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Author Topic:   Chronic Plug Fouling
mustang7nh posted 03-30-2004 07:19 PM ET (US)   Profile for mustang7nh   Send Email to mustang7nh  
The 225 EFI on my CONQUEST 23 keeps fouling plugs due to spending much of its time cruising slowly on the [Intracoastal waterway] in FL. Do the new DI engines load up when spending much of their time under 2000 rpm? The torque of a two stroke would probably be a big advantage overall on this hull, but the re-power goal would be to address this frequent occurance. Any thoughts are appreciated. Thanks
Sal DiMercurio posted 03-30-2004 08:27 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I troll on average of 5 - 6 hours at a time at dead idle on my 2000 - 200 hp Evinrude DFI, & have never ever fouled a plug, or even sputtered.
I see absolutly no reason for a computerized engine to foul a plug, as everything is controled by the computer.
The oil isn't pre mixed with the fuel & is not shot into the cylinder as the older 2 strokes were, it's sprayed into the crankcase & gets no where near the plugs.
kglinz posted 03-30-2004 08:34 PM ET (US)     Profile for kglinz  Send Email to kglinz     
Referring to DFI only: The oil still gets to the spark plug. It's carried to the piston topside by the air. Its just not mixed with fuel until fuel injection occurs.
jimh posted 03-31-2004 05:11 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "DI vs 4s trolling performance".]
JBCornwell posted 03-31-2004 08:25 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
"225 EFI" is not enough info, Mustang.

Is that a 2 stroke Merc, a 4 stroke Tammy, a 4 stroke Suzuki or what??

On smaller OMC/BMC 2 stroke engines that call for a .030" plug gap on J4C plugs it is often advantageous to open the gap to .040", switch to J6C plugs or both for extended low speed operation.

There may be equivalent options available to you.

Red sky at night. . .

JBCornwell posted 03-31-2004 08:26 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Ooops! "Tammy" = Yamaha.

Red sky at night. . .

mustang7nh posted 03-31-2004 03:22 PM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
1997 225 Merc Offshore EFI

Mechanic put it on the computer and said it was not getting up to operating temp at idle and slow speeds. Hence, the computer was always running it as if it was warming up. I was told that the cooling bypass opens too soon and lets too much water in. I was't there with the mechanic... so this is antecdotal, but it was suggested that there was a problem with the spring which delt with the bypass but there was no off the shelf fix. I believe there is a post on here about the same engine that described a similar phenamenon.

Lars Simonsen posted 03-31-2004 07:46 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
The cool running motor would certainly contribute to plug fouling. Also, if you're using a cheap 2 stroke oil, you might consider trying a higher quality oil. I had a similar problem with my 1998 Mercury Optimax, (I was using the Quiksilver Premium oil, which ain't cheap, but it wasn't the right oil). I now use Optimax oil (not what you should use in your motor, I suspect) and have absolutely no plug fouling problems.

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