I forgot to mention, as for finding out whether or not your running rich. Pulling the plugs is the best way to figure that out. If you go by having someone punching the gas while you watch the tail pipes, well....listen to this: When you hit the accelerator pedal, the carb dumps a deliberatly rich amount of fuel into the carb. This is to deal with the lean result of opening the butterflys. So when you hit the gas, the accelerator pump WILL make it look rich....but that isnt the main mixture your wantging to look at. The one you want to look at is when your cruising down the road. And there are only two ways I know of to effectivly check that....1)check your plugs and 2) take the thing into an emmisions station. Those are the only two ways I know of that are effective.

 

Thanks for all the great info guys.

I did notice that while messing with the adjusting screws the idle never changed until I bottomed out the pass. side screw. Doesn't seem right.

In theory, if I screw both all the way in, it should stall, correct? Any idea why adjusting them does nothing? Should I be turning them both at the same time?

It does run really nice now, so it's not a major issue. I just want to make sure I understand what's going on.

Thanks again!

Kevin K.

 

Kevin, Yes, in theory, it SHOULD die when you bottom out both screws at the same time. One reason it may not be dying is that it may need a rebuild, or possibly just a power valve, or maybe even just new idle adjustment screws. You may need new needle and seats also. I would buy a $35.00 kit from Jegs and rebuild it real quick. It only takes a couple hours to do even if it's your first time. However, you did say it's running good now, so maybe you might just want to leave well enough alone. Your choice.

 

I agree, usually if you shut down both screws, your power valve is blown, all it takes is one little backfire pop and the little suck is blown. Buy a power valve protector kit while you are at it and stop the problem for good. The power valve is also why you are too rich.

 

Again, thanks for all the good info.

Looks like I'll be rebuilding it over the winter. I've had other problems in the past where it was suggested the power valve was blown as well. I'll look into the protector kit too.

Thanks!

Kevin K.

 

Make sure your idle adjustment is correct (the screw where the throttle linkage is on the drivers side of the carb) Its common for people to screw this down to raise the idle. It should be backed off all the way then screwed down just enough so the throttle plates do not stick. If the screw is too far is, you will pull fuel from the main circuit, rather than the idle circuit only, which will allow the engine to idle with the mixture screws all thre way in. Set the throttle stop befre adjusting the mixture screws

When you take the carb off at some point, look in the primary bores....you will see a small vertical rectangular slot in each at the level of the butterflies. These are called transfer slots, and allow the engine to work smoothly between the iidle and main ciurcuits. THe butterfles should be in the middle of these slots.

 

Actually, you probaly will never get the main fuel circuit to flow using the throttle stop screw. You can however get into the intermitiate fuel circuit to flow which has ports down low, just above the idle ports. They are for off idle running before the mains sense enough vacuum to start tip in. The main jets feed mainly through the booster venturis. Of course, the main jets do control the max amount of fuel thru the carb, idle, intermitiate and high speeds combined. Some times you can't get an engine to idle with the butterflies full close. Just keep backing the throttle stop down as the mixture adjustments brings the rpm's up, around 600 to 700 rpms. I don't be then again I've done it along time and know where to cheat.

 

Thanks rescue.

I never thought of that, but it sounds like a possibility. I think I'm idling over 1000 rpm and I know that's too high. I'll reset that and give it a shot again.

Kevin K.

 

I'm sorry if I repeat anything, I didn,t read all the posts. First, off a 750 CFM is overkill on a stock 460. I know alot of you will ague that point, but just let me say, I worked for one of the top fuel men in the counry, he was a crew chief at the Indy 500. The way he taught me to figure CFMs a 750 is too big. Second, if you are having most of your problem off-road you might change the needle & seats to spring loaded off-road needle & seats. Third, an center hung float works better for off-road. Fourth, ALL HOLLEY CARBS SINCE 1992 HAVE ANTI-BACKFIRE PROTECTION BUILT IN BY HOLLEY. Power Valves are no longer an issue. Fifth, settings from Holley are very close, depending on elev. you may want to change jets, but in the case of a 750 on a stock 460 a jet change is most likely going to be a good idea.

