Johnson 35hp

"I have a late 70's Johnso

"I have a late 70's Johnson 35hp outboard fitted to a 17 foot Wilson style boat. My problem is speed, or lack of it. Flat out with two persons on board the boat will make 10knots. I would estimate the boat at 1600 pounds, the prop fitted has the following stamped on it
B3X10.1X13(M). The engine revs freely to wot and appears to run very well. I am thinking that the engine has been fitted with a prop for river use.

Any idea's welcome."

"Garry, quickly ran some numbe

"Garry, quickly ran some numbers for you in a prop calculator.

With that motor and weight your prop looks to be the right one - you should however be getting something in the mid 20 knots out of that.

If the prop hub isn't slipping, it would seem that something else is dragging your speed down..."

"Graham, Thanks for that now I

"Graham, Thanks for that now I know the prop is correct I have made the following checks. The engine compression is 140psi per cylinder, have taken off the prop to check hub and found ok. have also checked the fuel filter and found it to be clean. Should there be a filter in the carb air box, this one has none fitted. Have checked the carb throttle which is opening fully.

Will be taking the boat out at the weekend after fitting a tacho to double check revs at WOT.

Have also checked the boat, hull is clean, cant find anything which would slow the boat.

If you have any other idea's I would be grateful."

You have spark on both cylinde

You have spark on both cylinders?????