Tecumseh AQ148

[wristpin]

This engine is / was a special build by Tecumseh Europe for the UK mower company Atco Qualcast who used it on their range of domestic cylinder (reel) mowers. The nearest regular Tecumseh would seem to have been the BH.E or GE35
During its availability it was fitted with Tillotson, Delorto and Tecumseh carburettors. The one that’s giving me grief has a Tecumseh carb.
The story. I serviced it last year and the user says that it started and ran perfectly all season. It’s just come back to me for a service and sharpen. The issue ! Done the sharpen then found that it will only start with a mere sniff of carb cleaner on the air filter. It then runs and idles fine - no hunting at full or idle rpm. Leave it for any longer than about half an hour and it needs carb cleaner to start.
What I’ve done. Despite it running ok , I’ve ultrasonically cleaned the carb and replaced the O rings on the emulsion tube.
Finally checked the valves and found virtually no clearance on the inlet, so lapped and gapped both valves - 6 & 8 thou”.
New plug and checked for choke action and air leaks etc.
Absolutely no difference. Still needs at tiny drop of carb cleaner on the air filter for a cold start.
Before I send it back with a can of dope, What have I missed ??

[bgsengine]

Check compression, do a leakdown test (look for beginnings of a blown head gasket) try a new spark plug (new doesn't mean good, if there's already a new one in it) check the choke plate - does it close completely (check wear on throttle and choke shafts?) - tecumseh always been known for being a bit finicky when it comes to fuel delivery during start up, used to be we could just adjust it a tad bit richer (and it'd run a slight bit rich at operating temp) , check for any possible slight air leaks at gaskets.. leakdown test would be the first thing I'd run if I was pretty sure the carb was fine and gaskets, spark & plug were all good, because leakdown could spot beginnings of a burning valve (loose valve guide, valve might be coking sideways and leak slightly too) or loose valve seats... some of them just needed "extra strong" pull on starter cord (faster rotation, more air moving) are things that come to mind..

[KE4AVB]

If I remember correctly some of the older Tecumseh had to have the choke plate modified by reducing the air bleed holes. This might one time that needs to be done here.

[wristpin]

because leakdown could spot beginnings of a burning valve

Many a wise word - thank you.