went to the track last night for the first time..been running the car with liek 3 lbs of fuel pressure.. car didnt like that at the track.. first run 13.4@97mph bumped the pressure up and ran a 13.05 at 107mph then bumped the pressure up and messed iwth the timing a bit and ran a 12.83@106mph but everytime off the line i stumbled really bad. what can i do to change this?? i do have my choke stuck wide open seems to run better i wish i didnt have a choke actually anyways let me know what to do thanks

 

sounds like it's timer to start tuning your accelerator pump.

 

ok i need to know how to do that then this as most should know is my first carbed motor.. thanks

 

The Street Avenger is a vacuum secondary carb. Have you worked on the secondary springs at all? I assume, at least, you're talking about a bog (secondaries opening too soon), rather than a lean backfire (accelerator pump problem).

Check the instructions that came with the carb, or go to the Holley web site and look up their tech info on tuning.

 

This is a pretty long shot but I had this exact same problem. I thought it was carb issues but turns out it was because of my mallory fuel pressure regulator...

Do you have the vacuum port hooked up on the regulator? As you should know, the vacuum port is designed to lower/raise fuel pressure. So lets say you are at idle its only getting 2-3psi then when your RPMs increase it goes up to wherever you set it (6-7psi). My problem was when I'd launch hard off the line the car would stumble really bad (and sometimes backfire from the carb) because it was leaning out. The fuel pressure from the regulator was not raising fast enough to keep up with me.

Unplug the vacuum line from the regulator so it stays at a constant PSI and see if that helps.

 

i actually have the vacum plug on the reg. plugged right now lol.. i thought it was for turbo only.. guess i am wrong huh lol.. well i will try that.. also i have my choke open all the time i tied it open.. seems to run better that way.. could that cause it?? thanks for your help.. where do i plug the vacum line from the regulator into?? thanks

 

I too was just having a nasty off idle stumble on my Demon.I went up on squirter size to a #31(from a #28) and changed the pump cam (from pink to orange) on the accelerator pump..world of a difference.Like Jester said..tune the accelerator pump.I actually just did trial and error to get the best set up but got to Holley's site,they have a really good section to help you tune your carb..even when it's a Demon..lol

 

I don't have a Mallory regulator, but that just sounds bogus to me. A carb utilizes a "fuel bowl" (in this case, two - one for primaries, one for secondaries), which is a resevoir for fuel, nothing else. When sitting at an idle or even powerbraking, those resevoirs should be full. A fuel delivery problem will become evident under high demand situations - high RPMs, all throttle blades open, power valve open, etc., not off-the-line.

Pressure itself is not a direct factor in filling those fuel bowls. As stated in a different post, a couple of psi is all that's required to get to fuel up to the bowls and fill them. Too little pressure, no delivery, of course (or the regulator will reduce flow too much to feed it under full power). Too much fuel pressure, you can overwhelm the needle valve's ability to shut off the fuel when the bowl is full and flood it. Still, neither of those relate to an off-the-line problem.

Have you done the basics: checked fuel levels (sight plugs on the side of the bowls), checked for accelerator pump shot, etc.? Until you do that, all other speculations are moot.

Still sounds more like a bog to me, which means adjust the secondary opening rate.

 

5.7kid u are right its more like a bog or a dead spot to say.. so how do i adjust the 2ndary opening rate?? do i have to change the spring?? i have the yellow one in there now.. it said in the instruction book that was the one for performance?? so shold i go to the black one??

 

I thought the exact same but my regulator was feeding 1 1/2psi at idle, I'd launch hard and it would lean out. I disconnected the vacuum line from the regulator so it would stay at 6psi constantly and it instantly went away. So ....I dunno whats up with that.

2ponchos: definately check the easy stuff first like everyone has said before. Do you know if you were blasting out black smoke off the line? Have you checked your float levels? If its bogging down but there isn't any backfiring or "popping" from the carb its probably that you are getting too much fuel. Buy a Quick Secondary Change Kit from Summit/Jegs and play with stiffer springs ...its a real pain to play with secondary springs when you don't have this kit. It turns a 10+ minute job into a 30 second job.

When you are just cruising down the street at very light throttle at about 20-30mph then stomp on it does it do the same stumble?

 

no from a roll it doesnt have the same stumble or bog.. the carb came with the quick change kit.. i have like 3 springs right now to play with.. i will have to get some more at the parts store.. so should i try going stiffer?? there isnt any black smoke off the line either as i have been told.. it doesnt back fire or anything.. it did run out of fuel the first pass but i bumped the pressure up and that stopped that.. ill keep playing with it and see thanks guys

 

Holley sells a spring assortment kit p/n 20-13, which contains 6 springs. $7.75 from Summit, probably cheaper than getting the springs individually (even buying the other three that you don't already have).

