1992 - 25HP Mercury Outboard - HIGH IDLE ISSUES- Help please

[Austin Jester]

I bought this engine and it was running very poorly, hiccups, power surges etc.

S# 0D004203

This is what Ive rebuilt.

- cleaned the corrosion out of coils
- replaced leads (custom made from local auto supplier)
- replaced primer bracket P# 12803 (replaced worn plastic part)
- rebuilt Carburetor inc. primer with gasket kit P# 9803 (replacement part 97611)
- new fuel filter
- tiller handle stop switch kit P# 823609A10

Parts from ********** http://www.**********/parts/search/MercuryMarine/0D004203/367/100/Carburetor(25)/parts.html

The only thing non spec is the plugs - NGK BPR7HS (recommended plugs are NGK BP8H-N-10.) From my research one temperature range hotter should not cause wet plugs.


PROBLEM - After all that has been done, it starts and restarts easy, under load it runs well.

SYMPTOMS - Plugs are wet.IDLES REALLY HIGH

SUSPECT - Burning rich, improper air/fuel ratio



This is what Ive tried.

Re+Re Carburetor - look for any obstructions, none. double check gasket installation - DID NOT SOLVE

Adjust Ignition timing - RPMs drop until it backfires - readjust back to normal - DID NOT SOLVE (Note: when it would back fire, for a brief period after it would seem to have reasonable RPMs)

Adjust air/fuel screw - in, it dies. out, until it almost falls out. - Some minor improvement DID NOT SOLVE (when I choke it manually with my fingers RPMs drop, but exhaust emissions increase greatly)

Tried with and without, old and new fuel filter (new fuel) - DID NOT SOLVE


PLEASE HELP - Thank you

 

[oldman570]

Re: 1992 - 25HP Mercury Outboard - HIGH IDLE ISSUES- Help please

The normal setting of the idle screw is 1 1/2 turns out from lightly seated and final should be within 1/4 turn from there in eather direction. If it dose not set close to those settings then I would check the idle screw and seat for damage. The high speed jet is not adjustable and should be cleaned and everything blowed out with a air gun when cleaning or rebuilding the carb and pump. The float and needle setting could also be causing a flooding condition. The gasket between the carb to block would cause a lean mixture and dosen't sound as tho it is the trouble, but a check for good seal should be made. JMO
Oldman570