Briggs Platinum 120000 Engine Cold Start ok, Hot Start struggle

[jchau]

I am a little stumped on what the issue or fix but I have a Briggs Platinum (120000 series) engine on a Craftsman lawnmower (2013 model). This engine has the auto choke and primer. It has been acting up last year and this year too. It used to start with one pull and now on cold start most of the time it will work within 3 pulls. On a hot start I struggle with getting it going until the engine cools.

Engine Detail:

• Model: 128M02
• Type: 0962
• Code: F1

Things I have tried:

• Auto choke Thermostat replace: It was a little sticky at the end of last year so I thought that was the main culprit for the hot engine issue but problem still exist
• Spark plug has been replaced with Champion RJ19HX. I am getting spark with the spark plug checker.
• Air filter has been replaced
• Carburetor bowl and main jet (bolt holding the bowl) has been cleaned (without removing the whole carb) and spray as much around the choke
• Resistive check the ignition coil, measurement seems normal. Also re-gapped the coil to the flywheel.

What works:

• If I get a rod or something to manually close the choke when the engine is hot, I am able to start the engine and remove the rod immediately right after the engine seems to start up.

I am a little confused what is causing the problem and what needs fixing.

 

[7394]

Welcome Aboard !

 

[Rivets]

If it came to me with these symptoms I would be checking the float level. Seat may have swollen causing a lean running condition, which you rectify by choking the engine on hot start up.

 

[jchau]

If it came to me with these symptoms I would be checking the float level. Seat may have swollen causing a lean running condition, which you rectify by choking the engine on hot start up.

Question about the seat, even though it is a small part to replace but will require taking apart the whole carburetor, it is worth replacing the seat only or should I replace the whole carb? Also when I search up the carb there are a lot of aftermarket ones, are they trustworthy or not worth the effort?

I have tried tipping the mower to the side to start like what this video is showing

it seems to work with a hot start. Signs of a carb needs a full rebuild or replace?

 

[sgkent]

there are 3 things that any engine needs to work. Compression, spark at the correct time, and air to fuel mixture. Fuel ages so something sitting all winter doesn't behave like fresh fuel. I personally have found the best way to start any pull engine is to prime it when not fully warm, pull the rope slowly until the engine resists a bit then pull hard, or if the rope is too far out, let it in and pull hard. Doing that my Toro or Edger etc will start almost the first pull each time. I used to rebuild the carbs on anything I owned with great success, but finding good quality parts have been harder so I try to find a new old stock carb when i can now, replace, and rebuild the old one as a spare at my convenience. Older mowers and small engines tend to loosen the head gaskets over time and that can cause issues. So can tight valves on high use engines. Ethanol in the fuel can cause issues. Many years ago I had a boat whose engine did not behave properly and I spent hours on it. I discounted that the fuel was bad because it was only about 60 days old. In the end the problem was the fuel was stale. The point being, don't discount the small things. Figure what of the three items is missing when something won't start before throwing parts at it.

 

[jchau]

there are 3 things that any engine needs to work. Compression, spark at the correct time, and air to fuel mixture. Fuel ages so something sitting all winter doesn't behave like fresh fuel. I personally have found the best way to start any pull engine is to prime it when not fully warm, pull the rope slowly until the engine resists a bit then pull hard, or if the rope is too far out, let it in and pull hard. Doing that my Toro or Edger etc will start almost the first pull each time. I used to rebuild the carbs on anything I owned with great success, but finding good quality parts have been harder so I try to find a new old stock carb when i can now, replace, and rebuild the old one as a spare at my convenience. Older mowers and small engines tend to loosen the head gaskets over time and that can cause issues. So can tight valves on high use engines. Ethanol in the fuel can cause issues. Many years ago I had a boat whose engine did not behave properly and I spent hours on it. I discounted that the fuel was bad because it was only about 60 days old. In the end the problem was the fuel was stale. The point being, don't discount the small things. Figure what of the three items is missing when something won't start before throwing parts at it.

I have put fresh fuel with 0% Ethanol and was having issues.

If I need to close the choke on an auto choke system seems like I have air fuel mixture problem? I cannot prime the engine as this is also auto prime with auto choke.

 

[Rivets]

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.

 

[jchau]

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.

Yeah I am just debating if I should just swap for an Amazon special carb since the float and needle is half the price but more work to do and do the needle and seat swap on the old one later in time.

 

[Rivets]

I can’t answer that question.

 

[jchau]

well I don't want to take it all apart and open a can of worms to find out I need to replace more things like gaskets, pins, etc.