Magnum 18 fuel pump

[Mike McKown]

My Magnum 18 fuel pump quit pumping so I bought a replacement. I changed out the pump and the new one won't pump either.

I pulled the pump off and cycled the arm. very little movement gives me pressure and suction so I'm thinking I must have somehow missed the camshaft. I had to push down slightly on the pump to get the screws in so I'm sure the pump arm is on top of the cam. Still nothing.

I compare the pump arms and even though they look the same, I took the pump half off with the check valves in it and put it on the other half with the pump arm. Again, slight pressure gives me suction and pressure but when installed on the engine, nothing.

What simple little item am I missing?

[Terry C]

Can you check if the arm is actually moving? I mean is the cam lobe worn?
Other than that I've got nothing.

[Mike McKown]

Originally Posted by Terry C

Can you check if the arm is actually moving? I mean is the cam lobe worn?
Other than that I've got nothing.

I left the mounting screws a little loose and cranked the engine. The pump wiggled up and down like the cam was moving the arm. That thought crossed my mind but I find it hard to believe a cam lobe would wear enough against a steel arm, actuating a flimsy pump like that. The arm on the original pump is not worn.

[BIGMOZEKE]

Not sure that a fuel pump would be enough to wear a cam.
I have had a fuel pump fail and just gravity fed the carb for about 2 months before I installed the new pump as they are a PIA to replace.
Also, the new ones that you buy are not as solid as the originals.
I looked and looked trying to buy as close to the original as possible so that I could get the best most durable one out there and after ordering a couple, they are all plastic and look to be just a little different from one to the other.
Keeping with a STENS replacement should be just fine.

[J-Mech]

Originally Posted by BIGMOZEKE

Not sure that a fuel pump would be enough to wear a cam.

It certainly can!


Mike,
I'm sure you did, but are you checking flow with the lines hooked up on both ends?

A plugged fuel line or closed tank valve would keep it from pumping. As would a stuck needle valve in the carb. Not saying that you didn't check all that, but I've missed simple things before too. Try sucking fuel out of a bucket if in doubt. FWIW, they don't pump much at all.

[Mike McKown]

The original pump failed because one of the check valves fell out of it's seat so it wasn't because of a worn cam.

I didn't check gas flow. I just checked pressure and vacuum with my finger. With the pump off the engine and moving the pump arm, I can feel a strong vacuum and pressure signal from the pump. With it mounted on the engine, I feel nothing.

The main line from the tank is free flowing by gravity.

I suppose I could hook the main line to the pump and see if the pump will squirt.

[Mike McKown]

I put the pump on the engine and cranked it up. Guess what? It works!

I've learned something here. I could stroke the new pump by hand and get good vacuum/pressure as I stated above. Using my finger as a gauge. That proved to be a bad way to check it.

I guess my ignorance can be excused as I have never fooled with a lever action Kohler fuel pump, only the ones that work off crankcase pulses.

Looks like JMech nailed it.

Thanks for the responses.

[Terry C]

Glad you figured it out.

[Sam Mac]

Originally Posted by Mike McKown

I put the pump on the engine and cranked it up. Guess what? It works!

I've learned something here. I could stroke the new pump by hand and get good vacuum/pressure as I stated above. Using my finger as a gauge. That proved to be a bad way to check it.

I guess my ignorance can be excused as I have never fooled with a lever action Kohler fuel pump, only the ones that work off crankcase pulses.

Looks like JMech nailed it.

Thanks for the responses.

Now you went and did it, J-Mech will get a big head over this.

[Mike McKown]

Originally Posted by Sam Mac

Now you went and did it, J-Mech will get a big head over this.

I have found that over my 74 years, you don't have to be the sharpest knife in the drawer, just know those that are. Sometimes, you have to swallow your pride.