Holley truck avenger questions

[k5blazerguy]

I just bought a truck avenger from a guy in hopes to cure the problem off-roading I had with my edelbrock. I’ve had my edelbrock a lot of years and has always ran great. I’m new to the holley carbs, been researching a lot to learn how to properly tune them. Adjusted the float bowls and set the mixture needles. It idles about 1000 and that’s with idle screw backed all the way out. I’m gonna spray carb cleaner to see if I have a vacuum leak.
I’m at 6-7000 ft. I have the standard 68 front jets and 89 rear....I am goin to try 65s in front, do I need to replace rear jets too? To 86s? I’ve found a lot of articles on here and online but not certain if all jets need to be replaced or just main ones.
I will also get a cam kit as others had recommended using the blue one?

 

[USSkoval]

Something else is going on. Decreasing your jet size won't lower your base idle.

 

[diesel4me]

My guess is the Holley's base doesn't jive well with the intake or spacer under it and air is sneaking by ,a vacuum leak will make it idle faster and sometimes "stutter" instead of running smoothly..

I've had maybe a dozen Holley carbs over my lifetime and only about 4 of them worked well,the rest were always a pain,they would flood for no reason,a spit back on a cold morning would take out the power valve,they needed frequent adjustments and I had to but different accelerator pump springs and a cam to get it to not have a hesitation--one caught fire after a backfire and I was lucky the truck didn't burn!..

I went with Carter AFB's and Edelbrocks ,and Q-jets and didn't have hardly any problems, and they didn't need to be fooled with,they just ran good ..the Holley's did seem to make more power once you got them dialed in,but I never had good luck with most of them...

 

[k5blazerguy]

My guess is the Holley's base doesn't jive well with the intake or spacer under it and air is sneaking by ,a vacuum leak will make it idle faster and sometimes "stutter" instead of running smoothly..

I've had maybe a dozen Holley carbs over my lifetime and only about 4 of them worked well,the rest were always a pain,they would flood for no reason,a spit back on a cold morning would take out the power valve,they needed frequent adjustments and I had to but different accelerator pump springs and a cam to get it to not have a hesitation--one caught fire after a backfire and I was lucky the truck didn't burn!..

I went with Carter AFB's and Edelbrocks ,and Q-jets and didn't have hardly any problems, and they didn't need to be fooled with,they just ran good ..the Holley's did seem to make more power once you got them dialed in,but I never had good luck with most of them...

Yeah I have definitely noticed a power gain with the holley over the edelbrock. And I agree, I can just set the edelbrock and not mess with again........I sprayed carb cleaner around everything around the carb and hoses, and the only thing that made idle change was around PCV valve. It wasn’t very tight in the grommet. But still high idle after messing with it, it’s a new PCV valve. If I plug the PCV idle drops a little. I can force the Throttle linkage forward just a bit and hear rpm drop a little, but if I were to tighten that spring enough I may not be able to use gas pedal. Lol. It just won’t get below 1000. If there were a leak at the baseplate then carb cleaner would affect it right? I may do it again tomorrow just to be sure.
I had an idle surge for a bit today and reset the mixture screws. Seemed to help hasnt done it again. This carb is definitely a pain over the edelbrock and have been doin lots of research to learn about it. Im not an expert on carbs, but I’m sure I will be after I figure this damn thing out. I’m not gonna let it defeat me! Haha.
I just wanted it for the off-road capabilities,....I ordered a rebuild kit and offroad kit for the edelbrock a few weeks ago, but came across this deal and decided to try truck avenger over rebuilding the edelbrock.
im pretty happy to get more power out of my 305. That part has been nice. Pros and Cons I guess.
The other problem I have is when I’m driving up a hill and rpms get low, maybe around 1200-1400 rpms, it starts sputtering and not happy. I’ve read to change to the blue cam, so ordered those and hoping that helps. So while jets and cams come in I need to figure out this idle situation which I’m assuming is an air leak somewhere.

 

[diesel4me]

I'm not familiar with the truck avenger or any Holley's built after the 20th century,but I did a few google searches and came up with this thread with similar symptoms as yours..

