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Stumbling off the line

Old 09-23-2007, 09:29 PM
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Stumbling off the line

here is the dilema

I currently have Edelbrock E-TEC 200 heads, Performer RPM air gap intake and a thunder AVS 800 carb. Total timing is at 35 right now, tried 32 and 30 as well.

If i flash the converter at the tree the car stalls.
If i leave on the converter at 1800 or so it will stumble for 60' then take off and run great.

I emailed Edelbrock and they told me i had the wrong carb on the motor. At the time i was running a 750 electric choke performer series. They told me to buy the Thunder AVS 800 carb and it would take care of the problem..... regretfully it didnt.

The car runs great other wise, it goes through the traps at 105, but that does not do a lot of good if it stumbles for 60'

Also if i am cruising at 2500 rpm and floor it, it stumbles for a second then takes off, however if i slowly roll into it, its fine.


HELP PLEASE i dont know what else to try.
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Old 09-23-2007, 09:40 PM
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Adjust the secondary air valve.
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Old 09-23-2007, 09:56 PM
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Re: Stumbling off the line

would the Secondary air valve make the car stall like that at the tree like that?
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Old 09-23-2007, 10:09 PM
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In fact, that's why it's adjustable.
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Old 09-23-2007, 10:14 PM
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Re: Stumbling off the line

Thanks, it will be wed, before i get to try it. But ill let ya know how it goes.

Hope it works, it would be nice if it left like it pulls at the big end
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Old 09-30-2007, 08:30 PM
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Re: Stumbling off the line

I had a chance to tinker with the carb the other day and made no progess. I tried adjusting the secondary air valve, no go. I tried different metering rod combinations and springs, no go. I tried different fuel pressures, nothing. I ohm tested the ignition pick up and the coild and tested the spark plug energy at plug, all tested out good. I have checked for vacuum leaks and played with the timing and i dont know what else to do!!

From a dead stop in low gear, if i floor it, the car stalls. If slowly get into to it, its fine.


ANY ideas would be great. I hope someone can help, its killing my ET.


Thanks
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Old 09-30-2007, 09:21 PM
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Re: Stumbling off the line

if you hold it at 1/4 throttle just kinda creeping around 1500 rpm does it stumble?
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Old 10-02-2007, 04:06 PM
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Re: Stumbling off the line

No at 1/4 throttle its fine. In fact if i slowly get into it out of the hole its fine. Its only if i floor it from a dead stop, in which case it quits. I have pretty much stumped the Edelbrock guy as well as myself.........
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Old 10-02-2007, 04:45 PM
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Re: Stumbling off the line

if it was a holley i'd say more pump shot, don't know how those edelcraps work though. I would have bought a 750 double pumper instead of another edelbrock piece.
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Old 10-02-2007, 04:47 PM
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Re: Stumbling off the line

Which hole do you have the accelerator pump linkage in?
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Old 10-02-2007, 04:48 PM
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Re: Stumbling off the line

do the same with an edelbrock... more pump shot. put the pump cam in the top hole
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Old 10-02-2007, 08:44 PM
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Re: Stumbling off the line

Originally Posted by Captain Morgan View Post
...Edelbrock... thunder AVS 800 carb. .
well theres you problem right there.

I had edelbrocks on my last motor, a mild 350/355 and they were not worth a crap. Bought 2 of the damn things and nothing i could do would make that stalling problem go away. I wish edelbrock would just give up on the carbs, they are no good.

I have a holley 4150 on my new engine, and its wonderful, works great, havent even done a really good tune yet.
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Old 10-03-2007, 06:58 AM
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Re: Stumbling off the line

I would hope that Edelbrock doesnt have that big of a problem with there carbs. All of there other products are pretty decent and have never really done me wrong, Holley on the other hand has burned me. I tried out the infamous stealth ram and didnt really care for it. Of coarse every motor combination is different and likes different things. This weekend im going to mess around with the car a little bit, maybe for giggles ill try my buddies 770 double pumper.
----------
For reference i have already increased the pump shot to the top hole. That was the first trick i tried. I wish the magic answer fairy would come down and tell me what the hell is wrong with this thing. I find it very annoying.:help

Last edited by Captain Morgan; 10-03-2007 at 06:59 AM. Reason: Automerged Doublepost
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Old 10-03-2007, 12:05 PM
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Re: Stumbling off the line

How do you have the idle mixture set up?
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Old 10-03-2007, 12:55 PM
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Re: Stumbling off the line

The idle mixture screws are adjusted properly.
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Old 10-03-2007, 01:37 PM
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Re: Stumbling off the line

what's your timing curve? got a big enough stall for the cam you're running?
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Old 10-03-2007, 03:24 PM
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Re: Stumbling off the line

Originally Posted by Captain Morgan View Post
The idle mixture screws are adjusted properly.
That doesn't answer the question.

How much of the idle transfer slot is exposed below the throttle plate at idle?
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Old 10-03-2007, 04:20 PM
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Re: Stumbling off the line

Don't know if this will help, but I had a Q-Jet do that some time back and it was the float level. Don't know how similar they are to the Edelbrock.
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Old 10-04-2007, 06:07 AM
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Re: Stumbling off the line

Sounds like too small of an accelerator pump shot. If you are looking at the carb from the front, you will see a steel rod on the right side connected to the accelerator pump arm. There should be several different holes in the pump arm, each one delivers a different volume of fuel. I believe the bottom hole is the biggest pump shot and the top is the smallest.

