Will not start after engine is hot

[you tube mechanic]

Seems to be a common problem, but not sure what else to do. Working on a Craftsman 21" self propelled / walk behind model number 917.377823. Briggs engine 7.0 hp OHV model 128602 0304 E1 for a neighbor. Mower cranks with 2 pulls when cold (first start) but after shut down to empty bag it will not start without some serious pulling 20-30 times and sometimes backfires thru carburetor slightly (pops). A quick google search returned a hit to make sure engine isn't low on oil as they Briggs have a safety mechanism if engine is too hot, oil level is correct, also same post told me to watch the butterfly valve on the carb. I pulled the intake off to see it and marked the plastic lever above it connecting to the auto choke/throttle cable. Post said B.F. valve will be open at first start but should be closed on hot start. This mower has valve open anytime the engine is off, valve open on cold start and open on hot start, but nearly closed and fluctuating with engine running. From what I can tell that seems normal as you don't have centrifical force to actuate the lever near the flywheel so the spring on the auto choke/throttle pulls the B.F vale in the open position when engine shuts down. I manually closed the B.F. valve after engine was hot and it seemed to start better with about 5 -8 pulls. Not sure if my info is bad or not. Should the butterfly valve be open at cold start and closed or partially closed at hot start? Next task is to pull the carbureator off and start cleaning it and the fuel bowl internals, but I am waiting to see if anyone else has feedback. Thanks for any info and suggestions.

 

[Scrubcadet10]

the choke butterfly should be CLOSED when cold, and OPEN when hot.
Might have an issue with the thermostat on the muffler.

Not sure if this the correct one, having trouble finding out if it uses centrifugal force to open the choke, or the thermostat type on the muffler...

 

[bertsmobile1]

The butterfly at the front of the carb ( nearest you ) is the choke and should be closed when the engine is cold then open up fully and stay open till the engine gets cold again.
If it flutters then the spring needs to be replaced.

 

[you tube mechanic]

My auto choke system looks nothing like the video, maybe i am not using correct name for it, the butterfly control cable goes to a lever at the back of the engine that moves when the mower is running and you can see the butterfly valve nearly closed and fluctuating when running, shut off mower and the spring pulls the butterfly opens. Here are some pics of what I have. The black line on the plastic piece that the cable hooks too is for me to know what position butterfly was in when running and in stopped / hot condition. The last couple pics I am manually holding the lever back/closing the butterfly. I don't see any kind of thermostat in the muffler area either.

 

[you tube mechanic]

If butterfly is supposed to be closed on cold start and this one I am working on is exact opposite i.e; wide open at cold start, i can see right down the intake like in above pic 0536. how is this mower starting after two pulls? It seems this machine is opposite of what its supposed to be. I am confused.

 

[Scrubcadet10]

Oh, you don't even have a choke..... that's the throttle which controls engine speed. a choke would be right behind the air filter. that metal link going into it is the governor link, and the spring that goes to the control panel on the front is the governor spring, when tension is increased on that spring, it runs faster. it may need more tension or a new spring.
A choke would be where i circled.

 

[you tube mechanic]

I will try to post a video of it running tomorrow, but the only thing visible when running is the plastic lever on top of the butterfly, that is why I marked it with a line in the direction of the valve. Strangest thing.

 

[Mower King]

Your carb primer bulb is probably not working right. The prime from this primer bulb acts as the choke sending xtra fuel in the carb!

 

[you tube mechanic]

Ok, my bad. I was thinking this is choke system. this is throttle system, sorry. Ok now what. LOL.

 

[Mower King]

I will try to post a video of it running tomorrow, but the only thing visible when running is the plastic lever on top of the butterfly, that is why I marked it with a line in the direction of the valve. Strangest thing.

I'm sorry........I CAN'T RESIST!