Compression check
- Thread starter SLEMMON
- Start date
Update - primed the carb, and checked the lines and tried to start it. It coughed a little and a couple more tries later it fired off. Got it running but had to keep feathering the throttle. If I let my foot of the peddle it will die. I can fire it right up but I have to keep it running a higher rpm's's. Runs great at the higher rpm's, try to bring it down towards idle and it starts running like crap then dies.
I played with the idle screws and have about 3 1/2 turns out but it does not help. I also played around with the dizzy didn't see much help there.
Also why would the fuel drain out of the fuel line. You can watch it drain out of the fuel filter once the engine dies.
And I cant get the fuel to raise in the fuel bowl. I had the sight plug off and while cranking it, I couldn't see the fuel in the bowl. I adjusted the needle as high as I could and no change in the fuel bowl. Is the fuel by-passing somehow?
Plus the engine will only run for a couple minutes even with me feathering the throttle until it dies. Maybe starvation, using up what fuel is in the bowl
I played with the idle screws and have about 3 1/2 turns out but it does not help. I also played around with the dizzy didn't see much help there.
Also why would the fuel drain out of the fuel line. You can watch it drain out of the fuel filter once the engine dies.
And I cant get the fuel to raise in the fuel bowl. I had the sight plug off and while cranking it, I couldn't see the fuel in the bowl. I adjusted the needle as high as I could and no change in the fuel bowl. Is the fuel by-passing somehow?
Plus the engine will only run for a couple minutes even with me feathering the throttle until it dies. Maybe starvation, using up what fuel is in the bowl
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Scoutboy74
Moderator
Generally with a cold engine, you will need some choke applied to keep the engine running. As the engine warms, the choke can gradually be opened. I don't recall you mentioning what style of choke your carb has, manual or electric and whether it is functional. That's one thing.
For the idle mixture screws, the more turns out they are, the richer the mixture is at idle. Your engine is unable to idle right now, so that's kind of moot. A good starting point with the mixture screws is 2.5 turns out from gentle seating. Set them there and leave them alone for now. Both screws should always be an equal number of turns out.
You also have a curb idle speed screw. You should examine this screw to see if perhaps it has been backed off to the point that it is not applying any tension to the accelerator linkage.
Fuel should not be draining out of your fuel filter once the engine dies or is shut off. The only way your engine is able to run is at higher revs, so its burning fuel at a faster rate than you'd see at a true idle. Even so, a good pump will be able to stay ahead of even wide open throttle demand. Either the fuel pump is faulty or the carb is dumping excess fuel down the intake faster than the pump can replenish it.
The fuel filter drainage points squarely at the fuel pump. No other component would be responsible for this condition. Where is the fuel draining to? Back into the tank, or into the crankcase? I know you attempted a bench test and it seemed to pass, but I just don't know how much, if any faith you should put into those results. The real world indicators are pointing towards pump failure.
For the idle mixture screws, the more turns out they are, the richer the mixture is at idle. Your engine is unable to idle right now, so that's kind of moot. A good starting point with the mixture screws is 2.5 turns out from gentle seating. Set them there and leave them alone for now. Both screws should always be an equal number of turns out.
You also have a curb idle speed screw. You should examine this screw to see if perhaps it has been backed off to the point that it is not applying any tension to the accelerator linkage.
Fuel should not be draining out of your fuel filter once the engine dies or is shut off. The only way your engine is able to run is at higher revs, so its burning fuel at a faster rate than you'd see at a true idle. Even so, a good pump will be able to stay ahead of even wide open throttle demand. Either the fuel pump is faulty or the carb is dumping excess fuel down the intake faster than the pump can replenish it.
The fuel filter drainage points squarely at the fuel pump. No other component would be responsible for this condition. Where is the fuel draining to? Back into the tank, or into the crankcase? I know you attempted a bench test and it seemed to pass, but I just don't know how much, if any faith you should put into those results. The real world indicators are pointing towards pump failure.
FDChappie
Well-known member
First off, it runs! Good advice from sb, don't mess with any of the carb adjustments until the float level is set. It's not unusual for the filter to drain over night. Possibly you have a bad pump. Disconnect the fuel line at the carb and put the end in a 16oz or larger can. Run the engine for about 15 seconds. If the can is not over 1/2 full, check the filter if its good then try a new pump. If the can is over 1/2 full, pull the brass fitting the fuel line connects to on the carb and see if the filter under it is clean.
