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Discussion Starter · #1 ·
Hey guys, first of all I am a noob to this site so take it easy on me...

I need your help. I have a 1969 396 325hp original with a Rochester Qjet, 400 tranny

I installed a Lunati Voodoo 10110701 cam with new springs and flat lifters....I really took my time so I pretty sure the installation is good but I have a problem that I cannot figure out.

When I go for it from a slow roll, it takes off like a bat out of hell...then when I get close to the shift point, the motor chokes, sputters and almost dies off...almost feels like the I am floating the lifters....then it will pick up and run great until the next shift and does the same thing again...

I have tried alot of different timings and setups and nothing seems to make any difference....out of ideas...anyone have any idea what may be causing my problem....

Any help will be greatly appreciated....
 

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IHMO, you have a carb, tranny, or distributor/electrical issue....and are NOT floating the lifters.

When was the last time you need a basic tune up? Was the tranny working fine BEFORE you changed the cam?
 

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Discussion Starter · #3 ·
IHMO, you have a carb, tranny, or distributor/electrical issue....and are NOT floating the lifters.

When was the last time you need a basic tune up? Was the tranny working fine BEFORE you changed the cam?
Hey Tony, I didn't really think I was really floating the lifters (That's what it feels like...) and that I figured I had a problem somewhere else...the tranny was working fine before the cam installation...and tuning it was the very first thing I did...

Is it possible that I am having a tranny shift point problem...or a vacumn problem on the tranny governer...???
 

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If the tranny was fine before the cam change, you should be fine now.

Did you hook the vacuum line up between the Tranny and your intake? If you pulled the motor for the cam swap, did you push your TQ Convertor back in all the way/all three "slots"?
 

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Discussion Starter · #5 ·
If the tranny was fine before the cam change, you should be fine now.

Did you hook the vacuum line up between the Tranny and your intake? If you pulled the motor for the cam swap, did you push your TQ Convertor back in all the way/all three "slots"?
Tony, yes and yes...triple checked...
 

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Put a fuel pressure gauge on it and see if it drops off. Sounds like your running out of fuel. New found power may need a better fuel system.
 

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ok sounds like you have a stock/mech style fuel pump??
do you have a stock or liteweight fuel pump rod??
a stock fuel pump rod will float the pump around 48-5200rpm
causes 7psi fuel pressure to drop like a stone to about 1-1.5psi:frown2:
 

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A 120 GPH Edelbrock or Holley Mechanical Fuel Pump will be fine. There's a lot of 11 and 12 second SBC and BBC cars still running them with ZERO issues.

Now, it's totally possible that your old fuel pump is shot or you may need more than 30-40 GPH. Any chance you can borrow someone's just to test this theory?

However, having a fuel pressure gauge is a most, IMHO.
 

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May want to check the size of your needle & seat in the carb. Stock is usually .125 you'll need a .135 minimum.
 

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Are your valve springs the correct ones recommended for that cam? What is your shift point RPM? If you're trying to get more rpm than the cam is designed for, you could get valve float and lifter pump-up. Even if the correct springs are used, you could have them at the wrong installed height, which could lower the open pressure. Could have a weak spring too. If all else fails look into springs.
 

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Discussion Starter · #15 ·
Wow, thanks everyone...some very good ideas...Vince, yes it is a stock rod in the fuel pump and the way you describe the drop off sounds very much like what is happening....I have checked and replaced the fuel filter...I will check the fuel pressure and I think I may need to replace the fuel pump...remove a few possibilities...and Jim, I think the carb is .125....maybe after I eliminate the fuel possibilities I will try .135.

Thanks to everyone for the feedback....very much appreciated....
 

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One other thing. The original fuel strainer "sock" on the gas tank pickup (in the tank) can get partially clogged with rust and sediment, etc. Sometimes it will fall off the sock while the engine is off or idles, then get sucked back onto the sock when the engine is under load and starve the engine. This happened to me years ago. For a performance car it's better to get rid of the sock and have a good, large capacity in-line fuel filter between tank and pump.
 

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>>> "a stock fuel pump rod will float the pump around 48-5200rpm"

I've had a hell of a bunch of Chevy V-8s that ran a hell of a lot more than 48-5200 with a stock fuel pump pushrod. I'm not buying that. Sounds like something a vendor that sells lightweight pushrods would say.

Kinda like the old "HEIs quit at 4800" deal pushed by the ignition vendors.
 

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X2 on the springs. As weird as it sounds I once had an issue with a 351C where it would rev great to about 5500 then just die. No noticeable valve noise or anything. If you pushed past 5500 it came alive again at 6100 and ran great to 6500. I tried all sorted of things as suggested by guys on here and other forums/places. These were new springs on new Chi heads. When the heads were ordered I asked for dual springs but the supplier, who is a renowned can grinder in my part of the planet, insisted single springs were ideal. In desperation I changed to Isky 8005 dual springs and the difference was incredible. From my googling I'm sure we had a spring harmonic issue and at revs below and above the rev range it was happening the engine ran fine. Seems the OEM back in the day sometimes used this same "issue" as a built in rev limiter to stop engines being over revved. From what I've learnt about valve springs since I'd be looking hard at upgrading to a decent small diameter dual. This keeps the mass down etc. and helps with stability at higher revs.
 

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Wow, thanks everyone...some very good ideas...Vince, yes it is a stock rod in the fuel pump and the way you describe the drop off sounds very much like what is happening....I have checked and replaced the fuel filter...I will check the fuel pressure and I think I may need to replace the fuel pump...remove a few possibilities...and Jim, I think the carb is .125....maybe after I eliminate the fuel possibilities I will try .135.

Thanks to everyone for the feedback....very much appreciated....
It sounds like your Q-jet is mostly original ('cept for rebuilds). Those carbs were set up somewhat lean by GM to meet the then current emissions laws. It could be, besides running out of fuel, you might need to enrichen the metering rods a tad.

Q-jets can be marvelous carbs, set up properly, but can also cause problems when engine changes have occurred (like a cam). Cliff Ruggles has a rep as the Q-jet guru in racing circles. His site may be helpful to you (as it was me, esp, his Q-jet book)---

Cliffs High Performance Quadrajets :: Quadrajet Rebuild Kits, Quadrajet Parts, Quadrajet Rebuilding, Qjet Parts, Bushing Kits, Carb Tuning

Hope this is of some help.
 

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fuel tank sock, as stated previously
I cut mine off, dropped a tenth, picked up an mph!

Check the float level, could also be low

check all vacuum lines
 
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