Hello to all, I have been reading past post here hoping to find some thoughts on my issue. I see there are a lot of knowledgeable people on this site so I joined hoping to tap into this knowledge base.
Just started the (1978) Johnson 150 from 2 years of hibernation. At first, ran and idled smooth. After warmed it up, noticed a miss and looked around and found fuel being spit at about 1 second intervals from the lower half of the fuel filter cover on the top fuel pump with engine idle at about 1000 RPM. Removed cover to inspect and the seal ring is in tact and all was clean, then re installed. The timing of the miss and the spit are the same. So took the idle up to 2000 RPM and the miss/spit happens about every 2 seconds. Any thoughts would be appreciated. Thanks
The round rubber seal under the fuel inlet cap should not leak fuel under any circustances. You may want to replace that round seal. The original part number is 312679, which has been superceded. See your dealer for the correct replacement part. It is possible that you have a "lean sneeze" situation going on once the engine warms up somewhat. This is a carb issue, not an ignition issue. Does the engine run properly when at full throttle on the water? If so that pump is probably ok internally. If it does not run properly at full throttle, it is possible that the backfire may be affecting that cylinder where the fuel pump draws is vacuum pulse from. If the fuel pump internal rubber bladder is not intact (could have some holes in them), it is possible you could get some spitting from that fuel pump as a result of the backfire. You'd need to replace the fuel pump at that point. Best to evaluate the reason for the backfiring first, then get into the fuel pump issue. Lean sneezes are from dried fuel restricting the idle passages internal to the carbs. Only way to resolve that (if that's the problem) is to completely disassemble the carbs and clean them internally with a product which will dissolve dried fuel-like a gumout type product. I don't know how old your fuel pump is, but original pumps have rubber components in them which won't tolerate today's ethanol fuels. Possible that the internal rubber bladders have deteriorated. Any replacement pumps, hoses, etc are made to handle today's fuels.
Thank you for your thoughts and input. I will replace the gasket and the cover also (just to be on the safe side). Since I posted, I have bought a Clymer manual, not a lot of detail on the fuel pumps, but I do understand the principle of how they work. I will get the boat out today on the water and test full throttle as you suggest. And then follow through as you note.
I've had the boat/engine about 10 years, rough shape when I got, had the top end rebuilt in 04 but have not had much time to use....maybe have 10 - 12 hours on rebuild. I Use Stabill for storage and drain the fuel before starting coming out of storage. Can't be sure if it has or has not seen any ethonal prior to me, but not by me. Just a little history.