Series III surging

[raleighrover]

Hey guys,

I'm a new member and need some advice. My SIII has been running really well, but all of a sudden has started "surging" when I get in fourth - around 40mph. It accelerates and pulls strongly (for the 2.25) through 1st, 2nd and 3rd, but when I get into fourth it starts to surge or lurch as I accelerate, and I need to back off.

I was thinking perhaps the mechanical fuel pump is starting to fail but would think that would be an issue any time I'm accelerating. Any thoughts would be great.

Thanks!

[stomper]

Pop the elbow off the carburetor, and go for a short ride. See if this fixes the surging. I'm guessing your carb pipe of air filter are plugged. This would rule that out.

[raleighrover]

No such luck - still starts lurching around 40mph. Love your profile pic by the way; my kids nicknamed my rover Gromit.

[stomper]

Thanks! Love the old Wallace and Grommet episodes. The next thing to go through would be the ignition system. Points, vacuum advance on the distributor, rotor, etc.

The least likely culprit is the fuel syestem, but pulling the draw tube out of the tank, ensuring the screen is clean, changing the inline filter (if you don't have one on the fuel line, get one!) and then as a last resort, clean the carburetor. The Webber 34ich is known for clogged main jets, but more often than not, a fuel issue ends up being an electrical issue with these old trucks.

[Hauser]

I was thinking perhaps the mechanical fuel pump is starting to fail

You may be right. I had a couple instances where the truck seemed to die at speed and then once or twice the thing wouldn't start when hot. It would run fine but then when I'd shut it off and restart it a few minutes later it wouldn't start. Anyhow, I was leaning toward electrical but the car has a solid state points replacement and a new coil. Then I notice the fresh oil I'd just put in smelled faintly of gas and that's when I decided the pump was the issue.

The pump seemed to fail slowly and as things progressed the car would run ok up through 3rd gear (though I wasn't exactly flogging it) but often in 4th it would stall out and a quick save with the clutch would let the thing recover as it coasted along at idle for a few seconds.

Fuel pumps are not terribly expensive. I went ahead and ordered one and a rebuild kit so I could have the old one as a spare. The truck has been fine since doing the pump so I think I made the right call. I also discovered the feed tube had been cut and replaced with a rubber hose. They left the metal elbow, however, and inserted that into the rubber hose and clamped it. The inside of this 2 inch long section of metal tube was badly rusted. I replaced it with some copper for the time being but a proper replacement is in order.

So I rather suspect it was a combination of ailing pump and restricted inlet. My point is, it may be fuel related but it may not be the pump or just the pump. I just got it back on the road today and have not had a chance to get the old pump apart and rebuild so I cannot say for sure just yet.

Have fun finding the gremlin!

P.S. clamp or plug the line from the tank. It's gravity fed and you'll have a dangerous mess of gas about the garage if you disconnect the line and let it fall below the outlet of the tank. Don't ask me how I know.

[cedryck]

I have found that sometimes the stock mechanical pump can be a pain in the butt at times.

[raleighrover]

thanks for the pointers. I'm going to start running through the electrical system this coming weekend - points, timing, vacuum advance, rotor, etc. - then move on to the fuel system if that doesn't do it. We'll call it a good pre-winter checkup if nothing else. since i'll look at fuel pump last i'm sure that will be the culprit....

[erik88lr]

I have found that sometimes the stock mechanical pump can be a pain in the butt at times.

My Landy has symptoms similar to the OP's - runs out of fuel at high speed/load.

Fuel pressure varies between zero and ½ psi. I've gone through three replacement pumps, new filter, new screen on the pickup tube, new carb float, checked cam lobe, etc. I've put an electric pump inline between the tank and mechanical pump. It puts out 2½ psi and when switched on stops the bucking at high speed/load.

I don't want to rely on the electric pump, but can't seem to make a mechanical pump work. Don't know if a pump for a later 2½ liter engine would work any better. It's frustrating that I've not had this problem for the first 25 years, but for the last year or so I've been pulling my hair out...

~erik~

[raleighrover]

Points, rotor, timing looked good. I have a new fuel pump coming, but I could use some advice on how to check/test the vacuum advance?

[Contractor]

My Landy has symptoms similar to the OP's - runs out of fuel at high speed/load.

Fuel pressure varies between zero and ½ psi. I've gone through three replacement pumps, new filter, new screen on the pickup tube, new carb float, checked cam lobe, etc. I've put an electric pump inline between the tank and mechanical pump. It puts out 2½ psi and when switched on stops the bucking at high speed/load.

I don't want to rely on the electric pump, but can't seem to make a mechanical pump work. Don't know if a pump for a later 2½ liter engine would work any better. It's frustrating that I've not had this problem for the first 25 years, but for the last year or so I've been pulling my hair out...

~erik~

This is not a slam on RN as I buy a pile of parts from them, but their aftermarket fuel pumps are not great. I have been through several that just won't deliver enough fuel to keep the truck running at speed……pretty much exactly like what you all describe.

Find a nice original AC fuel pump and you should be good. There are several vendors state side that you should be able to pick one up from.