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Larry B.
Larry B., Marine Mechanic
Category: Boat
Satisfied Customers: 574
Experience:  Mercury/Mercruiser Certified/Verado/DTS / Yamaha Two and Fourstroke Certified 27 years experience
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I have a 1997 50 hp johnson 3 cyl. oil injected. I ran ...

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I have a 1997 50 hp johnson 3 cyl. oil injected. I ran out of gas a few days ago. A neighbor brought a tank of premixed gas out and I was able get back home. I ran the motor on double oil all the way in. Prior to running out of gas the motor was running very well. I filled the tank as I normally would with straight gas. Today I went out on the lake and could only get about 4000 rpm''s out of the motor, which will normaly run about 4900- 5100 rpm''s. It was also surging slighty. I''ve replaced the plugs, and installed a new fuel filter which only gave me a couple hundred rpm''s, and I still have the surging. I also tried pushing the electronic choke, and the rpm''s shot up word to 5000 rpm.s momentarily. HELP!!!!!!
Smitty, when you run this motor out of fuel, it is still pumping the same amout of oil and less gas until it runs completely out of gas and can fill the float bowl with straight oil. The oil is heavyer than the gas and can set in the bottom of the bowl and not mix with the incoming gas vey well and it will not go away very fast. I would try removing the air box from the front of the carbs, take out the drain plugs on the front of the float bowls and let them drain, then flush them out with a little fresh gas.
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Customer: replied 8 years ago.
Reply to Larry B.'s Post: Hi Larry: Thanks for your responce. My only, is how do I flush the bowls?
Lay something to absorb gas in the bottom of the cowling and with one drain plug removed at a time gently squeeze the primer bulb, will only take a little. do it outside, No smoking/or other ignition sources should be present, wear rubber gloves and safety glasses if you have them, and dispose of the gas or gas soaked rags properly. Never dispose of grease rags or gas soaked rags in the trash, put them in a metal can outside and allow it to evaporate.
Customer: replied 8 years ago.
Sounds logical....I'll give it at ry tomorrow morning (it's getting late now) and hope for the best.   Thanks so much for your help. Kip Smith (Customer)
O.K. If it works out for you please click accept if not then come back to this guestion, and we'll kick it around some more.
Customer: replied 8 years ago.
Larry---I'm back. I thought before I tried your suggestion, because it is going to cause me to pull the boat out of the water to work on it, I ran a 5gal. tank of gas through the system to see if it might flush the carbs free of oil. Afer about an hour of running time it still is surging and only reaching 4000 rpms with no significant difference. If you think your solution is still the way to go please respond to this reply as I intend to pull the boat in the morning and work on it. If you have other ideas please come forward with them now.    Thanks XXXXX (Customer)
Well if you are going to pull it out any way I would try it, if you ran the motor at high rpm's with the other tank for an hour and it was not smoking heavier than normal then I do not think the oil is the problem but could be trash in one of the float bowls causing it to surge. here is an idea, before you pull it out of the water, have a friend drive the boat where the problem occurs and look into all the carbs with a timing light hooked up to the motor, you can see the fuel coming out almost like stop motion, could almost count every drop. If you see one that stops up or comes and goes then look into that carb. and this would also be a good way to see an ignition miss at the same time, by running it on all three plugwires and seeing if it misfires.

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