V-8 flathead problems

[Tony Wheeler]

Originally Posted by BCA

I can get it to idle fine but there is no power above the low speed idle range. When I floor the pedal it just coughs and the only way to get it driving is to use very little gas pedal - obvious it won't go very fast. It gets worse as after about 15 minutes of 15-20 mph driving.

Based on my own experience Brian, it's a carby problem. I've struck these exact same symptoms several times when reviving long neglected Ford CMPs, in fact I've come to expect it! A good cleanout always gets them running properly, which leads me to suspect the problem is caused by blockage/obstruction of the main fuel supply passages. That would leave the motor nothing to run on but the idle fuel supply, which is only adequate up to around 1200-1500 rpm with very light throttle. You can sometimes suck a bit more fuel out by using choke, which increases vaccuum, but as the motor warms up it runs even worse on choke.

The question of course is how could your rebuilt carby be blocked? I can think of a couple of possibilities but the question is academic - the fact is you have NOT proved this carby, and you need to do so before looking elsewhere. The carby is the obvious culprit for these symptoms, which I think you already suspect, judging by your immediate replacement of it, and your attention to possible fuel starvation elsewhere.

As a first step you can simply remove it and blow compressed air into the main jets, by removing the main jet plugs (the two large slotted head brass plugs in the float chamber) and poking the air nozzle through. You can also backflow compressed air along the main fuel supply passages by poking the air nozzle into "G" Main Nozzle (see RH diagram). This is where you're seeing droplets emerging at idle, which is quite normal, but is NOT what the motor is running on at idle. It's a tiny insignificant amount of fuel, which will become a steady stream when the throttle is opened, and will be atomized by the greatly increased airflow. Unless of course there's a blockage!

This quick procedure has worked for me a couple of times with decent carbies, but more often than not I've had to deal with crusty old carbies full of rust flakes and scale and crap from years of running without a filter. Not to mention mud wasp nests after years outdoors with no air cleaner - that shit is harder than concrete! I don't know what the professionals do with these carbies, but no solvent known to man will get rid of that stuff, you need to completely disassemble them and thoroughly clear all fuel passages individually, which can only be done by poking bits of wire down them (preferably copper wire so as not to gouge them). That's what I do and so far it's worked like a charm every time, I don't even bother with a carby kit, just stick the old bits of gasket back on!

Anyway good luck Brian, and whatever the outcome it's worth getting to know the flathead carby, because it can save a lot of time and effort chasing non-existent timing problems in impossible to get at distributors!

[Tony Wheeler]

Any progress on the motor Brian? I'm interested to know where the fault turns out to be.

[BCA]

Thanks for all the responses. Chris, yes this was your Cab 12 F15A - getting dusted off after I got it from you in 2000 (!).
And Tony, I like your comments and they make sense. During this escapade I have changed fuel pumps, used an auxillery tank with fresh gas, checked fuel pump pressure and to day did a good flow test. With help from Stew Robertson we pulled the distributor and all looked good (no reason for the timing to have changed but points could have been bad or something). Two carbs have been tried. Two coils have been tried. No exhaust obstructions.: Still major lack of power over idle speed and no reaction when choke applied or accelerator pump activated. Spark always looked good from coil and at spark plugs. Couldn't see any errant sparking of the cables when it was dark outside.
So tonight I went for a test drive and it works great. Have no idea what solved the problem and I hope my luck continues. The only thing I can say is that tonight was cool, 65 degrees F versus 80 degrees F on previous days although there had been no reason to suspect a coil failing with high temperature. Maybe the rebuild carb just needed some exercise. .......... Brian

[Michael R.]

Ah yes, that wonderful rebuilt carburetor ... If the former carburetor is re-installed, do the lack of power issues return?

[BCA]

What do you think hold these parts in? Velcro? I wish it was so. I may revert to the original carb if only to eliminate other sources of the problem. If it works right off the bat then there is another unsolved problem.

[Lynn Eades]

Maybe all the squirrels hoardings blew out of the muffler? ( I saw a Canadian posted picture here once. We don't have them)