Holley Truck Avenger tips for Off Roading

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I’ve wanted to write a definitive Holley Truck Avenger thread, and I’m finally getting it done. I’m going to cover some tuning tips that I have applied with great success and also a review of my trail experiences on how well the carburetor operates.

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I see a lot of posts asking about whether the Truck Avenger works and what to do about the off-idle stumble/hesitation. Hopefully this thread will come up on some searches, and if not at least I can just link it and save myself more typing. :deal:

I had some bad luck with a couple of qjets, so I ended up buying a used Truck Avenger (TA) from a member here. It seems as though the TA is the last attempt to put off an FI swap. So this means you can find a lot of TAs for sale here, ebay, and Pirate with only 1-year’s use and low mileage. Don’t pay more than $250, because you should be able to find one for that price.

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Now here’s the first kernel of wisdom. Make sure to verify the list number on the airhorn. It needs to be 90670-2. See Figure 1 to find the list number. The serial is the key. If it is a old or no dash number, run away. Those versions had some sort of factory flaw that causes the infamous off-idle stumble and you’ll never get rid of it.

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The good news is that even if you already have a old or older version, all is not lost. Holley has been very good about replacing these older versions with the newest serial version. There are some observable differences between the carburetors, so I do believe there are some fundamental design changes.

You need to contact Holley and explain your problems, and they will swap out carburetors for the cost of you shipping them your carburetor. That is based on all the cases I’ve heard of from others.

When I swapped mine I didn’t need any type of proof of purchase, but I have heard from others lately that they are asking for a copy of the sales receipt, so beware. It was a great deal for me because I got a new carb for $250+shipping twice.

Now I know that Holley advertises all over the place the TA is a bolt and go carburetor. It has not been my experience that this is indeed true. I’ve only read a few instances where this is the case, and I don’t think any of these people were installing the carburetor on full size Chevy trucks with 350s.

All of the information I’m about to share is based on my experiences installing a 670cfm Truck Avenger on a rebuilt 350 with a mild cam in a full-body K5. Your results may vary some, but I think it will still provide a good basis for most CK5 trucks.

My primary source of information has been a website called www.thirdgen.org. There is a lot of information about GM engines related to tuning, carburetors, and fuel injection. I’ve never posted on the forum because I’ve found the answers to all my questions through searching. I will try to link some pertinent threads throughout this post.

It seems that there are some common tuning measures for Holley carburetors on 350s. Basically they seem to work best with a .035 accelerator pump discharge nozzle and Blue accelerator pump cam in the #2 hole. I’ll give a little detail on each of these items.

Refer to Figure 2 for what the accelerator pump discharge nozzles look like. They are sometimes referred to as squirters.

Figure 3 shows how the nozzles are installed/removed. It’s pretty self-explanatory; the only trick is to not loose the bottom washer. It’s not a huge issue as long as the primary butterflies are closed but just don’t let the washer fall own into the manifold. If it does, you gotta fish it out. I’ve had success using Vasoline to hold it on. The nozzles just barely fit between the choke butterflies and the airhorn. I use my pinkies to lift it in and out.

You can tune the nozzles by watching the exhaust. Increase size until you get black smoke out the exhaust when you punch the throttle. Then drop down one size. My exhaust is too short to see the discharge smoke, so I just went with the .035 nozzle and left it alone.

The next trick is to replace the accelerator pump cam. They are available in a kit, part number 20-12 pictured below.

The accelerator pump cams are sized by color lightest to heaviest shot as follows: White, Blue, Red, Orange, Black, Green, Pink and Brown. The other thing to take into account is the profile of the cam. From the research I’ve done, it seems that 350s like a heavy initial shot from the accelerator pump.

The searching I did on thirdgen.org recommended a blue cam in the #2 hole. That is what I did, and it works just fine.

In the picture below, note where the arrow is pointing and you will see there is a counter-sunk screw head. In the picture the screw is in the #1 hole. Below this hole you can see another open hole, it is the #2 hole.

On the blue pump cam and most of the other pump cams there are two holes and they correspond to the holes on the throttle lever. Top hole is #1 and the bottom hole is #2. So to install the blue cam in the #2 hole you put the screw through the bottom hole on both the throttle lever and pump cam.

After doing this you need to verify that the override spring is adjusted properly. Make sure that the pump lever to pump cam clearance is set correctly. Some people misinterpret the .015″ clearance figure specified by Holley. There must be a minimum of .015″ extra travel at WOT available to the pump diaphragm.

At idle there should be Zero clearance between the pump cam and the pump accelerator linkage arm. Any free play at this point can cause a hesitation even with the correct cam and shooter installed. I always add 1\2 to 1 turn preload to the pump spring after adjusting to zero clearance. Seems to help sharpen the pump shot. Pump shot should be immediate and sharp with the slightest movement of the throttle. Dribbling is an indication of a problem.

The only other adjustment I made was jetting down for altitude. Holley recommends 1 size for every 2,000ft change in elevation.

I have found that the idle setting can play a role in the off-idle hesitation. I was running my idle kinda high, about 700RPM in drive, after changing the pump cam. I still had a hesitation. I’ve dropped the idle down to 550RPM, and that was the final adjustment needed to eliminated and hesitation. I believe this is because the lower idle allows the pump cam to ramp up more to get that big initial shot.

Don’t think that what I’ve post above is guaranteed to work your truck, it is just what I’ve found to work for me. Hopefully at the very least it will give you a good starting point.

These are some helpful threads from thirdgen.org, which is basically where I found most of the stuff that I did. Pay special attention to posts by Chickenman35; he knows his stuff.






So how does the Truck Avenger perform on the trail? It’s worked great for me so far. I’ve only had it stall once and it started right back up. The following obstacle is where the carb stalled:

I’ve done other obstacles with no issues:

Winter of 2006, I flopped the truck on its side into a creek bed. It was actually still sputtering a little sitting on its side. I don’t think it would have actually ran long, but I did have to shut the key off. Once we got the truck on all fours sitting on that bank, I was able to reach in and it started right up. I drove the truck up the bank with assist from a winch.

I’m not claiming the Truck Avenger is better or even as good as fuel injection. But for those not ready to make that leap, I feel the Truck Avenger is an excellent option. For me personally, it is much easier to tune than a quadrajet.

Hope this helps some of you fellow wheelers.

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