Lots of good info there, I have a Holley electic choke on the carb, and it is working, wheater I have it adjusted right is another thing. The idle screws are set at 2 1/2 turns now.
The curb idle screw isnt set, at one time I did run it down to keep the Scout running while I was trying to make adjusted but the rpms were way high ( but that was awhile ago).
The fuel is draining out of the line going to the carb back down the line and ino the fuel pump and I guess from there back into the 5 gallon gas can I am running it from.
As for the bench test I did, it was just matter of seeing if would pump fuel, which it did. But as for holding pressure in the line to keep the fuel from draing I guess not. I pulled the fuel bowl off thinking the float might be stuck but it wasnt I had it adjusted way down. So adjuted the float so it could come almost to the top of the bowl and the pump still would not fill the bowl while canking the engine over. I took the set screw off of the needle valve and tried again, and fuel was spitting out of there.
It is like the arm on the pump isnt moving enough the actuate the pump properly
I will next test the pump like chappie suggested.
The curb idle screw isnt set, at one time I did run it down to keep the Scout running while I was trying to make adjusted but the rpms were way high ( but that was awhile ago).
The fuel is draining out of the line going to the carb back down the line and ino the fuel pump and I guess from there back into the 5 gallon gas can I am running it from.
As for the bench test I did, it was just matter of seeing if would pump fuel, which it did. But as for holding pressure in the line to keep the fuel from draing I guess not. I pulled the fuel bowl off thinking the float might be stuck but it wasnt I had it adjusted way down. So adjuted the float so it could come almost to the top of the bowl and the pump still would not fill the bowl while canking the engine over. I took the set screw off of the needle valve and tried again, and fuel was spitting out of there.
It is like the arm on the pump isnt moving enough the actuate the pump properly
I will next test the pump like chappie suggested.
Alright did the check that fdchappie suggested. I had a five gallon gas can for the pump to pull from and a 32 oz gatorade bottle for it to dispense into. After 15 -20 seconds of cranking it barely filled the the bottom of the bottle maybe a 3/8 of an inch. The filter looks good.
Question though I did not see an arrow on the filter for flow anywhere, which way does it go. It is the clear plastic kind with the filter in it. Let me go get a picture.
Question though I did not see an arrow on the filter for flow anywhere, which way does it go. It is the clear plastic kind with the filter in it. Let me go get a picture.
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Scoutboy74
Moderator
Look at the filter carefully in good light. They are directional and there will be an arrow. Every one of those filters that I've ever handled has had one.
Sorry for the late response. This weekend was busy for me. So back to business. As fdchappie requested I ran the truck as long as I could with the amount of fuel in the fuel bowl. May have been around 10 seconds. I had the fuel going into a 32oz gatorade bottle as shown in previous post, and in that time it filled the bottle to just shy of half way. So I think from previous suggestions that should be right on par with a mechanical fuel pump?
I hooked everything back up and tried to start the engine, it fired off but the carb soon started to push fuel out the vent tube. So I flooded it a little. I tried again with wot and I had forgot to to put the sight plug back in. But as it started to fire off and I seen gas coming out the sight hole I stopped and went over to take a look. You can see the fuel level going down fast in the bowl and watch the float bottom out. So where is this fuel going? Im at a loss!
Update to this post - went out and started it a couple times. It is running like a drowned pig. It is blowing fuel soaked exhaust out like crazy. Something is going on with this carb. It is dumping to much fuel in the intake.
Update to this post - went out and started it a couple times. It is running like a drowned pig. It is blowing fuel soaked exhaust out like crazy. Something is going on with this carb. It is dumping to much fuel in the intake.
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Draining the bowl dry like that I wonder if the idle air bleeds are plugged allowing fuel to siphon through.
Like chappie sez, get a kit. Get a good kit and post us pictures of your progress on tear down and assembly. Maybe we can help with the nuances of setting up a carb with the right gaskets and such.
I have a Holley rebuild kit on order (slow boat) from jegs.
I took the carb out and placed it on a make shift stand. Opened the sight hole and poured some gas in to make the float come up. As soon as I did that gas started pouring out of the bottom. I cleaned that up and took the bowl off. Everything looked okay there. I then took the metering block off looked at the jets ( I have a question about those) and power valve everything looked okay. I removed the jets and the power valve seemed okay, until I looked at a spare power valve still in the package and it had a gasket in there with it. There wasn't one on the carb. So I'm guessing that's where the gas was coming from.
