Does it die only in gear or in Neutral as well? Sounds like the low speed fuel passages of the carb are getting clogged with small bits of debris as the engine runs and draws fuel into them. Common issue on small engines that have sat unused for long periods...stale fuel /varnish may also partially clog up fuel...
Best answer: Does it die only in gear or in Neutral as well? Sounds like the low speed fuel passages of the carb are getting clogged with small bits of debris as the engine runs and draws fuel into them. Common issue on small engines that have sat unused for long periods...stale fuel /varnish may also partially clog up fuel passages..That's why it runs better at higher speed (which uses different /extra fuel passages) but stalls out after dropped down to low speed. It may start OK when cold if the debris is not clogging the passages until fuel starts to flow a bit. And internal carb fuel passages may be made smaller which restricts proper fuel flow due to stale fuel/varnish clogging them a bit.
You may need to locate/adjust the low speed mixture screw on the carb a bit richer ...counterclockwise...to avoid running too lean at low speed or causing starting issues.Or adjust the idle speed setting screw (differs from mixture screw) for best setting with engine idling in gear and prop in water. Repair manuals have specs for rpm's at idle in gear or neutral. Normally, you slowly adjust the low speed mixture screw in one direction until engine starts to run rough or die...take note of screw slot position... and then adjust it back the other way until that occurs again...then adjust screw to the midpoint of both settings for best low speed mixture between too rich and too lean.
I'd suggest to remove the carb and thoroughly clean the interior fuel passages with soaking/carb spray, use thin wires or needles to clean tiny passages or jets/ tubes, clean bowl ...check for small bits of debris...and check for proper float level...specs found in repair manuals or some online sites. May need a gasket kit to fully disassemble carb and rebuild it.
Remove the mixture screws (or at least the low speed screw) and clean out those fuel passages too with carb spray. Try to spray cleaner or use low air pressure in reverse of normal flow of fuel from mixture screw passage to the carb throat to force any debris out that may be clogging the passage. But before removing them, turn each one all the way in until lightly seated and count how many turns /partial turns it takes to seat them from their current setting...that will get you back to the original setting once you've removed them. You just screw each one all the way in and then back out to the same number of turns as they were before after cleaning. Usually they go about 1 1/2 turns or so out from seated to get to a rough setting.
Replace fuel filter and check fuel hoses from tank for deterioration/cracks, etc.. small bits of rubber can break off internally in fuel hoses or carb gaskets/seals and clog the fuel bowl/jets/passages. Replace any suspect / old hoses or bad seals/gaskets. If you see signs of corrosion/whiteish scale deposits in the fuel bowl or carb areas, then you'll likely have to replace the carb....cleaning /soaking won't remove those and small bits of scale can also clog fuel passages. Given the age of the motor, it might be best to just replace the carb and avoid any hassle of missing or unable to clean clogged fuel passage areas.
Newer mandated ethanol fuels can attract moisture if/when sitting too long which can cause corrosion in the carb parts.Best to use non-ethanol unleaded premium fuel sold at some stations for marine use or motorcycles and completely drain fuel from tank/carb/lines in the off season.
Also, if the prop has been changed/altered by the previous owner, that can also affect idle speed by adding extra drag in some cases which may cause stalling...adjust idle speed screw (not mixture screw) setting with engine idling in gear and prop in water to required idle speed specs. It sounds more like a clogged carb issue though.
1 day ago