1991 Mercury 40HP “Classic” Plug Fouling/Stalling

[anderso8623]

Hello all,

I have a 1991 Mercury 40hp serial number 0D070343. It died on my the other day after about 20 minutes of cruising right around 2,000 RPM. I swapped out the spark plugs as they were due and it started after a while of trying. It is not running as well as it once did and when I pulled the plugs they had excessive build up. Two were dryer more typical and two were “wet” with a chunkier build up. Has anyone had this issue with these motors? I have heard the spark plugs could effect the power pack and Mercury went from NGK BUHW-2 spark plugs to NGK BUZHW-2 with more insulation for the electric plus to avoid this. I had in, and replaced the plugs with the BUZHW-2 plugs. Not sure if that could be the culprit or if it is a more common issue.

thanks.

 

[Faztbullet]

I have heard the spark plugs could effect the power pack

Total internet BS as someone thought they understood how ADI ignition works. How old is fuel? Are you premixing as looks to rich on oil ratio? Is oiler still hooked up? if so look to see if metering rod to carb has popped off

 

[anderso8623]

Total internet BS as someone thought they understood how ADI ignition works. How old is fuel? Are you premixing as looks to rich on oil ratio? Is oiler still hooked up? if so look to see if metering rod to carb has popped off

I figured but was not 100% sure. Its brand new, ethanol free gas. Oil pump is still operational and not adjustable. I am not sure about a metering rod, I was not aware this model had one. Are you referring to the idle air mix screw? If so, I have them both adjusted out to 1-1/4 turn as advised from...the internet...lol.

I was also thinking reed valves but I can not find a diagram showing them on Mercury's parts catalog. I know they have to exist behind the carbs but I have no way of looking up the part as it essentially does not exist in Mercury's catalog.

Another note, I did "rebuild" the fuel pump but had to reuse the plastic "pop-rivet" for the one-way valves as the new ones did not "rivet" (?). The small dowel like piece that is supposed to side into place and separate the other end of the rivet was stationary and did not slide. it was all one piece of plastic. That said, the fuel pump seems to be working properly and has suction.

 

[racerone]

If this is a 4 cylinder motor the reed valves do exist.-----They are way inside the motor on the crankshaft assembly !----Easy to find on paper.----Many hrs of work to get your hands on them.

 

[Faztbullet]

As you open throttle there is a rod attached to oil pump, this varies the oil mix in fuel line. Its not a reed problem.

 

[anderso8623]

If this is a 4 cylinder motor the reed valves do exist.-----They are way inside the motor on the crankshaft assembly !----Easy to find on paper.----Many hrs of work to get your hands on them.

Thank you, it is the 4 cyl. Based on that, ill pass on looking for them. I knew they were there, I just cannot find them anywhere in the breakouts. I have even hovered over every little number in each photo incase they were extremely different from what I am used to seeing.

 

[anderso8623]

As you open throttle there is a rod attached to oil pump, this varies the oil mix in fuel line. Its not a reed problem.

This will be my next step. Is there a suggested starting point? Like on the air mix, should I be seating it and then turning it out 1.5 or 2 turns? or is it just an "adjust and test" scenario?

 

[racerone]

There are 2 reed blocks ( AKA bearings ) on the crankshaft parts page.----Easy to find.

 

[Faztbullet]

Fuel /air mix has noting to do with over oiling. If oil pump is feeding to much the fuel/oil ratio will be rich.

 

[anderso8623]

Fuel /air mix has noting to do with over oiling. If oil pump is feeding to much the fuel/oil ratio will be rich.

I understand that, I meant, is the adjustment similar to the oil air mix where you have to count the rotations of the screw to seat it or is it a completely different way to adjust the oil mixture?

 

[Faztbullet]

The idle air screw has nothing to do with oil mix. Oil/fuel ratio is controlled by oil pump or if disabled how much oil you add to fuel tank. This is oil pump and rod(pic) and rod should be connected to carb.

 

[anderso8623]

The idle air screw has nothing to do with oil mix. Oil/fuel ratio is controlled by oil pump or if disabled how much oil you add to fuel tank. This is oil pump and rod(pic) and rod should be connected to carb.

Mine does not look like that. Here is a pick I took of mine and also the parts catalog.

 

[anderso8623]

So, to update. I swapped out the plugs. It was hard starting so I replace the battery and it started up well. It ran well and I started down the river. I had her at 1500-2000 rpm. About 15 minutes down the river, the same thing happened. I could hear the motor losing power. It dropped a couple times before it quit. When it quits, it slowly loses RPM until it cuts out, maybe 15 seconds from 2000 rpm. I got back to shore and checked the plugs again to see what they looked liked. The pictures have my fingers sticking up to denote the cylinder. 1 finger is top cylinder going down in order.

I do not believe I can adjust the oil mix as previously mentioned. My mind goes straight to pistons not firing 100% of the time. One looks like it was never used. I know they all are because it runs fairly well.

 

[anderso8623]

I was thinking all last night and it hit me, when I rebuilt the fuel pump, the one way valves were held in with a plastic pop rivet. The kit I bought had replacement pop rivets but the pin that you push through did not actually slide, it was molded to the rivet. As a result of not being able to push the pin through, I reused the old pop rivet.
Could this be a possible reason? Maybe the plastic valve is not seated enough and allowing gas to flow backwards?

any suggestions on where to get plastic pop rivets that actually slide?

 

[Faztbullet]

You have the correct rivets...you take a flat punch and tap it in