Running great, but running lean???!

Beater

Seaman Apprentice
Joined
May 22, 2005
Messages
30
Ok, I posted a while ago about getting a 1979 140 horse merc that had been stored for 7 years and used sporadically the previous 20 years. It started right up for me and the only thing I could see was that the bottom float stuck for a couple minutes cause it peed out the overflow hole. I didn't like the tell tale stream flow so I replaced the impellor and that took care of that. The motor pushes my 1984 16 foot Thundercraft at 40 plus mph no probs with three adults aboard at about 5000 WOT. It planes out almost immediately. It also idles and starts great. My question is, is it possible that this motor could be running lean even though it seem to be running so well? I keep reading about burning pistons from running lean and this motor is so mint and running so well that's the last thing I want to see. I could have the carbs taken apart and cleaned but I've always been of the camp "if it ain't broke don't fix it". Opinions please!
 

andrewkafp

Lieutenant Commander
Joined
Mar 15, 2003
Messages
1,668
Re: Running great, but running lean???!

Check the plugs.<br />There is a chart in the Merc manual showing the effects of lean burning by looking at the plugs and their colour.
 

timmathis

Lieutenant
Joined
Apr 24, 2005
Messages
1,295
Re: Running great, but running lean???!

one thing is to make sure your timing is not to high. That will burn it up in a heartbeat! Tim
 

briannh1234

Petty Officer 1st Class
Joined
May 19, 2003
Messages
233
Re: Running great, but running lean???!

Beater -<br /><br />Ain't broke don't fix it is generally a good idea. I recommend that you by a $5 can of seafoam and add it to one tank of gas. A common reason for a lean engine is a gummed up carb, and the seafoam will help clear the gum out of the carbs. From your post it sounds like the bottom carb allready has extra gum in it.<br /><br />The oil is in the gas which is controled through the carb. If the carb's not working right your not getting enough oil. Not enough oil will lead to a burned engine.
 

timmathis

Lieutenant
Joined
Apr 24, 2005
Messages
1,295
Re: Running great, but running lean???!

Also make sure your tank is clean.
 

Beater

Seaman Apprentice
Joined
May 22, 2005
Messages
30
Re: Running great, but running lean???!

Thanks for the advice guys. I keep hearing about this sea foam but I don't think it is available in Canada. Any input on where to get it from my Canadian counterparts would be appreciated.
 

riccd2001

Recruit
Joined
Sep 7, 2005
Messages
5
Re: Running great, but running lean???!

Add my name to the growing list of satisfied Seafoam customers.<br /><br />This season I started to use Seafoam in-tank treatment as well as Deep Creep. After three 20-litre tanks and a couple of decarb/smokeout sessons, the old '76 Merc850 performance is very much improved. Even my kids and their friends are amazed at how fast the old boat is running this year.<br /><br />Bilingual cans are now widely available. You can find Seafoam in Canada at an auto parts supply store in your area. I get my supply in Oakville at Carquest on Speers Rd.
 

jheron

Petty Officer 1st Class
Joined
Jul 21, 2004
Messages
284
Re: Running great, but running lean???!

Yep carquest is the place to get it in Ontario :) <br />Jon
 
Top