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.
#2
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.
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.
As Scrubcadet10 said, that = a dirty carb inside. Clean the carb first.
On the 30 minute deal, look for vacuum leaks around the carb and intake pipes. Spray carb cleaner around carb sealing areas and intake ports/gaskets. Parts heat up and expand causing leaks. Also would take an old spark plug. Gap to 0.25" or 6mm. Check for a good blue spark. Report back with what you have. Check your spark at initial cold startup and at 30 mins.
Amazon carbs are risky. They are NOT guaranteed to work 100% like OEM Briggs carbs. Some Chinese Gambler Series carbs do work.
So you dump 20 bucks on a Chinese and it doesn't work. Then have to shell out 50 smackers for a rebuild kit. Not saving any money if the Chinese carb is junk.
Last Chinese carb I installed needed machining. It was on a Briggs 3.5hp horizontal with a pulsa-jet carb. The fuel pump spring area in the carb body was too small. Needed opening up with a file and sandpaper so the fuel pump would work proper. The spring and diaphragm protector ring wouldn't plunge into the carb body deep enough. It does work now I have to say. Think the carbs with some flaws are sold on ebay and amazon at cheap prices.
Used the rebuild kit; carb was really spotless inside. Needle valve a bit worn.
Started right up and idled well; have to see how it behaves later this week after 30 minutes of mowing.
If it gets goofy, I think next step is a new head gasket, not much else to go wrong i don't think.
Success!
Ran fine, no odd idle.
I replaced needle valve, intake manifold gaskets and the two in the carb. One or more fixed the issue.
Thanks all for the help!
