Lawn tractor B&S engine "putting" loudly

[Tom NJ]

This is a 24 HP B&S engine in a four year old Husqvarna lawn tractor. I had had trouble initially starting it this season but that seems to be resolved. Last week it ran perfectly for about 20 minutes of cutting, and then suddenly started putting loudly, as in scary putting. It was worse under load but still present in idle. Choking the engine stopped the putting, but then the engine ran more roughly, as in a choked engine.

After maybe 10 minutes of cutting slowly with the engine choked it suddenly sounded better, so I opened the choke and it ran perfectly again for about 40 minutes, after which the putting started again.

This week before starting I checked the air filter (clean), changed the fuel filter, installed a new battery, and added Seafoam to the gas. At first it wouldn't crank at all, but after manually cranking (with some effort) I freed the pistons and it started right up. It ran fine for 10 minutes, then the putting started again. Like last week, after a period of running choked the problem went away and the engine ran fine with the choke open, and like last week the putting returned a few times, on and off.

Really weird - what could cause this problem to start so suddenly and go away so suddenly, with long periods of perfectly normal performance in between??

One friend suggested it was bad gas as she had the same problem once before that was resolved by replacing the gas. My gas is ethanol free and was stored in a large shed over winter, but I never had this problem before, even with old gas. If the gas is a possible factor, can it be fixed with an additive such as methanol or do I need to drain it? Any other ideas?

I should note that my two other lawn tractors are using the same over-wintered gas (but from different containers) and running fine.

Thanks!

Tom

 

[mrsilv04]

I assume at 24hp, that it is has 2 cylinders.

Is it possible that one cylinder is cutting out, and it is only running on one cylinder when it is "putting?

It might not be fuel related... but spark. It is doing it when it gets hot. Electrical components like to act up once they get hot.

I had the same issue with a Kawasaki V-Twin in a John Deere, and one cylinder was cutting out once the engine was hot, and then it would come and go randomly. The solution was a $20 electrical part, that I installed myself in 15 minutes.

 

[Snagglefoot]

Reminds me of old diesel tractors where it’s obvious one cylinder catches before the others. Agree with Mrsilv04. . Check spark plug, sparkplug wire, and coil.

 

[mk378]

These have a two barrel carb with separate jets for each barrel. So a clogged jet can cut out only one cylinder. You can spend as much time and money as you have on putting voodoo in the gas tank, but it inevitably comes down to removing the carb for internal cleaning.

Also it's due for a valve adjustment. When the valves are too loose, starting becomes difficult because the compression release feature stops working. The engine will not turn readily, it will act like the battery is weak, even though the battery and starter are OK.

 

[Convert]

Is the gas cap venting properly?
Could be it might be venting just enough to only feed the cyl that's the easiest
TOMB

 

[Tom NJ]

Originally Posted By: mrsilv04
I assume at 24hp, that it is has 2 cylinders.

Is it possible that one cylinder is cutting out, and it is only running on one cylinder when it is "putting?

It might not be fuel related... but spark. It is doing it when it gets hot. Electrical components like to act up once they get hot.

I had the same issue with a Kawasaki V-Twin in a John Deere, and one cylinder was cutting out once the engine was hot, and then it would come and go randomly. The solution was a $20 electrical part, that I installed myself in 15 minutes.



Yes it is two cylinders. I'll change the spark plugs and check the connections.

What was the $20 electrical part you installed that solved your similar problem?

 

[JHZR2]

When was it maintained last?

Id run some B12 chemtool in the tank and perhaps a bit into the intake as well. Doing this has always kept our old stuff running well. I always change the oil right after.

The basics of fuel, air and spark are what they are. You need to figure which is deficient. There are so many more ways for fuel to be an issue, so that may be your start or end, depending upon your confidence in the other two.

 

[UncleDave]

Could be electrical-

How old is it/ how man-hours on it - and have the valves ever been adjusted?

I had this same behavior with a burned valve - hard start, needed lots of choke (sounded like it was [censored]) once warmed up it seemed to run OK

Most ignore valve lash on these engines till the valve rides on the base circle and stops closing and burns.

UD

 

[boraticus]

Considering that experimenting with the choke setting improves engine running temporarily, I'd venture to say it's a fuel issue. Pull the carb, inspect and clean with a piece of wire, solvent and compressed air. That would be my first step.

 

[old1]

Since it starts running ok after choking it, I would probably concentrate on the fuel system, but it probably will need some physical cleaning. Won't hurt to try some cleaners though.

 

[bubbatime]

Probably a clogged carburetor. Something I always try, and works 30-40% of the time to clear this.... rev the engine up as high as it will go, then quickly slide the choke lever up to choke. Do this 5 or 10 times and "sometimes" it will suck the carburetor restriction through the jets and clean it out. Like sucking a loogy through your nose when you have a cold. '

If that doesnt work you need to rebuild the carb.

 

[Tom NJ]

The engine has a little over 100 hours on it. Late last season I changed the blades, oil, air filter, and oil filter, and cleaned the plugs. I also ran a good dose of Techron in the gas. It was running great up until this season.

Is the putting more likely to be from a misfiring cylinder or valves?

 

[GravelRoad]

My best guess with your description is one of the two ignition modules is bad.

First replace spark plugs. RC12YC or equivalent.

If/when it does it again, pull one spark plug wire off with insulated tool (unless you like getting shocked). If engine shuts off, that cylinder is working. Reconnect spark plug wire. Restart engine,
assuming engine is still running rough (putting), remove other spark plug wire, if no change, that's the cylinder causing issue.

Could be two barrel carb, but doubtful.

 

[LeakySeals]

I'm no fan of Seafoam in an auto engine. But its great for seasonal small engines. Removes water, top cyl lube, some cleaner for the bowl and piston tops. Then a couple of years ago I found Gumout Multi-System Tune-Up at Walmart. It comes in a bottle that looks like Seafoam. There may be a real reason for doing that, because the MSDS shows its a Seafoam/techron brew. I run this year round now. No more rough sticky valve starts, no throbbing idles. https://gumout.com/multi-system-tune-up/

 

[Lubener]

Originally Posted By: mrsilv04
I assume at 24hp, that it is has 2 cylinders.

Is it possible that one cylinder is cutting out, and it is only running on one cylinder when it is "putting?

It might not be fuel related... but spark. It is doing it when it gets hot. Electrical components like to act up once they get hot.

I had the same issue with a Kawasaki V-Twin in a John Deere, and one cylinder was cutting out once the engine was hot, and then it would come and go randomly. The solution was a $20 electrical part, that I installed myself in 15 minutes.


I agree with a cylinder cutiing out. A twin cylinder should not pop but have a steady rumble. I have on old Tecumseh twin that sounds like that when one cylinder cuts out after washing down the engine and smooths out after drying out..I just live with it.