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Backfiring Mariner

S

strata

Member
"Took my boat out today, A cou

"Took my boat out today, A couple of times while it was idling it backfired and stopped. Started again straight away.

Then on the flushing muffs it actually backfired out through the prop, but kept running. Any ideas? I'm thinking carbs/fuel mixtures?

Motor is a 1999 75 HP oil injected Mariner."
 
"Just a thought - I haven'

"Just a thought - I haven't had the boat long - about a month. This is only the second time on the water. I did have to replace the fuel in the tank for the auxillary motor, because it was stale. Could this be because maybe the fuel for the main motor is stale too?"
 
"bad gas or running lean. When

"bad gas or running lean. When they sneeze or cough its running lean. The safe thing is to remove and clean all carbs. You can try fresh gas but if 1 carb is plugged that part of the engine doesn't get oil. You can also open the idle mixture jets 1/4 turn and see what happens, but you have been warned."
 
"Well, today I pumped out both

"Well, today I pumped out both fuel tanks and cleaned them out. Plenty of crud in the bottom of both. Removed all 3 carbs and fuel filter, all full of crud. Cleaned out with methylated spirits. Found plenty of crud in the float bowls, none in any of the idle passages, but traces of water in the idle passage area of 1 carb, so hopefully that was my problem.

Carbs were surprisingly easy to get off and surprisingly simple. Less complicated than my 9.9 carb!"
 
"While I had the motor apart I

"While I had the motor apart I found a sticker that had 1995 stamped on it. It was like a white label with a barcode, stuck to the water jacket. I was led to believe the motor was a '99 model.Obviously not?

Is there any difference between the 2? Is there a certain way of telling what year it actually is? The serial number is:0G144196, carb numbers are WME 3301-824924-C.

Lastly, I've put the carbs back on, will pull down and clean the fuel pump tomorrow. Removed the fuel filter (White plastic factory one), full of crap. Could I replace it with one of the automotive type ones - the glass ones with the sintered filter inside? I'd prefer one of these so I can look inside it and clean it out when needed. I will be adding an external filter/water seperator as well.
Cheers"
 
"That serial is for a 95 model

"That serial is for a 95 model. But no, no difference between a 95 and a 99 model.

In fact, the Merc "serial" is just a production number and has nothing encoded in it.

So that motor could have been sold as a "brand new" 99 model if that's how long it sat in a showroom. Merc did that on purpose so a dealer would never have "last years model" or "old stock" on hand.

You can use the inline automotive filter, but personally I would also add a marine water separating filter (10 micron) between the tank and the engine - does a way better job."
 
"Good news and bad news. I hav

"Good news and bad news. I have solved the slow starting problem I had - the motor starts more quickly and easily now - but the backfiring is still there. In fact, I think it may even be worse than it was before!

What now?? I cleaned out the fuel pump as well. Should I buy kits for the carbs and pump and go again? Is there another possible problem that would cause backfiring? It is definately popping out through the prop. Seems to build up revs, pop out exhaust then slow. 2-3 times per minute..."
 
"Well, another update. I took

"Well, another update. I took the carbs back off, pulled them down, looked through them, clean as a whistle. Blew them out again, put them back on, started it up fully expecting the problem to be still there but no! So far so good, sounds a lot better. I'll have a go at setting the mixtures, idle speed, timing etc tomorrow. Fingers crossed. Test run next weekend...

Don't know how I fixed it, but anyhoo....I'll take it lol"
 
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