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Truck Avenger tuning tips????

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jtl_77

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Truck Avenger tuning tips????**update**

I installed my new holley truck avenger yesterday and have a few ??
It started and idled fine but when easing into the gas like a normal take off it has a bog in it. If I give it a little more gas it will clear up.

Is that the air/fuel mixture adj.? If so is it a lean or rich bog?

Also with the 600 cfm holley my clear in line fuel filter always stayed full of gas with just a small bubble of air in it. Now with the 770cfm truck avenger the filter will fill up when first started but after it runs for a while I can watch the fuel level drop in the filter until there is barely any gas in it. and it looks like there is hardly any gas getting pumped into it. The truck does'nt die and it will drive down the road but it has the above bog in it.
I have never experinced(sp?) vapor lock before. Is that what this sounds like?

It has a 454 in it. The cam is a little bigger than stock but not huge. The rest of the motor is pretty much stock.
 
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I'm feeling a similar bog on my new holley 600 matched to a 350 and Edelbrock Performer Manifold... never happened before with the 327, but when I'm at idle and let the clutch out enough to grab the tranny, it bogs down big time. My timing is set at 16 degrees, and once I give it a little gas, it winds up and gets a move on.. I have not experienced this problem in any other gear except in Low and first, likely because I never get down to idle speeds with 2 and 3...
 
I would try the springs for the secondarys, sounds like the secondarys are coming on to fast. You can buy a spring kit from your local parts place.
 
You might need to change the discharge pump nozzles for something larger, or (try this 1st) change settings on the accelerator pump cam. It has several different mounting hole that change the timing on the spray, they also have several cams available as well. You can do a web search on Holley tuning for more ideas. Good luck :)
 
What he said. I was having a similar problem with my Edelbrock. I know they are very different from one another, but all carbs work pretty much the same. Mine was due to a DRY accelerator pump. It wasn't shooting any gas when the engine comes off of idle. Instant bog. Check that first
 
I have a truck avenger 770 on my truck. Change the pump cam and your problem will most likely go away. If not you might have to step up the discharge nozzles too. I think the yellow cam is the one that most people use.
 
Thanks for the ideas so far. I had done some searching on the truck avengers before I bought it and knew it was going to take some tuning to get right. I guess I was just hoping the a\f screws and maybe a spring change would get it.
Another ? Should the fuel line from the filter to the carb be under any pressure? After it runs for a while if I take the fuel line off it sounds like a shook up soda bottle opening.
 
*update*

After trying to get through to Holley tech all day yesterday. I finally got through first thing this morning.
Told him about the bog problem and he said the 770cfm is made for high performence motors and with mine being close to stock it would'nt work right. So he said box it up and send it to them and he would replace it with a new 670cfm!!
I just wish they had it spelled out better when buying.
 
I did the same thing. Bought a 770 and it would run fine until the secondaries opened the it fell on its face. I now have the 670 and it runs great. I had a 750 double pumper at one time on the same motor and it ran fine. When I talked to the holley tech I asked him about why it ran with the 750 but not the 770 avenger and he said they were completely different, like comparing apples to oranges I guess.
 
Since you have a 454, I don't think going to the 670 will solve the problem with a bog off idle. It may get worse. But don't worry , you can easily solve it. Changing the Acc pump cam is the right place to start as mentioned above. I ended up changed my nozzles to a couple sizes bigger after I had a bog and it was completely eliminated ;) .
 
Why do you think the 670cfm will still have the bog?
Is the bog a lean or rich bog?
 
i don't think the smaller carb will cure the problem since a 770 cfm carb is just about the smallest i would run on a 454 cid motor.
i feel a little tuning is in order as is with any carburetor you install on a stock or modified engine.
The part throttle stumble you are experiencing is caused by a incorrect power valve.
When idling in drive while stopped you should hook up a vacuum gauge to the manifold and install a power valve that is at least 2 sizes smaller than the lowest reading you obtained on manifold pressure (vacuum).
Once that is corrected then you can disconnect the secondaries and begin tuning the primary jets for optimum fuel/air mixture.
The discharge nozzles which were mentioned earlier and later can be changed but i doubt that will correct the problem (just my opinion)
Holley makes 2 versions of each size power valve: high-flow and standard flow), make sure you get the standard flow power valve.
That carb is probably jetted a touch on the lean side so do some plug readings and adjust accordingly.
a jet kit from Summit cost about $40.oo and gives you a wide range of jets to choose from.
Don't call the ball on that 770 yet and try to work the bugs b4 swapping out for the smaller 670 cfm mixer.
 
I'm just going by my experience with this (and most) carbs out of the box. Seems most are set for stock engines on the low end of the displacement / performance scale.

According to Holley, the 670 is build for small blocks and mild big blocks and the 770 is for more performance oriented engines. I have a 670cfm Truck Avenger on a 350 ZZ4 which is a moderately built performance engine. It had significant under fueling which was corrected by the nozzle size increase. I suspect even a stock 454 will need more fuel than the stock 670 settings.

I was assuming that the 770 was also not giving enough fuel so going smaller to a 670 might be even worse. It is true that you may have the opposite problem ( rich) but I have never personally had a carb too rich out of the box. I have not checked the nozzle size on the 770 so I don't know how the size would compare to the 670.

The real difference with the 770 vs 670 should come when the secondaries open and not so much at off idle.
Jeff
 
Mad-Dog said:
The part throttle stumble you are experiencing is caused by a incorrect power valve.
Click to expand...

Bingo!

The accelerator pump only gives you extra fuel for a second when you open the throtel plates. After that second the vacume has droped enough to start pulling from the valve and the primary jets.

Basicly the idel adjustment screws work when your throtel plates are closed.

Then when you open them the pirmary jets are added in.

Under low load (going up a slight grade on the highway) the power valve is added in.

Finaly you can apply enough throtel that your secondarys will kick in and add more in.


Personaly I would be worry of the big avenger. It was never ment for stock type motors just like the guy from holley said. Even the 600 has problems on small block motors.
 
When I talked to Holley he asked what motor I had and I told him small chevy, he said 670. Whether it was a high performance or bone stock the 770 was to big. He said the difference is in the metering and something about the velocity of the air being brought in not how much fuel it was dumping. But this was when the secondaries where kicking in , I'm not sure about at idle.
 
I'm confused here...u told holley that u had a SBC and u told us u have a BBC.........which is it...?
 
Sorry, I went back and read my reply and..... well I'm running a 400 sbc semi built, mainly heads a little cam.
 
Ok, I'm going to recommend you stay with the 670 cfm unit and rejet accordingly.
Go back to my reply on tuning and start there.....any questions, gimme a shout.
good luck bro....
 
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