95 mercy 115 2+2 still having problems

[hareymike]

https://www.youtube.com/watch?v=pvEoUjwmcRA

Here is a video link.
It runs great, other than when i come off plane it runs like this 95% of the time. Seems like its still trying to fire the two cylinders that have shut off.
Any help greatly appreciated.
Mike

 

[flyingscott]

Have the carbs been serviced at all? Has a link and sync been done? Those motors are kind of tricky

 

[hareymike]

It only does this after driving on plane. I didnt think it was carbs because it runs perfectly otherwise. Also, once i rev it up, it smooths out.

 

[flyingscott]

I would look at the carbs on it. That motor always fires all 4 plugs the bottom 2 cylinders are controlled by the carbs. They pretty much eliminate the idle circuit except for allowing a miniscule amount of fuel mix thru for lubrication. The bottom 2 carbs also have accelerator pumps on them that can leak fuel through and cause the cylinders to try and fire.

 

[hareymike]

Hmmm ok. I wonder if when it shuts down then its bleeding by. I also see there are 14psi fuel jets. They are supposed to stay closed below 14psi. They may be bleeding by.
I will check into the pumps. How do i check for leaks.

 

[flyingscott]

I would rebuild the carbs completely with the factory kits. It could also be a bad needle and seat. What do you mean by 14 psi fuel jets? Mechanical fuel pumps usually run around 6 PSI. Also for that motor a factory manual is a must and make sure you get the factory kits that have the replacement pumps.

 

[hareymike]

I found this diagram, see link below. Shows two fuel jets that open at 14psi. I wondered if maybe one or both are sticking open a bit.

http://boatinfo.no/lib/mercury/manuals/75-90-100-115-125.html#/200

 

[flyingscott]

Those are check valves opened by the accelerator pump when it operates. I am going to stick with the carbs as a starting point and change filters as you go