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Old 08-09-2006, 02:27 PM
78 Arizona Chief 78 Arizona Chief is offline
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Truck Avenger tuning tips?

Everyone,
I recently finished installing my S&S motor. I had the Holley Truck Avenger on the old motor and it ran fine. The new motor has a little higher compression and a different cam, and the carb need tuning. Bear in mind that I live in the Phoenix Valley, and the air is hot and thin.

Anyway, I had a steady stream of black smoke coming from the tail pipe when cruising down the road. I reduced the size of the primary jet from the factory 68, to a 65. The smoke is now gone and the car feels better. However, when I hit the gas fairly hard from a stop, the truck hesitates really bad, sometimes throws a small backfire through the carb, and then takes off. This I assume is the accelorator pump. My question is, for those of you with a Truck Avenger, which position do you have the acc. pump on, 1 or 2? Secondly, did you change to a different accelorator pump cam? When the truck heisitates, there isn't a black puff that comes out the tailpipe, so I know it isn't too rich of a shot. Do I need to try a different accelorator pump all together?

Finally this weekend I put enough miles on the jeep to feel comfotable taking the truck into higher rpm ranges. My base initial timing is 12-13 degerees BTDC, and the Z&M HEI dizzy puts approximately 16-17 degrees of mechanical advance for a total of about 29 degrees. What I noticed, is that the truck pulls nice and smooth through second gear until I hit about 65 mph (Second will go just past 70). At that speed, the truck surges and can not accelerate any faster until I shift into third. It feels like it hits a speed limiter and just kind of bucks and surges until the rpms drop down in third. I was always told that surging is a sign of a lean mixture, however, I have also read that the 89 secondaries are too large. For the record, I have never hear this engine ping yet, and it runs nice and cool out here in AZ 100 degree nights. What should I be looking at to solve the surging problem?

Thanks for any insite.
Kevin.
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Old 08-09-2006, 02:53 PM
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PlasticBoob PlasticBoob is offline
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Can you please post more info about the engine and cam? And is this a 670 or 770cfm Truck Avenger? I had some initial problems (off-idle stumble I couldn't get rid of) because I bought a 770cfm. Holley traded me a 670cfm (model 2) and things are perfect. i think 68 is good for the primaries. I am using the stock acc. pump and cam and have no problems...however, do look into changing the acc. pump discharge nozzle, that might help. As for the surging, how are your float levels?
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Old 08-09-2006, 03:08 PM
78 Arizona Chief 78 Arizona Chief is offline
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PlasticBoob,
Thanks for the reply, the carb is the 670 cfm version. As for the motor, it is a 360 .030 over with 9.0-1 hypereutectic pistons. The cam is an Elgin RV cam, and the heads are studded with Comp Cams chromoly roller rockers. Performer intake manifold. Floats are set a little below the site plugs, maybe 1/8 of an inch below site plug. Power valve is the stock 65 and I checked it last night when I changed the jets, and it is not blown.

It is funny, the truck seems to run better for the first 1/2 hour or so. Once it has been on the freeway, off back in traffic, the power does not feel as good. When I shut off the truck, it occasionally will 'diesel' once. Regarding the jet size, I have taken the truck back to Manhattan Beach to visit my parents, and the truck definitly runs much better at sea level at 60 degrees.

Thanks in advance for any other advice or input.
Kevin.
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Old 08-09-2006, 03:17 PM
Ristow Ristow is offline
 
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many of the truck avengers have a 2.5 power valve-which is for a very lopey cam-if you're running a milder cam you need a 6.5-8.5 power valve.

look on the choke horn,if it has a -2 after the list number(09670-2)it has the 2.5 p/v,it needs to be changed,that will cure your stumble and restore acceleration power.
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  #5  
Old 08-09-2006, 03:24 PM
78 Arizona Chief 78 Arizona Chief is offline
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Ristow,
I had searched through all the previous truck avenger tuning threads and that was the first thing I checked. My instructions said that it had the 6.5 (65) power valve, and I verified that last night when I changed the primary jets. In the previous threads, people had gone down to a 82 secondary jet. I would do that, however, the wide-open throttle surging at high rpms indicates a lean condition so I have been told. However, I drive the jeep up to Big Bear Lake in Cali every year, and once I get up into the altitude, the truck would surge as well at half to full throttle regardless of rpms. I would definitely figure the truck is running very rich up there.

