Mercruiser 470 starting issue

[Flyer9113]

So I bought a boat with a mercruiser 470 in it. I think it is a 1981 engine. I replaced the coil and put an electronic ignition on it. It already had the alternator conversion kit on it. Started and ran good. One day I had it running for about 30 minutes in my driveway with muffs on to get it up to temperature for oil change. Ran good. Turned it off. Changed the oil. I started the engine again and it ran good again. I was leaving it run like the manual says for 5 minutes before checking oil again. It stalled after about 2 minutes. Checked and did the oil like the manual said. Oil was down to the fill up line on the dip stick like expected. Refilled it like the manual said. I can’t get it to start though ever since it stalled. It turns over and starts to sputter like it wants to start. Never fully gets going. I tried to give it gas when it sputters and it does start but backfires and stalls again. Backfire is in the carb. You can see a puff come out of the carb when it happens. I also replaced fuel pump recently so I know it isn’t that.

I checked the the oil pressure sensor after looking at a different post on here. I don’t think it is that sensor. Gauge on the dash works. I cleaned off all the corrosion on the sensor.

Not sure where to go from here to get it running again. Any help greatly appreciated.

 

[Bondo]

I tried to give it gas when it sputters and it does start but backfires and stalls again. Backfire is in the carb. You can see a puff come out of the carb when it happens.

Ayuh,..... Welcome Aboard,..... It's Lean,...... I'd be lookin' at the carb,.....

Maybe crap in the fuel filter, or water in the gas,........

 

[Flyer9113]

Fuel filter on the fuel pump is new. Also has new gas. I drained the tank and sucked old fuel out when I got it. Replaced with new gas.

It must be the carb then. Carb looks clean. I haven’t taken it apart yet though. Only looked in through choke plate. Choke plate is really easy to move but I don’t think that would cause this issue. Maybe I should buy a rebuild kit and do it. Boat sat for 2 years only running on muffs sporadically before I bought it.

Thanks for for the reply.

 

[Scott Danforth]

welcome aboard

did you clean the tank, or simply add new gas to the crud in the tank? that would make chunky crud soup that you are now sucking into the carb.

looking thru the choke plates means nothing. the carb needs to come off, onto a bench and pulled apart to clean the inside passages.

 

[Flyer9113]

I am going to take apart the carb and clean it. Thanks for the advice.

I just drained the the gas tank. Put new gas in with an additive. Sucked a bunch of the new gas through the lines just to flush it out before I ran it through the engine. Tank was pretty much drained when I got it. There is probably crap in it though that I didn’t get out.

 

[Flyer9113]

Wanted to give an update. I rebuilt the carb. That was part of the problem. Newly rebuilt carb got the engine started. Engine was then way out of time. Hooked up a timing light and the engine runs great now. Great advice guys thanks.