670 Truck Avenger Issues

[Suddendeath]

So, I just got a PM from another IFSJA'er whos having the same problem. I need to hear from other users with the 670 Truck Avenger. When I stomp on my gas pedal, the truck stalls out, almost like something isn't set up right in the carb. If I stomp it in first, it'll stall and die. In second or third if I stomp it it'll die out until I really floor it and the transmission downshifts.

What is the deal, guys? Is the 670 just too much airflow for the 360, or is my carburetor messed up? I have a rebuild kit, I just haven't gotten a chance to take it apart yet.

[derf]

You need to calibrate your accelerator pump.

When you stomp on it, the sudden flow of air doesn't draw enough fuel at first so the accelerator pump squirts in a bunch to hold it over until the venturies catch up.

Read this: http://www.automedia.com/Holley_Carb...ht20000718hm/1

Edit: This one looks like a better article: http://www.stockcarracing.com/techar...ent/index.html

[Ristow]

Are you running the stock powervalve. Holley puts a 2.5 inthe 670's, which is too low for a mild motor. Step up to a 6.5 or higher.

[Suddendeath]

Are you running the stock powervalve. Holley puts a 2.5 inthe 670's, which is too low for a mild motor. Step up to a 6.5 or higher.

I did this already in my carb. I had been reading up on people using the 670 and dropped in a 6.5 before I even put the carb on the motor. I have good response and drivability up until the time comes to really drop the hammer, then the truck makes a slight spitting noise or a "poof", not a backfire, and stalls out. I have to quickly release the pedal to prevent the engine from completely dying.

In regards to the accelerator pump, I read both articles and I'm still kinda fuzzy. Seems like one of those things I have to let sit in my mind for a bit. Is my problem too much gas from the pump, too little gas, too soon of a shot, too late of a shot? There are a lot of things to consider, I guess, eh?

[derf]

I did this already in my carb. I had been reading up on people using the 670 and dropped in a 6.5 before I even put the carb on the motor. I have good response and drivability up until the time comes to really drop the hammer, then the truck makes a slight spitting noise or a "poof", not a backfire, and stalls out. I have to quickly release the pedal to prevent the engine from completely dying.

In regards to the accelerator pump, I read both articles and I'm still kinda fuzzy. Seems like one of those things I have to let sit in my mind for a bit. Is my problem too much gas from the pump, too little gas, too soon of a shot, too late of a shot? There are a lot of things to consider, I guess, eh?

I vaguely remember tuning my 670 TA on a 360 back several years ago and I had to step up how much fuel it was squirting. I think I adjusted the screw from the lever to the pump arm and changed holes in the cam but don't quote me on that.

Regardless, the accelerator pump being out of whack is what causes the stumble when you hit the gas. Get it into whack and you'll be fine.

[sungoesdown]

I had the same problem with my t/a and changed out the acc pump cam and it fixed the bog. Basically the acc pump gives you a shot of gas that the carb can't do by itself and changing the cam revs up the time and amount of fuel given from the acc pump

[PlasticBoob]

Pump cam, cam position, or discharge nozzle size. I had to play with all three until I found the perfect combination.

What happens if you stomp it in neutral?

[Suddendeath]

Pump cam, cam position, or discharge nozzle size. I had to play with all three until I found the perfect combination.

What happens if you stomp it in neutral?

It's fine if I stomp it in neutral, it screams like I would expect it to. Though honestly I don't like revving it up too high without load.

I'll play with the accelerator pump stuff then. See if I can't help it out with the cam I have, if I can't, which color cam do you guys have good luck with?

[78 Arizona Chief]

I think every engine is different so the color cam will depend on trial and error, also if it is placed in the #1 or #2 position. Biggest thing for me was to dial back the primary a couple jet sizes and dial back the secondaries way back to near the primaries. As for the acc pump discharge nozzle, I chucked the 28 and put in a 35. 35 is the largest without changing out the acc pump diaphram. I think no matter what you do, the truck avenger as described to me by a Holley Tech, will never rid itself of all quirks. The way the lack of high speed air bleeds will always bring with it day to day street issues that one can be tuned out or the other but not all. I have great highway, decent fuel economy and fantastic offroad behaviors, but still have that random stumble off the line.
Kevin

[jamesdart]

squirter too small

[serehill]

Yep

I just went through this & went all the way to a 8.5 power valve with no luck upgraded the pump & cam & it rocks. The mileage sucks but it runs.
Not enough fuel to get it started. I can't believe Holley thinks these are coming out of the factory good this way becacuse we are not the only guys seeing this. They do the same thing on Fords & dodges. Bad engineering. Tech support wasn't much help either.
I was really impressed with the tech telling me I should have never bought one unless iI was going to use it offroad only.

[Blake]

I'm running a 670 TA on my 360 in the J10. It has absolutely no hesitation, even on a FULL stomp of the gas pedal on idle. I have several different accelerator pumps and PV's - none of them make a difference with regards to an off idle stumble.

Jetting, however, does.

I have several different jets for it. Currently running a 64 main and stock 89 secondary at 6k feet.

What jets are you running?

PS - I've read somewhere that some of the 'early' 670's had a casting problem will have an off idle stumble. It might be worth your time to call Holley and give them your serial number. They may hook you up with a new unit...

[maccj5]

Since the vacum secondary is adjustable
what spring are you running? If a vacum issue is there
they might not open at all

[Blake]

Since the vacum secondary is adjustable
what spring are you running? If a vacum issue is there
they might not open at all

IIRC the 'vacuum secondaries' aren't really 'vacuum'.

They open based upon a large amount of air going through the carb - not technically 'vacuum'.

Doesn't matter anyway - a bad secondary won't cause a low end stumble.

[PlasticBoob]

PS - I've read somewhere that some of the 'early' 670's had a casting problem will have an off idle stumble. It might be worth your time to call Holley and give them your serial number. They may hook you up with a new unit...

This is correct, numbers were 670-1 I believe. Make sure yours isn't one of the affected units or you will go nuts trying to solve it. Like Blake said, they will replace it with a defect-free unit for free.