The Stovebolt Site Forums The Shop Area Engine Shop sputtering problem

Hey everyone.
Since I got my truck a few months ago I have been having a problem with a rich gas mixture causing fouled plugs. I also get sputtering when I press the gas, and the truck will even stall if I’m not really careful.
The other day I committed myself to solving the problems, and here is what I did.
I normally set my timing with a timing light, but this time I set it by hooking up a vacuum gauge to the wiper port on the intake manifold and adjusted the timing to where the vacuum is the highest steady reading. I disconnected and plugged the vacuum advance port on the carb when I did this.
I adjusted the carb idle and mixture screw until I got the highest steady vacuum reading also
I don’t know if this is normal, but when adjusting the mixture screw on the carb I turn it nearly all the way out for the best vacuum, and it also sounds better. I have read that it should be set somewhere around 1 and a half turns out from bottoming out.
I looked down the carb and I see a squirt of gas what I open the throttle.
I also checked the oil and it smells like gas but I did a compression test and all 6 cylinders are 120 psi give or take 1 or 2 psi.
How do I get my carb to not run so rich? Is there a screw or something I have to tighten?
And what could be causing the sputtering when I try to rev the engine? Could that be caused by a rich fuel mixture?

Gecho,

It sounds like your carb float may be set wrong, or worked itself into that position. Is your carb leaking where the carb splits at the top? If so, and these carbs were notorious for this, check your float level both high and low. Let us know. Hope this is helpful.

Mark

There are a couple of problems to your adjustment procedure. The mixture screw only affects the mixture at idle, so unless you're idling all the time, you've done nothing to affect the fuel mixture while driving. That's the function of the float level, main jet, and power valve, and the float level is the only thing that's easily adjustable. Using the vacuum gauge is a good way to set the idle mixture, but here's a better way to do it. With the gauge attached to full manifold vacuum (The wiper port is a good place), turn the screw in clockwise (lean) until the vacuum starts to drop, then turn it out (rich) until you get the highest vacuum reading. If you get things too rich, the vacuum will drop aagin. Once you've found the best vacuum reading, go 1/8 turn rich, to help the tip-in, where the transition from idle to part throttle is made. The float level is very critical to a good tip-in, even slightly too low will create a flat spot. If the spark plugs are getting sooty in normal driving, you need to work with either the power valve or the main jet. Make sure the power valve piston moves freely, and the ball in the power valve is sealing well, and reduce the size of the main jet slightly if necessary. A lighter-weight spring under the power piston will delay the power valve opening if necessary. Good luck!

Ignition timing- - - - -If you want to set it by ear, do so on the road, by listening for detonation, that light rattling noise under load, like climbing a long hill, and retard the timing a degree or so at a time until the rattle stops. Don't worry about the vacuum advance, it goes away when you load the engine. Its only function is fuel economy at light throttle.
Jerry

Thanks guys. I checked the power valve and it appears to be moving well. There is a leather plunger type gasket on the power valve plunger that is in good shape. I will try adjusting the idle mixture screw again, and do as you suggested Hotrod Lincoln and turn it back in 1/8th turn. I adjusted the float according to the manual.

That leather plunger you're seeing is on the accelerator pump. The power valve is a long rod that rests against a ball bearing and pushes it off its seat under low-vacuum conditions. Under higher vacuum, the rod is lifted, and the valve closes, forcing all the high-speed gasoline to go through the main jet. The power valve assembly is attached to the top of the carburetor, and hangs down close to the bottom of the float chamber. The vacuum piston is lifted against a light-tension spring to the lean position, and drops to unseat the power valve when extra gas is needed for pulling.
Jerry

okay, i went out and dissassembled the carb. i found no ball bearing what so ever. maybe this is the problem. are we talking about the carter w-1?

I was describing a Rochester Model B. The Carter uses a metering rod to richen the mixture as the throttle is opened, instead of a power valve. You can bend the linkage a little to lean the mixture, by withdrawing the metering rod less for any particular throttle opening. According to my Motor manual, there is a special gauge to check the metering rod setting, so without it, any adjustment will involve a little guesswork.
Jerry

Thanks Hotrod,
I will give that a try in the next few days. I don’t know why it sputters when I press the gas though, I wouldn’t think a rich fuel mixture would cause this, and if it does why is it only happening now (the last few weeks) since I have not touched the carb at all.