I have a 85 Johnson 70 VRO. I had a lot of trouble with low speed operation and bogging down when trying to accelerate. My powerhead was a rebuilt unit and after installing the rebuilt unit is when my troubles began. I suspect I was sold a 75 hp powerhead. The 70 hp motor has fixed jets. The 75 hp motor has adjustable low speed jets. I found a set of 75 hp carbs, put them on my motor and was able to adjust my low speed jets until all the low speed and acceleration problems were eliminated and it runs great now. It took me 2 years to get it finally straightened out. You first need to make sure you check all your basics first before you go buying anything. Check your compression and make sure all 3 cylinders are over 100 psi and are all the same within 10%. If your compression is not what it is supposed to be you are wasting your time fixing anything else. Secondly you need to test your spark with a spark tester which you can get for about 10 bucks at your local auto parts store. I got mine at Auto Zone. Your spark needs to jump a 7/16 gap with a bright blue snap. If your compression and spark are verified good then the next step is to clean and rebuild your carbs. Its not hard to do. Just make sure you have a nice clean place to lay out all the parts. Then put the carbs back on and do a complete link and synch which you can find in a shop manual or search previous threads on this site. If the motor still won't run right then I would look into obtaining a set of 75 hp carbs. Also running the motor on muffs in your driveway is pretty much useless. The motor has to be submerged in the water in order to properly test out any adjustments you make. Good luck. There are a lot of smart guys on this site who can help you.
