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Engine miss at idle, installed new carb kit, carb idle screws do not seem to make a difference

S

swc65

Regular Contributor
Hi
93 Galaxie OMC King Cobra, rebuilt crate Chevy 5.7L, spread bore Holley 650b carb

Back on the water this spring and pulled carb to get inserts installed to repair carb bowl bolt hole that I stripped last year. Put in new kit. When I go to start engine I have to give it full throttle to get it to start. It runs rough but will idle. I have checked timing as best as possible and looks to be 8 degrees before TDC per manual. Last year, I could start it with one bump and it idled perfect.

I know it has to fuel or fire or both. Trying to figure out where to start. When I pulled plugs they looked to be fouled by fuel. Plugs were black but dry however smelled like fuel. I cleaned and reinstalled and had same miss.

No matter how I adjust the carb adjustment screws it does not seem to make much of difference.

What is best way to check fire at the plugs. Its hard to get my head down into engine compartment to see the spark. Any tips?
 
No matter how I adjust the carb adjustment screws it does not seem to make much of difference.
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Ayuh,.... Sounds like the carb needs to Rebuilt, rather than just adjusted,....
 
I was thinking that already. I put in a kit myself basically it was needle/seat, accelerator pump and gaskets. Not sure if I did something working in reassembly.

So would poor carb adjustment lead to rough idle? I understand I can read plugs to see if engine is burning lean or rich. My understanding is I should see a grey to brownish color on plugs if combustion is proper, correct?

What is best way to check spark plug wires. I read and watched videos on ohming them out but I'm not sure what type wire I have, copper, INductive, carbon.

Should I get carb redone then see where I am?

Yesterday after post I took boat out and it stalled, had to be towed in. I noticed electric fueld pump not on. It appeared to be loose wire. After I repaired connection engine dfired up but still has a miss.
 
I removed carb today and went back into it. Discovered there were two small o'rings on a small transfer tube that connects the primary metering block to carb body. I replaced them and reinstalled and had immediate difference. I was able to adjust mixture screws and engine stumbled per manual. I turned full closed on both sides and open hlaf turn and engine seems to run perfect. I get about 16" Hg at idle (800RPM) over 20" when I throttle up. Needle is steady at idle.

I took it out for a run and ran great for about 20 minutes then at a cruise around 3000 RPM, engine stumbles and died. Restarted immediately and did it one more time before I got back to the house where I have a lift. So I solved for the very rough engine idle but now not sure what caused it to stumble. I'll refer to my manual however if you guys have any direction on where I should look next I'd appreciate it. I will not be back on water for at least a week so have some time to think on it and listen to any advice.

Bt Doctur, if I have anti siphon valve, I don't know where is is.

From here, I guess I can check fuel pressure on electric fuel pump. Not sure if it could be ignition. Look forward to your insight.
 
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swc65 said:
I removed carb today and went back into it. Discovered there were two small o'rings on a small transfer tube that connects the primary metering block to carb body. I replaced them and reinstalled and had immediate difference. I was able to adjust mixture screws and engine stumbled per manual. I turned full closed on both sides and open hlaf turn and engine seems to run perfect. I get about 16" Hg at idle (800RPM) over 20" when I throttle up. Needle is steady at idle.
I would lower the idle RPM to approx 650/700............... 800 RPM is too high for your KC Dog Clutch..... or for that matter, it is too high for a KC CC drive!

I took it out for a run and ran great for about 20 minutes then at a cruise around 3000 RPM, engine stumbles and died. Restarted immediately and did it one more time before I got back to the house where I have a lift. So I solved for the very rough engine idle but now not sure what caused it to stumble. I'll refer to my manual however if you guys have any direction on where I should look next I'd appreciate it. I will not be back on water for at least a week so have some time to think on it and listen to any advice.

Bt Doctur, if I have anti siphon valve, I don't know where is is.
The Anti-Siphon valve will be installed in the 90* fitting at the top of the fuel tank pick-up tube. The first section of fuel line will be connected to it.
I would also pull the tube from the tank and inspect the debris screen.

