Re: Hard starting 71 Johnson 9.5
Assuming that you have proper compression and spark.........
Fuel flows thru the high speed jet before it obtains access to any other fuel passageway. However, the high speed jet you speak of replacing due to an altitude change is strictly a jet change for high speed, top end performance.
Starting depends on what amount of fuel is provided to the engine via the adjustable slow speed jet. Either the slow speed jet is out of adjustment or something has been overlooked within the carburetor. Obviously fuel flows sufficiently thru the high speed jet or the engine would never run at the higher rpms.
Spray a small amount of premix fuel/oil directly into the carburetor's downdraft throat. If the engine now starts as it should, concentrate your efforts towards the carburetor's slow speed fuel passageway.
If the tip of that adjustable slow speed needle valve is not perfect but rather has a groove worn in it, that alone will create many problems.
(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.
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.
