78 K30 Carburetor Issue

[68_Step]

I have a 1978 K30 with a 454 that has never run like it should, so I decided it is tune-up time. Need to make it a more reliable ride. I knew the carb was a 600 double pumper, but have never paid that much attention to it. It is a model #4776, mechanical secondaries. I went to Holley's website to look up adjustment info and a found this as a description for my current carb.

"Intended for lightweight vehicles w/ manual trans or automatics with high stall & low gearing".

That is the exact opposite from what it is setting on: A 1 ton, 4 wheel drive, that gets used for hauling feed and hay and getting me to work when the snow is real bad...

Is a mechanical secondaries carb what I need for what I use it for?

What do type carb do I need to be looking for? CFM rating? Thanks for the help!

[mrolds88]

That application is exactly what Holleys are good for. WOT. Get yourself a good early Qjet. Go through it and put i ton. Use either a Chevy or Cadillac unit. Make sure the number starts with a 70. The early units are tunable. Get a book if needed. They work well, very well. The 2 main parts to tune are the idle screws on the bottom in the front and the secondary air valve. A little tuning on one goes a long way.

[enaberif]

Originally Posted by mrolds88

That application is exactly what Holleys are good for. WOT. Get yourself a good early Qjet. Go through it and put i ton. Use either a Chevy or Cadillac unit. Make sure the number starts with a 70. The early units are tunable. Get a book if needed. They work well, very well. The 2 main parts to tune are the idle screws on the bottom in the front and the secondary air valve. A little tuning on one goes a long way.

1708 series Qjets are good too. I have a 800cfm version on my truck right and they are just as tunable as the 70 series. The 1708s also generally have a better provision for electric choke compared to the earlier years which are more hot air choke setups.

[68post]

A Qjet would be best , and get better mileage too.

The dbl pumper in question is so small for your 454 - the normal characteristics
don't quite apply. I'm sure it drives fine and has excellent throttle response , but if it were an 850 on a stock 454 - it would be a mismatch.

Do you have an aftermarket manifold, or is there an adapter under the carb ?

[68_Step]

Originally Posted by 68post

Do you have an aftermarket manifold, or is there an adapter under the carb ?

It has an Edelbrock Performer 2.0 manifold and headers, not sure if there is an adapter
under the carb or not but reading the description on Edelbrock's site it looks like the manifold is spreadbore - isn't the 4776 a squarebore?

[68post]

Originally Posted by 68_Step

It has an Edelbrock Performer 2.0 manifold and headers, not sure if there is an adapter
under the carb or not but reading the description on Edelbrock's site it looks like the manifold is spreadbore - isn't the 4776 a squarebore?

The 4776 is a sguarebore holley , and your intake can use it or a spreadbore carb. You may have a thin steel adapter plate under your carb, some manifolds require them so the squarebore carb will seal.

[68_Step]

Originally Posted by 68post

The 4776 is a sguarebore holley , and your intake can use it or a spreadbore carb. You may have a thin steel adapter plate under your carb, some manifolds require them so the squarebore carb will seal.

Whew, thought I had written the wrong numbers down!

[68_Step]

Originally Posted by 68post

The 4776 is a sguarebore holley , and your intake can use it or a spreadbore carb. You may have a thin steel adapter plate under your carb, some manifolds require them so the squarebore carb will seal.

You were right. I pulled the carb last night, will be rebuilding it this weekend. It had a thin metal plate (in the square bore shape) between the manifold (really is spread bore) and the Holley 4776. The PO had 3 gaskets on it. Two between the metal plate and the manifold and one between the plate and the carb.

Do I really need 3 gaskets, or just 2 - one on each side of the plate? Do I use any sealer when putting is back together?

[68_Step]

Originally Posted by 68post

I'm sure it drives fine and has excellent throttle response

I wish that was true, it is running very rough and bogs down when you hit the gas hard. I am thinking I need to do compression checks and rebuild the distributor and carb - then decide if the carb is the problem. Over the past few years it has not seen much driving at all which may explain it's rough running.

[Bears63]

You should only need 2 gaskets, one on each side of the plate and don't use any sealer.

[68post]

Hope you find the issue. That 600 should perform like an economy carb on your 454. ( dbl pumper = bad for mileage/ 600 = small for even a 350 )

I used a 500 AFB on a warmed-up 350 many years ago - for the main objective of fuel economy , then - torque up to 4,000 max, hp be daymd !