The rule of thumb is to use the weakest spring that won't cause a bog.

 

As posted above, check your float levels to make sure they are correct. If the secondary springs don't help, up the size of the squirter and see if that solves your problem. Leave your fuel pressure set to 6 pounds. Don't mess with the fuel pressure in order to try and tune, all the tuning will be done with the carb.

What do you have your timing set at? If your timing is too far retarded, this could also cause a hesitation.

 

the timing is at 34 degress total.. i think like 10 base timing.. i didnt set the timing the guy that built the motor was at the track wheni was there so u set it.. i will try the springs.. and see what that does the float bowls seems fine..

 

Hi 2ponchos, I had a similar problem and solved it with a Quick-Fuel adjustable secondary housing. It has a needle valve installed so you can fine tune the opening rate. I've found that the springs tend to adjust the opening starting point but once they begin to move they will still flop open without the chack ball and will not open fast enough with it. The adjustable housing allows me to fine tune this to exactly where my car likes it. The part is only $35.00 and I have much more control of my secondaries. In fact, it worked so well that I don't plan to run another VS carb without one. It is as important to me now as the quick change kit.

I don't work for them or anything, the part just worked very well for me and it might help you too. The $35.00 cost is an absolute steal considering the gains I got.

It is super easy to tune too. You just bolt it on, open the needle 1-1/2 turns and run it. Then turn the needle in 1/8 turn at a time until the bog is gone. Currently, just over 1/4 turn open seems perfect for my car.

Good luck, and congratulations on the 12 second runs :hail: we have similar setups but I'm using a 357 and th350 with a 9.5"/3500 stall. Hope to hit the 12's too but haven't been to the track yet, still some chassis work to do.

Andy

 

Where do you get this part? I tried searching Summit's website, got from 5 to 141 pages with nothing that matched "quick-fuel" or "quick fuel".

 

Can I say the J-word?

I got mine from Jegs.

Adjustable housing from Jegs

I really am impressed with the simplicity and effectiveness of this part. IMO Holley should have done this from the beginning.

 

I had a bad stumble off the line with my 3310 750 cfm vac. sec. car, when I went from a 9.5 to an 8 power valve, and changed the jets. it cured the proble. just somthing to think about.

 

Sure, why not?

I think I'll be putting in an order soon. I assume the quick change spring housing fits on top of it.

 

i think the street avenger carbs have the quick change already on them.. atleast i think thats what it is called where the vs spring goes right?? 2 screws and you have yoru spring out

 

Yes, Five7kid, it all fits together just fine. The instructions say to use the spring that comes with it, but I tried my others and found one that works a little better for my combo.

2ponchos, the SA comes with the quick change kit but that's not what we're talking about. Click the link I posted above and look by the two front mounting screws. That needle valve allows you to fine tune the air restriction to your secondary diaphragm. You can slow down the secondary opening rate, independent of the spring, just enough to get rid of the bog.

 

thats cool can i use holley springs with that if so i am getting one!!

 

Here's a pic

 

Mine arrived yesterday. I found the spring that came with it was nice and square, whereas the Holley spring (from the assortment kit) was a simple open-end. I didn't measure them, but the one that came with the adjustable housing is supposed to be the weakest available, and it did "feel" close to the Holley spring.

So far, I've turned the screw out 1/2 turn from the preset 1-1/2 turns, and still no bog but it's feeling better (my issue is the secondaries don't open up soon enough - to eliminate a bog, you need to turn the adjustment screw in). Only nit I have with it is the electric choke housing gets in the way of getting a small flat-tip on the adjustment screw, so I have to loosen the 3 choke mount screws every time I want to adjust it. A little grinding on the housing may fix that (it's the bolt hole boss for the thermostat mount screw that's in the way).

 

Try using the lightest holley spring. I placed all my springs on my bench, small end up, and pressed down on them to compare. The one that came with the housing was almost identical to to holley's medium spring in shape, size, and strength. I know what the instructions say but try this and see.

Also, another idea, when you put your quick change cover on did you leave the check ball out? Make sure there is no vacuum leak between the housing and the carb body too, this happend to me but wasn't too hard to fix.

That sucks you have to remove the choke housing to make adjustments. I'm not running a choke so I didn't even think about that.