So while waiting for the kit to come in and carb disassenbly, have been doing some reading on here about jets and power valves. My 7448 came with 61 jets. And that is supposed to be good sea level to 4000 ft. I live at 2800 ft but will go to above 5000 at leased when wheeling in the near by mountains. Jets should be changed out for 2000 ft of inrease. So I really should have a #60 or #59. But while on the Holley page (this is odd
) a #61 and #60 are the same hole size. But a #59 is two hole sizes down. Weird.
Power valve. Right now I have a 4.5 with the carb, I have a spare 5.0. And most everything that I have read suggests that for my 304 I should run a 5.0 or 6.0. This is based of off vaccum pressure, which I cant check right now. But since I have the carb tore down why not put as close as stuff I will need in it now
I took the carb out and placed it on a make shift stand. Opened the sight hole and poured some gas in to make the float come up. As soon as I did that gas started pouring out of the bottom. I cleaned that up and took the bowl off. Everything looked okay there. I then took the metering block off looked at the jets ( I have a question about those) and power valve everything looked okay. I removed the jets and the power valve seemed okay, until I looked at a spare power valve still in the package and it had a gasket in there with it. There wasn't one on the carb. So I'm guessing that's where the gas was coming from.
So while waiting for the kit to come in and carb disassenbly, have been doing some reading on here about jets and power valves. My 7448 came with 61 jets. And that is supposed to be good sea level to 4000 ft. I live at 2800 ft but will go to above 5000 at leased when wheeling in the near by mountains. Jets should be changed out for 2000 ft of inrease. So I really should have a #60 or #59. But while on the Holley page (this is odd
) a #61 and #60 are the same hole size. But a #59 is two hole sizes down. Weird.Power valve. Right now I have a 4.5 with the carb, I have a spare 5.0. And most everything that I have read suggests that for my 304 I should run a 5.0 or 6.0. This is based of off vaccum pressure, which I cant check right now. But since I have the carb tore down why not put as close as stuff I will need in it now
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I concur. Nice stand! A little stain and chrome nutz, you could sell those at a swapmeet 
your jets should be fine. I used to run #58 on my 345, then went to 61 when the switch to ethanol fuel was mandated.
It's more than just a hole diameter, there's also the profile of entering and leaving angles that effect flow. Usually these are miniscule changes but do affect engine output/driveability to some degree. For an appreciable change, 2 jet sizes makes a noticeable difference in performance, (+ or -), and mpg.
Usually you just lived with a carb going from optimum to sub-par when driving through large altitude changes. Unless you plan on staying awhile or racing, I wouldn't mess with settings you use for most of your driving.
There was a high altitude carb offered on trucks that featured an adjustable main jet, but all I've seen them on where 1 bbl bodies. They're collector's items now afaik.
your jets should be fine. I used to run #58 on my 345, then went to 61 when the switch to ethanol fuel was mandated.
It's more than just a hole diameter, there's also the profile of entering and leaving angles that effect flow. Usually these are miniscule changes but do affect engine output/driveability to some degree. For an appreciable change, 2 jet sizes makes a noticeable difference in performance, (+ or -), and mpg.
Usually you just lived with a carb going from optimum to sub-par when driving through large altitude changes. Unless you plan on staying awhile or racing, I wouldn't mess with settings you use for most of your driving.
There was a high altitude carb offered on trucks that featured an adjustable main jet, but all I've seen them on where 1 bbl bodies. They're collector's items now afaik.
Whooo hoooo. The damn thing runs and idles.
I put the new 5.0 power valve and #59 jets in, set everything up and gave it a shot. Cranked right over, fired off, almost started to idle. Little adjustment on the idle screw and it sits a little over 700 rpm's. I think the float maybe a little too high so I need to check that. I am so happy this beast is running again, even backed it out into the driveway and drove it up and down the cul de sac.
Lacks get up and go, so not sure there. But I have a bunch more stuff to get done before it is road worthy.
Thanks everyone for the help. Without this site, I would have been chasing my tail.
I put the new 5.0 power valve and #59 jets in, set everything up and gave it a shot. Cranked right over, fired off, almost started to idle. Little adjustment on the idle screw and it sits a little over 700 rpm's. I think the float maybe a little too high so I need to check that. I am so happy this beast is running again, even backed it out into the driveway and drove it up and down the cul de sac.
Lacks get up and go, so not sure there. But I have a bunch more stuff to get done before it is road worthy.
Thanks everyone for the help. Without this site, I would have been chasing my tail.