Thanks for the replies.
Kevin.
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  #6  
Old 08-09-2006, 05:21 PM
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JeepsAndGuns JeepsAndGuns is offline
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Are you sure its a problem with the carb and not with the fuel supply? When your flooring it and doing those long hard pulls, it may be sucking the fuel out of the bowls faster than the pump can fill them back up. When I re jetted mine I would drop both jets (main, and 2nd) the same number. I ended up useing 65pri and 86sec to keep my 401 from running rich. Check your plugs, the can tell you a lot about a engine. If they are white, your too lean, black, your too rich, you want a nice brown color to them. That means its running right.
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Old 08-09-2006, 05:43 PM
78 Arizona Chief 78 Arizona Chief is offline
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JeepsAndGuns,
Thanks for the reply. I am running a Holley Red electic fuel pump. The Fuel filter with the return is down on the frame near the power steering box. This kept the number of fuel lines going to the engine to a minimum. It worked fine with the last motor. I did change that filter to rule it out. What would be a good way to check and see if the bowls were going empty? I am hesitant to say that is it because as soon as it shifts into third gear the problem is gone. The tranny has a shift kit in it and it shifts fast. I would imagine if the bowls were getting sucked dry, it would take a second or two to recover the two bowls and I would feel a little bit of hesitation once it was in third. But as soon as it hits third, it pulls hard again. I am thinking I will end up taking down to a shop called Automotive Diagnostic specialties where they can Dyno tune it with a 4-gas anylizer. There is a guy there that is very good with carbs. When I talked to him, he had mentioned that we could also try a 2-staged power valve as well.

From what I gather, the vacuum advance is not operational at wide open throttle. So I don't think that my 29 degrees total advance is too much. I think once the jeep cools down today after work I will pull plugs to check, and will most likely take the secondary jet to 86 as well.

Thanks again for the replies.
Kevin.
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\'78 Cherokee Chief - 360/TH400/QT Front high pinion 44/ARB/4.10-1, Rear 44/ARB/4.10-1, SOA w/Alcan front springs, Alcan full-leaf (w/shackle eye flipped) rears, custom bumpers, Multi-mount Warn XD9000i, more money into her than I want to admit. Dad purhcased new, still have window sticker. 310,000 miles.
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  #8  
Old 08-10-2006, 04:37 PM
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JeepsAndGuns JeepsAndGuns is offline
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That pump should be able to keep up. Its probably something else, I just remember hearing about the bowls running dry with a slow pump. Let us know what ya find out.
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79 Cherokee Chief 401/T18/D20, MPFI fuel injection, hydroboost, otherwise stock.
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93 Wrangler 4.0L/AX15/NP231,SYE,CV, OME 2.5 lift, WJ knuckles and brakes, 31X10.50's Warn M10000 winch.
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  #9  
Old 08-10-2006, 05:19 PM
78 Arizona Chief 78 Arizona Chief is offline
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JeepsAndGuns,
I have been searching the internet reading as much as I can. It sounds like I will be increasing the pump discharge nozzle size. After that and decreasing the secondaries to 86 or so, I will drive it again. I need to first cure the off-idle stumble, and then I will look into the high rpm surging.

Has anyone else changed their pump discharge nozzle or even the size of the accelerator pump? and if so what sizes did you use?

Anyway, thanks for your suggestions... keep them coming.

Kevin.
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\'78 Cherokee Chief - 360/TH400/QT Front high pinion 44/ARB/4.10-1, Rear 44/ARB/4.10-1, SOA w/Alcan front springs, Alcan full-leaf (w/shackle eye flipped) rears, custom bumpers, Multi-mount Warn XD9000i, more money into her than I want to admit. Dad purhcased new, still have window sticker. 310,000 miles.
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  #10  
Old 08-10-2006, 05:37 PM
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Josh D Josh D is offline
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I'm out in AZ right now in the GW. I'm running 64 primary and 68 secondary with a 6.5 PV on a stock 360. It's running great! I love the added power from dropping 4K foot of elevation. It was pinging pretty good when I first got here (initially I had my advance at 16*). I backed it off a bit, but I don't have my timing light here, so don't really know where I'm at. But, it's running really well. I'm probably a bit lean on the secondaries, but 89 is way, way too rich for a 360.
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Old 08-10-2006, 05:54 PM
Ralph Rogers Ralph Rogers is offline
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So where are you at, Josh?
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  #12  
Old 08-10-2006, 09:00 PM
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J10-401 J10-401 is offline
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Are you sure the secondaries are even opening? Could be linkage bind or something rubbing on the vacuum plunger. IIRC they have a lock that blocks the secondaries from opening until the choke is full off. I always take stuff like that off. I'm not that stupid that I would buzz a stone-cold motor anyhow.
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Old 08-17-2006, 08:40 PM
Bob Barry Bob Barry is offline
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Quote:
Originally Posted by 78 Arizona Chief
JeepsAndGuns,
I have been searching the internet reading as much as I can. It sounds like I will be increasing the pump discharge nozzle size. After that and decreasing the secondaries to 86 or so, I will drive it again. I need to first cure the off-idle stumble, and then I will look into the high rpm surging.

Has anyone else changed their pump discharge nozzle or even the size of the accelerator pump? and if so what sizes did you use?

Anyway, thanks for your suggestions... keep them coming.

Kevin.

AMC's like a lot of initial advance to avoid stumbling; lighter centrifugal advance springs can help in that department, as long as they don't make it ping.

I ran into ping on my 360 when using a Holley 600cfm carb, so I upped the squirter size from a stock #25 to a #37, and I went with a blue pump-cam on the #2 screw setting. You may not need to go that extreme. That eliminated all bog for me, though.
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Old 08-17-2006, 10:13 PM
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J10-401 J10-401 is offline
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"AMC's like a lot of initial advance to avoid stumbling; lighter centrifugal advance springs can help in that department, as long as they don't make it ping."

