B&S 11HP tractor runs 15 minutes and dies

mks113 · 06-24-2009, 11:30 AM

I've got an old lawn tractor with a B&S 11HP engine. Last year it started to die after running for 10-15 minutes.

This spring I replaced the coil and had the carb and air filter cleaned. I replaced the battery as well.

It worked for a while, now it is back to the old pattern.

The pattern is that it runs fine for a while, then I detect a slight loss of power, then it dies very suddenly. As it dies the governor slams the throttle to full, but there is no response. Even if I flip off the PTO as it dies, it does not recover.

A concern is that it won't turn over after it dies. I thought it was a battery/charging problem as it would start fine after 15 minutes on the charger. Then I realized it would start find after sitting for 15 minutes.

I'm thinking either the engine needs a complete rebuild (is it worth it?) or possibly the exhaust is blocked. I'll check the exhaust tonight. The carb, fuel supply and ignition are all in good shape.

Any suggestions? Should I break down and buy a new mower?

**Basementgeek** · 06-24-2009, 01:36 PM

Hi and welcome to the forum

My very first thought, since appears to be locked up when hot, is a new engine or rebuild the old one. Worth it ???

BG

mks113 · 06-25-2009, 05:54 AM

Well, we had a break in the weather last night. Rain stopped after a week, dried off for most of the day. I started up the tractor and it ran for 5 minutes before it died. I removed the muffler on the odd chance that it was plugging up when hot -- it didn't make any difference.

So yeah, I'm leaning towards the engine rebuild as the only solution.

but... having fought with the mower for 2 years (and more) now, I went out last night and bought a Honda engined Poulan self-propelled. I still might rebuild the tractor for other things, but no longer an urgent thing.

**Basementgeek** · 06-25-2009, 08:00 AM

Now you have time to rebuild it

Possible cracked piston.

BG

**pat mcgroin** · 06-27-2009, 07:20 AM

try to loosen the gas cap.
It may be building a vacumn in the tank and not allowing fuel to come out of the tank.
This could explain the 5 - 15 minutes run time.

Also check any crank case vent that it may have.

mks113 · 08-04-2009, 07:38 AM

Well, repair went on the back burner as I bought a new walk-behind mower. It is a lot more work to get the lawn done though!

So this weekend I decided to take the head off and see if anything were visible. Lots of carbon in there, but valves and piston looked fine. Cylinder is scored but it is an old engine.

At some point I decided to drain the gas tank. Dropped the fuel hose in the gas can and opened the valve -- a few drops came out. Took the filter off and tried again -- a few more drops. I took the tank off and drained it through the filler hole.

I popped the valve on the bottom out and found that it was full of crud. Likely sucking it into the valve as it drained, blocking flow. With no suction it would back off a bit and let fuel in again. I blew in the valve outlet and the crud went flying. It was not in there too tightly!

So now I have to get a new head gasket to see if that was the only problem. I might get more use out of my tractor after all!

**pat mcgroin** · 08-04-2009, 08:28 AM

That makes sense. No gas means no run.
I would think that you found it.
Good luck Pat

06-24-2009, 11:30 AM	#1 (permalink)
mks113 Registered User Join Date: Jun 2009 Posts: 3 OS: win xp SP3	B&S 11HP tractor runs 15 minutes and dies I've got an old lawn tractor with a B&S 11HP engine. Last year it started to die after running for 10-15 minutes. This spring I replaced the coil and had the carb and air filter cleaned. I replaced the battery as well. It worked for a while, now it is back to the old pattern. The pattern is that it runs fine for a while, then I detect a slight loss of power, then it dies very suddenly. As it dies the governor slams the throttle to full, but there is no response. Even if I flip off the PTO as it dies, it does not recover. A concern is that it won't turn over after it dies. I thought it was a battery/charging problem as it would start fine after 15 minutes on the charger. Then I realized it would start find after sitting for 15 minutes. I'm thinking either the engine needs a complete rebuild (is it worth it?) or possibly the exhaust is blocked. I'll check the exhaust tonight. The carb, fuel supply and ignition are all in good shape. Any suggestions? Should I break down and buy a new mower?

06-24-2009, 01:36 PM	#2 (permalink)
Basementgeek Moderator, Home Support Join Date: Feb 2005 Location: Central Ohio, USA Posts: 1,504 OS: XP Pro SP2/Vista Ultimate SP2 Blog Entries: 3	Re: B&S 11HP tractor runs 15 minutes and dies Hi and welcome to the forum My very first thought, since appears to be locked up when hot, is a new engine or rebuild the old one. Worth it ??? BG __________________ Donating to the forum keeps TSF free for all. Proud member of ASAP

06-25-2009, 05:54 AM	#3 (permalink)
mks113 Registered User Join Date: Jun 2009 Posts: 3 OS: win xp SP3	Re: B&S 11HP tractor runs 15 minutes and dies Well, we had a break in the weather last night. Rain stopped after a week, dried off for most of the day. I started up the tractor and it ran for 5 minutes before it died. I removed the muffler on the odd chance that it was plugging up when hot -- it didn't make any difference. So yeah, I'm leaning towards the engine rebuild as the only solution. but... having fought with the mower for 2 years (and more) now, I went out last night and bought a Honda engined Poulan self-propelled. I still might rebuild the tractor for other things, but no longer an urgent thing.

06-25-2009, 08:00 AM	#4 (permalink)
Basementgeek Moderator, Home Support Join Date: Feb 2005 Location: Central Ohio, USA Posts: 1,504 OS: XP Pro SP2/Vista Ultimate SP2 Blog Entries: 3	Re: B&S 11HP tractor runs 15 minutes and dies Now you have time to rebuild it Possible cracked piston. BG __________________ Donating to the forum keeps TSF free for all. Proud member of ASAP

06-27-2009, 07:20 AM	#5 (permalink)
pat mcgroin TSF Enthusiast Join Date: May 2009 Location: Toledo Oh. Posts: 603 OS: XP Professional SP2 Vista Ultimate SP2	Re: B&S 11HP tractor runs 15 minutes and dies try to loosen the gas cap. It may be building a vacumn in the tank and not allowing fuel to come out of the tank. This could explain the 5 - 15 minutes run time. Also check any crank case vent that it may have. Last edited by pat mcgroin; 06-27-2009 at 07:22 AM.

08-04-2009, 07:38 AM	#6 (permalink)
mks113 Registered User Join Date: Jun 2009 Posts: 3 OS: win xp SP3	Re: B&S 11HP tractor runs 15 minutes and dies Well, repair went on the back burner as I bought a new walk-behind mower. It is a lot more work to get the lawn done though! So this weekend I decided to take the head off and see if anything were visible. Lots of carbon in there, but valves and piston looked fine. Cylinder is scored but it is an old engine. At some point I decided to drain the gas tank. Dropped the fuel hose in the gas can and opened the valve -- a few drops came out. Took the filter off and tried again -- a few more drops. I took the tank off and drained it through the filler hole. I popped the valve on the bottom out and found that it was full of crud. Likely sucking it into the valve as it drained, blocking flow. With no suction it would back off a bit and let fuel in again. I blew in the valve outlet and the crud went flying. It was not in there too tightly! So now I have to get a new head gasket to see if that was the only problem. I might get more use out of my tractor after all!

08-04-2009, 08:28 AM	#7 (permalink)
pat mcgroin TSF Enthusiast Join Date: May 2009 Location: Toledo Oh. Posts: 603 OS: XP Professional SP2 Vista Ultimate SP2	Re: B&S 11HP tractor runs 15 minutes and dies That makes sense. No gas means no run. I would think that you found it. Good luck Pat