Intake plenum gaskets

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yellowdog5

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Does anyone have the chart for float level for the various quadrajets? Mine is 17059226.
 

yellowdog5

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I have a ‘75 K25 350 with an 80’s vintage Quadrajet that is similar to yours. Some suggestions.

- if you can’t see fuel squirting in, you definitely need a new accelerator pump assembly. Get one that has seals designed for new ethanol mix fuel. Old pumps had rubber gasket that do not hold up well to new fuel.

- are you sure you got the fuel filter and spring in the proper order and orientation. It’s very easy to forget how they came apart, and the wrong installation will really screw up fuel flow.

- I see two T fittings in the line to the PCV. Do they go to a vacuum canister to vent the tanks? If they do, there is also a purge valve in the system and the purge is vacuum controlled. If not working correctly it could cause a big vacuum leak.

- have you changed the PCV valve? I had mine pop out once from a backfire and it caused the engine to run really bad at idle. Mine was laying on its side, so it was open and causing a big vacuum leak.

- have you verified base timing and that the mechanical advance is working? Factory base timing recommendation is probably about 6 BTDC, but the engine will run much better with about 12 BTDC at 650 rpm, with the vacuum advance line unplugged and capped. Then use a setback timing light to verify that you get about 18-20 degrees more (so it’s now 30-32 total) when rpm is at about 2500-2800 rpm.

Reconnect the vacuum advance line at idle and check to see that you get about 18 degrees from vacuum advance. You need this to help your highway gas mileage.

- do you have a 3 port fuel pump with a return line to the tanks? It will work with a 2 port, but you may have vapor lock issues in hot weather. The tank return keeps circulating fuel and cools it down.

- you said the fuel tank lines and solenoid were worked on recently. Did that mechanic understand the system? It’s not real complicated, but hooking up a few lines incorrectly can screw up fuel flow. For example, if you have a fuel return line they must use a 6 port valve that switches both fuel feed and return. 6 port valves are no longer available new. The vent lines for the tanks T together and run up to the vapor canister.
1. Ok changing the accelerator pump today.
2. Yes but I think it needs a grommet, got a new one today.
3. Pretty sure fuel filter is correctly installed but I'll check
4. Yes I think so I'll take pictures of what I think are vacuum cannisters. Can I eliminate them or do I just need to find where the purge valve is?
5. I have never checked timing, would need instructions on how to do it. The guy that came and looked at it did check timing and thought it was ok. I have a timing light but not sure what kind, probably a cheap one, inherited it from my father in law. I know what TDC is what's the B?
6. Yes 3 port fuel pump.
7. The valve was either re-used or replaced with a used one, never was sure which it was, Yes I'm sure he knew what he was doing he did a lot of work for us, that was 3 or 4 years ago and there were no problems (other than needing to prime the carb to cold start which has been that way for a long time) until this recent one in the last few weeks. The truck was not driven regularly until about a year ago, now I use it about once a week to pull my horse trailer.
 

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Does anyone have the chart for float level for the various quadrajets? Mine is 17059226.
I've got the instructions at home for all the quadrajet setting instructions. I can post them tonight when I get home if I remember. Float level for all truck quadrajets as far as I've seen is supposed to be 3/8". You measure it by gently pushing the other end of the float arm down to set the needle in the seat and then you measure from slightly back from the tip of the float to the top of the carb body casting. You should have a plastic float, if you have a brass one, it actually should be set a bit higher to offset the heavier float.
 

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I suggest only checking the Quadrajet for vacuum leaks, and replace the accelerator pump. Once you start to take the rest apart you are on a potentially long road to get it back together and adjusted correctly. Even verifying float level means you have to remove the top, and there are clips that get lost, gaskets misaligned, etc.

There is also an old saying that 90% of all carburetor problems are ignition or electrical related. Correct timing is really your friend when you need power.

It’s easy to use a dialback timing light to check your ignition advance. You can use a cheaper one, but I suggest biting the bullet and getting something like the Innova 5568, which has a tach and a digital timing display. It’s about $110 on Amazon, and it’s great for troubleshooting.

FYI - I tried using a cheap equivalent from Harbor Freight, and after buying two that both showed my truck idling at 1400 rpm when my dash tach showed 800, I gave up. They still had the gall to charge me a restocking fee because it was an electronic instrument.
 

yellowdog5

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I suggest only checking the Quadrajet for vacuum leaks, and replace the accelerator pump. Once you start to take the rest apart you are on a potentially long road to get it back together and adjusted correctly. Even verifying float level means you have to remove the top, and there are clips that get lost, gaskets misaligned, etc.

There is also an old saying that 90% of all carburetor problems are ignition or electrical related. Correct timing is really your friend when you need power.

It’s easy to use a dialback timing light to check your ignition advance. You can use a cheaper one, but I suggest biting the bullet and getting something like the Innova 5568, which has a tach and a digital timing display. It’s about $110 on Amazon, and it’s great for troubleshooting.

