1993 Johnson 48 SPL Idle

[onildera]

Ok, here is what I have done...

Rebuilt Fuel Pump
Rebuilt Carbs - super clean
Replaced Leaf Valves - Two Stage Boyeson's
Sync and Link - by the book (OEM Manual)
New Plugs

Compression Test - 144 and 144
Spark Test - Bright Blue

Now, the issue. Same as before all of that...

This engine runs great. Best I have had. Except at idle.

Starts without effort. Runs all out like a champ.

At idle (both in gear and out) it will run fine at first, then start to shake, then start to cough, then die. By the sound of it, it is running rich.

When adjusting the slow speed needle, it says to softly seat it and then back it out 2 1/2 turns. The issue is that it never feels like it seats. The spring is totally compressed before that happens. I don't really know if I am out 2 1/2... I am going to get it on the water and see what I can do with that.

The other thing is the manual has two pictures on page 2-38. One for the 40, 45,48 carb and one for the 50,55. I have a 48 but the carb is surely the one pictured in the 50,55. Is that common? Were they interchangeable? Does the sync and link need to be changed for that carb? I used the lengths of the throttle cam link per the 48...

Thanks in advance!

[Joe Reeves]

At idle... Does constantly pumping the fuel primer bulb make (acting as a manual fuel pump) any difference?

[onildera]

I'll give that a try. Increasing the throttle just a touch will keep it running. It is just in neutral and just clicked into gear. Forward and reverse.

[onildera]

Ok. Pumping the bulb does not change anything as it is dying...

[Joe Reeves]

Ok. Pumping the bulb does not change anything as it is dying...

Check that the carburetor is not flooding when you pump the fuel primer bulb.

On a flushette, the engine, depending on the shaft length, should idle as follows:

20" shaft = 1000 rpm
25" shaft = 1200 rpm

With the engine running, pull the spark plug wires, one at a time, to see if the response on both cylinders is the same.

What is the compression PSI reading of all cylinders?

With the spark plugs removed, do you have spark that willl jump a 7/16" gap with a strong blue lightning like flame... a real SNAP? Note that the gap is important!

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark.

[onildera]

Ok! Took her out on the water and adjusted the low speed screws.

Idles very smoothly now. I might change the coil pack, as there is a small stutter every so often.

The thing that confuses me is that the low speed screws had to be in far enough that the springs are totally compressed. Wrong springs? Wrong screws?

I also still find it confusing that the manual shows a different carb for the 48. I definitely have the 50 carb... Is that common? Did they do that if for some reason they didn't have the 48 carb when they built the engine?

Thanks for the help!

[Joe Reeves]

Ok! Took her out on the water and adjusted the low speed screws. Idles very smoothly now. I might change the coil pack, as there is a small stutter every so often.

The thing that confuses me is that the low speed screws had to be in far enough that the springs are totally compressed. Wrong springs? Wrong screws? I also still find it confusing that the manual shows a different carb for the 48. I definitely have the 50 carb... Is that common? Did they do that if for some reason they didn't have the 48 carb when they built the engine?

Didn't you need to adjust the threaded trunion of the throttle cable to change the rpm.... where the throttle cable is clamped into a fitting at the engine?

If someone before you has installed different carburetors in a attempt to obtain a higher horsepower, speed, whatever, that would complicate matters. If this is the case, or if you simply suspect it, it would be best to contact the previous owner before going further.

Having those mixture screws is as far as they will go should cause the engine to die out.

[Joe Reeves]

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