.Holley street avenger won't idle down - Third Generation F-Body Message Boards

The other issue may be a power valve problem,if that carb has one...could be a vacuum leak too...if you have a vacuum advance distributor,where is its hose connected too,manifold or ported vacuum ?..
I read carbs built after 1992 had a check valve to prevent the power valve from being ruined by a backfire,most likely yours is newer than that..

 

[k5blazerguy]

I'm not familiar with the truck avenger or any Holley's built after the 20th century,but I did a few google searches and came up with this thread with similar symptoms as yours..

.Holley street avenger won't idle down - Third Generation F-Body Message Boards

The other issue may be a power valve problem,if that carb has one...could be a vacuum leak too...if you have a vacuum advance distributor,where is its hose connected too,manifold or ported vacuum ?..
I read carbs built after 1992 had a check valve to prevent the power valve from being ruined by a backfire,most likely yours is newer than that..

Vacuum is connected to ported I think? It’s the one higher up on the carb. Not the one down by the PCV vacuum. It’s what was recommended to connect to.

 

[diesel4me]

Might try using manifold vacuum and see if that helps--first set the timing with the advance hose off and plugged ,if your truck has a ECM you'll have to use the right procedure,I think there is a brown wire you must unplug first (others here know way more about computerized trucks than I do..)...I'm only familiar with HEI 4 prong module distributors and points ..

The combination of ported vacuum and possible base timing being advanced might create the sputtering issue,it might be losing enough vacuum under a load to retard the timing,or make it erratic ...could be its jetted a tad too lean too,but I'd check the basics first..usually you can "read" the spark plugs after its been driven some and tell if its running rich or lean..

 

[Wes Harden]

Always need to snug up the bowls on holley's, they loosen up and allow gas and vacuum to seep by

 

[k5blazerguy]

Might try using manifold vacuum and see if that helps--first set the timing with the advance hose off and plugged ,if your truck has a ECM you'll have to use the right procedure,I think there is a brown wire you must unplug first (others here know way more about computerized trucks than I do..)...I'm only familiar with HEI 4 prong module distributors and points ..

The combination of ported vacuum and possible base timing being advanced might create the sputtering issue,it might be losing enough vacuum under a load to retard the timing,or make it erratic ...could be its jetted a tad too lean too,but I'd check the basics first..usually you can "read" the spark plugs after its been driven some and tell if its running rich or lean..

I swapped distributor vacuum to port on bottom and also learned there is a fast idle screw. lol. Backed it off a few turns.
Truck warmed up and drove around. Between both fixes, Low rpm sputter seemed to almost go away. And idle came down to 600,....shut truck off and went fishing. Came back and idle was high again. Just drove around and it seemed to go back down. Maybe I need to loosen fast idle screw little more? Is it high because of temperature and goes down when warms up? Thanks for all the help

 

[diesel4me]

When the choke closes ,the idle speed usually goes up on most carbs,they have a fast idle cam with "steps"the fast idle screw bears up against-- that keeps the idle higher until it warms up,as the choke gradually opens, the fast idle screw will go down a notch or step on the cam, and the idle gets progressively lower until the curb idle screw is the only one setting the idle speed, by opening the throttle butterflies just enough to attain the desired idle speed after its fully warmed up..

Usually the fast idle speed is set with the engine cold right after a cold start,after that it should be within the correct range not to affect the curb idle speed after it warms up to operating temperature..

If the secondary throttle butterflies fail to close completely that will cause a fast idle all the time too--sometimes a base gasket will interfere with then being able to close fully,or an issue with the linkage can cause it too..

Another thing I forgot to mention is if you have an EGR valve,that can stick open slightly and cause much the same effect as a vacuum leak,only instead of sucking in "fresh" air,it will be sending exhaust gases into the intake, and at lower rpms the EGR is supposed to stay completely closed,until it reaches a certain rpm ("cruising speed" around 30-40 mph usually) when it opens and lets the exhaust gases get re-burned ...
This can cause the stuttering and hesitation also,if it opens at the wrong rpm ..if it fails to close all the way ,at idle, it may make the engine want to stall,some however end up with a constant fast idle instead,due to the un-burnt fuel being reintroduced to the cylinders--every engine reacts differently to vacuum leaks,and EGR "leaks" ..

