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Old 01-30-2007, 10:08 AM
black thumb learner
 
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670 Truck Avenger Holley Qs

As if there aren't enough Holley questions on the board, right? I want to apologize first off for being mostly a lurker here, and not having much to contribute to this board. However, this is the best place for real tuner information and I know when I come up brainless this is where to go. Thanks!

Specs:
74 Jeep J10, bone stock 350 chevy motor w/about 3-5k miles on it after rebuild. Performer intake, Holley TA 670 (gen 2) carb. Only mods to the carb are to increase shooter size (2 steps I think) and to change the stock 2.5PV to 6.5.
I get a steady 20" of vac at idle w/16*BTDC and 1 turn out each side on the idle mix screws.

Here're my issues: 1) I finally took my truck out for a long enough drive to calculate mileage and figured I was getting about 6-7mpg out of a stock 350.
Part of the drive was up hill and at 3-4000', and I definitely got worse mileage driving up there than back in the LA area but that wasn't calculated, only eyeballed on the gas gauge. I found my truck lacked power on the hills and I had to keep my foot in it frequently to maintain freeway speed. On the way up to Arrowhead I barely pulled 30mph with a 1/4 cord of wood in the back.

While trying to figure out the proper jetting for my carb, I also removed the 6.5 pv I had put in and put the stock one back. Turns out that stock 2.5 was blown and took me a while (see my title) to figure out what the hell was going on. Truck would barely start and would run like hell unless I held the throttle WO- and fuel fouled the plugs. Took them all out (one at a time so I don't mix wires), blew out the cylinders and put in new plugs.
SO I with the good 6.5 in I start messing with the jets, and find that 66 causes a flat spot on the freeway at about 60mph, same with the 67, and then the orig 68s so I think I have a bad fuel filter. I replace that, but still have the bog. I even get it to bog down on the street right about when I'd think the secondaries should open, or just before redline. It falls hard and acts like someone threw a brake on it until I let off the gas.

Thoughts? I don't remember it doing this before, but can't rule out the possibility that when I put the 6.5 pv in I didn't seal the metering block to the carb right and was running with a slight vac leak.

Should I be able to manually work the plunger on the secondary vacuum unit? seemed like it was locked when I tried to work it.

Thanks again.
Ed

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Old 01-30-2007, 05:49 PM
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Quote:
Originally Posted by gawdzilla

Part of the drive was up hill and at 3-4000', and I definitely got worse mileage driving up there than back in the LA area but that wasn't calculated, only eyeballed on the gas gauge. I found my truck lacked power on the hills and I had to keep my foot in it frequently to maintain freeway speed.


Truck would barely start and would run like hell unless I held the throttle WO- and fuel fouled the plugs.

, but still have the bog. I even get it to bog down on the street right about when I'd think the secondaries should open, or just before redline. It falls hard and acts like someone threw a brake on it until I let off the gas.


Should I be able to manually work the plunger on the secondary vacuum unit? seemed like it was locked when I tried to work it.

Thanks again.
Ed
4000 ft you will lose noticeable power 12 %, and mixture will be getting richer by the foot.

Poor fuel delivery and higher altitude causes more open throttle which decreases vacuum and vacuum advance. Do you have a good centrifugal advance curve?

Kind of confusing. Runs good except when WO
Then flat spot on freeway....
Then bog when secondaries "kick in"...

Jetting & power valve are probably FUBAR now.

First you need to start at square one and check floats, etc.
Check fuel pressure under load, and fuel delivery volume.

Secondaries should be smooth operation.
then, secondaries open gradually and progressivelly unless the spring is too soft, un-noticeable kick-in. Put a paper clip on secondary rod and drive. When secondaries open, the paper clip will be slid down to the open position. So you can see what they are doing.

Off hand I'd say your power valve is bad. You need pv about 3 smaller than usual load vacuum.
Your floats are wrong
Your jets are wrong
The secondary spring is too soft.... go up 3 sizes.
make sure secondaries are not binding.

Last edited by xntrik; 01-30-2007 at 05:59 PM.
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Old 01-30-2007, 08:30 PM
black thumb learner
 
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Quote:
Originally Posted by xntrik
Poor fuel delivery and higher altitude causes more open throttle which decreases vacuum and vacuum advance. Do you have a good centrifugal advance curve?
Yes, at least if stock is considered good. I get to full advance by 3k IIRC.