I learned that as a lad with my new AMC '68 AMX 390. After a Group-19 cam-kit, R4B Edelbrock intake, Holley 3310 carb and Hooker headers, it liked tons of advance and a big 50-cc accel-pump shot to be happy (good for 12's with crappy tires). But back then you could get 100-octance Chevron pump gas! And for 38-cents. God, I miss those days!
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Last edited by J10-401 : 08-17-2006 at 10:15 PM.
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Old 10-09-2006, 07:32 PM
crawler16 crawler16 is offline
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I tried just about every ones tips and i just couldn't get rid of that stumble. When i had my new gears installed(3.54 to 4.56) the stumble went away. Once in while i get a slight hesitation but no more stumble and back fire. Hope this was some help.
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Old 10-09-2006, 07:47 PM
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funwheeling funwheeling is offline
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This is some real good information. Currently getting the same issue:
Holley TA 670
Compcam 260H
Edlebrock shorties
Performer intake
msd offroad
billet dizzy and blaster coil.

Went down to a 64 primary. Did not change secondaries. Didn't know about the secondary blocks (need to check my choke). Change the power valve to 6.5. I am at about 7 degrees on the timing will up that a little tomorrow.

Will be following this thread intently.
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Old 10-09-2006, 07:59 PM
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my 2j20's my 2j20's is offline
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Truck Averngertuning tips?

What it has #1 on the choke horn
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  #18  
Old 10-10-2006, 07:19 AM
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Ok earlyier you said it runs better but after awhile it seems to run more sluggish I would check the fuel pressure while running I had a holley blue on my 1985 Rx7 when I did a holley 600cfm carb conversion and the fuel pump gave me all kinds of problems I hated it I wanted to toss the pump in the trash it would start off with 6psi and after like 20-30 mins it would drop down to 3 psi at idle and at wide open throttle the float bowls would go dry I hated that pump and swore I would never go back to holley pumps
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Old 10-10-2006, 11:38 AM
bluesman2a bluesman2a is offline
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OK, I've been running into some of the same stuff on my M-715, GREAT tech here, I have a little more to add to the pot...

After a bit of reasearch I was able to determine that there is problem with the Truck Avenger Gen-1 carbs. The issue is an off-idle stumble and other assorted tuning problems.

The Gen-1 Truck Avengers (part number 90670-1) had a couple of design problems. While Holley did not have a general recall on them, if you call and talk to them, tell them you are having problems, they will swap you the updated 90670-2 free of charge.

You can reach Holley's tech support Monday through Friday, 8AM to 5PM CST @ 270 781-9741.
==========================

So I did that, and they sent me a newer model carb no questions asked (Gen-2, Identifiable by part number 90670-2).

My setup:
Specs:
Vehicle: Heavy *** M-715
Engine: 383 stroker with vortec heads and air-gap intake 9.5 to 1 compression
Cam:LIFT 486intake, 508 exhaust, DURATION @ .050 234 intake 244 exhaust
Carb base specs: Holley Truck Avenger 670CFM (Gen#2, so that's taken care of)
Ignition: MSD HEI distributor, with AC Delco plugs 41-932 gapped at
.045

Where we started (stock):
Stock Jetting: primary 68 secondary 89
pump: nozzle .028 30cc diaphragm orange cam
Power valve 2.5
Secondary spring: black

INITIAL PERFORMANCE:
The carb ran super rich right outta the box. Also had the flat spot everybody talks about at around 2500 RPM's. Per Spicergear's post, I checked the linkage on the accelerator pump and it was WAY off. Essentially it was running partially depressed all the time and probably responsible for fouling at least one set of plugs.

Adjusted linkage and flat spot cleared up, but coming off-idle, it'd still fall on its face, then pick up. If I blip the throttle sitting still it would sputter and die.

CHANGES:
Moved up to .035 squirter
Performance improved, again, but coming off-idle is still not great. Almost acceptable except pulling off from a dead stop.

CHANGES:
Moved up to 50cc diaphragm and .040 squirter.


I tested the 0.040 nozzle with the 50cc diaphragm. It was good, again a seat of the pants improvement, but had no acceleration on the top end, and a VERY slight stumble coming off-idle. I put in a lighter secondary spring so they kick in around 2.5-3 grand, and that smoothed out quite a bit.

Based on what I learned from Holley Tech support (not much help, but I was persistent): above 0.037 requires a 50cc diaphragm. You are also supposed to use the hollow screws with the larger nozzles.

Next steps: I didn't use the hollow screws (didn't know when I set it up) so I'll change those out. At this point I have at least addressed the symptoms. I'm not sure I've solved the problem. I'll put some more miles on it tomorrow and read the plugs. If it looks like they are running lean, I'll go up to a set of 70 main jets.
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Old 10-12-2006, 04:05 PM
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funwheeling funwheeling is offline
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Dumb questions. What's the choke horn? I don't see that called out on any of the illustrations.
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