1993 Yamaha- foul plugs

[Maxum21]

Well, i finally bought my new-used project boat. Its a 1993 20' Wellcraft with a 115 v-4 Yamaha.. The owner told me it would start fouling spark plugs if he let idle for 4-5 minutes. or it would "once in a while" foul plugs when running it normally(higher rpms).. Ive owned a merc force 90 before and have never fouled a single plug. I could let it idle all day without a problem, so i'm thinking this isnt normal?.. so my question is what could be causing this to foul plugs? Bad carb settings? too much oil in gas mixture? the thing is, he said other than the occasional fouled plug, it ran strong. even topped out over 40mph.. so i'm confused on this one

 

[Talonz82]

Re: 1993 Yamaha- foul plugs

Greetings, typically when I find this problem its usually a combination of things. Make sure you have the proper plugs and gap. Improper float height, leading to a too rich mixture can cause this as well. Hope this helps

 

[seahorse5]

Re: 1993 Yamaha- foul plugs

Service the poppet valve and thermostats to make sure both cylinder heads are warming up to around 140?F at idle.

There are carburetor adjustments and linkage synchronization that have to be done in addition. Start with a complete engine decarbonization then check compression to make sure each cylinder is within 15% of each other.

Have a trained tech set the oil pump linkage correctly, or use the factory service manual and set it yourself along with the carb linkage.

 

[robert graham]

Re: 1993 Yamaha- foul plugs

Old, degraded fuel can cause plug fouling. Are your plugs new or clean to start with? Could be a cooling problem from engine not reaching normal operating temperature(rich mixture). A bad fuel pump diaphragm can cause exessive fuel to be sucked into motor causing a rich/wet plug situation. I run the Pennzoil 100% Synthetic oil for very clean, carbon-free operation. Motor really shouldn't be fouling plugs. Good Luck!

 

[Maxum21]

Re: 1993 Yamaha- foul plugs

thanks for the replies...i will most likey take it to a mechanic but i will at least know whats going on with it. Is it common for this engine foul plugs if it idles too long? The previous owner said its common on any 2stroke motor, but like i said i didnt have that problem on my force.

 

[robert graham]

Re: 1993 Yamaha- foul plugs

My motor is a 1999 2 stroke and I've never fouled a plug, just every now and then take them out and clean them with carb cleaner and a old toothbrush, then blow off with air hose. Are your plugs fouling with fuel/wet or carbon. If they're wet with fuel(you can smell it on plug), then you probably have a fuel pump or rich mixture problem. Maybe change your oil to the Pennzoil 100% Synthetic and a new set of plugs. Good Luck!

 

[triumphrick]

Re: 1993 Yamaha- foul plugs

One more thing not mentioned. Make sure you aren't overpropped. Too high a pitch and that motor wont reach wot rpm's. Even though you won't be running wot, the wrong load on the motor can cause it to foul.
Best advice was poppit, thermostats, decarb, etc....

 

[Islandbrah]

Re: 1993 Yamaha- foul plugs

you bought a 16 y/o motor that probably needs full servicing. Remove the carbs and clean/rebuild em(cheap and easy). I would replace the fuel pumps at 40 each because rebuilding never ensures anything. new plugs gapped properly, these motors are very well made and sounds like just some old dirty issues. replace the impeller just because again its cheap and necessary. Never take a sellers word as they just want the loot. run a compression check for your own piece of mind bit I would say for less than 400 bux you should have a fresh yammie to run barring no rebuild issues needed. good luck, yammies rule!