1986 mercury fuel/oil ratio

[pete32]

I just bought a 1986 mercury motor. The owner said that it was a 20hp and he had changed the carb. to a 25hp. I asked him what he used as the mixture ratio he said 36 to 1. When looking thru this site it seems that eneryone is saying 50 to 1. What is the correct ratio and octain to use when using this motor. Also this motor gets used at altitudes from sea level to 7000 ft.
Thanks for the info.

 

[j_martin]

Re: 1986 mercury fuel/oil ratio

50:1 is the correct ratio. Use good oil. I doubt the carb story also.

I'd read the plugs after a hard run at sea level to be sure you're not too lean, otherwise shouldn't be a problem.

hope it helps
John

 

[rickdb1boat]

Re: 1986 mercury fuel/oil ratio

The correct mixture is indeed 50:1 no matter the altitude. In fact, a richer oil mixture will somewhat reduce the fuel combustibility, not to mention foul the spark plugs more often..

 

[Ranger_man]

Re: 1986 mercury fuel/oil ratio

50:1 regular, but I heavily suggest 100:1 AMS oil.

 

[j_martin]

Re: 1986 mercury fuel/oil ratio

50:1 regular, but I heavily suggest 100:1 AMS oil.

If you want to wreck yer motor. If an engine (like the 1930's stuff) needs 16:1, and you use a TCW3 oil capable of ;100:1, you mix it at 16:1 for that engine.

Manufacturer spec for your engine is 50:1. No matter what oil you use (provided it meets minimum spec, which is TCW2, I think) you mix it at 50:1

Sorry Ranger, I've seen too many wrecks by AmZoil.

John

 

[pete32]

Re: 1986 mercury fuel/oil ratio

Could he have damaged the motor if he ran it at 36:1? Also he showed me the carb that he replaced it had a much smaller opening than the one that was on the motor. The guy I bought it from was a mechanic and had the motor for a number of years. Just seemed like if he was running it at 36:1 he would have had issuses with the motor.
Just want to make sure I'm doing the right thing.
Thanks for your info.

 

[j_martin]

Re: 1986 mercury fuel/oil ratio

Naw, that ignition will burn 25:1 with little trouble. In fact, that's how you're supposed to break it in. It's just a waste of expensive oil on a smooth free engine.

Just slapping on another different carburetor without carefully dialing it in at all speeds can cause trouble. If it's too lean at any speed, it could actually burn down the motor. I don't know about that particular swap, but someone here does and could make a recommendation for jetting or adjustment.

If it seems to run good, I wouldn't worry too much. If you've a mind to, you could idle for awhile, then check your plugs. Put in new ones, run wide open for awhile, then check the plugs. Then again at mid range, just to be sure the carburetion is dialed in.

I'd recommend getting the oem maintenance manual, and do the "link n sync" procecure in the manual. It'll give you a good feel for how the motor is supposed to behave, and also assurance that it's set up right. You should really do this before you dial in the carb.

hope it helps
John