Kind of confusing. Runs good except when WO
Then flat spot on freeway....
Then bog when secondaries "kick in"... flat spot and bog are simultaneous but it pulls steady until then. Not necessarily strong but it's never been a rocket.

Jetting & power valve are probably FUBAR now. can jets foul? I've got the stock 68 primary/89 secondary in there now. I'll try putting a new pv in.

First you need to start at square one and check floats, etc. front bowl just drips fuel from sight plug. Haven't checked the rear floats since I set it up.
Check fuel pressure under load, and fuel delivery volume. how do I check pressure under load?

Secondaries should be smooth operation.
then, secondaries open gradually and progressivelly unless the spring is too soft, un-noticeable kick-in. Put a paper clip on secondary rod and drive. When secondaries open, the paper clip will be slid down to the open position. So you can see what they are doing. thanks I'll do that.

Off hand I'd say your power valve is bad. You need pv about 3 smaller than usual load vacuum.
Your floats are wrong
Your jets are wrong
The secondary spring is too soft.... go up 3 sizes. Spring in there is supposedly the stiff one (silver)
make sure secondaries are not binding. will do. should I be able to work them by hand?.
btw...like the quote.
So far I haven't had any luck with that line though [save a horse...]
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Old 02-02-2007, 08:04 PM
black thumb learner
 
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update

[Do you have a good centrifugal advance curve?]

---Yes, at least if stock is considered good. I get to full advance by 3k IIRC.

[Kind of confusing. Runs good except when WO]

---On the street as soon as it would wind up past maybe 3k it would bog bad. If I took my foot off the gas and tried again it seemed to pull further.

[Jetting & power valve are probably FUBAR now.]

---can jets foul? I've got the stock 68 primary/89 secondary in there now. can a pv go bad just from taking it out?

[First you need to start at square one and check floats, etc. front bowl just drips fuel from sight plug.]

--- fuel just drips from sight plugs front and rear

[Check fuel pressure under load, and fuel delivery volume. ]

---how do I check pressure under load?

[Secondaries should be smooth operation.
then, secondaries open gradually and progressivelly unless the spring is too soft, un-noticeable kick-in. Put a paper clip on secondary rod and drive. When secondaries open, the paper clip will be slid down to the open position. So you can see what they are doing.]

---I put a zip tie on it since I didn't have a paperclip. However, it was too tight and kept secondaries from opening and the problem was worse.

[Off hand I'd say your power valve is bad. You need pv about 3 smaller than usual load vacuum.]

---idle vacuum is 21. In gear it's 18. 18/2 = 9, -2 is 7. I have a 6.5 in now so I'm good, right?

[Your floats are wrong
Your jets are wrong
The secondary spring is too soft.... go up 3 sizes. ]

---Spring in there is supposedly the stiff one (silver)

[make sure secondaries are not binding. ]

---they are not

-----Also checked for vacuum leaks, might have a little bit of a leak at carb base, snugged a bit more and seemed better.
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Old 02-05-2007, 10:44 PM
black thumb learner
 
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I just went and vacuum tested all my power valves. They are all good, including the 2.5 I thought was bad.

Checked plugs. All carbon rich and sooty.

Before I tested the power valves today, I put a new one in per xntric's suggestion. Truck barely ran it was so rich. I tried again this afternoon and it was better (ran) but would only run w/the idle screws turned in all the way.
I manually worked the needle seats when I had the bowl off and they moved ok.
I don't see excess fuel pouring out of the sight plugs when I remove them (just trickles).
Why am I running so rich?
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Old 02-05-2007, 11:09 PM
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If it runs with the idle screws all the way in then the throttle blades a likely open too far allowing the main circuits to feed through under idle. You need to dial back the throttle blades so the idle circuit can control the fuel mixture.
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Old 02-06-2007, 08:48 AM
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why would that have changed? I never removed the carb, only changed the power valve. It ran w/the mix screws out 1.5 times before I changed the pv the first time, then 1 turn out before this last time.
something screwy going on in there.
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Old 02-21-2007, 11:30 PM
black thumb learner
 
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update to truck avenger carb

just to give y'all an update:
sent the carb back to Holley.
They sent it back, telling me the check valve in the primary metering block was in upside down.
put it back on and it fired right up.
For the next guy who runs into this....
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