QuestionMy MTD riding mower with Briggs engine won't idle. It surges up and down when the throttle is opened up. It doesn't surge when the engine is under load like when the mower deck is engaged but the engine doesn's seem to be running at as high rpm as it should. It also doesn't surge when the choke is pulled out part way. I don't know if I have a governor problem or a carb problem. Also, does this have a fuel pump that might be giving me trouble. This is an 18.5 hp twin cylinder gas engine circa 1995. Thanks.
AnswerHiya Bruce
Yep it DOES have a fuel pump, also has a debris screen and a fuel filter. Sounds like its leaning out, which indicates an air leak or faulty gasket. Closing the choke richens the mixture, which, in the case of an air leak OR semi-clogged filter would make it smooth out.
1- follow the fuel line from the tank, look for a filter, change it.
2- Spray some heavy lubricant around the exterior of the carb while its running, especially around the throttle plate shafts and where the carb bolts up to the engine. If at any point it suddenly runs right- you found your air leak (assembly lube in a spray can from autozone works well)
3- If the above test does nothing, then remove the filter assembly, run it, spray small amount of gas directly into carb. If it smooths out, you have insufficient fuel flow (clogged screen, filter or line tank pickup.
Let me know how this works out for you ok ?
CYA
