18.5 hp OHV Intek only run on choke when hot

[bob22cn]

I've about a 15-year old Craftsman lawn tractor (917.275760) with a 18.5 hp OHV Intek engine (engine model 31p777-0299-e1) that only runs on choke when hot.
I can keep it running if I run the mower deck engaged as the momentum of the spinning blades keeps it running; if I disengage the blades, it will die on choke.
This started last year and I thought it might be valve clearance so I adjusted valves over the winter.
Same issue this year; I redid them a week ago and same symptoms. Hopefully, I did it right, some concern about which valve is ex vs intake but I'm pretty sure I got it right:

upper valve	5-7 exhaust valves
bottom valve	3-5 thousandths intake

The carb has a restriction of adjustment of the mixture and changing it doesn't seem to help much.
I haven't taken off the carb bowl yet as I don't see dirt as a problem since it runs well for about 30 minutes and then starts acting up.

I'd appreciate any thoughts on how to investigate/fix.

 

[Scrubcadet10]

The reason it runs better with the blades engaged is it's running on the main jet under load and the throttle is Wide open, i'm thinking the low speed/idle passage is blocked.
OR, the first thing i would try, get it hot, and when it starts wanting to die, loosen the gas cap.. if the problem goes away, the tank is not venting properly.

https://outdoorpowerinfo.com/repairs/#id_briggs

would you mind posting the engine date code, which is the series of numbers after the Model and Type numbers you posted, as this engine used a Walbro Carburetor and a Nikki carburetor.

 

[bob22cn]

Scrub,
the other numbers on the engine:
5bsxs.5012vp 276016

I thought about the gas cap but forgot to try that last time. I'm going to cut grass tomorrow, so I'll give that a try assuming it acts up again.

 

[Scrubcadet10]

Those are the EPA numbers, the numbers i mentioned will be stamped near where you found the engine model number.
On the valve cover.
similar to this

 

[bob22cn]

31p777 0299e1 0?091???
I'll go out and look at it with eyes.

 

[Scrubcadet10]

 

[bob22cn]

My eyes now say:
31p777 0299e1 040910ze

 

[slomo]

Take a greasy oily red shop rag. Wipe the numbers with it. Stamped numbers will be more visible.

slomo

 

[bob22cn]

Here it is with some black grease I had.


Loosening the gas cap did not change anything. I can blow through the hole in the cap so it isn't blocked.

 

[slomo]

Here it is with some black grease I had.
View attachment 57441

Loosening the gas cap did not change anything. I can blow through the hole in the cap so it isn't blocked.

Not much difference on your valve cover stampings. Sure helps me sometimes getting the numbers.

slomo