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1994 Mercury 15 HP 2stroke buckin and hard stall

major_tom

Regular Contributor
"I have a 1994 15 HP mercury 2

"I have a 1994 15 HP mercury 2-stroke with the following problem. Starts O.K once warm (there's no choke, only a primer system that appears to be broken), runs O.K. for 10-15 seconds, bucks hard and (usually) stalls. Starts back up and repeats the performance. Seems like it has a hard miss or two (ignition perhaps?).

Fuel delivery appears good. Spark was verified at one plug."
 
"Try turning the idle mixture

"Try turning the idle mixture screw out half turn,could be a bit lean,causing it to backfire.my 18hp merc does that.also check yr plugs are the correct ones"
 
"Thomas, those are great littl

"Thomas, those are great little motors and not too much goes wrong with them (if maintained).

The ignition in particular is pretty solid.

If Ian's suggestion doesn't work you may have a bad powerhead base gasket.

I have seen more than a few of those bad on that model (including the 6, 8 and 9.9 horses which are all in the same model family).

The problem that I have noted is that the powerhead works itself loose from the leg and lets some extra air in causing a backfire that appears to come from (under) the carb.

The powerhead is only torqued down to 10 foot pounds (which is "just" tight plus about 1/4 turn if not using a torque wrench).

Really "reefing" it down can damage things, so it doesn't hurt to make sure it's snug at the start of each boating season.

So you could try simply tightening it down and see if anything was loose...."
 
"Thank you both for your sugge

"Thank you both for your suggestions. I was traveling this past week so I have not had time to respond or to fiddle with the motor. When the noreaster finally lets up hear in N.E. (10" of rain locally) I will turn out the main jet and see if it helps.

Regarding the powerhead base gasket, is this between the powerhead and the upper gear case or are you talking about the powerhead to carb gasket? I could see how the latter could lean out the mixture but I'm not sure about the former unless maybe it lets air into the crankcase?

Are there any solutions or any way to trouble shoot the primer pump on these little engines? Mine appears to be defective. It wouldn't start until I removed the plugs and introduced gas into the cylinders using a straw. Then it fired right up but bucked and stalled every 10-15 seconds regardless of throttle setting. Thereafter I made my own choke by stuffing a paper towel in the carb throat, which worked equally well. Personally I would rather have a real choke versus a primer system but I suppose the engineers know best. The plugs were new (just replaced by the Merc technician) and I was getting a nice white spark (to the engine block at least). Over $600 spent on a tune up and this is what I get....

Thanks and best wishes,

Tom"
 
"Tom:

Are you sure the &#34


"Tom:

Are you sure the "choke" linkage is adjusted properly? The mechanismis supposed to push that little plunger in the carb all the way down. If it does, then your carb needs cleaning.

Jeff"
 
"Hi Jeff:

There could be a


"Hi Jeff:

There could be a problem somewhere it the carb. It looks like the plunger goes up and down but doesn't deliver any gas (based on no start and on the condition of the plugs). The carb was rebuilt as part of the $600.00 service (along with the water pump), so I was expecting to find it in good working condition."
 
"Rebuild the carb.

Jeff


"Rebuild the carb.

Jeff

PS: If you have a bad heart, be sure to take your medicine BEFORE you find out what a rebuild kit costs for that motor!"
 
"Jeff, I picked up a rebuild k

"Jeff, I picked up a rebuild kit (OEM) off Ebay last fall for this model for 22 bucks - you saying I got a deal


Just a note to others with similar models (1986-94 - 6, 8, 9.9 and 15 horse models). A brand new carb for these is about 275 bucks from Merc. If a dealer wants 300 to rebuild one for, buy an new one and bolt her on - you will save money and have less problems in the long run...."
 
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