From here, I guess I can check fuel pressure on electric fuel pump. Not sure if it could be ignition. Look forward to your insight.
Your ignition system should be producing a whitish/blue spark..... not a yellowish spark.
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Continuing to research problem, I wonder if perhaps I may have some water in my tank. I think I do have a water fuel separator, it looks like an oil filter and is mounted in engine compartment. Fuel line from tank goes through it prior to electronic pump. I have been burning ethanol free fuel since last season to prevent water collection.

Thoughts? How would I check for that?

Further question on anti siphon valve, pardon the question but I'm going from memory. I do recall a square fitting on top of tank which I assume in the 90 degree referenced by Ricardo. Is the valve part of the fitting? I am trying to decide if I can buy one to take with me versus, taking apart then having to make another run. Boat is on lake in East Texas marine parts stores non existent. I line in Dallas, TX and there are several West Marine. If this is a universal type part I could pick one up. I should have taken pics but did not.
 
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swc65 said:
Continuing to research problem, I wonder if perhaps I may have some water in my tank. I think I do have a water fuel separator, it looks like an oil filter and is mounted in engine compartment. Fuel line from tank goes through it prior to electronic pump. I have been burning ethanol free fuel since last season to prevent water collection.
From what you have described, you have one of the standard type marine fuel filters. These rely on the limited filter media absorption.
A true water separating fuel filter will be a Parker/RACOR.

Thoughts? How would I check for that?
Dump the contents into a clear container. Let it settle out for a few hours and look for signs of water.

Further question on anti siphon valve, pardon the question but I'm going from memory. I do recall a square fitting on top of tank which I assume in the 90 degree referenced by Ricardo. Is the valve part of the fitting?
No.... the anti-siphon valve threads into the 90* fitting.
It will look as though it is a long barbed hose fitting..... but it will have the mildly spring loaded check ball inside of it.

I am trying to decide if I can buy one to take with me versus, taking apart then having to make another run. Boat is on lake in East Texas marine parts stores non existent. I line in Dallas, TX and there are several West Marine. If this is a universal type part I could pick one up. I should have taken pics but did not.
The TP Threads and fuel line ID will determine which one you need. I suppose you could buy several and then return the units that did not work.
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Ricardo, I've not learned how to reference quotes the way you did so I'll do old school.
When you say"Dump the contents into a clear container. Let it settle out for a few hours and look for signs of water. " Do you mean empty the gas tank? Obviously,Hard to do.

Trying to understand how an anti- siphon valve might cause my issue. If I understand its function, the valve would not allow flow from tank to bilge when there is a break in fuel line with very low differential pressure between tank and bilge. The anti siphon valve has to allow fuel under normal operation because fuel pump pulls fuel from tank. How would the anti siphon valve cause the engine to die? I suppose it is some sort of check valve (ball and spring?) that only seats under low dp?

Can you help fill in the blanks? :confused:
 
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swc65 said:
Ricardo, I've not learned how to reference quotes the way you did so I'll do old school.
When you say "Dump the contents into a clear container. Let it settle out for a few hours and look for signs of water. " Do you mean empty the gas tank? Obviously,Hard to do.
No.... empty the fuel filter cartridge into a container. Let it settle out and look for any separation.

Trying to understand how an anti- siphon valve might cause my issue. If I understand its function, the valve would not allow flow from tank to bilge when there is a break in fuel line with very low differential pressure between tank and bilge. The anti siphon valve has to allow fuel under normal operation because fuel pump pulls fuel from tank. How would the anti siphon valve cause the engine to die? I suppose it is some sort of check valve (ball and spring?) that only seats under low dp?

Can you help fill in the blanks? :confused:

The anti-siphon valve is nothing more than a light weight spring loaded check ball style one-way-valve.
It is designed so that the fuel pump's suction will easily overcome the check ball's resistance. In other words, the fuel pump' suction will open the passage that is blocked by the ball against the seat.
However, the check ball's resistance is just enough to prevent a gravity siphon in the event of a lower-than-the-fuel-level fuel line breach.

If/when the anti-siphon valve should become dirty, corroded, blocked by debris and/or stuck closed, it may prevent the fuel pump from pulling in enough fuel for the engine. They are inexpensive and are easy to change out.
Click to expand...
 
I have one additional question. Can I reuse the fuel water separator? If so do I nee to apply oil on the sealing ring?
 
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