willem wikkel spies
Moderator
so I have 2x 75 hp Yamaha 2 strokes.
they do run well without any problems.
just to check if all were well, I decided to download the manual and see what is what.
I found that the 75hp motors are actually 85hp motors and that they have been choked.
so I did some reading through the manual to see where they ended up in screwing the end user.
there is not much difference.
both are 1140 cc motors.
they use different carbs, numbers only.
carb trout size is still unknown.
the 75hp carb jet sizes are about the same.
the main jet is 0,10mm bigger then the 85hp.
air correctio are the same.
emulsion tube on the 75 is 3,2mm and 3,4mm on the 85hp.
so how do you get 10hp more on a engine, with a main jet being 0,10mm smaller and 0,2mm bigger emulsion tube.
there has to be something else.
10 hp is not being hidden in the above.
so scrolling through the manual further.....
I found that the motors have different reed valve assemblies.
the 85hp allows the reed valve to open to 10,1mm with specs being 9,7mm to 10,1 mm
the 75 horse power the reed valves are set to a maximum of 3,2mm
so in essence, preventing the engine to breathe properly is done by choking the reed valve assembly.
lets see where this takes me.
do note, I have much knowledge regarding 2 stroke engines, their operation etc.
I have studied Jennings book on 2 stroke engines.
playing with 2 strokes, port timing etc. but not on my boat engines. so don't worry about these aspects.
it is mere a discussion tread.
they do run well without any problems.
just to check if all were well, I decided to download the manual and see what is what.
I found that the 75hp motors are actually 85hp motors and that they have been choked.
so I did some reading through the manual to see where they ended up in screwing the end user.
there is not much difference.
both are 1140 cc motors.
they use different carbs, numbers only.
carb trout size is still unknown.
the 75hp carb jet sizes are about the same.
the main jet is 0,10mm bigger then the 85hp.
air correctio are the same.
emulsion tube on the 75 is 3,2mm and 3,4mm on the 85hp.
so how do you get 10hp more on a engine, with a main jet being 0,10mm smaller and 0,2mm bigger emulsion tube.
there has to be something else.
10 hp is not being hidden in the above.
so scrolling through the manual further.....
I found that the motors have different reed valve assemblies.
the 85hp allows the reed valve to open to 10,1mm with specs being 9,7mm to 10,1 mm
the 75 horse power the reed valves are set to a maximum of 3,2mm
so in essence, preventing the engine to breathe properly is done by choking the reed valve assembly.
lets see where this takes me.
do note, I have much knowledge regarding 2 stroke engines, their operation etc.
I have studied Jennings book on 2 stroke engines.
playing with 2 strokes, port timing etc. but not on my boat engines. so don't worry about these aspects.
it is mere a discussion tread.