spark plug gap

milehi · Post by **milehi** » Fri May 08, 2020 11:30 am

Anyone know the gap for a 2001 mercury 115 hp 2 stroke, carbs?

WRB · Post by **WRB** » Sat May 09, 2020 3:44 pm

Plug number? L78YC Is .040- .042 You need to reduce the carb jets dia about 10% for high altitude.
Tom

Lawley · Post by **Lawley** » Sat May 09, 2020 4:49 pm

Yes carb jets get smaller for high altitudes

I once had a 60 hp outboard that wouldn’t even hardly run with the jets that work perfect at sea level
The larger the engine displacement the less adverse effect at high altitude. You might be ok depending on engine size
For maximum performance jet size absolutely changes with altitude
It may not be worth the trouble if you are not going to stay for extended amount of time

milehi · Post by **milehi** » Sun May 10, 2020 9:35 am

Thanks. This a remanufactured 115 merc 2 stroke, has run fine couple of years I've had it, all of a sudden very hard to start first thing. Will talk to my mechanic about that as I'm at 5200' Thanks

WRB · Post by **WRB** » Sun May 10, 2020 11:02 am

Hard starting is typical with carb merc's. Simple things like fuel filter, bad prime bulb to electrical issues like power packs. To check plug fowling you need the engine and hot, then shut it without idling, pull the plugs the color should be very light tan, white is too lean and dark is too rich.
BB lake where I grew fishing is 7,200' and 20% hp loss is common with OB's.
Good luck,
Tom

Lawley · Post by **Lawley** » Sun May 10, 2020 11:26 am

Did you just move to 5,200 feet?

milehi · Post by **milehi** » Sun May 10, 2020 11:48 am

Personally been here since 1981, motor came from back east but only run here since the rebuild. Big Bears right up the road

Dave A · Post by **Dave A** » Mon May 11, 2020 4:11 pm

I have a 1999 Mercury 2 stroke 115. The dang thing is pain to start cold. I hear the same from others with these engines. I’ve come to live with it. Once it starts it runs like a champ

.

Dave A · Post by **Dave A** » Mon May 11, 2020 4:17 pm

Oh, and yes. At altitude performance suffers for sure. I lose about 10% to 15% performance when I go to Bass Lake and that’s only 3,500 feet. Getting on plane with any weight on board is a chore at times.

WRB · Post by **WRB** » Mon May 11, 2020 7:47 pm

Don't want to go off into too many tangents on this thread. 3,500' should be a major affect unless the set up is marginal to start with. If that is an issue drop 1" in prop pitch; 20P to 29P for example.
Tom