Holley570 Street Avenger Carb (user) problem

[KTM2FORD]

I dont know what i'm doing and about to give up and take it to a machanic. I'm handy but have no clue how these things work, so if you can help please use small words %). I bought at 1970 302 about 4 weeks ago. I drove it 60 miles home with no issue other than a headache from it running rich. My neighbor recommended the Holley Street Avenger, so I broke out my check book and got to it.
1st i installed it, somehow the fuel pump went out when i tried to fire it up. After replacing the fuel pump, I got a friend to help with the fine tuning and adjustments of the carb. Seemed to be running good in the driveway... so I moved on to the next project
2nd. replaced the power steering pump, and removed the AC unit. (going for that clean look, no clutter)
so I thought I was done (are we ever) went to fire it up to test drive it and couldn't get it started, found out I had a bridged plug (easy fix). but still couldn't figure out the carb, so I had a retired mechanic take a look, adjusted the floats and mixture...again seemed to run great in the driveway. He left, I pulled it around the block.....it was hesitant to go then when I got it into 2nd gear and gave it some gas I could feel how great it wanted to run, as soon as I took my foot off the gas it was popping, not like a crazy back fire...just popping until I hit the gas again...after a few trips around the block, I decided I better not push my luck...the second I hit the driveway it stalled. that was yesterday, today I tried to adjust it myself...It will start but wont stay running unless i slightly pump the gas. if I put my hand over the tube coming out of the carb and close the plate it stays running.

sorry for the long story, just wanted to get all the info out there...is it normal to have to constantly adjust the carb? I changed out the distributor cap and rotor, no change. any suggestions for tomorrows guessing game are welcome...i just want to drive the truck around town and not have to worry about have to walk home.
Thanks!!!!

 

[RODRIG3911]

My guess would be you have a vacuum leak... Maybe a vacuum port on carb isn't plugged right or your carb to manifold gasket is leaking a bit (I know it's new, but check it out). I had similar symptoms on mine that ended being a vacuum port rubber cap came off. Just an idea

 

[KTM2FORD]

the retired mechanic sprayed something out of a can and said he was looking for vacuum leaks. said the engine would rev. up if there was a leak anywhere...all seemed fine

 

[El Kabong]

Yeah, since it runs better with you manually closing the choke, a vacuum leak is a possible cause. A certain sized vacuum leak will make it idle terribly, if at all, but will scream once it gets going. Even though he checked for it, still check around the base of the carb. Sometimes a new one will not sit right, or hang up on something that will hold it up a little. I have had to add a short spacer before to allow a carb to clear & seat properly. Check for vacuum lines that have been undone or cracked during the nearby work.

 

[Fairlane514]

Street and truck avengers typically have off idle stumbles. You can improve them with a more aggressive accelerator pump cam (try blue) and larger squirter.

They will idle ok, but under load and transitioning from idle to mains stumble, but once they recover run fine.

My truck avenger was so bad I had to put in the largest idle jet inside the metering block to finally cure it.

If you have known good running carburetor, try it and see if your problems go away. May also help you determine if you really do have a vacuum leak.

 

[SHX669]

Several old reliable tuning tips - 80% of all carb problems are something else - improper install , vacuum leak , fuel pump issue , timing , spark --etc.
Then there is the mismatch to your engine and distributor.
I've got a Street Avenger and a Truck avenger and never had Off idle stumble - but have put SMALLER jets in both- but they're 670cfm. And no you don't have to constantly tweak with them .
Go back and check your float levels to see where they are - you said you did some readjusting. Also recheck your initial timing and recheck for vacuum leaks.
SHX

 

[jckkys]

I wasn't aware that TAs have replaceable idle feed restrictions. I do know some of the racing models have screw in idle air bleeds. An off idle stumble could be addressed by either a smaller idle air bleed or larger IFR.

 

[SHX669]

What type of fuel pump do you have and how much pressure does it have - Holleys like 5-7# and also want 12v to the automatic choke .
Have you checked to see if the choke is "opening " when warm ?
Also what type of ignition system ?
You said you removed the AC - is there any type of vacuum control for that you forgot to plug .
Also what ports did you use for PCV and for distributor vacuum advance?
SHX

 

[Joker11]

When it is in the driveway, is it level or on a slope? That could affect your float levels.

But you said you didn't know how they worked and to use small words. So I will try and explain that part.
The carburetor is simply a mixer. It mixes in fuel to your incoming air. The incoming air is pulled in by the vacuum created when the piston goes down on the intake stroke.
So what we have to do is achieve proper mixing of fuel and air.
There is an idle circuit that keeps the mixture right, obviously, at idle.
The problm is that once you step on the gas pedal, your engine needs more fuel instantly. So, to take care of that problem, there is an accelerator pump that squirts some extra fuel into the mix.
Then you are out of idle and into throttle. Then you carb has a circuit to flow the right amount of fuel at off idle needs.

A lot of times we have to find the perfect transition mixture. This is difficult sometimes depending on the engine. It does take some experimenting to get a good transition. You don't want to starve the engine and you don't want to flood it.
The install instructions usually cover this process. But Holley has a decent user forum on their website.

Now, let's say you want to go balls out and pass the guy texting, eating, shaving and trying to drive all at once. So you mash the pedal. Now your engine needs a good deal of fuel. This is where your secondaries open up and your mixer (carburetor) will feed the proper fuel into the now heavy airflow.

If your carburetor is too big it will never be able to idle nicely. If your carb is too small, it will never give you full potential at full throttle. The idea is to get the right sized mixer for your engine.

If the engine is popping on deceleration, usually it is running lean.

I hope I am helping and not confusing.

 

[72Quarterhorse]

New carb and new fuel pump so that should be all good. I would drop the gas tank and take off the sensing unit inspect and clean the tank and filter thats at the end of the pick up then, disconnect the fuel line from the fuel pump and blow that line out. You can also blow out the fuel line between the fuel pump and carb and check the filter over there. Thats if it has one over there. then you will have no doubts that your fuel system is clean.