1964 18hp Johnson 18hp not reaching full RPM

[oldfarmall]

Hello-

Have a 1964 Johnson 18hp model FD-18E. Decidied to start a new thread since I have my results from test on the lake today.

OK, just got back from the lake. I had a chance to retest compression, and test RPM with a laser tachometer this time. Compression was 100 and 105. RPM at WOT was only 3,700 RPM max. My book says it should be at 4,500 at WOT. Cam and carb open completely (link & sync). The 3700 RPM would explain why it is slow at top end. But what is causing it. In previous replies we ruled out ignition and compression. Also, put a brand new fuel pump on last fall. I am running 50:1 mix.

Questions:
1. If I have a plugged high speed jet, wouldn't the engine die off at WOT because it is starving for fuel?

2. When I sprayed gas/oil mix with spray bottle in throat of carb when running at WOT, the engine did not speed up, it acted like I had the choke on leading me to believe it is getting enough fuel. Also, tried pulling choke out a bit ot WOT, did same thing, slowed down. What does this mean?

3. Should the glass bowl with fuel filter be full when running?

4. could weak spark cause motor not to reach full RPM?


Also, pulled 1 plug wire off at a time, restarted motor, motor ran rough and had no power. Did the same with other plug wire, got same result which leads me to believe it is not ignition?

I am leaning towards carb, but it runs smooth at the 3700 RPM and idles and runs well at low RPM, just stumped as to why I can't get top 4500 RPM. I am running a 9X10 prop. Any thoughts? Running too rich? Thanks!


Jesse

 

[oldfarmall]

Re: 1964 18hp Johnson 18hp not reaching full RPM

bump

 

[tmcalavy]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Have you tuned/adjusted the carb needles on the boat while running? If so and you're only getting 3700 out of a 4500 rated motor, I would say carb problems or just a tired motor. F_R will probably weigh-in soon with more and better advice...like maybe a prop change.

 

[dew2]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Has your prop been changed? Myself I would remove the carb and do a good cleaning,From what you say it doesnt sound like the carb,BUT its easy, fairly low cost, and it will be eliminated.Make sure the hi speed,(without looking it up) I'll guess Needle and seat are cleaned GOOD.

 

[kbait]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Those are strong motors, but if your pushing a barge, it won't get to 4500rpms.

 

[oldfarmall]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Those are strong motors, but if your pushing a barge, it won't get to 4500rpms.

The motor is on a 1960 starcraft 14ft aluminum v-hull boat. Hope this helps. Thanks!


Jesse

 

[oldfarmall]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Hello-

forgot to add that prop is a 9X10. My 1964 parts book says original is a 9.25X11 prop. How much of a difference will this make? Thanks!


Jesse

 

[kbait]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Your current, 'shorter' prop should give 200-300 more rpms than the original at wot, and should reach full rpms, especially w/your current prop/light boat. I'd check spark w/tester to ensure 1/4" blue bolt. Ensure plug gap at .030". Clean carb and ensure proper float setting (level w/inverted carb body) + new fuel line carb to fuel pump. Link/sync armature plate/carb butterfly. If all that doesn't work, ensure points are each correctly gapped to .020" (changing the gap changes timing and if they are different, the cylinders 'fight' each other by not firing exactly 180 degrees apart).

Unless you've got a couple 400 lb guys plus a 170 lb dog in the boat, you should plane out easily and get over 20mph. Strong motors and your compression #'s look fine. Good luck!

 

[jedidiah012]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Are you sure that the correct oil-fuel mix is 50:1? I have a 63 and I have been told it should be 24:1. Not sure if there's a difference between the two model years.

 

[Bass boat fix]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Had a similar problem, I have a tiller control motor. I was stumped at why my boat would not come up on plane and I started to look at different things. What I found was the pinion gear on the motor end of the tiller handle that matches up with the gear assembly for the throttle had jumped a couple of teeth and wasn't allowing the throttle to fully throttle up. And the pin in the vintage lever control was broken.

 

[kfa4303]

Re: 1964 18hp Johnson 18hp not reaching full RPM

Hi farm. I would suggest you start fresh and check each engine system (fuel, ignition, cooling). Thankfully, the compression is good, so all the rest is pretty easy to fix. I would rebuild the carb, replace the points and condensers, and install a new impeller. You can get all the bits you need right here at iboats for about $20 each. Use the link below to help you through each job. Once you have it all put back together, you should be able to get +/- 20mph on most 14'-16' boats.

Maintaining Johnson E & FD Serie

1964 Johnson FD-18 18 hp Outboard Motor Parts

 

[valvebounce]

Does it reach max revs if it is out of gear?if not,you have a fault.
I have a 1964 18hp Evinrude,and a 14ft fibreglass boat(remotes/steering etc.)
The prop on it is a 9.25 X11"pitch.(012013) the motor is at the correct height on the transom.
It runs sweet,puts out a huge wake,but fails to get the boat on the plane.It fails to reach max revs.
I have come to the conclusion that it is the prop.
There is the one you have on your engine-9" X 10" or a (9" X 9")(012109)
The latter has better cupping and is the one I am going to use to replace the 9.25 x 11.
The difference on the Michigan prop site is the 9 x 10 is for a 12ft to 14ft boat,and the 9 x 9 is for a 14ft to 16ft boat.
I throttled back to half throttle and the speed was the same with the present prop,I also used a 5hp yamaha engine I have as an emergency engine,the speed
was about he same.I boiled it down to the wrong prop.
Hope this helps.

 

[tomhath]

Does sound like it's running too rich. I believe the High speed needle should only be about 3/4 of a turn out from fully seated.

 

[GA_Boater]

It's too late for help. This thread is over 3 years old and the OP's last visit was 1 1/2 years ago.

Closed.