1993 lawnboy 10201 hot start/run issues

[stienut13]

Hi guys,

This is for the old timers with 2 cycle lawnboy experience. The subject is a '93 Silver Series 4.5 hp model with a Walbro LMR-16 carb. This is the only year with this carb. Runs like crap on a hot restart. Mod 10201, # 3908961.
Here is what I have:
Cold compression per my HF compression tester is 120 cold, 100 hot. Spec is 90-115.
When cold, it runs to spec: Max rpm 3050 -3080, spec is 3050+/- 100., idle is 2450 -2490, spec is 2200-2800. Cranks on second pull, too!!! Has loads of torque. It runs like a champ till I shut it off and have to restart after 5 minutes. Max speed after hot start is 2900 and idle has decreased to 2100. Sounds like 5 o'clock Charlie's airplane on MASH. Just like it's not getting gas, but why only on a hot start? This condition could last anywhere from a couple of minutes , or doesn't go away. I've been thru and thru the carb. I'm wondering if the needle is sticking the bore after the carb gets hot? Exhaust ports are clean, new crank seals 2 weeks ago. Sprayed carb cleaner around carb base, no change. Seems a fuel issue, I just don't know where to look. I know I could just fill it up, tile the brake handle down and mow till I'm done and be done with it. This just irks me to no end.

All advice appreciated,

Thanks,

Jim

[bgsengine]

what fuel are you using? Try changing it to a higher octane rating and see if that makes a difference - bear in mind these were designed and built before E-10 became commonplace - If you are using the cheapest 87 octane gas, try bumping it up to mid range 89 octane, which is less prone to vapor lock. - It only takes a couple tiny air bubbles from boiled fuel to cause a restriction around a needle and seat or main nozzle until they "pop" and then fuel flow returns to normal - which fits your symptoms, no?

[smallen]

as bg posted, sounds like fuel is boiling,vapor lock, make sure carb heat shield is installed with large side down between carb/engine, if you have an ir thermometer measure the carb bowl on shutdown, then again in 5 minutes to check temperature rise
also check all engine shrouds are in place

[stienut13]

Thanks Brian and smallen,


That makes sense, I'll get 89 and report back.

Thanks again,

Jim

[stienut13]

Hi guys,

Still no joy. Got regular unleaded from sunooco, no ethanol. Still have misfire on hot start. I changed the coil 5 weeks ago, and no change. I'm thinking carb issue, like needle hanging up.

Any ideas?

Thanks, Jim