The Stovebolt Site Forums The Shop Area Engine Shop Help troubleshooting power loss, please

My '48 with the original 216, has been losing power lately. I freely admit my analytical skills on this engine are limited. I suspect it's carburetor related, but I can't rule out electrical.

I pulled a plug to see if the problem was there, and discovered a white corrosion inside the plug nipple, so I replaced the plugs and wires. No change.

Power is down, and I've had to dowmshift on hills the truck normally climbed without trouble. It still starts really well, and after it warms up, it idles fine.

I get some backfiring from acceleration from a stop sign on occasion, as it feels like it bogs down, then "pop!," but that's not consistent.

Any ideas?

Might want to make sure you have no crud in the fuel system, and double check timing. If plugs were full of white residue - sounds like you are running lean. Is engine temp OK ?

If it were me, the first things I'd be doing are verifying the carb's settings (mixture and idle), checking points/gap, and timing.

What carb are you using? How long since rebuild?

Are your valves properly adjusted? I think the standard is every 3000 miles. My power decreases as clatter increases.

Bill

The plug residue was at the top of the plugs, in the wire nipple, not at the tips. The plugs seemed normal, but were definitely worn, so I replaced them. Engine temp is okay - right around 180, where it's been.

The carb is a W-1. It hasn't been rebuilt since I put it on the road in 2008. Whether the previous owner rebuilt it, I can't say.

Good point about the valves. I haven't adjusted them since the truck was put on the road in 2008. I've got maybe 5,000 miles on it since then. Would that cause the dramatic loss of power and gas mileage? I forgot to mention the mileage. It's down in the 10.5 range now, where it was 14.75 before.

Thanks for your help.

Start off with the easy stuff change you're fuel fillter.

Pete

Pete, I don't have a fuel filter on the truck.

I messed with the fuel mixture today. I turned the mixture screw in until the engine slowed, then backed off a half turn. that improved the power a bit, but then I was getting backfires, small ones, during shifts. I backed the screw out another half turn and the backfiring went away, but the power did too, somewhat.

I think you owe it to yourself (and your bolt) to adjust the valves, Tom. For me, I've had to adjust the valves about every 12 - 18 months, waaaayyyy less than 5000 miles. I do it when the clacking gets noticeable, and after doing the adjustment, notice immediate power improvement. Before doing the adjustment, my power loss is so gradual that I don't really notice it until I've done the adjustment.

It's free to do- if nothing else, you can "check the box" that valve adjustment is NOT part of the problem.

You also should confirm your timing is set right. If you don't have a timing light, usually you can borrow one at a local auto parts store.

Double-check your vacuum hose connections to make sure you don't have a hose that wiggled loose. I'd check at the fuel pump, the carb base, and the vacuum wiper motor.

Bill

Because you've mentioned that it's back firing thru the carburetor and getting gradually
more sluggish, the first place that I'd look is to the timing. Sounds to me like the timing
may have slipped for some reason.

Unless someone has been in there and tried to improperly adjust the valves three years or
more running on a valve adjustment is just going to loosen up the clearance, which
simply means the valve is not going to open fully. Even if a lock nut came loose the
clearance is only going to get greater not tighter. On the other hand, it’s possible you
might have a sticking or burnt valve or some carbon build up under a valve holding it
open. If timing it back to the "Ball" doesn't cure the problem then a compression test
would be my next step to see if the valve train is still on track.

Oh, and once you make sure the timing is correct and the valve train isn’t your trouble,
then it sure wouldn't hurt to get a fuel filter in the system and rebuild the carburetor
if it hasn't been serviced in a while. A fuel filter was a good idea when these trucks were
now and an absolute necessity now that they are old.

Denny Graham
Sandwich, IL

If You've been running without a fuel fillter I'll bet you need a carb rebuild.After you get the carb rebuilt install a good fillter.

Pete

After you check your carb and add a fuel filter check your points, as they wear down your timing will change. It may not be necessary but I change my plugs, points,etc. ever year, just for peace of mind.

Well, I've taken a closer look at the carb. It apparently has been spewing fuel, because there's varnish at the base, and the outside of the carb is wet. I figure a rebuild is in order. As best as I can tell, the tab says 420 5 or 420 S, which makes it a carb from a 1939 or 1940 Chevy. Funny, another carb came with the truck, and that appears to be from a 1933 Chevy. Does anyone want to trade a 1948 carb for a 1940 carb and a 1933 carb?

Since the 420 S carb has been working for the past three years, I guess I'll rebuild it, or have it rebuilt. I hesitate to do it myself because I don't have the facilities for cleaning everything properly, but cost may overrule that.

Okay, here's the final report on my truck. As previously stated, I replced the wires and plugs. no change. then replaced the points. Same. I'd never worked with a timing light before, but my father brought one over, and although at 87, he's hazy on details, we figured it out and timed the truck. what difference! It'll climb hills with ease, runs 100% better all the way around, too. The ball mark wasn't even in the window when we started the timing process. Now it's centered and everything is fine.

Sooo, Denny Graham, TxLaTx and tcox, you all hit it.

There's no clatter from the valves, but I'll adjust them at some point this season.


Thanks, everyone!!!

Now that she runs great, PUT A FUEL FILTER ON IT!

It will save you aggravation later. Congrats on getting her fixed!

Jeff

Yeah, it's something I should do, but I hate cutting a gas line...