5HP Won't Run Hot

[CT18fireman]

I have a 5hp Briggs on a Leaf Blower. Engine will start cold on second pull with choke, it will run at full power for 30-45 minutes then loses power. At that point it will run at idle fine and will run a bit better at higher RPMs with the choke half open. It will lope up and down though and occassionally backfire through the carb (air cleaner removed).

When it dies it is very hard to get to restart.

I checked fuel tank cap for vent
Running without air cleaner
New Spark Plug
New oil (since I was working on it)

Any thoughts?

[fixer67]

It sounds like the coil may be overheating. Check the spark with the engine cold and then when it starts to act up. NOTE==The engines now days do not run well with the air filter removed. Thanks to the EPA engines now days run so lean that just by removing the air filter can cause the to lope.

[CT18fireman]

This engine is about 5 years old. Not sure if that makes a difference.

I just cleaned out the carbuerator and it had no effect.

I will check the spark. It does idle though, wouldn't that mean it has spark? What about the backfiring?

[UNISCAPER]

This one is a longshot, but here goes. Check the flywheel key. If it is in the least bent, or severed, it will throw the timing off enough to back fire after it gets hot. Typically when this happens, the engines won't start, but we had one years back that this was the problem and it solved it.

[CT18fireman]

Pulled the new spark plug and it had a lot of carbon on it. Spark seems present but not great? Not sure what to compare it to. I do see spark. Engine temps do not seem to change it. The flywheel has a bit of surface rust.

This machine ran fine for years and even this year. Problem just started. Ran most of the day yesterday and we shut it off. Went to restart and problem developed. Enigne turns easily by hand no mechanical problems felt or heard.

At idle the machine runs smooth up through about half throttle. In the upper RPMs it develops the lope and seems to be missing. Smokes a bit at high RPMs as well dark smoke not white.

[CT18fireman]

Ok
I was checking everything again and I discovered a slightly loose head bolt on the exhaust valve corner of the engine. I removed the head and notice a blow through mark and the gasket eaten away at the bolt.

Does this sync with the engine problems? I can replace the head gasket easily enough if this could have been the problem. I am thinking that the cool engine was sealing "OK" but as it heated up it expanded a bit to leak, even at idle it would run ok but higher RPM would cause loss of power, etc.

[Travis Followell]

Blown head gasket could be your problem. Replace it and see what happens. When you put the head back on be sure to tighten the bolts in the correct sequence and to the correct torque. You can look in a B & S repair manual for this information.

[CT18fireman]

Can someone give me the torque specs and sequence? It has 8 bolts. I will go get a gasket in the morning.

[Travis Followell]

I won't be able to give you the sequence and torque specs until tomorrow night because my book is in the shop. Maybe someone else can help sooner.

[CT18fireman]

Alright. I replaced the head gasket which solved the compresssion problem. It starts and runs perfect now but is still stuttering and then dying when it gets warm. It will restart for a second or two and then die when warm.

I don't see spark when I test when warm but it does start for a second.

Coil?

[Travis Followell]

If you don't see a spark when its warm and will not run then it is the coil. I would say if you replace it, it will run fine since the head gasket didn't solve the problem.

[CT18fireman]

Replaced the coil this afternoon. Seemed to fix the problem. The test will be working with it all day Tuesday.

I have an 8hp also but I love the 5HP for its lighter weight when working on hills.