1980 115hp merc loosing power

[bajamark]

Hi my fellow boaters, I have a 30 year old very faithful 115hp merc on a Baja 16ss that has been extremely problemless over the years, until recently.

It seems to loose power and bogs down for the first 45minutes-1hr of use (very badly) and sounds like it is running on 2 cylinders (It is an in-line 6 cylinder). I do get some blue smoke at slow speeds only. I launch my boat in the river and it is about a half mile up the river to the lake at 5mph (no-wake zone) so I'm wondering if this slow speed may have something to do with it.
After I run the motor for a while (30-45 minutes or more) power slowly starts to return to normal and the boat will run perfect for the rest of the day.
This seems to happen after the boat sits for a week or so on the trailer.
At first I thought it may be the surface gap plugs (I'm running Champion L76V). I did pull the plugs out the other day and they were all carboned up pretty bad. I'm wondering if I switch to the conventional "j" plug if this might help. I'm running quick silver 2-cycle oil 50-1 ratio.

any suggestions would be extremely appreciated. and thanks!!!!!

MarktheShark

 

[achris]

Re: 1980 115hp merc loosing power

Mark,

I would give the chumpion plugs a 'float test' and fit NGK BUHW spark plugs. I would also get a can of 'Power tune' and run that through. Change any and all fuel filters and consider pulling the fuel pump and replacing the diaphragms.

Chris.......

 

[bajamark]

Re: 1980 115hp merc loosing power

Thanks very much Chris. Would you go with the conventional gap NGK plug (if still available) or the surface gap?

 

[achris]

Re: 1980 115hp merc loosing power

Thanks very much Chris. Would you go with the conventional gap NGK plug (if still available) or the surface gap?

Only ever use surface gap plugs in those engines. 'Conventional' plugs run the risk of popping a piston....

 

[bajamark]

Re: 1980 115hp merc loosing power

Thanks again Chris, I will try the NGK-BUHW plugs and also the Power Tune.
I'm not sure where I can get the power tune? Is it available only on-line and also is it something you pour in your gas tank?

 

[starcraft1982]

Re: 1980 115hp merc loosing power

I have seen power tune at local marinas,merc shops,etc.Just call around.NAPA carries NGK plugs.Some may have to order,i checked 2 stores and found them in stock.Sometimes if they have to order,they want you to buy all of the box.If youve got the money and you plan on keeping boat/motor it may not be a bad idea to have the extras.

 

[walleyemanII]

Re: 1980 115hp merc loosing power

Advanced Auto normally carries the NGK in stock. Use can also use seafoam for a a cleaner sold at the same location.

 

[CharlieB]

Re: 1980 115hp merc loosing power

I would almost bet that if you did two compression tests, one stone cold and the other hot, that you will see a pretty big difference on at least a couple of cyl's caused by carbon sticking the rings until it gets up to temperature.

Power tune or Sea Foam at twice the maintenance level will soon clean it out and restore cold compression.

I would not recommend WOT any longer than it takes to get on a plane while using these additives as both increase combustion temps.

Check you new spark plugs once in a while to see if one carb is running slightly richer than the others and causing increased carbon deposits on those 2 cyl's. A carb clean and rebuild may be required an pay particular attention to float level settings to ensure all are the same level as prescribed in the service manual.

You can download a copy of the manual here

http://forums.iboats.com/showpost.php?p=2072211&postcount=3

Remember the password noted at the bottom of the page, you will need it to unpack the compressed file.

 

[bajamark]

Re: 1980 115hp merc loosing power

I tried a can of power tune yesterday, and so far so good!! The merc ran
very good and idle seemed much better. I also purchased the NGK-BUHW plugs,
(to replace the Champion L76V plugs) but the ole merc ran so good after the power tune I didn't bother replacing them *yet*. So thanks Chris for suggesting the power tune and thanks everyone else for replying. This sight if fantastic and can save you huge $$$$$ on repair bills!!

 

[arsenalpsu]

Re: 1980 115hp merc loosing power

I would still replace those old spark plugs, Champs are junk- i had one die on me a few weeks ago. Switched to NGK and never looked back. Keep the Champs in your boat incase you fowl a plug. Also try EBAY for the NGK, i got a set for like 21 bucks delivered, saved like 10 bucks compaired to Autozone.