 

Well, I dont know who your fuel guy is/was, but I know from experience, that a 600 is too small on a 351w thats a little warmed over. With the 600 it was only 460hp/390ftlb. But with the 750, it put out 503hp/462ftlb. So, I would say that a 750 vac secondary is just about right for a stock to (very)mild 460. I dont usually go by what "experts" say, I usually listen to what "real" people who do it on a regular basis say. In theory, yes, a 750 is too big, but in reality, and in practice, it is the best thing depending on what you are trying to accomplish. If you are racing with it, then you might even want more. But if you are trying for low end grunt, then you may want a 650, but I would still stay with the 750 because it allows you to build bigger.

Engineers...sheesh...They think they know everything...lol

 

Ummm, wasn't the Quadrajet that came standard on the CJ at least a 750CFM carburetor?

Also, wasn't the spread-bore 4300-series that came on the rest of the 429's (except the SCJ--or do I have those two backwards, with the SCJ having the Quadrajet, and the CJ having the Holley?) and all the 460's rated at 750CFM as well?

750CFM is FAR from being "too much", as you can see by the fact that the factory even installed them on these engines!

I agree with 53wa2fl--I would say that a vaccuum-secondary 750/780 would be OK for a mild, mainly street-driven 460, but if you want to go racing, your best bet would be a bigger carburetor, possibly a Barry Grant 850 or something similar.

 

Street carburation and racing carburation are two different worlds and what works for racing has no place on a street engine. For street engines use one of these and it will get you close enough.

CFM = RPM(Max) X CID
3456

or

RPM = CFM X 3456
CID

Both these formulas were used by the factories for starting points for their HP motors. Sometimes it's even right on. Example; 428 CJ and SCJ's; 428 cid, 6000 RPM(this is where the auto shifts by itself) and 735 CFM carb. Stick the numbers into the formulas and see for yourself. Over carburation on a race motor usually helps WOT horsepower numbers, but then again they never use low RPMs or carry heavy loads. A street engine spend most of its life in the idle to 3000 RPM range and only rarely see 5000(a stock 460 runs out of cam by 4500, you can feel the engine start to run out of breath) A bigger carb only over carburates(to much fuel and air) and cause a flat spot(expecially the double pumpers, a major no-no on a street motor) at low and off idle RPMs.. Some guys mistake the pause then go as more power, a trip to the quarter mile track will show that it is usually slower than stock. I was told by a Holley Factory Tech back in the 60's that if you must run alot of CFM, "a lot of little holes is better that a few big ones".

 

Ok guys, I'm ready to rebuild the carb but I'm not sure which kit I need to do the job. I'm not even sure what all has to be rebuilt. I would like to get the thing that protects the power valve but I don't know what it's called either.

I saw the kits on jegs but I also see a few on ebay. One is made by AED and the other is a Barry Grant.

The AED kit has:
High-flow .110? needle and seats.
Nylon reusable needle and seat gaskets.
Nylon reusable bowl screw gaskets.
New brass idle mixture screws.
New needle and seat nuts and screws
New accelerator pump squirter check valves.
Special no-leak fuel inlet gaskets.
High-flow power valves
Special alcohol components
Reusable Bowl and Metering Gaskets

The BG doesn't list what's included but claims to have everything you could possibly need including the power valve.

Is there anything else I'd need that a standard rebuild kit doesn't have?

What about the center mounted floats? Someone stated they might help in off-road situations. For the price, I might get those anyway along with the clear float bowl window thingys.

Any thoughts?

TIA.

Kevin K.

 

The secondary metering plate is held on with some funny screws. They look like stripped out slots or sort of bow-tie shapped. Your supposed to use whats called a clutch-type screwdriver. I don't know what that is, nor was I able to find one locally. I just used a regular slot driver. It wasn't pretty, but I got it done. Only reason to take it apart is to replace the gasket which will be full of solvent if cleaning.

 

Ok, the BG kit would work fine. Do you know when the carb was purchased new? What is the list number? That would help in identifying whether or not your carb already has a Powervalve blowout protection device built it. It will also let us know if you already have center hung floats. I am thinking you do, but could be more certain if I had the list number.

As for a "clutch head driver" You can pick one up at Sears in their tool dept. It is usually just a bit you can buy and costs about $4-$8. Pretty cheap to have the right tool and save yourself some headaches.

When you get it all apart, it may look a bit daunting, but be persistant and thourough and you wont have any problems.