Lawn Tractor Engine Problem

[Pavel314]

My old lawn tractor, that I use to haul stuff around the farm, has suddenly started running irregularly. It starts right up, but runs in pulses, incre asing in RPM for about a second, then tapering off, then running high again , like a sine wave. It calms down a bit after a while but still runs with a noticeable pulsing. It ran well over the winter for hauling firewood, but with the warm weather suddenly went crazy. I suspect something in the carbu retor so I put some gumout in the tank to see if that would help. Tomorrow I'll see if I can adjust the idler screw to calm it down. Any other ideas?

It's a Craftsman tractor, automatic transmission, 24 HP B&S two-cylinder en gine.

Paul

[Terry Coombs]

If this is going on at low and part-throttle , it's probably a partly/plugged jet . Give the gumout some time to work .

[clare]

sure sounds like it is running lean. Make sure the carb isn't falling off or apart.

[Paintedcow]

Or the carb is loose or spme part of it, or a bad carb gasket.

ALSO

Check the governor. If it has the old governor plastic flapper, that flapper could be gummed up on the shaft, or else it's coated with greasy gunk making it heavy and and unable to move properly. Or the spring to the gov is weak. Remember, the governor controls the speed, and pulsing is often a symptom of a gov problem.

You can often check if it's the gov, by just holding it in place and see if that stops the pulsing.

A 3rd but less likely problem could be burnt points or the condensor is failing.

I'd start with the gov, hold it in a stationary place. If it still pulses, look for anything loose on the carb. After that, it's a tossup of whether to rebulld the carb, or replace the points and condensor next. It probably needs a tune up anyhow.

[Stormin Mormon]

around the farm, has suddenly started running irregularly. It starts right up, but runs in pulses, increasing in RPM for about a second, then tapering off, then running high again, like a sine wave. It calms down a bit after a while but still runs with a noticeable pulsing. It ran well over the winter for hauling firewood, but with the warm weather suddenly went crazy. I suspect something in the carburetor so I put some gumout in the tank to see if that would help. Tomorrow I'll see if I can adjust the idler screw to calm it down. Any other ideas?

24 HP B&S two-cylinder engine.

When I took a small engine repar course, the instructor called that "hunting" for the proper speed. The problem is that the spring on the throttle att he carb gets rusty and stiffens up. So, when the governmor tries to regulate the speed, it swings too far. The answer is to replace the springs at the throttle.

[clare]

I don't think there has been a V twin Tecumseh, Briggs, or Kohler engine built with points and condensor - al least not in th last 35 or more years.

[clare]

That MAY end up being the fix, but I don't touch governor calibration untill I'k 110% sure it isn't a fuel mixture problem. Water in gas, dirt or corrosion (greenies) in jet, carb loose on manifold, manifold loose on engine, something loose on carb etc.

In my experience other than a governor linkage being rusted solis or restricted by an accumulation of crud, governor issues have been next to non-existant. Fuel quality and backed off screws have been the VAST majority of "hunting" problems - with fuel quality/restricted jets being the majority of those.