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Tractor Talk Discussion Forum

'79 Ford pickup cranking away !!

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JJ. in B.C.

02-20-2006 17:18:23




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'79 Ford pickup with 460 motor. After standing overnight it seems like all gas drains back to tank. It takes forever to crank gas up to Carb. before it will start. Does this sound like fuel pump or ???
JJ.




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JJ. in B.C.

02-20-2006 20:52:15




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 17:18:23  
Hi Guys Thanks for replys. I have a number of the symptoms mentioned!!
I have the Holley 4barrel Carb.,the Choke is a manual replacement and opens and closes ok,i do get gas sitting on top of motor sometimes when hot, also floods sometimes when hot and requires open throttle to start it and long cranking. I'm sorry i don't understand what the power valve is . It dosen't squirt any gas out with the accl. pump until it cranks up fresh gas.
Thanks JJ.

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Jon Hagen

02-20-2006 22:38:13




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 20:52:15  
The power valve is a vacuum operated valve that adds a little extra fuel to the carb jetting for more power when the engine pulls hard. The problem is that this valve has a rubber diaphram that has gasoline from the fuel bowl on one side,and a vacuum passage to the intake manifold on the other side. If this diaphram gets a hole in it,then gas from the fuel bowl will run through the hole and directly into the intake manifold,causing warm flooding and an empty carb if parked overnight.
If you see gas on top of the intake manifold,there is a good chance that the rubber accelerator pump diaphram has a hole,or the pump cover is warped allowing gas to leak out of the fuel bowl and on top of the engine. Either problem will drain the carb in a few hours.

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Bob

02-20-2006 22:56:09




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 Re: '79 Ford pickup cranking away !! in reply to Jon Hagen, 02-20-2006 22:38:13  
Jon,

He said he had a Holley, so the power valve is INTERNAL, and NOT covered by an external (leaky) bottom cover, as is the power valve in Ford carburetors, so he's not gonna see fuel on top of the intake, due to a bad power valve.

However, a bad Holley power valve will cause poor mileage, and "flooding" at idle.

The Holleys are sure prone to leaky float bowl and metering block gaskets, though, which will drip gas on the intake manifold.

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Jon Hagen

02-21-2006 11:18:43




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 Re: '79 Ford pickup cranking away !! in reply to Bob, 02-20-2006 22:56:09  
Your right Bob,I may not have made myself clear.My intent was to say a Motorcraft or Holley will leak fuel on top of the intake manifold if the accelerator pump diaphram is leaking or pump cover is warped. A blown powervalve in either brand will dump fuel inside the intake manifold through the vacuum passage.



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JJ. in B.C.

02-21-2006 10:28:51




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 Re: '79 Ford pickup cranking away !! in reply to Bob, 02-20-2006 22:56:09  
So if i go buy a rebuild kit does this contain all the parts i need to fix this problem ??
Thanks, JJ.



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Jon Hagen

02-21-2006 11:39:11




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-21-2006 10:28:51  
Yes,a new carb kit will have a new power valve and accelerator pump diaphram which are made of materials compatible with fuel that contains 10% ethanol,so fuel blend should not be a problem after the carb rebuild. You should lay the accelerator pump cover,gasket/diaphram side down on a flat machined piece of metal. Hold it up to the light and see if any light shows between the pump cover and flat piece if metal,which would indicate a warped cover. A warped cover should be replaced or filed/ground flat to prevent any fuel leakage. I have milled flat many Motorcraft or Holley pump covers by laying a sheet of emery cloth on a sheet of glass,and rubbing the pump over over the emery cloth untill the entire gasket surface is ground shiny and flat. Be carefull to keep your manual choke on untill the engine warms up a bit. A lean backfire in a cold engine without enough choke applied is the cause of 90% of power valve failures. That backfire in the intake manifold will raise a pressure spike that can rupture the power valve diaphram.

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JJ. in B.C.

02-21-2006 14:32:42




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 Re: '79 Ford pickup cranking away !! in reply to Jon Hagen, 02-21-2006 11:39:11  
Thanks very much Jon and everyone else for the valuable information, all i need is for it to warm up a few degrees out there and i can get to it !!
Regards, JJ.



