Briggs Platinum 120000 Engine Cold Start ok, Hot Start struggle

[Rivets]

I don’t mean to sound rude, but from your last post I suggest you stop right now and find a mechanic. You definitely don’t know what you are doing. I suggested you had a choice of replacing the float needle and seat or replacing the carb. You don’t seem to understand in both cases you need to only remove the air filter assembly and the carb. In either case you also should replace the gasket. No one has suggested anything different. By continuing yourself, you could easily get get in over your head. Just have to be honest, sorry.

 

[Scrubcadet10]

those carburetors are very very simple.

 

[slomo]

there are 3 things that any engine needs to work. Compression, spark at the correct time, and air to fuel mixture.

4

 

[slomo]

On Briggs carbs I always replace the float needle and seat before replacing the carb. But with that said, I’ve done more than I can count and have a couple of tweaks to get the float set slightly rich. Briggs part number #398188. Not everyone on this forum agrees with me, so it is up to you.

I set mine to JUST below level on the float setting, slightly low. All of my mowers tend to run on the rich side with clean air filters and no chokes on. Plugs are tinted black with carbon.

 

[slomo]

those carburetors are very very simple.

For some people. Not everyone is a super tech like you, Bert, Star and so on...... Huge group of very helpful people on here.

 

[sgkent]

people aren't being mean when they suggest taking it to a shop. They are trying to save the owner money, time and grief when they sense someone might be in over their head. Lots of people here have thousands of carb rebuilds under their belts, and sometimes even they hit one that doesn't want to play by the rules. Some parts aren't meant to be rebuilt these days too.

 

[Hammermechanicman]

I set mine to JUST below level on the float setting, slightly low. All of my mowers tend to run on the rich side with clean air filters and no chokes on. Plugs are tinted black with carbon.

Is it running rich or is the spark plug not operating in the self cleaning operating range. Many people don't run equipmebt hard enough to get the plug temp into the self cleaning range. Unlike a car engine with water cooling and a thermostat. Most air cooled small engines have no temperature regulation so they are designed to operate in high ambient temperatures at max power. Nearly all the flathead push mower engines don't get hot enought to get the plug into the self cleaning range. Carbon deposits from running rich and carbon deposits from being too cold look very similar. OHV OPE engines have higher compression so they run hotter than a flat head engine so they tend to get the plug(s) into the self cleaning range much better than flat head engines. A flat head briggs uses a champion plug with a 19 heat range (RJ19LM) whereas a OHV uses a 12 heat range plug (RC12YC) which is a colder plug. Every time an engine is started the spark plug(s) are developing carbon deposits, regardless of the mixture, until the plug(s) reach the self cleaning range and burn off the carbon.

 

[slomo]

Is it running rich or is the spark plug not operating in the self cleaning operating range. Many people don't run equipmebt hard enough to get the plug temp into the self cleaning range. Unlike a car engine with water cooling and a thermostat. Most air cooled small engines have no temperature regulation so they are designed to operate in high ambient temperatures at max power. Nearly all the flathead push mower engines don't get hot enought to get the plug into the self cleaning range. Carbon deposits from running rich and carbon deposits from being too cold look very similar. OHV OPE engines have higher compression so they run hotter than a flat head engine so they tend to get the plug(s) into the self cleaning range much better than flat head engines. A flat head briggs uses a champion plug with a 19 heat range (RJ19LM) whereas a OHV uses a 12 heat range plug (RC12YC) which is a colder plug. Every time an engine is started the spark plug(s) are developing carbon deposits, regardless of the mixture, until the plug(s) reach the self cleaning range and burn off the carbon.

Run at a min of 3400 to 3600 revs ALL the time. Even on models with adjustable throttle levers. Max revs all the way.

These slow burn combustion chambers and no efi create a rich looking plug.

 

[jchau]

Anyway issue has been fixed by swapping out with an Amazon special carb. All by myself in 15min or so ?

Thanks for the suggestions

 

[efred]

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Speaking of compression, have you checked the compression, both cold AND hot? There are tolerances in the valve train to accommodate the expansion of those parts, and the wear on the engine changes those tolerances. It's possible that you're not getting enough compression. It's an easy check.