Briggs 15hp will not run properly

[Swatter]

Briggs 15hp OHV
Model 28N707
Type 016101
Code 9410254A

Installed on a Craftsman 917.257572 riding mower. Purchased used May 2021.

Changed oil, cleaned gas tank, added fresh fuel. Rebuilt deck.

Engine started immediately and ran smooth for first hour of use. Ran engine out of fuel. Filled tank and engine ran as normal for next 15 minutes under load. Engine stalled. Would start with full choke but not stay running. Engine began back firing through carb. Would not run even with choke.

Replaced fuel filter and spark plug. No change. Removed, disassembled, and cleaned carb. No change. Replaced air cleaner, fuel line. No change. Replaced coil. No change. Set valves and tried starting engine. No change. Repeated multiple times. No change. Removed flywheel and checked key. No damage, keyway properly aligned.

At some point in this process engine started and ran smoothly but then died. Engine no longer backfiring. Removed carb again and cleaned. Engine would start but rough running and would not throttle up. Sometimes engine would run faster but very rough. Sounds like it is missing or timing is off.

Local repair shop could not determine the issue. Suggested blown head gasket.

Removed head. Lots of carbon. No obvious wear or damage to valve train. Thoroughly cleaned head and valves. Replaced head gasket and lapped valves. Reset valves. As before engine starts but runs very rough at low idle. Cannot increase engine RPM with throttle. Sometimes engine will increase in RPM but chugs and huffs and sounds like it is blowing compression though a hole in the head or cylinder (whaap whaap whaap whaap whaap) Sounds like timing is off. Engine seems to run hot.

Re-installed original coil. No change.

Have spent way too much $$ on this unit which was promoted as “Needing nothing, ready to work”…(Rebuilt entire deck, new battery, engine work, tires all leaking fluid which in closer inspection appears to be anti-freeze????……)

Have I missed something simple? Something complex?

 

[StarTech]

Sound you had and have multiple problems.

First on the leaking tires. That is tire slime which is something I never recommend as inner tubes are a better option. It is one heck of a mess to clean up and gloves are needed for your safety. But the the slime can also damage the rims along with the tire inner liners.

It does sound like you had a blown head gasket with all the carbon. But when you adjusted the valves did you check the rocker arm movement to make sure they are same? I suspect you may have a bad camshaft lobe (likely if so being the exhaust lobe).

 

[Swatter]

The fluid from the tires is sweet (yes I tasted it) and green like glycol. Going to pull all the tires off their rims but not until I get the engine running.

What is the procedure for measuring rocker arm movement? I’m assuming a bad cam means a complete engine tear down.

Is there something else to check? Don’t have the time for a complete rebuild right now.

 

[StarTech]

I wouldn't be trying taste it. It is likely poisonous.

Using you eyes both rockers should move the same amount, +- a few .001"; but they should be nearly identical. I had several cams over the year with worn exhaust lobes.

If it is the camshaft yes it a tear down but not complete rebuild.

 

[slomo]

Engine began back firing through carb

Cam issue as StarTech said

Removed flywheel and checked key. No damage, keyway properly aligned.

Would start with full choke but not stay running.

Carb issue or fuel delivery

Sounds like it is missing or timing is off.

You said flywheel key was good??

Sounds like timing is off. Engine seems to run hot.

Is the top of the engine block, behind muffler, around crankcase breather plate and cooling fins clean?
Even the smallest dirt and oil layer will insulate the block causing over heats.

 

[Swatter]

Entire machine is sparkling clean. I guess I will pull the engine and check out the cam shaft.

 

[Richard Milhous]

Running too lean, probably a fuel supply problem. Counterintuitively, this can cause carbon buildup too, because bad mixture = incomplete combustion. For Gawd's sake, don't use Slime, it's worthless, let alone taste it. WTF????