Move yours down one hole and see if it improves, if it gets worse, go up one from where you were before and retest.
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Old 10-04-2007, 06:28 AM
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Re: Stumbling off the line

Originally Posted by Apeiron View Post
That doesn't answer the question.

How much of the idle transfer slot is exposed below the throttle plate at idle?
Not sure what you mean there. I adjusted the idle screws according to the book by RPM. The system for idle shouldnt have an effect on WOT, at that point that circuit is closed is it not? Not really a carb guy. Although lately i wish i was!

The tried the pump shot in both upper and lower holes. For reference the upper hole is the larger of the pump shot.

The float level idea would make sense, just weird it would do the same thing with two different carbs. I will have to look into adjusting that.

As far as cam its a Comp Cam 268XFI it has 220 intake duration and 230 exhuast duration and i am running a hughes 2500 stall, with 3.42's
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Old 10-04-2007, 07:04 AM
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You have to take the carb off and flip it over to see the idle transfer slots. Check the owner's manual or on-line information to see where they are and how they work.

Doing the same thing with different carbs means it probably isn't in the carb. Where's your timing set?
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Old 10-04-2007, 12:20 PM
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Re: Stumbling off the line

The timing started at about 10-12 on the balancer and has progressed to about 16-17. As of right now, its at 40 total. That was one of the first things i messed with, figuring it didnt have enough timing, but it had zero impact on the problem. I no longer feel it is in the carb either, seeing that Edelbrock is out of ideas and i have tried just about every carb related thing i could think of.

The only theory that i have left is: I am running a Spectre top hat into my factory TPI air filters and housing and i thought maybe at low air speed the choke tower was interfering with the air movement through the venturi's and not operating properly.

Anybody think that is possible or am i just stretching becuase i dont know where else to look. lol.

The car ran fine before with stock heads and a performer intake, but i was also running a regular air cleaner.

So the only things i changed were the heads, intake, and air cleaner. It seems like it has to be one of those.......
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Old 10-04-2007, 01:06 PM
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Re: Stumbling off the line

If you think its the air cleaner, and you don't have a standard one to put on, you can take it off and run it for a short period of time w/o a filter just to see if thats the problem. My grandpa had a 350/350 combo in a little Toyota truck with a flatbed and dual rear wheels. LOL That thing ran for the better part of 10 years with no air cleaner...
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Old 10-04-2007, 03:52 PM
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40 degrees advanced? Is that with the vacuum advance hooked up?

You should have around 36 degrees of mechanical advance total. The vacuum should be on top of that.
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Old 10-04-2007, 04:17 PM
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Re: Stumbling off the line

and you've checked for vacuum leaks? over and over?
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Old 10-07-2007, 06:22 PM
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Re: Stumbling off the line

Yup, i have checked for vacuum leaks three times, it was the first thing i did and i have double checked it twice more just to be safe.

I have the timing at 40 mechanical advance right now to try and fix the problem. I was running 32 at the strip and it was running great. Seems to pull even harder now though with 40, so i havent taken any out yet... lol. NO such thing as to much timing... till it pings.

I dont want to just take my air cleaner off and go out and push the pedal to the floor, there is to much money in the motor for that. So i am working on getting an air filter that will work with my set up off my buddy. Its a long shot in the dark, but who knows.

If none of this works im just going to put 4.10's in it with a 4500 stall.
not really....
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Old 10-08-2007, 12:12 PM
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Re: Stumbling off the line

Originally Posted by Captain Morgan View Post
Yup, i have checked for vacuum leaks three times, it was the first thing i did and i have double checked it twice more just to be safe.

I have the timing at 40 mechanical advance right now to try and fix the problem. I was running 32 at the strip and it was running great. Seems to pull even harder now though with 40, so i havent taken any out yet... lol. NO such thing as to much timing... till it pings.

I dont want to just take my air cleaner off and go out and push the pedal to the floor, there is to much money in the motor for that. So i am working on getting an air filter that will work with my set up off my buddy. Its a long shot in the dark, but who knows.

If none of this works im just going to put 4.10's in it with a 4500 stall.
not really....
i have similar problems with my edel, it usualy goes away if i richen it up at idle, also fuel pump was a big factor went back to mechanical and all is fine, nothing but burnt tire smell at wot from line
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Old 10-09-2007, 06:49 AM
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Re: Stumbling off the line

What electric pump and regulator were you running before you switched it over to mechanical? What mechanical pump did you put in?
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Old 10-09-2007, 11:46 PM
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Re: Stumbling off the line

could never get rid of my edelbrocks flat spot, so i went and got a double pumper.

i'm not a fan of throwing new parts at things without trying to fix the old first, but this is one of those times.

...but, just for giggles, what is your accelerator NOZZLE size?

before my 1405 hit ebay it seemed to run best with a .33
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Old 10-10-2007, 09:31 PM
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Re: Stumbling off the line

Air cleaner idea didn't work....


Running out time in the summer so the car is going to storage and the problem will haunt me all winter....


Thanks for all the ideas and time!!!
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