SOLVED Continental O-470 only firing on 3 cylinders

[bowbender13]

Hey everyone,

Having some issues with my O-470. Took it out of storage today (last run 3 months ago) and I couldn't get it to crank. Battery is good, just put new spark plugs in today, fuel is free of water. I was able to get the boat to finally turn over but I have minimal throttle response, so I checked throttle cable, its good. Thought maybe I just flooded it so I let it sit for a while. Tried again... checked fuel pump, its working as advertised. Finally got it to run, but it wouldn't break 1500rpm at full throttle and also won't idle without dying. After running it for 2 mins, checking mags for rpm drop (which there wasn't any). After I shut the engine off, I felt the port side cylinders and they were cold. The starboard cylinders were all too hot to touch. So it seems like I'm getting only the starboard cylinders to fire which leads me to believe its not a mag issue since each mag should control both sides. I pulled the plugs on the port side and they were all still brand new. The starboard ones had obvious signs of use. Not sure where to go from here. Any help is appreciated!

 

[Slidin Gator]

Wow, that's a brain teaser for sure!

My first guess is 1 mag ain't working at all and the 2nd skips every other beat. Pull plugs on bad (port) side top and make sure they are sparking. After that the dirt dobbers have plugged up one side of your intake. Pull a port plug and put that cylinder on intake valve open. Blow air into the spark plug hole and make sure it's blowing out of the carb.

 

[John Fenner]

Pull top plugs, "safely" put finger over plug hole(s)while spinning it over, feel for lack of compression, there may be a stuck valve on intake side or a broken valve spring causing reversion into the intake.

 

[bowbender13]

SOLVED !

Thank you everyone for the input! I took it to a friend that has his A&P and as I was showing him the issue, we discovered that the boot from the air intake was slipping off on one side creating a big vacuum leak. We put it back on, blew out the gremlins, and now its running as advertised.

 

[Slidin Gator]

SOLVED !

Thank you everyone for the input! I took it to a friend that has his A&P and as I was showing him the issue, we discovered that the boot from the air intake was slipping off on one side creating a big vacuum leak. We put it back on, blew out the gremlins, and now its running as advertised.

Bobender,

Thanks for reporting back on the resolution! I love a good test question, but without a score/resolution it's less than satisfactory.

Please tell us all how you changed the thread title to add the "Solved" part! That's a very useful feature if I/we knew how to use it.

 

[bowbender13]

Bobender,

Thanks for reporting back on the resolution! I love a good test question, but without a score/resolution it's less than satisfactory.

Please tell us all how you changed the thread title to add the "Solved" part! That's a very useful feature if I/we knew how to use it.

Hey! I agree - I always Google issues but there are never any comments on the real fix so i wanted to make sure the info was shared!

At the top of the post that you create, it should give you options like "jump to new" "unwatch" and then 3 dots for more options. Click the three dots and select "Edit Thread" and you can change the title. Hope that helps!