Can Low Speed Jet Cause Engine to Run Rich at WOT?

[oldfarmall]

Hello-

I am still in the process of diagnosing my 1964 Johnson 18hp model FD-18E. Thanks to all who have responded to my previous threads. I have rebuilt carb, soaked, blown out with compressed air, new float and adjusted, putting in new high speed orifice plug. My question is, if the new high speed orifice plug (63D) does not fix my running rich problem at high speed, could it be my low speed jet that is causing motor to run rich at high RPM? Also, fuel pump is new, so I doubt it is leaking into cylinder. Both spark plugs are wet. Spark tester verified spark jump over 1/4", so ignition is fine, new plugs and spark plug copper core wires. Also, lync & sync is good. Compression is 100 and 105. Any thoughts on the low speed jet? Thanks!


One last thing, I am running 50:1 gas oil mix.

Jesse

 

[Joe Reeves]

Re: Can Low Speed Jet Cause Engine to Run Rich at WOT?

The spark you speak of jumping a 1/4" gap should be a strong blue lightning like flame... a real SNAP! Anything else is a problem. The HS jet size of 63D is correct.

If the fuel pump diaphragm is okay, and being new, I assume it is, and if you still have a rich fuel problem at full throttle after adjusting the carburetor slow speed needle valve as follows.... double check the carburetor as that would indicate a internal leakage, a nozzle gasket missing or damaged, something of that nature.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[oldfarmall]

Re: Can Low Speed Jet Cause Engine to Run Rich at WOT?

any other ideas? Thanks!

 

[Joe Reeves]

Re: Can Low Speed Jet Cause Engine to Run Rich at WOT?

Why..... do you need more ideas? Your reply doesn't indicate whether the problem is corrected or not.