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Discussion Starter · #1 ·
Let me start off by saying this carb runs extremely well compared to the 850 VS that was on my car, I know now what torque steer is :D. The problem is when cruising and trying to maintain a steady speed, if I give it just a little throttle to keep the rpms around 2200 to 2400 it sounds like the engine is missing but it actually feels smooth. If I raise or drop the rpms the sound goes away. The only thing I changed on the carb was the power valves to 2.5's becuase I typically have 6 to 7 inches of vacuum in gear (with the old carb), although I think I've picked up some vacuum with the 950. The idle mixture screws are out 1 full turn on all 4 corners and I squared the idle transfer slots with the throttle blades (front & back) to initially start the engine and the rpms were too high so I backed out the idle screws about half a turn each and I'm not sure how much of the slot is now showing. Here's the rest of my combo

454 .030 over
Brodix Ovals
10:1 Compression
Cam 251/262 @ 050 (595/595 lift)
MSD Dist. with 6al box, locked out at 38*, full manifold advance
10" converter, stall should be around 3200
12 bolt rear with 4:11's
 

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Discussion Starter · #3 ·
See what happens when you put higher 5.5/6.5 primary PV back in .assume you blocked your rear PV and jetted up
Okay, I haven't had a chance to check the vacuum in gear with the 950 (need a helper for that, don't trust the e-brake) but I will get the correct ones in there. Oh and I did leave both power valves in and stock jets (78) both front and back.
 

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John, is this the 80496 carb? New or used? Make sure it has the right air bleeds front and back. I had several of those carbs and each one ran flawless. Sounds like your having problems holding a steady speed...this would eliminate any PV concerns.

Also, not sure if you had PCV and vac advance before...you probably dont now. The 950HP runs real rich at part throttle, and the PCV does help clean it up a bit. If you eliminated the vac advance, you lost that part throttle additional t iming that's needs for our sloppy cammed motors.
 

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Discussion Starter · #7 ·
Sounds to me the accelerator pump linkage needs adjusting. 2200-2400 you probably cruising on the idle circuit.
What size feeler gauge do you use to make that adjustment?
 

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I'd get rid of those 2.5 power valves. They're very slow to open and quick to close. ALso, they're unrelated to the idle or your part throttle cruise. As mentioned, you're probably cruising on the idle transition circuit, it's not likely the main system is metering at 22-2400.

This means that changing the primary main jets won't make any difference to your cruise. What you might do is try 2 sizes larger and smaller on the primary idle air bleed. Do you have a wide band O2 meter? Borrow one?
 

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Discussion Starter · #12 ·
John, is this the 80496 carb? New or used? Make sure it has the right air bleeds front and back. I had several of those carbs and each one ran flawless. Sounds like your having problems holding a steady speed...this should eliminate any PV concerns.

Also, not sure if you had PCV and vac advance before...you probably dont now. The 950HP runs real rich at part throttle, and the PCV does help clean it up a bit. If you eliminated the vac advance, you lost that part throttle additional timing that's needs for our sloppy cammed motors.
I believe this is the 80496 and it is used. It was a mess when I first got it, I had to clean the entire carb and purchase the correct air bleeds/jets/squirters/etc. so I know their correct. Regarding the lack of vacuum ports, I took a 4 hole spacer and drilled/tapped 2 ports for the PCV and vacuum advance, although I'm not sure the PCV valve is optimal for my for my engine because I bought a stock valve for a 454.
 

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Take all the slack out with the throttle at idle position. You only check with a feeler gauge at WOT to make sure you are not stressing the pump diaphragm. Want to say a .020 feeler gauge should slide in snug at WOT. You'll need to look that up to be sure.
Again, how do you see this causing a problem at a steady cruise?
 

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He's got a 3200 converter. At 2200-2400, there is no load. Very similiar to my own setup. If I get on flat ground and let up on the throttle, it will cruise down the road on the idle circuit. He has the transfer slots closed. He says as he gives it a little throttle so I assume he is not talking about holding it at a steady throttle position, the problem is in the transition - if I understand what is explained. As soon as you give it a little throttle, the primary squirter has to supply fuel. States as higher RPM or lower RPM it's fine. Most likely witha 3200 converter, higher RPM means more throttle as the motor sees load. Lower RPM is most likely all idle circuit. Not saying it's only this, but first thing I would do is check the simple adjustments first - accel pump lever adjustment and float levels. Heck, could be a weak signal needing more jet. Unless someone is there to physically look at it, all you can do is guess. My guess is - rule out the simple things first.
 

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I believe this is the 80496 and it is used. It was a mess when I first got it, I had to clean the entire carb and purchase the correct air bleeds/jets/squirters/etc. so I know their correct. Regarding the lack of vacuum ports, I took a 4 hole spacer and drilled/tapped 2 ports for the PCV and vacuum advance, although I'm not sure the PCV valve is optimal for my for my engine because I bought a stock valve for a 454.

Wonder if the 4 hole spacer is the issue. I would imagine that one hole has the PCV connected to it...making that corner run a little leaner. I would use an open spacer, or tap the intake so the PCV is pulled more evenly from each bank. If you have a dual plane, you can tap each side of the intake and use a T to the PCV, or just use an open spacer and put the nipple under the center of the carb, under the front bowl or rear.

Maybe you can elim. the PCV just for testing purposes.
 

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Discussion Starter · #16 ·
Thanks for all the replies, I probably won't have an opportunity to mess with this until the weekend but now I have some direction. I definitly see a wide band in my future!
 
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