140 mercruiser wont idle or troll slow

[skipbehr]

140 mercruiser3.0 litre I took the boat out today fishing. It ran good at trolling speed for 2 hours and then. started missing and stalled.I could only restart it if I throttled it but when put into gear would stall. I managed to start it and forced it by throttling and ran it back to the marina but was surging.dont know if it could be water or electrical.It did level out on the way to marina but after idling for a couple of minutes stalled.

 

[Scott Danforth]

what is your idle RPM? should be 650 in gear.

trolling for long periods of time will foul the plugs as there is no heat being generated. you could also have crud in your fuel system.

you may need to drop pitch if you use the boat for fishing. that will slow it down.

 

[skipbehr]

Idle speed was correct at 650 -700 under load but after 2 hours running at 850 to 1000 rpms just quit and would only start. If throttled, but try putting in gear would stall. And at 3500 rpms would surge

 

[skipbehr]

Maybe misunderstanding me about trolling slow.This was trolling fine untill the problem happened,

 

[Scott Danforth]

not misunderstanding at all. a smaller pitch prop would have you at a higher RPM which would then prevent fouling

surging is fuel system related, most likely crud in the tank made it to the carb. do you have a fuel/water separator filter?

 

[skipbehr]

Yes there is a sepertor have not had a look at anything since I Came in. Will be checking fuel system out tomorrow thanks

 

[Bondo]

Yes there is a sepertor have not had a look at anything since I Came in. Will be checking fuel system out tomorrow thanks

Ayuh,...... When ya swap the filter, examine the Contents of the old one for anything but clean fresh gasoline,.....

My guess is, yer gonna find crud, some of which has made it to the carb, pluggin' the idle circuit,......

 

[skipbehr]

Hooked up muffs to outdrive today. It started up fine and idled perfectly . Checked plugs before starting and they look good. I put in stp water displacer and run the engine at idle for half an hour and idled okay. I don't know if I should try it on the water don't want to get stranded?