in mind those vehicles had a sock/filter on the end of the pick up in the tank. Stock mechanical pump?

[inforcer958]

Yeah it is a stock mech fuel pump, and i know the sock isnt on the pipe in the tank.... I have almost given up... in my mind its either the carb, fuel pump, or the tranny. After its driven for about 10-15 mins... the problem goes away...

thats why i dont see it as being a fuel problem bc if i had bad pressure or if i had something wrong with the carb why would it go away with the drive train warming up....

[777stickman]

I'll add a couple of thoughts.

Edlebrock 600--HEI dist w/ vacuum advance. Vacuum line from carb to dist needs to be on the passenger side of the carb base. This is called "ported vacuum". It has no vac at idle but supplies vac to the dist when the throttle plates are opened off idle. The port you're hooked up to now has full vac to the dist at idle. I know you have run this way for 3 years, but it's not right.

Check the vac canister on the dist for proper ops and that it will hold vac. Timing with vacs disconnected should be 6-10 deg BTDC.

On an EDL carb fuel press at IDLE should be no more than 6 psi and at WOT no less than 2 psi.

Since your trouble seems to be at part throttle (cold) I would suggest checking the choke settings and then maybe a good carb rebuild as some junk may have gotten into the carb (it does happen).

By the way is your tranny a 700R4?

Hope this helps and good luck.

[inforcer958]

The vacuum line from the carb to the vac adv is on the ported vacuum as u speak. I must have made it difficult to understand when i wrote about it last. The choke i kno is working correctly. I have played with it when the engine is cold till it gets warm and it works no problems. I agree that i may need a carb rebuild..... its been at least 6-7 years since this one has seen any new parts...

And the tranny is either a th250 or th350... i cant remember which it is.... same pan....

i spoke with a mechanic at a transmission shop, who was nice enough to actually get on the phone and talk my problem over with me. He told me that I wont need a transmission rebuild.. and that it sounds like a misfire and ign problem.... Since i have changed everything from spark plugs though the dist rotor... i am going to head torwards the radio cap, and the ign module.... We will see what it leads too.