Re: problem shifting
Begin with the basics.......
Remove the spark plugs. Do they look alike? Describe their appearance.
Check the compression..... should be 100+ psi and even on both cylinders. What reads did you get?
With the spark plugs removed, rig up a spark tester. The spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! What did you observe? No spark tester.... build the following.
(Spark Tester - Home Made)
(J. Reeves)
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
..........X1..........X2
.................X..(grd)
..........X3..........X4
The carburetors may need cleaning BUT your explanation stating that the engine does run fine at times tends to indicate that they might be okay..... carburetors do not fail intermitently, they are either fouled or they're okay. However, the adjustable slow speed needle valves may be out of adjustment, and if so, adjust as follows.
(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.
NOTE: Before starting the engine (every time), pump the fuel primer bulb up hard as you would do initially. If this makes a difference, fuel is siphoning backwards into the tank.... check the anti siphon valve if using a built in tank..... suspect failing valves in the fuel primer bulb if using portable tanks.
(Fuel Anti Siphon Valve)
(J. Reeves)
Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.
NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.
The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.
The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.
Hopefully you're using Champion QL77JC4 spark plugs, gapped at .040 . If not, do so.
Assuming your control box is okay, has no internal loose components, the idle warm up lever does not wobble all over the place etc, adjust the throttle cable at the engine as follows.
Temporarily disconnect the throttle cable from the engine.
Notice the vertical throttle arm located on the starboard side of the engine, you'll see a idle stop screw roughly about halfway up that arm. With the engine running and having the idle rpm exactly where they should be, that screw should be screwed in so that it is against the powerhead which prevents it from retarding any further.
Now, making sure that the control box is in neutral and the idle warm up lever is set at a dead idle, reconnect the throttle cable and adjust the threaded trunion that is located on the throttle cable at the engine's retaining clamp so that a slight bit of tension of the cable keeps that idle stop screw against the powerhead.... BUT NOT excessive tension as that will result in tension at the control box.
Lastly (this time), Check the shift cable adjustment (centering) so as to eliminate any possible tension conflict within the control box (as follows).
(Centering Shift Cable)
(J. Reeves)
When all is as it should be, the proper method to adjust the shift cable is to disconnect the cable from the engine. Move the shift linkage on the engine to find the center of the play in neutral, and when found, leave it centered.
Now, grab the end of the shift cable sleeve, push and pull it to find the center of the play there, and center that play.
Adjust the trunion on the threaded portion of the shift cable so that the centered play of the cable lines up with the centered play of the engine's shift linkage. Install and lock the shift cable with the retaining clamp in that position. That's it.
That should keep you busy until lunch time. Let us know what you find.