I would make sure the base timing is set correctly to spec also,and check that first..manifold vacuum advances the timing at idle and that makes it idle faster..

 

[mrk5]

I ran a truck avenger for years in Colorado. Have to see if I can dig up my old notes.

You should reduce jet sizes on secondary side like you did primaries.

I really had to richen the accelerator pump circuit. I don't remember which cam I used, but it ramped up quicker. Also installed bigger pump nozzles.

I always run manifold vacuum on the distributor. Set base timing with it disconnected and plugged. 12° btdc if not higher. The engine I had the truck avenger on liked 16°. After timing is set, hook vacuum advance up again and check idle. It's possible you're having to open the primary too much to get idle up with vacuum advance on ported vac. Having too much transfer slot exposed causes a lot of issues.

Some carbs can have trouble with the secondaries getting stuck partially open. Also could just be the high idle for the choke. The carb in my C10 rarely kicks off high idle until I put it in gear and drive a bit. For whatever reason I can't blip the throttle to get it to come off. Maybe yours is similar.

The truck avenger worked pretty good for me offroad. Did lots of the more difficult Colorado trails with it.

 

[mrk5]

Added some more info to my post above about setting timing. In short you might have the primary blades open to far exposing too much of the transfer slot. This can cause carb tuning issues.

 

[k5blazerguy]

Thanks!
Went home and checked timing again, I had just double checked it a few weeks ago (right before I finished the drivetrain rebuild and took out of garage). I had it set to 12,.....checked it today and it was around 8? What the heck?. So I put it just below 12 notch and seems to like it there best. Then reset mixture screws.
So far seems to be doing a lot better today. Drove to baseball practice and came home. It did a little studder once, I was on the gas driving up hill and turned on my road....I’m thinking when the jets get replaced it may help? I have them on order. I have the factory 68s in front and 89s in rear. I ordered 65s and 86s. The guy I got the carb from lived in California when he had his blazer goin. I’m up around 6-7000 ft. But I may go wheelin anywhere from 5-8000

 

[mrk5]

Sometimes the timing will move a little when you tighten down the clamp. I've also messed up and forgot to tighten the clamp when I was done.

Jetting should help. I live at 5000ft so I've always just done 2 numbers down. The trails we run are 7,500ft-10,000ft and truck avenger always did fine. The only trouble I ever had with it was an off idle stumble. Knowing what I know now, I'm pretty sure I was too lean on the accelerator pump circuit.

 

[k5blazerguy]

Wanted to post an update in case someone also has issues.
Over last month been learning all about the holleys. They are a pain, but in my opinion, a better carb once you learn how it works. I seemed to have gained more power over my edelbrock and helped my 305 a lot. Feels like a 350 now.
First I set fuel bowl levels, then ordered new jets, went to 65 fronts and 86 rears, Ran better, but still had a bad stumble. If I hit the throttle too quick it fell on its face. Learned about the accelerator pump and Checked the clearance at wide open and set with .015 gauge. Made it a little better. But still had stumble. Finally got me a vacuum gauge to set the mixture instead of doing it by ear. Much easier!

Ordered pump cams after reading articles on here. Installed blue cam in position 1....2 made it worse. stumble wasnt as bad, but still there, would also stumble at low rpm under load. Ordered a 35 pump nozzle, not much of a change. So Decided to try the black cam.....stumble gone!! I had a tiny spit goin uphill, loosened accelerator pump spring one turn and so far so good! Running great and no stumble issues so far and very happy. I really love this carb over the edelbrock.....even after all the problems over last month, but I’m happy to have learned all about it and how it works. I got my front shaft connected and tested out some hills where i had stalled before with the edelbrock and the truck ran great! In appreciate everyone’s help.

