84 Mercury 150 hurt pistons

[B4Istart]

I have a 1984 Merc 150 V6. The powerhead was changed by the previous owner in 1994. Over the weekend I scored two of the pistions and cylinders #2 10pci & #3 45pci all the rest of the cylinders look good and have between 118pci and 120pci. I suspect oil injection problems because I had no pressure in the oil tank on the motor when I looseed the cap to check when this happened. I have taken both ends off and the reeds look good. If the carbs got trash in them could this cause those 2 cylinders to lean out? I just rebuilt the carbs about 5 weeks ago and put a big canister filter in the fuel system. The motor had been sitting up for almost a year. I want to fix it but I want te be sure I don't miss something. The oil injector is comming off! I'll mix my own gas.

Thanks for your help!

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

I have a 1984 Merc 150 V6. The powerhead was changed by the previous owner in 1994. Over the weekend I scored two of the pistions and cylinders #2 10pci & #3 45pci all the rest of the cylinders look good and have between 118pci and 120pci. I suspect oil injection problems because I had no pressure in the oil tank on the motor when I looseed the cap to check when this happened. I have taken both ends off and the reeds look good. If the carbs got trash in them could this cause those 2 cylinders to lean out? I just rebuilt the carbs about 5 weeks ago and put a big canister filter in the fuel system. The motor had been sitting up for almost a year. I want to fix it but I want te be sure I don't miss something. The oil injector is comming off! I'll mix my own gas.

Thanks for your help!

The pressure in the reserve tank is less than 2 lbs, and plumb full, so you wouldn't feel any pressure let off. It will run with a negative pressure of -2 lbs if the supply hose gets pinched. It holds a 1/2 hour reserve at WOT while the alarm is going off.

Most likely cause is lean mix, or cooling, or a combination.

hope it helps
John

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

would the carbs cause a lean mix?

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

would the carbs cause a lean mix?

What do you think?

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

Well the oil is mixed in the gas before it goes into the carbs. But if the mixed fuel dosen,t reach the cylinder from the carb then I guess the answer is yes. I checked the carbs they look clean with no blockages. Floats moving freely so I guess either needle sticking or improper float adjustment.

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

You are very confused. Let me try to help.

We are not talking about the oil, we are talking about the fuel. If the fuel/air mixture goes lean in a 2 cycle engine, it will overheat and burn pistons. Most kids burn down their first motorcycle or snowmobile by tuning it for maximum performance at WOT, which is too lean to survive.

That engine has a separate carburetor barrel for each cylinder, so often individual cylinder failure can be traced to carburetor failure.

On the oil thing, folks have decided to be good to their motors and add too much oil to the fuel. The resulting higher viscosity of the fuel then causes the mixture to lean out, and they burn a piston.

The other factor in burn-downs is the cooling system, either a weak pump, or in some cases selective plugging in the power head with debris.

hope it helps
John

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

Thanks John!

I understand now. Thats exactly what I was looking for (B4Istarted). I love to play with motors but have never had much dealing with 2strokes. The power head comes off tonight. I did rebuild the water pump as soon as I got the motor. I be sure to check for any blockages while it's apart. I'll let you know how it turnes out.

Thanks again
Doug

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

The other thing we see on used motors sometimes is the wrong carbs or jets on a motor. Folks seem to think that they can just put on higher horse carbs and gain a lot of performance. In trying to tune them, they may go over the hill. It can be done, but it's more involved than just swapping parts, and it takes some time and expense to close in on final safe yet strong tune. Unless yer grinding on the ports till you can spit rivets, leave the carbs alone.

If you can fill me in on what your motor is, (including serial number) and what carbs are on it. I can look up jetting for you and you can check that item off your **** list.

'nother thing to look at is that if an advance module or idle stabilizer module shorts out, it pulls the bias toward advanced quite drastically. Been known to grenade power heads.

Fact is, it burned down. Question is, why?

hope it helps
John

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

Ok, I'll be back in touch. Also I think you may have hit on something. The idle stabilization module had a wire that had shorted out. I found that when I started tearing it down.

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

Ok, I'll be back in touch. Also I think you may have hit on something. The idle stabilization module had a wire that had shorted out. I found that when I started tearing it down.

Bingo!

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

Hey John

I got the powerhead off last night. Got to get a fly wheel puller. My wheel pullr won't work. Any why the carbs are WH-29 the serial #is 6569594. But the powerhead was changed in 1994. There are some #'s on the block 061884 115 don't know if they mean anything. It looks like th jets in the carb's are .064 and .026

 

[j_martin]

Re: 84 Mercury 150 hurt pistons

Jets in the WH29 should be .064 mains and .056 idle air jets. Vent jet holes should be unpopulated.

just remember, dyslexics are teeple poo.

hope it helps
John

 

[B4Istart]

Re: 84 Mercury 150 hurt pistons

Hey John

Had to walk away from the Merc for a while. I have it completely apart now and will need to order a book for it but before I do I want to be sure I will have enough cylinder wall to bore. Do you know what the cylinder bore is? I have found pistons for .030 over.