RPM's increase @ idle

[will941s]

My 98' merc 25, 2 stroke is increasing idle by itself when it's idling. It starts fine, runs pretty smoothly (to be a 25), runs strong, but just a few minutes after idle it will start to gain rpm's own it's own. It'll gain, pop, drop, gain, almost stall, gain, pop and so on. I was wondering if has something to do with that crappy little enrichment selonoid (since it idles fast when it's engaged) or do I need to break the carb down and rebuild it? Any suggestions would be GREATLY appreciated.

 

[will941s]

Re: RPM's increase @ idle

May have solved the problem. I disconnected the electric choke and started the motor. Idled high, so I gave it a little gas and let off, the rpm's dropped and never went back up. It does not rev up like it did with the choke selonoid hooked up. I adjusted the screw on the butterfly adjustment to bring my rpm's down a little bit more and ran the motor through all power ranges, it seems to be doing fine. Now my only question is I checked the plugs and they have a little bit of oil on them but are pretty dry, and the top of the pistons look a little dry (very light coat of oil). How much oil should I see on those parts, and do I need to richen the mixture a little?

 

[will941s]

Re: RPM's increase @ idle

In addition to disconnecting the choke and the engine going back to regular rpm's, I noticed the plugs were a little dry looking to me...which would mean a lean condition right? On the carb there is a plunger to prime the carb, I think the plunger went bad, it is pouring fuel from the top of the plunger which that of all things should be dry. My question is, would that be causing a lean condition, maybe sucking in air from the plunger while it's running? What exactly does the plunger do while it's running? Thanks in advance,

Will

 

[will941s]

Re: RPM's increase @ idle

Primer and plugs....98' 25hp merc 2-stroke

 

[hdodt]

Re: RPM's increase @ idle

Reading your original post, I was going to suggest that there may be air getting into your fuel system because when fuel is ran out a 2 stroke will increase in RPMs just before it dies, but since the choke thing fixed it, I dont know. Just run the factory oil fuel mix, probably 50:1, but Im not sure. Someone will chime in and let ya know Im sure. I know that todays modern engines dont require as much oil as the older ones.

 

[clooney2]

Re: RPM's increase @ idle

i thought the same. typically 2 stroke to increas when running out of fule. i would have suggested false air too, a fule line sqees or the fule filter getting clogged up, eighter in the fule tank inlet or the engine fule filter. any way, the 25HP 2 stroke i have runnes fine with 2% oil mix (synthetich oil) and the quicksilver (ngk) spark's look wery good