[68_Step]

Originally Posted by 68post

Hope you find the issue. That 600 should perform like an economy carb on your 454. ( dbl pumper = bad for mileage/ 600 = small for even a 350 )

I used a 500 AFB on a warmed-up 350 many years ago - for the main objective of fuel economy , then - torque up to 4,000 max, hp be daymd !

The carb rebuild this weekend is a temp measure to get it runing decently again. I have been checking out the Holley 4160 #3310S, 750 with vacuum secondary. Took the carb apart last night and it is soaking in parts washer fluid. Will finish clean up this morning and put it back together. Also picked up plugs, cap...

[nonstop]

What are you using the truck for? A Holley is great if you want to keep tuning it. A Quadrajet is a great carb for economy, but will definitely give you power. I have a 750 vacuum secondary Holley sitting in my garage, but I can not bring myself to throw it on. The Quadrajet just seems to run great on it.

[68_Step]

Well the day did not end well. When cleaning I found a crack on the front right corner. Of course as I was fiddling with it the corner snapped off. Pretty sure JB Weld won't fix that! Since it looks like I am in the market for a carb, what do you guys suggest? This is basically a work truck so gas mileage is not a huge concern. I use it to pull a cattle trailer, haul post and wire, 1000lbs of feed at a time - you get the idea

[Fixwhataintbroke]

Originally Posted by 68_Step

Well the day did not end well. When cleaning I found a crack on the front right corner. Of course as I was fiddling with it the corner snapped off. Pretty sure JB Weld won't fix that! Since it looks like I am in the market for a carb, what do you guys suggest? This is basically a work truck so gas mileage is not a huge concern. I use it to pull a cattle trailer, haul post and wire, 1000lbs of feed at a time - you get the idea

Honestly for as overwhelmingly simple as they are, i'd go with an edelbrock 1411. 750 CFM, vacuum secondaries (if i recall), and an electric choke. I use one on my warmed up 454 and it's about a perfect match.

[tucsonjwt]

I just put a US Carburetor Qjet rebuild in my 83 454 and it seems to work OK. Of course, I knew that the "automatic" choke would not work properly because they never work for me, so I used my existing manual choke and that works fine. I got this carb because it was the cheapest, but I will have my original Qjet rebuilt by a good shop, probably Sean Murphy, and keep it in reserve. The US Carb is far from being a show piece - components look generic and lack the factory dichromate, teflon, and other coatings of OEM parts.

I have had many carbs for my squares over the years, and have never had good luck with the Edelbrock, and former Carter, carbs. The quality of the components was not as good as OEM and did not hold up very well over time. Plus, I don't think they make a Qjet spread bore direct fit, so you have to deal with adapters for their square bore base plate and jigger the linkage and air cleaner connections. So far, a high quality OEM Qjet rebuild seems to be the best option.

With all of the carbs, I highly recommend a manual choke. The factory chokes of any type (hot air, divorced, or electric) can never be adjusted to work properly in both cold and hot engine conditions. If you adjust them to close when cold, they don't open fully when warm. Or if you adjust them to open when warm, they won't fully close when cold. I have tried different types of coils in the choke housing with no success. I am sure many posters here will say they never have any trouble with their choke, but I have not been so lucky. For a $12 investment I know for sure when the choke is fully opened or closed, or I can keep it partially open if conditions warrant that.

[68_Step]

Originally Posted by tucsonjwt

With all of the carbs, I highly recommend a manual choke.

I agree 100℅, whichever carb I get it will be a manual choke. One less thing to worry about.

I think I have my choices narrowed down to either the Holley 3310s or the Edelbrock 1407. Both are 750s with vacuum secondaries.

[Your41Plague12]

Originally Posted by 68_Step

I agree 100℅, whichever carb I get it will be a manual choke. One less thing to worry about.

I think I have my choices narrowed down to either the Holley 3310s or the Edelbrock 1407. Both are 750s with vacuum secondaries.

Out of those two, go with the Edelbrock. I ran the 1411 (same thing, but an electric choke) and it was a great carb. Ran right out of the box, barely needed tuned.

[enaberif]

Looks like someone tightened down the carb too much at some point.