Intake plenum gaskets

[85K304SPD]

Show us some pictures of your K20 and the 400, please. We can probably "practically fix it" (everything but the work) with a little more info. Then you can go to your mechanic and tell them what you want done and why.

 

[yellowdog5]

Show us some pictures of your K20 and the 400, please. We can probably "practically fix it" (everything but the work) with a little more info. Then you can go to your mechanic and tell them what you want done and why.

I had the carb gone through twice a couple of years ago, the second guy I thought knew what he was doing, the truck was running fine and starts right up warm but took 80 pumps (no exaggeration) or hand priming to start it cold. This guy wants to replace the carburetor to intake manifold gasket and what I think I learned from you guys are just ordinary manifold gaskets. There are other problems with the truck now too, but he wanted to start there, he found some air leaks around the gaskets.
I can probaly replace those myself with a little coaching, but I really don't know if the carb needs work also. I would like to address the other problems as well, I can live with priming it to start temporarily. I have changed all ignition parts: plugs and wires, coil cap rotor and icm. Also changed the fuel pump. It runs really rough and weak until it gets up to about 45mph then smooths out. None of the stuff I did helped much, fuel pump maybe alittle. It did need a tuneup.

 

[85K304SPD]

Nice looking old truck. Did you replace the little fuel filter in the carburetor? All of that sounds like a carburetor problem. Maybe it needs cleaned up again. I can't think of how new intake manifold gaskets will help that problem.

 

[yellowdog5]

Nice looking old truck. Did you replace the little fuel filter in the carburetor? All of that sounds like a carburetor problem. Maybe it needs cleaned up again. I can't think of how new intake manifold gaskets will help that problem.

Me either, would they help with cold starting? Yes I did replace the fuel filter.

 

[85K304SPD]

Cold starting would be more about the choke adjustment and pump shot. If it starts with a primer of gas down the carburetor, that would indicate that it is not getting enough gas. I am thinking it is the accelerator pump plunger, or nozzle is clogged up. That would explain the slow acceleration, without the squirt of gas when you step on accelerator. Can you look down thie top of the carburetor and see if there is a nice strong pump shot of gas coming out of both sides of the squirter nozzle when you work the accelerator?

 

[DoubleDingo]

Me either, would they help with cold starting? Yes I did replace the fuel filter.

Nope. If there is a vacuum leak anywhere along the intake, yes, it will help it run better, but only if every other vacuum leak is fixed. If it doesn't start when cold, as stated, things are out of adjustment.

My truck is cold blooded, but it'll start in the cold. The only time it takes more cranking is when it has sat for a long time. Even then, a few pumps of the pedal, crank it a few seconds, repeat until it fires. I am not a fan of long cranking of the starter because the engine isn't splashing the oil like if it's running. It does take less revolutions to fire the way I do it. You should not have to prime the carb when it's cold, these were not designed that way, they were designed to run in every weather condition and elevation.

 

[yellowdog5]

Cold starting would be more about the choke adjustment and pump shot. If it starts with a primer of gas down the carburetor, that would indicate that it is not getting enough gas. I am thinking it is the accelerator pump plunger, or nozzle is clogged up. That would explain the slow acceleration, without the squirt of gas when you step on accelerator. Can you look down thie top of the carburetor and see if there is a nice strong pump shot of gas coming out of both sides of the squirter nozzle when you work the accelerato

I tried it both with the engine running and not running, as far as I can see there is none coming out of the nozzles, when I work the accelerator. Picture to see if I was looking in the right place, I'm not very up on carburetors. Also not good at drawing with the computer

 

[85K304SPD]

That is the problem. Your accelerator pump is not working. The plunger is probably torn or hard or something. The top needs to come off of the carburetor to put a new accelerator pump plunger in it. While it is off and open, it can be cleaned out and sprayed out with carb cleaner. You will possibly need a new gasket between the top and main body. You may be able to buy these parts without buying the whole carburetor kit, but it may be faster and a better value to just buy the kit.

 

[yellowdog5]

That is the problem. Your accelerator pump is not working. The plunger is probably torn or hard or something. The top needs to come off of the carburetor to put a new accelerator pump plunger in it. While it is off and open, it can be cleaned out and sprayed out with carb cleaner. You will possibly need a new gasket between the top and main body. You may be able to buy these parts without buying the whole carburetor kit, but it may be faster and a better value to just buy the kit.

Is this the stuff I need? https://quadrajetpower.com/accelerator-pump-assembly-with-air-horn-gasket/
I am a little worried that not getting enough fuel might be a blockage in the lines or in the electrical part that switches the tanks. When I first started trying to figure this out, I tried to check the fuel pressure by disconnecting the fuel line at the carburetor, cranked the motor for 10 seconds and got 6 ounces of fuel, someone on this forum told me to try it that way, he said it seemed low but was still more leaning toward the carb being the problem. About 1500-2000 miles ago the tanks were removed and the fuel lines replaced. They couldn't find the part that switches the tanks, I don't know if they re-used the old one or ended up putting a used one in.
I had to get a load of hay this morning about 10 miles away, really puny with a load on. Good thing it was flat ground

 

[85K304SPD]

That looks like what you need, as long as it is the correct one for your carburetor number. It sounds like your fuel pump and lines are probably fine. 6 ounces in 10 seconds is like 67 gallons an hour. I dont think you could burn that much, even with a big load of hay on back.

 

[yellowdog5]

That looks like what you need, as long as it is the correct one for your carburetor number. It sounds like your fuel pump and lines are probably fine. 6 ounces in 10 seconds is like 67 gallons an hour. I dont think you could burn that much, even with a big load of hay on back.

Ok thank you, is there an instruction sheet or video that would help me with this?

 

[DoubleDingo]

Ok thank you, is there an instruction sheet or video that would help me with this?

There are tons of videos on youtube about the quadrajet. Worth a look. If you prefer reading, Cliff Ruggles book will have plenty of info. There are also manuals online you can buy and keep.

 

[yellowdog5]

That looks like what you need, as long as it is the correct one for your carburetor number. It sounds like your fuel pump and lines are probably fine. 6 ounces in 10 seconds is like 67 gallons an hour. I dont think you could burn that much, even with a big load of hay on back.

Is my math wrong? I get just a little less than 17 gal/hr., is that still enough? Seems like it to me but I'm no expert.

 

[Ricko1966]

Is my math wrong? I get just a little less than 17 gal/hr., is that still enough? Seems like it to me but I'm no expert.

Yes it's plenty. Now 6 ounces in 10 seconds is 36 ounces a minute x 60 minutes in an hour is 2160 ounces an hour divide by 128 to get gallons ,yep 17 gallons an hour at 10 miles per gallon that's 170 miles in an hour.

 

[yellowdog5]

That is the problem. Your accelerator pump is not working. The plunger is probably torn or hard or something. The top needs to come off of the carburetor to put a new accelerator pump plunger in it. While it is off and open, it can be cleaned out and sprayed out with carb cleaner. You will possibly need a new gasket between the top and main body. You may be able to buy these parts without buying the whole carburetor kit, but it may be faster and a better value to just buy the kit.

I am a little worried about taking the top off without removing the carburetor from the engine, afraid I might drop a screw into the motor. Any suggestions? I'd rather not take it off but I will if it seems smarter to do it that way. I haven't ever done any carburetor repair, so I'm new to this.