1972 100h.p. V-4 Johnson hard start warm

[ctyslickr]

SOMEONE HELP ME!!!!!!!!! I recently acquired a 1972 V-4 100h.p. Johnson. Since I have had this motor I have replaced the Pulse Pack, Ignition coil, Plug wires, Plugs, Distributor cap and rotor, Crank sensor, Starter, Battery, Fuel filter, Fuel pump, Battery cables, and added redundant ground straps, Overhauled both carbs.(Carbs don't have any mixture adjustments... only idle adjustment) All at the request of a "marine tech"... for a hard starting issue. <br /><br />The outboard starts fine cold and runs for at least 10 minutes, after about 10 minutes the outboard starts to run rough, unstable idle, hesitates, and frequently dies. If it dies it will not restart until it cools down or you have to choke the carbs... and sometimes even when it's choked it will not restart and drains the battery. the boat hasn't been in the lakes yet, due to it's unreliable operation. But when it is running with a flush adapter the engine temp, when checked with a laser Raytek, is about 120F on either cyl. head. <br /><br />If anyone has an idea on what I should test next please tell me and if there may be some diagnostic worksheet I should use, other than a aftermarket shop manual, please let me know

 

[Joe Reeves]

Re: 1972 100h.p. V-4 Johnson hard start warm

Michael... As you state and I quote you replaced all those expensive items "All at the request of a "marine tech". I strongly suggest that you find another "marine tech" before he puts you in the poor house!<br /><br />Having a engine run normally for a ten (10) minute period before it acts up, assuming that it is not overheating, would indicate a fuel restriction. The fact that you would need to choke the engine to restart also leans in that direction. Failure to start occasionally with choking after it dies out could be simply that you have inadvertently flooded the engine.<br /><br />You should be using Champion L77JC4 or QL77JC4 plugs gapped at .030 on that model engine. The "Q" indicates a suppressor plug which helps to quiet ignition noise etc.<br /><br />Regardless of the problem, always check the compression and spark first. Compression should be 100+ psi and even on all cylinders.<br /><br />Rig up a spark tester whereas you can set a 1/4" gap. The spark (with the s/plugs removed) should jump that gap with a strong blue lightning like spark.... a real SNAP!<br /><br />A fuel restriction could exist at the fuel primer bulb and just about anywhere. However, if you're using a built in tank, the restriction is usually at the fuel tank as follows.<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 />Let us know what you find.

 

[Solittle]

Re: 1972 100h.p. V-4 Johnson hard start warm

It pains me when I read stories like this of guys willingly take out their wallet, turn it upside down and shake vigerously just because" someone" said that your problem might be - - - -.<br /><br />Michael - Joe is one of our senior resident experts. You can take his advice to the bank. I would only add for you to get the OMC shop manual for your motor. I got mine here:<br /><br /> http://www.theoutboardwizard.bizhosting.com/parts_service_and_owners_manuals.html

 

[R.Johnson]

Re: 1972 100h.p. V-4 Johnson hard start warm

Makes me wonder if that engine is original with it's three ring pistons'. I wonder also, if after 32 years how many may be stuck. That is a lot of exspensive parts, and no mention of a compression test.

 

[ledgefinder]

Re: 1972 100h.p. V-4 Johnson hard start warm

Sounds like it's running out of fuel for some reason. Restriction in the fuel line? Try squeezing the bulb next time it starts to idle rough. When it idles rough, does it run better if you close the choke flaps a bit?<br /><br />Normally, the problem would show up way faster than 10 minutes, but because you're running on just the flushmuffs, that still might be it.<br /><br />With all that new ignition, at least it'll run well when it's fixed. Hope you put a new impeller in the water pump.