Any outboard mechanics?

[Stein]

I have a Yamaha 4MLH that runs like garbage at low idle - not so good for sockeye.  I drained all the gas, replaced it with fresh ethanol free treated with Seafoam and cleaned the carb (twice, the second time more thorough), changed the oil and cleaned and checked the plug gap.  The engine is a 2006 and looks to be pretty much unused. 

It idles extremely rough and bogs down a bit until it gets up in rpms and then seems to run great.  I ran the carb screw all the way in to all the way out and it doesn't seem to make any difference (did this out of gear in the driveway as well as under power in the boat at the lake).  It does much better since the carb clean and fresh gas, but it still isn't running that well.

I also took the fuel pump out and put it back together and checked it by pulling the starter cord.  I also placed the fuel tank high above the motor and it doesn't make any difference - I think the problem isn't there.

I can run the boat ok at 3 mph or greater but anything under that is not so great.  The guy I bought my boat from bought it new and said it never ran that well.  He has receipts for several tune ups but they didn't fix whatever is wrong.

Any ideas, my very limited knowledge has been used up?

[TheHunt]

The only thing I can think of is the fuel lines.  I would also wait to see what the experts say on this site.

[lokidog]

The only thing I can think of is the fuel lines.  I would also wait to see what the experts say on this site.

I would try new fuel lines as well, they tend to deteriorate from the inside when gas sits in them, especially with the ethanol.  I have had a dark sort of varnishy stuff in there as well as bits of rubber.   

Good luck. 

[Fishnclifff]

FUEL FILTER.

The new ones have a chitty element that melts and clogs up.

I change mine at least twice a year.

[Bmcox86]

Fuel filter.

[BigGoonTuna]

you might want to find someone who has an ultrasonic cleaner and run the (fully disassembled) carb through it, then do a full rebuild.  your issue sounds like a partially blocked idle circuit to me, something might be lodged in there.  it doesn't sound like a fuel filter, if that was an issue the problem would get worse as you throttled up.

[Stein]

you might want to find someone who has an ultrasonic cleaner and run the (fully disassembled) carb through it, then do a full rebuild.  your issue sounds like a partially blocked idle circuit to me, something might be lodged in there.  it doesn't sound like a fuel filter, if that was an issue the problem would get worse as you throttled up.

Thanks.  What parts are replaced during a rebuild, the seals and gaskets?  There aren't many parts in a 4 hp carb.

[L-ofalab]

you might want to find someone who has an ultrasonic cleaner and run the (fully disassembled) carb through it, then do a full rebuild.  your issue sounds like a partially blocked idle circuit to me, something might be lodged in there.  it doesn't sound like a fuel filter, if that was an issue the problem would get worse as you throttled up.

I agree with low speed circuit. I thought someone was recommending adding a fuel filter instead of it being dirty, either would be good to add or clean but because it runs OK at  higher RPM that would probably not be the problem. I used to work on lots of motors of all kinds and there used to be 2 carb needles, HI & LO. Many motors have gotten away from that design and frequently there are only pre set jets where there is no adjustment. Many carbs are sealed with plugs that are tough to remove without ruining the carb but your plugged LO speed passage could be where it is not cleanable and only a new carb would help.

[Stein]

Thanks everyone.  I picked up an ultrasonic cleaner on clearance at Midwayusa and we'll see if that works.  A new carb is $205, so I'm hoping that isn't the cure.

[L-ofalab]

A good quality ultra sonic cleaner would cost more than $200. If you didn't pay that much it probably won't work. I bought a couple from Harbor Freight and returned them after seeing how poor they worked. When you put stuff in a quality cleaner and turn it on it is easy to see the stuff coming out. We used to put wrist watch metal bands in ours and it was amazing how much dirt came out of the links.

[Stein]

We'll find out, Midway has a great return policy.  Should be here Friday.

[Kc_Kracker]

I was for 10 years. run whatever you want thru it, it wont matter, you need to strip the carb down and scrub it out. if theres junk in the jets and there usually is it wont idle down nice. if you need help yank the carb off and bring it to me.

[pilebuck]

Take it in and get it fixed unless its something simple boat motors are a pain to work on period.....Good chance the carb needs to be rebuilt. I have a Johnston 3 cylinder seahorse 70 hp with 3 carbs sent the motor in and got them all cleaned out and rebuilt and tuned again anything to do with boats r expensive break out another thousand =boat 

[Kc_Kracker]

outboards are the easiest thing on the planet to work on, take it into a shop right now you wont see it til after the season ends

[Gobble Doc]

KC,

I've got a 40 HP Yamaha and I too am intimidated to tear the carbs apart.  I took mine to BaySide and it was indeed expensive.   I think there are 3 carbs.  Are there timing adjustments to make when you reassemble?  Or is it really as easy as taking it all apart and cleaning and then just reassembling?