Is re jetting 78 115 mercury outboard hard to do?

[jbigtrout]

I have been told I need to re jet the carbs for elevation. It doesn't look to hard in the repair manual but I am by no means a mechanic. Would I need any special tools? I have searched for the main jets and back drag jets I think I need but have not been able to find them online. The book says I need .068 for the main and .094 for the vent? The carbs are the side bowl back drag type. Any suggestions?

 

[Coloradolakeboy]

Re: Is re jetting 78 115 mercury outboard hard to do?

Most of the service shops here in Denver (and now Merc) do not recommend changing the jets for elevation. They say to use a smaller prop instead. I think they are worried the motor will be run in a lower elevation with those jets.That would lean out the motor and toast it. What manual do you have?Are the jets you listed for the carbs you have on the boat? Once you determine the correct jets, Go to mercurypartsexpress.com and get the OEM part number of the jets you need. Then just google the part #. You need a screw driver that fits the slot exactly on the jet so as not to bugger it. They are brass. Try a smaller prop first. My .02

 

[sschefer]

Re: Is re jetting 78 115 mercury outboard hard to do?

Agree, there are jetting specs for high altitude but those were written for fuel blends of that era. Today just drop 2" of pitch or 1" diameter and 1" pitch and run regular gas instead of premium when operating above 5000 ft. You will notice a lack of power regardless but this is from lower oxygen levels in the atmosphere and there's not a lot you can do about it.

 

[jbigtrout]

Re: Is re jetting 78 115 mercury outboard hard to do?

okay, right now the motor is jetted for 0 to 2500 ft. I'll be running it from arount 4,000 to 6,000 ft. The prop on it is a 17. Maybe down to a 15? The manual I have is SELOC.

 

[jbigtrout]

Re: Is re jetting 78 115 mercury outboard hard to do?

Thanks Colorado! That is a great parts site. So the shops don't reccoment it even if it is jetted sea level to 2500? hmmm.

 

[Coloradolakeboy]

Re: Is re jetting 78 115 mercury outboard hard to do?

Shops here don't recommend the high elevation jets because the motor can run too lean. The only way you can tell is to look at the plugs after you try the high elevation jets. I currently have high elevation jets in the carbs but haven't run them yet. I plan on fishing some lakes above 7000 ft. this summer. I will post back what I find on the plugs and how you can tell.

 

[jbigtrout]

Re: Is re jetting 78 115 mercury outboard hard to do?

Colorado, what kind of prop, pitch are you running? Mine has 19 pitch, thinkin' of getting a 17.