FYI - I tried using a cheap equivalent from Harbor Freight, and after buying two that both showed my truck idling at 1400 rpm when my dash tach showed 800, I gave up. They still had the gall to charge me a restocking fee because it was an electronic instrument.
Don't I have to remove the top to replace the accelerator pump?
 

75gmck25

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Sorry for being unclear. I was just suggesting a quick and dirty check to see if you can get the accelerator pump to squirt properly. That and a choke adjustment might solve the hard starting problem

You will have to unbolt and lift the top to replace the accelerator pump, so there are still parts that can get dropped or lost. However, in the past I have been able to do that by just lifting up the top a few inches and gently working the pump up and out to replace it. Then I carefully drop it back down, and if I’m lucky the rods drop in correctly and I’m ready to put the bolts back in. YMMV.

If I go any farther I will always remove the carburetor from the engine and put it on the bench so i am less likely to lose small parts. Then I start down the road of cleaning it all and the job gets longer. It’s often hard to know where to stop cleaning and checking.
 

yellowdog5

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Sorry for being unclear. I was just suggesting a quick and dirty check to see if you can get the accelerator pump to squirt properly. That and a choke adjustment might solve the hard starting problem

You will have to unbolt and lift the top to replace the accelerator pump, so there are still parts that can get dropped or lost. However, in the past I have been able to do that by just lifting up the top a few inches and gently working the pump up and out to replace it. Then I carefully drop it back down, and if I’m lucky the rods drop in correctly and I’m ready to put the bolts back in. YMMV.

If I go any farther I will always remove the carburetor from the engine and put it on the bench so i am less likely to lose small parts. Then I start down the road of cleaning it all and the job gets longer. It’s often hard to know where to stop cleaning and checking.
Ok thank you. I have it off, it needs a new mounting gasket anyway.I think I'm just going to replace the accelerator pump and clean it up and check the float for now, Many of the other parts have been recently replaced. I know there are charts that come with rebuild kits that tell where the float should be set. If anyone has that my carb is 17059226.
 

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Ok thank you. I have it off, it needs a new mounting gasket anyway.I think I'm just going to replace the accelerator pump and clean it up and check the float for now, Many of the other parts have been recently replaced. I know there are charts that come with rebuild kits that tell where the float should be set. If anyone has that my carb is 17059226.
Be sure to take some pics while you're doing the work.
 

yellowdog5

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Is the part indicated in the picture just for air conditioning? If so can I remove it? AC is history in this truck.
 

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Bextreme04

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Is the part indicated in the picture just for air conditioning? If so can I remove it? AC is history in this truck.
Yes, that is the idle kick up solenoid that engages when the AC is engaged. The two prong electrical connector that is next to it(not plugged into anything) is the connector for the AC compressor.

I totally forgot to check for the carb instruction sheet last night, I'm getting some stuff ready to swap out an engine in my wifes suburban tomorrow and got distracted. I'm 99% sure that the correct setting is 3/8" for your float level though. The performance guys recommend setting it between 21-24/64", which is easier to do with the little white hard paper ruler that comes in most of the rebuild kits.
 

yellowdog5

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I got the carb off the truck and apart today, got the air horn off ok. I poured the gas that was in there out. The power valve with the two needles was stuck and a little bent, and the needle valve was completely off and the wire spring that holds it on the float was off. How did that happen, did I do it pouring the gas out? don't think I bent the power valve part, and I think I got it straightened out ok, but maybe the needle valve fell off when I poured the gas out? I put it back together and hung it on the float, should I get a new one? Having trouble figuring out how to check the float level. I found a really good video that is pretty helpful but this is kinda scary for me. Not sure how I'm going to get the needles on the power valve into the jets, and I don't want to try until I know if I should get a new needle valve.
 
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Grit dog

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1. Ok changing the accelerator pump today.
2. Yes but I think it needs a grommet, got a new one today.
3. Pretty sure fuel filter is correctly installed but I'll check
4. Yes I think so I'll take pictures of what I think are vacuum cannisters. Can I eliminate them or do I just need to find where the purge valve is?
5. I have never checked timing, would need instructions on how to do it. The guy that came and looked at it did check timing and thought it was ok. I have a timing light but not sure what kind, probably a cheap one, inherited it from my father in law. I know what TDC is what's the B?
6. Yes 3 port fuel pump.
7. The valve was either re-used or replaced with a used one, never was sure which it was, Yes I'm sure he knew what he was doing he did a lot of work for us, that was 3 or 4 years ago and there were no problems (other than needing to prime the carb to cold start which has been that way for a long time) until this recent one in the last few weeks. The truck was not driven regularly until about a year ago, now I use it about once a week to pull my horse trailer.
So it runs good enough to pull a horse trailer down the highway? Seems only problem then is the priming issue?
 

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