4.3 replacement motor. Having some fuel problems

[jbwrangler]

I did not try Mitchlevy's test. I took the needle and seats out and polished them with a polishing pad on my dremel to reduce friction (this may be hokey, but I'm running out of ideas). I also readjusted my floats. With the top of the carb off, I had a hard time getting them to stick. I don't know how much up pressure the floats put on the needles when the bowl is full. When I reinstalled I made sure the needles were down , It fired up and ran great. I restarted it a few times with no issues. Then, I wait about an hour and go out and it restarts, runs for 15-20 seconds and dies. Will not restart.

 

[jbwrangler]

I agree Rick but it would be a good way to see what is happening, wether it’s just the needles and seats getting stuck or something else. Also it costs nothing which is even better!

Mitch, what would I be looking for in this test?

 

[nola mike]

To see if fuel comes out--if the needles are opening and if that's actually the problem.

 

[Mlevy]

It seems like the bowls are emptying while sitting. I would loop the wires to the oil pressure switch so when you put power to with key on it will run. Then I would “prime” the carb by letting the pump run for 10-15 seconds before starting. It could also be the switch itself so that would rule that out as well.

 

[alldodge]

Even if bowls are leaking out (don't think so) the motor running for 5 seconds it would be full again.

 

[Mlevy]

Yes as long as the pressure switch is working correctly, if not the pump could be getting mixed emotions from the switch or none at all. The bowls seem to be empty when he has this issue as stated in the original post he removed the top of the carb and the bowl was empty so it is going somewhere weather it be no delivery and consuming until empty, evaporating, or leaking into the intake. Also a very easy + quick way to rule out and is free!

 

[alldodge]

Wouldn't happen to have the wrong switch, a NC instead of NO contacts. If so, pump runs when starting but shuts off when oil pressure comes up

 

[Lou C]

Wouldn't happen to have the wrong switch, a NC instead of NO contacts. If so, pump runs when starting but shuts off when oil pressure comes up

ahh excellent point!
that's why I like simple mechanical fuel pumps!

 

[jbwrangler]

The pump seems to run as it should. FP comes on when oil pressure reaches 7-8lb. Will stay on until oil pressure drops below 7-8lb (with key on engine not running)

Couple of things maybe? Let me know if these ideas have any merit.
1. Check valve in FP messed up? I have tested the FP, and seen it pump fuel into a gas can, but not actually pump under pressure.
2. At 7-7.5 lb, my fuel pressure is a little high according to edelbrock recommendations. Could this somehow cause the rubber part of the needle to get jammed into the seat? If the bowl filled too quickly? Doesn't seem likely to me.

 

[nola mike]

Wouldn't happen to have the wrong switch, a NC instead of NO contacts. If so, pump runs when starting but shuts off when oil pressure comes up

From post #1:
"After cranking with the key in th eon position I can hear the fuel pump pumping until t he oil pressure falls below 8lb."

But agreed that jumping the switch would take that out of the equation...

 

[nola mike]

b, my fuel pressure is a little high according to edelbrock recommendations. Could this somehow cause the rubber part of the needle to get jammed into the seat? If the bowl filled too quickly? Doesn't seem likely to me.

Interesting you say that. My pump was putting out 7.5-8psi when the needles appeared stuck. I was flooding though at that pressure.

 

[Mlevy]

The fuel pump having too much pressure would flood rather than starve of fuel. Like I mentioned before it might not hurt to test with top of carb off. Loop the pressure switch and then you can play with the floats while it’s pumping fuel. Being able to see what is happening would be valuable in this situation. Also take pictures of the inside of the carb and floats etc when you have it apart, it would help us to be able to see as well.

Mitch

 

[jbwrangler]

The fuel pump having too much pressure would flood rather than starve of fuel. Like I mentioned before it might not hurt to test with top of carb off. Loop the pressure switch and then you can play with the floats while it’s pumping fuel. Being able to see what is happening would be valuable in this situation. Also take pictures of the inside of the carb and floats etc when you have it apart, it would help us to be able to see as well.

Mitch

I am in process of doing this test, except on a bench.

Today I installed new seats and needles. They were hi flow because that was all that was readily available. I thought it had fixed the issue, but I ended up with the same result. I took the top off the carb and did not disturb the needles (stuck in the up position) I blew through the fuel inlet as hard as I could and it did not unseat the needles. I talked to Edelbrock, this was not an issue that they had documented. He is sending me a new set of needles/seats.

The needles are so stuck, I now think that their may me some sort of vacuum sucking them back up into t he seat? Is this possible?

 

[Mlevy]

How high was the gas inside the bowl after bench testing?

 

[jbwrangler]

Ok, results of the benchtest are in... I connected the pump to draw from a gas can through the water sep filter and into the carb. I ran the pump for 3 min , the shut off for 10 min. I repeated this two more times. There was no gas leaking/overflowing from the carb.

Then I took the top off the carb. The needles were stuck in the up position. (edelbrock says this is normal and the 5.5 lb of the FP will easily open the needles) I held the top of the card over a bucket and turned on the fuel pump. The needle closest to the fuel inlet opened immediately. When I closed that needle manually ( to simulate the bowl filling), the other needle opened up..

So, I am back to something other than the pressure of the floats is causing the rubber part of the needles to jam into the seat? Any ideas? Does this sound plausible?

 

[nola mike]

Makes me think that the floats aren't dropping when the top is on there.

 

[Mlevy]

Check the bowl baffles, it in backwards they will prevent the floats from dropping, they should look like they are overtop of the jets.

 

[jbwrangler]

Makes me think that the floats aren't dropping when the top is on there.

How would the carb fill the first time? On my bench tests, the bowls are filled as they should be.

 

[Mlevy]

[No message]

 

[Mlevy]

It can only be the floats not opening or you don’t have a fuel delivery problem if your fuel pump, anti siphon, pickup, fuel lines, ops, And needles + seats test good.When you put the top of the carb on without gas in the bowls can you see the floats hitting anything or are they hanging down all the way until you can see anymore when the top is seated to the carb?