See full version: Mercruiser 4. 3 hard starting when warm fix
I posted a while back about my merc 4.3 1991 engine being hard to start when warm. It always starts right up when cold, but after sitting for an hour it takes forever to start. This seems to be happening to a lot of you with this particular engine, and it is always blamed on vapor lock.
I found out through here it could be flooding after sitting, due to the wrong type of needle/seat being used, or something along those lines. I was told the next time i let it sit after it is warm, to hold the throttle at WOT when starting. Apparently it helps a flooded engine start. Sure enough, fired in about 2 seconds instead of 15 seconds. I also then pulled the flame arrestor and there was a little bit of gas running down the throat. here
I found a fix, at the help of the board members here, so i figured i'd share. I too, was determined it was vapor lock. Did all the things you guys have done to fix it. run the blower the entire time on the water, let it idle for a while before shut down, open engine compartment etc. NOTHING. Still took 15-20 seconds to start after it heated up.
NOTE. Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models. here
The fuel primer bulb collapsing indicates a fuel restriction, read on.
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.
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. here
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. more
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