Still can't get WOT out of 1964 Johnson 18HP

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oldfarmall

Seaman
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Jun 18, 2009
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63
Hello-
Can anyone point me in the right direction as to what I should check next on my 1964 Johnson 18hp model FD-18E? Here is what I have done so far:

-installed brand new condensers, spark plugs, points, coils, copper core plug wires, gapped points to .020, plugs to .030.

-taken carb apart, put new float, needle and seat, soaked and blew out ALL pasages and jets (high speed jet is a fixed jet, it is perfectly clean)

-spark tester shows bright blue lightning bolt that jumps 1/4" on both cyclinders

-compression is 100 and 105

-did test on carb by spraying fuel into it at WOT, engine want to die when extra fuel sprayed in throat, or when pulling choke out slightly. Choke plate is open all the way.


I still can't get engine to rev up to full 4500 RPM, can only get to around 3700. MAx speed of my 14ft aluminum v-hull with just me in it is 17MPH. Tried all 4 trim adjustment holes on motor. Didn't make a difference. My prop is a 9 X 10.

I took out my spark plugs after being on lake for test run today. They seem shiny with black spots on white porcelin, smelled like it was running rich. Did not seem nice brown color that a proper plug should look like if it is burning good. The thing is the motor seems to run great at 3700 RPM, doesn't miss, surge, or die out.

Could this just be a carb problem, float setting wrong? With carb inverted, it sits almost level with carb body (slighty upward). This motor has a fixed high speed jet in carb. It is spotless. Is it possible the high speed jet holes get bigger or worn out over time? Also, my fuel mix is 50:1 ratio.


I am at my witz end with this. After diagnosing everything that poeple said on this forum, I think it is the carb. If anyone can please help with opinions. Thanks!


Jesse
 
F

F_R

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Re: Still can't get WOT out of 1964 Johnson 18HP

You mentioned the high speed jet. They don't wear over time, but they do get oversize when somebody jams wires and stuff through them. So it's a good guess. Try a new one.

3700 isn't terribly off, so we know it is running on both cylinders. Is the carb throttle butterfly opening all the way?

EDIT: How about the little cork gasket that goes around the main nozzle? If it is leaking or missing, the resulting result is the same as an oversize jet.
 
O

oldfarmall

Seaman
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Re: Still can't get WOT out of 1964 Johnson 18HP

F_R said:
You mentioned the high speed jet. They don't wear over time, but they do get oversize when somebody jams wires and stuff through them. So it's a good guess. Try a new one.

3700 isn't terribly off, so we know it is running on both cylinders. Is the carb throttle butterfly opening all the way?

EDIT: How about the little cork gasket that goes around the main nozzle? If it is leaking or missing, the resulting result is the same as an oversize jet.
Click to expand...



Thanks for the reply!

The carb butterfly does open all the way. I just installed a new OEM rubber gasket that goes around main nozzle. I don't think a wire could have damaged the high speed jet, since it is a large open jet with large holes on the sides. Could it be the float setting? MAybe I should try and lower the float a bit? Thanks!


Jesse
 
A

AlTn

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Re: Still can't get WOT out of 1964 Johnson 18HP

is the av plate 1" or less from the bottom of the keel?
 
bktheking

bktheking

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Re: Still can't get WOT out of 1964 Johnson 18HP

When you took the carb apart was the boss gasket present?
 
F

F_R

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Re: Still can't get WOT out of 1964 Johnson 18HP

oldfarmall said:
Thanks for the reply!

The carb butterfly does open all the way. I just installed a new OEM rubber gasket that goes around main nozzle. I don't think a wire could have damaged the high speed jet, since it is a large open jet with large holes on the sides. Could it be the float setting? MAybe I should try and lower the float a bit? Thanks!


Jesse
Click to expand...

Hold on there, Jesse, that isn't the high speed jet, that is the main nozzle. The high speed jet is in the very bottom of the float bowl, behind the hex head drain plug. It is a precision orifice through it and easy to damage by shoving stuff through it, even drill bits have been known to violate those things.
 
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oldfarmall

Seaman
Joined
Jun 18, 2009
Messages
63
Re: Still can't get WOT out of 1964 Johnson 18HP

F_R said:
Hold on there, Jesse, that isn't the high speed jet, that is the main nozzle. The high speed jet is in the very bottom of the float bowl, behind the hex head drain plug. It is a precision orifice through it and easy to damage by shoving stuff through it, even drill bits have been known to violate those things.
Click to expand...



F_R-

Thanks for the clarification. I did remove this orifice and it was clean, however I suppose it is possible that someone damaged it before I got this motor. Is there a way to measure the orifice to see if it is oversized? Oversized would give me a rich running engine, correct? Also, tried lowering float, this did not make a difference, was still not reaching WOT on lake today. Spark plugs still seemed wet. I will try replacing it and see what happens. I see it is about an $8 part. Thanks
 
J

JMJohnsonII

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Jan 10, 2009
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Re: Still can't get WOT out of 1964 Johnson 18HP

Is your timing plate advancing to full timing? Also, I had one of those motors doing the same thing. I found the thrust bushings in the lower unit were worn out causing drag.
 
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oldfarmall

Seaman
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Re: Still can't get WOT out of 1964 Johnson 18HP

JMJohnsonII-

The timing plate is advancing all the way, also checked carb butterfly, opens all the way too. The lower unit on this motor is from a 1969 evinrude 25hp, been gone through, nothing seems to be binding or creating a drag but I could be wrong. Still think it is a carb issue. I am going to try and change high speed orifice with a new one. Thanks!
 
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oldfarmall

Seaman
Joined
Jun 18, 2009
Messages
63
Re: Still can't get WOT out of 1964 Johnson 18HP

I think I may have found the problem. I took out my high speed orifice out of the carburetor today. Had 64 stamped on it. I thought it was supposed to be a 63D orifice. Can anyone verify this. Again, this motor is a 1964 Johnson 18hp model FD-18E. Thanks!


Jesse
 
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