Orig fuel filter question

[GregL]

Hey Guys,

I just received my orig fuel filter from John at MWM and started reading up on it in the maintenance manual. The diagram shows a hose called 'filter-to-primer pump line' coming out the right side of the filter. My truck doesn't have that line anywhere, probably since the current filter is a modern inline filter. Is that hose necessary? What does it do and should I try to plumb one in? Thanks.

[Drew M.]

The hand primer was only installed on early M37s. It was dropped as the units frequently developed leaks. It was plumbed off the fuel filter housing - where the square head plugs are located.

You do not need it. I added it - makes starting when the truck after sitting for weeks and on cold days much faster.

[GregL]

Drew, so on those cold days do you pump the lever a few times before starting? My truck does have the lever on the fuel pump. Maybe I'll look into plumbing it back in. Thanks for the info.

[monkeymissile]

Greg,
two different primers: all the original fuel pumps had a priming lever, but early trucks had a primer system installed in the dash. That's the one being referenced here. Forgive me if I presumed you didn't know!

[Drew M.]

MM got it right. I'm not talking the lever on the f/p. I do not run the mechanical f/p. The hand primer looks like a typical aircraft hand primer that is located on the dashboard. They used to be common on 1920-1950 vehicles - especially for vehicles like our BB carbed 230 that lacked an accelerator pump operated by the gas pedal. By the 1960's, carb designs allowed gas priming by pumping the gas pedal with the driver's foot, so the old standby hand primers became redundant and were discontinued.

I'm starting to feel old now, . . . then again maybe that was when my favorite music started playing on the classics station.

[GregL]

I see, got it now. Still learning here, only had my truck a few months. You guys have been a lot of help, a great resource, thanks!

[monkeymissile]

I've only had mine about a year, but this and the PWA forum have been invaluable for bringing me up to speed. I am also thankful these trucks are simple and straightforward enough for a total newbie like me to confidently work on.

[monkeymissile]

. They used to be common on 1920-1950 vehicles - especially for vehicles like our BB carbed 230 that lacked an accelerator pump operated by the gas pedal. By the 1960's, carb designs allowed gas priming by pumping the gas pedal with the driver's foot, so the old standby hand primers became redundant and were discontinued.

Drew,
so if my truck is a '53 and lacks the hand primer in the dash, would pumping the gas pedal before starting be a good idea or not, assuming my carb is original? Thanks.

[Drew M.]

Your M37 came with a Ball & Ball EW1 carb. Its accellerator pump is not controlled by the throttle/gas pedal.

Therefore, pumping the gas pedel will not prime an engine with the B&B carb. The M37 Operation Manual advises against pumping the gas pedal for this reason.

So you are wondering why the military dropped using the hand primers right?
Good question. The skuttlebut is the hand primers sometimes leaked and the military was concerned about using trucks with fuel leaks in the cabs. As a safety precaution, I put a shut-off valve under the dash on the fuel inlet side of the primer should the primer start leaking while driving the truck.

As to helpful perople on the forums - please give what you get. I was helped when I started too and am glad I can pass some things. Most military vehicle owners, like the tractor restoration crowd IMHO, are a pleasure to deal with.

[monkeymissile]

Your M37 came with a Ball & Ball EW1 carb. Its accellerator pump is not controlled by the throttle/gas pedal.

Drew,
so the EW1 does have an accelerator pump? How is it controlled then?
So far my experience with this crowd has also been great, I just stay away from the politics/religion, stick to truck talk and away I learn!
Thanks.

[Drew M.]

The B&B carb accel pump works off vacuum. How? I do not know.

[Lifer]

I'm starting to feel old now, . . . then again maybe that was when my favorite music started playing on the classics station.

I feel your pain! Just the other day, I heard one of my favorite songs from my own "early days" while riding in an elevator. A little later, I heard the same song while I was on "infinite hold" with one of those blasted automated telephone answering systems.

[AmarilloCorey]

The accelerator pump is spring loaded. When there is no vacuum (for example the engine is not running) the spring forces the accelerator pump in the downward position.

When the truck is started the vacuum is applied to the top of of the accelerator pump cylinder and overpowers the spring causing the pump to be "pulled" upward. When the pump lifts up the accelerator pump cylinder, fuel is pulled into the cylinder past a small ball bearing. As long as the vacuum is applied, the pump remains in its upward position leaving the spring compressed on top.

When you press the throttle, the vacuum to the engine drops dramatically. This means the vacuum holding up the accelerator pump drops and the spring presses the pump downward. The pump forces the fuel in the cylinder out of another ball bearing controlled passage and directly into the carb throat.

When the vacuum recovers, the pump is again "pulled" upward overpowering the spring and "sucking" more fuel back into the accelerator pump cylinder.

Or something like that.

This is why pumping the pedal before you start the engine (on these types of carbs) has absolutely NO affect on how it starts. It does nothing.

Corey

[monkeymissile]

Corey,
thanks for the very detailed explanation, very informative and helpful.

[gwalker]

I beleive they found little real need for the hand primers on the dash, an so deleted them(also to save money). Just using the hand choke is enough to get the truck started, unless it sat long enough for the fuel in the carb to evaporate then there was the hand lever on the fuel pump for that. I had heard that in some cases that dash primer would start a fuel flow and then wouldnt stop an flooded the engine badly.