Need some F tuning help.....

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Oct 10, 2007
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Location
Arlington, VA
I've got a '73 40 with F engine. Just rebuilt the carb, replaced fuel filter, removed gas tank... drained and flushed it clean. Purged all fuel lines with compressed air. No crap was found in the fuel system. Engine will not start without pouring gas in the carb. With choke on, engine idles and runs perfect. With choke off, it idles fine but starves for fuel when you hit the pedal. Accelerator pump is new and linkage looks to be operating correctly. Also, no apparent vacuum leaks via the "piece of cardboard over the air horn" test. Anyone have any ideas what's going on here?
 
Check the fuel pump, disconnect fuel line at carb extend line to an empty container.
disable ignition, crank engine and observe fuel flow and pressure.
Do it outside and have extinguisher handy just in case.

Hero
 
Yes, already tried that as well. Disconnected fuel line at the carb and turned motor over. The jar I placed the fuel line in filled up nicely with clean fuel. And, the sight glass on the side of carb shows fuel halfway up the glass which I believe is correct. This ones got me stumped....
 
Idle circuit clogged? Solenoid wire attached and with power?
 
Ran into the exact same problem with my fathers 78 (except it would crank with the choke on) pulled the top off and put the old accel. pump back in and now it accel. almost as if the new pump was a smaller dia. If you looked down the carb and manually pumped it it would squirt only a small amount. Idled great but as soon as you touched the gas it would die.
 
Didn't replace the float, but adjusted it to show gas halfway up the sight glass. If idle circuit was clogged, the motor wouldn't idle, right? My engine idles perfect so possibly there isn't a blockage. Would a faulty solenoid cause the failure to start and rough acceleration? When fully warmed up, I still have the fuel starvation problem, so I'm not sure what's going on....
 
I've checked the AP circuit...when you work the accelerator linkage back and forth, I can see a small stream of fuel squirt into the carb. Now whether or not it's squirting enough fuel...I'm not sure. I think I'll make sure idle solenoid is working and if so, remove carb, disassemble, and check AP passage and low and high jets. I've had my carb off too many times now...at least I've got removal time down to about 5 mintues. I think I could dismantle and reassemble that carb blindfolded!!!
 
The most frustrating thing about this problem I'm having is that the motor runs perfect with choke on and after pouring gas in carb. It sounds like a smooth sewing machine, but stomp the pedal....and the problems arise.
 
I had a hell of a time with the accel pump plunger on mine one time. Even with a new plunger, it would not squirt enough gas. Ran similar to what you are describing. Sometimes new plunger will not expand enough, even with gas. Cheap kits do this most commonly. I finally got it to work, but I had to massage the leather and soak it really good in some light oil. Then put it together wet with oil. Stayed working after that.

Otherwise, without the AP, it will be hard to start. The squirt, with a good long push of the linkage is actually pretty forceful, and will almost turn to mist with a real hard fast push. The plunger will actually empty the bowl in a few good strokes.

It won't idle worth a damn if you have a vacum leak, or the idle selonoid is not working. Will idle good with choke, but not hardly at all without choke.

Also on the AP, there are several checkballs in most kits you get. If you used the wrong sized one in the opening in the bottom, then it may allow fuel to backfeed into the bowl, and not out the little nozzle when pumped, that is, if the pluger is actually sealing properly. The ball I speak of, is at the bottom of the plunger well, under a "G" shaped retainer. Unless it looks gunky down there, you may not have removed it.

I bet the plunger is not sealed properly. Will it accelerate very slowly? The AP is needed, but opening the butterflies slowly will induce the high speed curcuit due to vacuum. On a flat road, it will still run without the AP, but badly.

I have taken the top of the carb off on the vehicle many times, you can do this to get to the AP plunger, without taking the carb clear off.
 

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