Bottom End Problems

[cbcmarine]

Hi all so here is the problem I have a 1978 85 hp merc the drive shaft broke, So I found the bottom end of a 1978 90 Hp (6 cyl) they seem to mount up and work fine on the muffs. When I put it in the water and put it into gear it stalls this did this every time. Is it possible the gears are different or could the motor be the problem? The motor starts and runs great !!

Help would be great

 

[Chris1956]

Re: Bottom End Problems

The gear ratio may be different, but that is not a problem at idle. It is likely you have dirty carbs or misadjusted idle mixture.

As for the different gear ratio, run WOT and see what your max RPMs are. If you are below 5000RPM, swap your prop with one with 2" less pitch.


BTW I ran my '77 Merc 1500 LU on my 850 motor for years. I uses a 17" prop on the 850 whne I had the inline 6 LU on it, vs a 19" prop with the original LU

 

[cbcmarine]

Re: Bottom End Problems

Hey chris thanks for the reply, I used the same prop the 85 had on it when it ran fine. As soon as I go to slip it into gear it dies even when I tried to increase the idle and slip it into gear it dies. In both forward and reverse.

So it's stumped me