 

[k5blazerguy]

Another update. I guess I spoke too soon, almost 2 months later and I’m still getting a stumble, I thought I had it but I didn’t!! I should have waited a few days before making my last post Lol I’ve been adjusting and changing settings since July and still can’t figure this out.....
Basically if the engine is below 1500 rpms while driving, and I mash the pedal it will cough and spit and fall on its face. After 1500 it’s great no problems. I have SM465 if that makes any difference. I’ve gotten used to driving my blazer like that and have adjusted to hills and such. But sucks when you pull into traffic and drop the clutch too fast and it stumbles.
I drive it almost daily and I have spent days adjusting, Driving, then adjusting something else. I’ve tried blue, white, green, pink, orange, and black cams all in slots 1 and 2. I like the response of my throttle better with green cam. But all just make for different pedal feel and stumble is there on all cams. Along with all cams, I have change the pump nozzle from factory 28 to 35, then ordered a 40...still same. Ordered a 25 thinking I was too big on the nozzle.....stumble still there just lost power with 25. Tried all cams with all nozzles. It’s gotta be something else. I changed my timing to 14.
I haven’t posted anything I was hoping to get it fixed before I made another post. I refuse to let this carb beat me. Just at a loss of what to try next. I’ve spent a lot in nozzles and cams already. Just wondering if anyone else has had this happen as well and figured it out? If it’s useful to help diagnose, if rpm is above 1500 I can stomp on the gas and works perfect, below 1500,........if I just barely press gas pedal it won’t stumble, but anything more chokes it out. Now this isn’t the truck running in neutral at a stand still, this is while I’m driving. That’s usually how I test to make sure if I fixed the problem I’ll get the truck to about 30-35 and put in 4th gear low rpms about 12-1400 and hit the gas and see it if it chokes.

 

[diesel4me]

It could be another issue besides the carb --if the coil was weak the spark may "blow out" under a heavy load or pull and cause a sputter,a pick up coil's wires can break inside and when the vacuum advance moves it to advance the timing it can cause a split second loss of contact and make it misfire--there's a ton of things besides the carb that can do it..but if it didn't do it with the edelbrock,then the carb is a prime suspect..

Just past idle is when the EGR valve usually opens some too--have you tried unplugging it and cap the hose off and go for a ride ?..

I've seen engines with an aftermarket aluminum intake with an "open plenum" cause issues like yours in street driving..they are more suited for racing,higher rpm uses...

 

[k5blazerguy]

It could be another issue besides the carb --if the coil was weak the spark may "blow out" under a heavy load or pull and cause a sputter,a pick up coil's wires can break inside and when the vacuum advance moves it to advance the timing it can cause a split second loss of contact and make it misfire--there's a ton of things besides the carb that can do it..but if it didn't do it with the edelbrock,then the carb is a prime suspect..

Just past idle is when the EGR valve usually opens some too--have you tried unplugging it and cap the hose off and go for a ride ?..

I've seen engines with an aftermarket aluminum intake with an "open plenum" cause issues like yours in street driving..they are more suited for racing,higher rpm uses...

I don’t think I have an EGR on my intake? Maybe I’m wrong ?

 

[mrk5]

I was never able to fully eliminate the stumble you describe in the Truck Avenger you have. I just got it to where it was barely there and easy to work around.

Green cam sounds right (it's been 8 years since I owned the K5 with that carb). I'm pretty sure I was at 37 on the nozzles. I also had my initial timing at 16 to 18 without the vacuum advance connected. The vacuum advance was connected to manifold vacuum. You could also see if you can fatten up the idle mixture a little to help.

I know the 350 in my C10 I have now likes a fat acceleration shot. Different carb on it tho.

 

[mrk5]

Does the part number stamped on the choke riser have a "-1" after it. That was the 2nd generation. The first generation apparently was nearly impossible to tune the stumble out of. At that time (like 10 or 12 years ago) if you and one of the 1st gen carbs you could send it in to Holley and they would send you the new version as a replacement. That was a really good deal for me, because I bought mine used and then ended up trading it in for brand new.