Here is a link to site that give good information about your motor with pictures and stuff.
https://www.sschapterpsa.com/ramblings/OMC_6hp.htm (click link or copy paste)
First thing you need to do is check to make sure that your water pump is working and your engine is not over heating and cutting out. You will see a mixture of exhaust and water coming out of the middle of the back leg. Now this is probably not the case but always wise to make sure!!!
So your engines runs for a little while ( 4 yo 5 minutes and cuts out). Couple of things to consider!
1.) You pumped up your fuel bulb and it fills the carb bowl and slightly pressurizes the line. The motor runs and then it cuts out. (
Your fuel pump maybe bad) If diaphragm is torn or weaken due age or possibly the ethanol in the fuel messing it up. These fuel pumps and diaphragms were made prior the addition of ethanol to our fuels.
- When you get it running and it starts dwindle or kill and revives after pumping up the primer bulb on the fuel line then that is a good indication that the fuel pump is bad.
- If you raise the fuel tank slightly higher than the motor and the fuel is somewhat gravity fed to the carb and the motor no longer is cutting out, then that is a good indicator t
hat your fuel pump is bad.
- When you choke the motor, you are bringing in more fuel to the motor and keeping it somewhat running.
2.) If the above suggestion doesn't work, then your carburetor may need cleaning and a carb kit. If you are going to take down carb, do it properly. Clean it and put in a fresh carb kit ( any wheres from $18 to 26 dollars depending if you have float with the kit. The link I provided above give you a good idea how to remove the carb and return it back to position.
***Just remember carb cleaner eat up/dissolves plastic, rubber, and seals and etc.....please remove of this stuff off the carb when you go to soak it/clean it. (Do it outside it the open air or you will inhale that stuff and get sick)
(
That brings up a point. The original floats had cork floats with a sealant covering. Ethanol eats the sealant up and then the cork can get soaked and not function properly. The floats that come in the new kits are resistant to the ethanol in the fuel.)
You can go to https://www.marineengine.com or https://www.boats.net and look up the year and model number of your motor. If the carb kit is not listed then call them and they can assist you with the part number for the kit. https://www.boats.net site has a user friendly parts diagram for the motor and will help id parts.
Some information on how to set your low speed needle if you have to take your carb apart.
Carb Needle Adjustments For Asorted Carb Variations by Joe Reeves
these adjustment are for the older engine. 1980 and earlier, and the current small hp ob's. not for fixed jet outboards.
(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: 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.
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.
3.) If the above 2 suggestion doesn't pan out then you may want to consider check your spark on both cylinders. I know stated that the their is spark on both and it runs for a little while, but if those coils are old and one or both are starting to crack, then you will have intermittent spark issues. When they are cracked and the engine starts to warm up
(4 or 5 minutes motor cuts out). Points could be dirty!
Some information about points and coils in if your motor was manufactured prior to 1977.
The information is found on iboats. (Not trying to steer you away from here, that is where the pictures and article is located. You have to join the site just like this one to see the pictures and stuff and its free just like this one)
Please get a spark checker. It cost about $6 at autozone, napa or any auto parts store. It gives you a better assessment of the ignition system. It tells you the quality of the spark not just a spark. Set the gap on the spark checker to 1/4 to 5/16. If can jump that gap then you have a good strong spark and don't forget to ground it to the motor.
Here is a nice article by JBJennings ( he did an excellent job) regarding points and coils.
https://forums.iboats.com/showthread.php?t=294072 (click link or copy paste)
You can only adjust 1 point at a time then you must rotate shaft to do the other ,you can't adjust them both at once as one is in the closed position and the other is in the open mode. The rubbing block must be on the high lobe of the points cam (points open) this would be the gap setting position, turn the crank by hand and observe the rubbing block while also watching the points open, the rubbing block will remain on the high spot for a few degrees of turning the flywheel before it drops back off. (Place the flywheel nut on the crank shaft and use a wrench or ratchet set to turn it.) Please make sure the spark plugs are out so you don't accident start the motor.
When done please make sure to torque the flywheel to 40 foot pounds
Personally, like you stated, it seems like a fuel issue, so suggestion 1 or 2 are likely culprits.
