Briggs 18 HP OHV Wont Throttle Up When Hot

[darrinster]

Model: 31p777-0299-e1

When cold the engine will throttle up fine. After about 10 minutes it starts surging really bad and dies. It will run at idle speed, but once you try and throttle it up it wants to die. Really stumped.

Engine has a Nikki carburetor.

I have done the following:

Pressure washed engine
Changed the oil
New fuel line, fuel filter
Cleaned carburetor 2 times
Cleaned gas tank
New spark plug
Installed a good used coil
Adjusted the valves
Installed good gas cap

 

[darrinster]

Ok, I did more testing but still have not found the issue. I don't have a compression gauge but it seems to have a good compression. Could the valves be causing this? Head gasket? No smoke at all.

Other testing:
Switched out carburetors no luck
Checked voltage to fuel shut off solenoid 12.76 volts. Wiggled wires to make sure of a secure connection, no change.
Removed kill wire

 

[mechanic mark]

Did you check air filter for replacement?

https://www.briggsandstratton.com/n...nginemanuals.html?searchrequested=31P777-0299

Your engine operators manual & parts list. See page 5 in operators manual for tune up specs., valve adjustment etc.

https://www.amazon.com/Briggs-Strat...ie=UTF8&qid=1466602877&sr=8-1&keywords=591731 this should be your carburetor if after code date 08051300.

https://www.amazon.com/Briggs-Strat...82&sr=8-1&keywords=briggs+and+stratton+796184 this should be your carburetor overhaul kit if before code date 15113000, see pages 11 & 12 in parts manual after getting your code date. Carburetors are manufactured for specific engine numbers in order to operate properly.

 

[darrinster]

Did you check air filter for replacement?

https://www.briggsandstratton.com/n...nginemanuals.html?searchrequested=31P777-0299

Your engine operators manual & parts list. See page 5 in operators manual for tune up specs., valve adjustment etc.

Yep. Brand new filter. Cleaned engine shroud also. Really can't figure this out.

 

[mechanic mark]

Yep. Brand new filter. Cleaned engine shroud also. Really can't figure this out.

http://faculty.missouri.edu/~schumacherl/276781SingleCylinderOHV.pdf

your engine repair manual, see section 2 troubleshooting.

http://www4.briggsandstratton.com/m...on_Troubleshooting_Detail_Reference_Guide.pdf

 

[darrinster]

Possibly found the problem. I completely removed the breather tube it stays running but it does struggle. I'm going to remove the flywheel and replace the breather reed. Never had one go bad but who knows?

 

[darrinster]

Changed the reed valve, intake manifold and breather tube no luck. Really frustrating. Completely out of ideas. Seems like it doesn't want to pull gas. Last thing would be pulling the head to see if the head gasket is bad. If anyone has a suggestion let me know.

 

[BlazNT]

Ok so it should be a fuel delivery problem.
Fuel filter in tank.
Fuel line
Fuel filter
DIRTY CARB Including dirty fuel shut off valve(spraying the carb with carb cleaner does not clean a carb)
Air entering after carb.
Check those. Don't change carb unless it is the exact same one from exact same engine. Check all gaskets. Especially the ones in between engine and carb.

 

[darrinster]

Ok so it should be a fuel delivery problem.
Fuel filter in tank.
Fuel line
Fuel filter
DIRTY CARB Including dirty fuel shut off valve(spraying the carb with carb cleaner does not clean a carb)
Air entering after carb.
Check those. Don't change carb unless it is the exact same one from exact same engine. Check all gaskets. Especially the ones in between engine and carb.

No fuel filter in tank.
New fuel line.
Fuel filter is new. It's the small red one that has a screen inside, so it shouldn't be any issue.
Carburetor was taken off and cleaned. All small ports cleaned and shot air through them. Nikki carburetor. Also have another engine with carburetor that runs fine and same results after testing it on this one.

Checked gaskets and tried other gaskets. No matter what after it warms up it wants to die at full throttle. If I lower the throttle to idle it will run.

I've fixed a decent amount of these Briggs Inteks and never had a issue like this. It's like the engine stops pulling fuel in.

 

[bertsmobile1]

OK so lets start by narrowing down the possabilities.
Put an in line spark tester on both plugs
remove the wire to the shut off solenoid on the carb pour some gas down the carb and fire up the engine.
Keep on dribbling small amounts of fuel down the carb or spraying short shots of starter fluid done there.

No difference then you have a cam / valve / govenor problem

Better then you have a fuel delivery problem

Did the known good carb come with it's own shut off solenoid ?

If not try replacing the solenoid with a bowl nut- No diference solenoid not guilty

Next step hang a fuel tank above the engine and hook it up directly to the carb ( gravity feed )
Problem goes away then you have a fuel supply problem.
I had several Cubs that did similar, pull the fuel line off and fuel ran fine but when the pump sucked, a plug of crud wedged into the end of the tank outlet all but blocking off the fuel supply.


As you have fixed several engines , you should be able to hear the differecne beween an engine that is choking because the exhaust is blocked and an engine that is starving because it can't get enough fuel and an engine that has no ignition.