18HP saga continues. Can’t get past 14mph and 3,900 RPM.

[rjoynt]

FrankR suggested checking out the fuel pump. I had an 18hp that had the small square fuel pump on it and didn’t run properly. Changed it for the bigger pump and it had a huge difference in performance.

[stephenspann27]

21mph!! 5,050 RPM. 21mph was my top speed, I’m running 19mph most consistently at 4,950RPM

[david-bartlett]

Stephen,

You are moving in the right direction. Glad to see progress. Can you remind me what you have for a boat? Just curious, as I have a 14′ MirroCraft Deep Fisherman that I run 18’s on occasionally and I got 24MPH with a 1960 Johnson 18 that I fixed for a friend this summer.

[stephenspann27]

This was posted on another forum.

I had read that they changed from 24:1 to 50:1 around 1959 when they went from clamshell to needle bearings. However, this document shows 1964 as being the change from 24:1 to 50:1. That would explain why the fixed jet carbs went from a #64 main to a #57 main.

[stephenspann27]

quote david bartlett:

Stephen,

You are moving in the right direction. Glad to see progress. Can you remind me what you have for a boat? Just curious, as I have a 14′ MirroCraft Deep Fisherman that I run 18’s on occasionally and I got 24MPH with a 1960 Johnson 18 that I fixed for a friend this summer.

It’s a 1964 14′ lone star v bottom boat.

[stephenspann27]

Looks like the bearings have always been caged.

[phil-b]

quote stephenspann27:

21mph!! 5,050 RPM. 21mph was my top speed, I’m running 19mph most consistently at 4,950RPM

congrats! What do you credit for the improvement?

[stephenspann27]

quote Phil B:

quote stephenspann27:

21mph!! 5,050 RPM. 21mph was my top speed, I’m running 19mph most consistently at 4,950RPM

congrats! What do you credit for the improvement?

The fixed jet style carb was running too rich. I swapped in a bowl with the adjustable high speed circuit and tuned it on the water. It’s now faster, uses far less fuel and doesn’t have tons of unburned oil dripping all over the place.

[billw]

Now I bet if you go up an inch of pitch, you will see a slight improvement in speed and get the RPM back down a bit. Also, the speed improvement is great news; but with great power comes great responsibility….Don’t run it so lean as to burn it up. Find the sweet spot in the adjustment, half way between where it looses RPM from being too lean and looses RPM from being too rich. If anything, favor on the rich side. Now that you have the engine right where you want it, make sure it will last!

Long live American manufacturing!

[fleetwin]

Cool, glad you have found success finally. Try the next size up in pitch and see how that performs….

[Author]

Posts