Re: Motor chokes when thottled up
You keep saying "the motor acts like it is being choked", but you don't say exactly what the engine is doing. Do the rpms drop down? Does the effect of being "choked" cause the rpms to increase? Does the engine act like it's going to die out?<br /><br />If you have 100+ psi compression on all cylinders and that reading is even or very close on all cylinders, and the spark (with the s/plugs removed) will jump a 7/16" gap with a strong blue lightning like flame... a real SNAP, check the following.<br /><br />With the engine not running, check the timer base under the flywheel. It should move smoothly from its idle position up to its full throttle full spark advance position (up against the rubber bumper advance stop). If it sticks at any point, correct that problem.<br /><br />Your carburetors may be fouled and restricted which would cause the engine to lean out at throttle is applied. If this is the case, the cure would be to remove, clean, and rebuild them.<br /><br />Possible the carburetors are starving for fuel which may be caused by a sticking Anti Siphon Valve. Check the following:<br /><br />(Fuel Anti Siphon Valve)<br />(J. Reeves)<br /> <br />Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vaccum 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.<br /> <br />NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models. <br /> <br />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.<br /> <br />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.