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Bryan in Iowa

02-20-2006 19:28:42




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 17:18:23  
Well ,,first I'd make sure choke is closing all the way . Check Accel pump ,,make sure your getting good shot of fuel first time you pump throttle .79 460 could have Holley 4 bbl , or Motorcraft 4 bbl on it . Holley can have leaking power valve, or accel pump ,,either may drain fuel bowl.Motorcraft carb may have jet well crack or leakage . Also ,,make sure your getting good spark right off the bat . Seem some pickup coil problems that caused ahrd starting ..Keep us posted

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the tractor vet

02-20-2006 19:15:20




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 17:18:23  
More then likely it is a bad power valve that is leaking because you got ahold of some gas that has alchol of some sort and it does not matter ifit is the holley of the motorcraft carb they both do it . Just get a rebuild kit and clean it out and throw the kit in it and all will in Whoville and watch the kind of gas ya put thru it . Back in the days of the go fast cars a cheep gas co. was sellen hightest for less then most places sold reg for and there gas was laced with alchol and gave us fit in the holley carbs it would eat a power valve out in less then a week and after awhile it would take the fuel pump out .

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bo

02-20-2006 18:20:03




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 17:18:23  
That can't happen. Let me explain why. If you are driving and you stop, your carb bowl is full of gas. It is not possible for that fuel to drain back. It might syphon out into the intake manifold but I don't think so. If the bowl is full, then it ought to at least fire up and then die after it uses up that fuel and if no more is getting into it.
If you told me that it sat for a week or two and then did that, I'd tell you that the fuel evaporated from the bowl and that's a possibility.

First off, check to make sure your choke is closing and the choke pull off is cracking the choke plate a bit. If it isn't, manually close the choke and try it and then come back here with a report. If the choke plate is closing, and it still does that, you'll need to tell us what type of carb you have. Two barrel, four barrel, mechanical choke, or electric choke and you'll also need to tell us if the choke is closing is the choke pull off working.

With out this info, no one can help you.

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Bob

02-20-2006 19:40:35




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 Re: '79 Ford pickup cranking away !! in reply to bo, 02-20-2006 18:20:03  
bo,

If you have ever been around a Holley carb, you'll know there is no such thing as there being enough gas in the float bowl overnight to even fire up the engine, so it can then die!

Them gas wasting things will leak, boil out, or evaporate more gas than about any other carb known to man!!!

(OK, I'm exagerating just a little, but it ain't far from the truth!)



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bo

02-20-2006 20:06:47




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 Re: '79 Ford pickup cranking away !! in reply to Bob, 02-20-2006 19:40:35  
Ok...still, it's a carb problem and not a "leak back" problem...as I said, I have no clue what carb he has on that thing. I don't even know if he knows how to set a choke and if he doesn't, he'll crank the heck out it to start it.



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Jon Hagen

02-20-2006 18:42:40




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 Re: '79 Ford pickup cranking away !! in reply to bo, 02-20-2006 18:20:03  
On some model motorcraft carbs a leaking or loose power valve will drain the fuel bowl dry overnight. This will also flood the engine after a 15-30 min shutdown when warm,requiring open throttle and long cranking to clear it out. Also a leaking accelerator pump diaphram or warped housing cover will drain the fuel bowl onto the intake manifold. In this case you should see/smell raw gas on top of the engine at the carb base when warm.

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bo

02-20-2006 18:45:31




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 Re: '79 Ford pickup cranking away !! in reply to Jon Hagen, 02-20-2006 18:42:40  
Yes, but the still the fuel won't drain back and as you say, you should smell some nasty gas even outside the truck. So, need more info.



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Bill(Wis)

02-20-2006 17:42:52




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 Re: '79 Ford pickup cranking away !! in reply to JJ. in B.C., 02-20-2006 17:18:23  
How about filling the tank and see if it does it then? You might have a slight leak at a connection up front that opens up when it gets cold and allows gas to drain back to the tank. I'd look over the lines and pay particular attention to connections that are up higher than the tank.



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