Holley Avenger Carb

[edison1970]

I got this carb from a friend of mine a few years ago. It's a 770 and was too big for his Ford 351. Any thoughts on this carb? I only have used Carter AVS or Thermoquads in the past. I also have a Eldebrock 750 carb but needs rebuilding. 

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[Chryco Psycho]

The Avengers are a decent carb , you cannot do the extreme tuning with Air bleeds , but they work very well overall , I wrote up a tuning guide in the reference section , you need to follow the steps & do it in order Or you will be chasing your tail as changing 1 thing will affect another

[gzig5]

Took me a moment to find the procedure so I copied the link here to help the similarly search impaired.

https://forum.e-bodies.org/reference-material/18/holley-or-similar-tuning-tips/215/

[bennydodge]

Since you have it, try it. I know my 870 has been the biggest headache of a carburetor I've owned. The fuel curve in the avenger carbs is nice for a street car though.

[Chryco Psycho]

Why Benny ?

[bennydodge]

Once in a while it will randomly shoot fuel out of the vent tube(s). I bought this carb brand new direct from Holley 4 1/2 yrs ago and have dealt with it since day 1. Changed both needle and seat assemblies and both floats-no difference, taken apart and thoroughly cleaned 3 times, stock 340 mechanical fuel pump. Being a carburetor guy for over 30 years, I can honestly say it's the only carb that's ever beaten me lol. By the way, Holley's tech line is of very little help as well.. 

[HP_Cuda]

Wow that sucks, I know what you mean about having the carb blues.

I have a Avenger 870 which I have had little problem with, had to do some mods based on my motor but overall not bad. I will step up to the Proform 950 soon though.

[Strawdawg]

that sounds like the float is sticking shut

[bennydodge]

If the float was sticking shut wouldn't the carb run dry? One fact of note, when I spent some time in Phoenix(almost a year), It never burped any fuel at all. Not even once. Moving to Phoenix from Denver created big time detonation problems which were eventually resolved by reducing the lead-in timing by 12 degrees. Now moved back to Denver, the problem has returned and of course the engine will not run with the reduced initial timing. Still "brainstorming" the situation...

[Chryco Psycho]

Are you running brass or nitrile floats ?
If the needle was sticking shut it would starve , you have the opposite problem the needle is not closing off the flow , could the high altitude but affecting the brass floats as in too heavy in thin air as they are air filled ?

[bennydodge]

They are Nitrophyl. I have not tried the brass floats. I wonder if brass is heavier and therefore more stable?? Seems unlikely but plausible

[jimynick]

If the floats check out, then the only other thing I can think of may be in the interface between the float and the carb. Do the floats move easily up and down? Is the float tight on it's pivot point? Is the float perhaps skewed to one side enough to contact the side of the float bowl? Does the needle move smoothly over the ramp in the float? Is the float height correct? Is there a pressure regulator in the system to prevent a possible fuel surge? Just some thoughts here and hope you can sort it out. 

[bennydodge]

All of the above checks out with the exception of fuel pressure. While I have not checked fuel pressure, I have swapped on several known good carbs(3 of which are Holley 4150's) and have had no issues. Thanks for ideas though.

[HP_Cuda]

Definitely a float issue, would be interesting if you swapped between the brass and plastic floats to see if there was any difference.

Btw, are you running an electric fuel pump - say a Holly Blue pump?

[bennydodge]

Stock 340 mechanical pump. I think I'm going to try running a little richer on the idle mixture and colder plugs. With 11.25 to 1 compression the cylinder temperature is pretty hot.