Holley Truck Avenger

I have purchased and installed the second carb on this page:
http://www.nationalcarburetors.com/performance/holley7.aspx

It is not a stock Truck Avenger, but it was custom built as a 600 cfm TA by National Carburetors and I've installed it on my 304. I have it running pretty good, but I'm having difficulty setting my fast idle and curb idle.

The electric choke is operating properly as far as closing on throttle depressing and opening as 12v hits the spring. Where I have the fast idle screw set now, it idles around 750 rpm on cold starts which is too low. As the engine warms, the idle increases. What I've found is when I increase fast idle setting, after the engine warms the curb idle wont go below 1000 rpm. I believe it to be a linkage issue, but I wanted to pick the brains of the experts here, even before contacting National Carburetors.

I have cleaned the linkage pivots with carb cleaner. My throttle return springs are new, but its kind of like they don't have enough tension. I can't see any binding.

Any suggestions or pointers are welcome.

Thanks.

Merry Christmas and Happy Holidays!

 

The 304 had a CTO that might be messing up your vac signal. Make sure that's connected/functioning properly first before you go on a wild goose chase.

 

I didn't mention I'm running an Edelbrock non-EGR intake, and I didn't reinstall the CTO. My only vacuum lines are the PCV (carb to PCV valve) and the vacuum advance (carb to distributor). The vacuum advance line is installed on the port that Holley says to connect to: passenger side near sight glass screw. All other vacuum ports are capped.

Back before my resto, I had no functioning CTO (lines capped and only had line going from carb to distributor) and it ran good with the MC2100 and stock intake. The carb needed a rebuild and EGR system was clogged, and I wanted to make this change. That got me to the Holley/Edelbrock intake setup I have now.

 

The fast idle screw on a Holley is behind the choke housing (almost impossible to get to with the carb installed!)
As soon as the choke comes off, the fast idle cam (red plactic arm behind the choke) should drop down, and the regular idle speed screw comes into play.

 

The fast idle screw is difficult to reach, but it takes some weird maneuvers to get at it. I have found it works best to pull back on the throttle while a 12-point box-end 1/4" wrench is setting under the screw head, drop the screw into the box-end, then turn, let off the throttle and repeat. It is impossible to reach at WOT although any instructions say turn screw at WOT.

But, back to my original post, I have screwed in the fast idle screw until my jeep idles on cold start around 750. When it warms, the rpms increase to 1000 and the fast idle cam drops like normal and the choke opens. I have searched for vacuum leaks and none I see. The curb idle screw is let all the way out. If I pull forward on the throttle, the rpms will drop to 800-900.

 

There was the smallest cotter pin I had ever seen on the choke blade linkage and it was hanging it up causing the choke not to work right. I took the pin out because I figure it was just a shipping thing.

Tweaking here and there, I finally got the jeep to warm up on fast idle around 1200 and die down at the blip of the throttle to 7-800. But it was still not smooth. Since I had been messing with the air mixture screws, I ran them both in to see how many turns they were out. One was about 2.5 out and one was closer to 3 turns out. I ran them both back out to about 2.5 turns, cranked it, and the jeep now stumbles like crazy. I had to mess with the screws and run the curb idle way up to keep it running. I got tired of being smoked from the rough running, so I just got frustrated and came in. Carbs for Dummies, anyone?

 

I guess I'll start over using this info. It says start out with mixture screws only out 1-1/4 turns http://www.junkyardgenius.com/holley/tune01.html

 

Turns out my primary metering block is flooding so I adjusted the fuel level down and got it to run much smoother. However, I'll have to adjust the float down more because fuel gushes out the site plug and the adjustment nut. I came in to do some more research on how to do it. Odd how this just started and things were running fine until the jeep ran out of gas (other thread). But, the jeep ran fine on the way home from the gas station too. Weird stuff, at least to me.

 

What would keep making this thing pour fuel out of the sight plug holes when I'm checking. I readjusted the floats yesterday. Cranked it today and ran great for a few minutes. All of a sudden it started stumbling. Checked the sight plugs and gas poured out. Fuel pressure was steady at 5-7 today and not jumping up to 9-10 when flooding occurred before. I could sense maybe pinholes in a float, but both???

 

If gas is pouring out of the sight plugs, you're getting too much fuel. Float set WAY too high,
bad float, bad needle & seat, or debris in the needle & seat. One thing people often miss on
Holleys is the o-ring around the needle & seat-make sure it's not damaged, and lube it with a
little WD when you install the needle/seat assembly.

 

If any of that is what I have wrong, I have nothing good to say about the company I bought this carb from. This carb was supposed to have been built and fully gone over...when a novice like me gets to play with something as inconsistent as this thing has been, it makes me more confused

 

With my pressure increases, it would seem I would have a clogged or sticking needle(s), hmmm?

 

Simple tests you can try.

With the engine warm and the choke pulled off completely, you should be able to stall the engine by backing out the idle stop screw. The throttle plates should close completely and suffocate the engine. If not, you have something like the fast idle stop or your linkage holding the throttle plates open.

Next, you should be able to stall the engine by leaning out the idle via the idle mixtruere screws. If you cannot stall the engine at idle with the idle mixture screws, then you are not running on the carb's idle circuit. This could be because the idle is s high that the main circuit has taken over, or becasue you have gas coming from another source besides the idle circuit. At 1000 RPM, the idle transfer should be underway, and both the idle and main circuit contributing fuel. At 700-800 it should be all idle circuit, choked or not.

 

I gave up on the custom 600 "truck avenger" from National Carb, bit the bullet and bought a new 470 Truck Avenger. So far, so good. A little choke adjustment, float adjustment, and high idle decrease, and it starts and runs perfectly. One press of the accelerator to set the choke and squirt a little gas, and it fires right off. No pumping required to start it, and it idles perfectly.

I'll probably be posting that 600 in the classifieds soon. I just got tired of everything to seem to go wrong and I'm not experienced enough to troubleshoot properly.

 

You're money ahead with the 470. I'm running it on a Buick 300 and it performs quite well. As the carb ages, you will occasionally have to tap on the float bowls to unstick the needles if it sits for long periods of, say, a few weeks or more.