troutmaster93010 Loc: SOCAL

My thoughts exactly!!

Fishandrods Loc: Alpine Ca foothills of San Diego

First thing I'd check is the fuel flow, if something is slowing fuel to the carb it will idle or run low RPMS but not getting enough fuel for higher RPMS, a weak spark might also cause the low RPMS maybe. LW.

Fishandrods Loc: Alpine Ca foothills of San Diego

I found out the best way to check the prop is to lock the flywheel and put the shifter in forward and then step on the right side blade with your body weight and if it doesn't slip the rubber hub is fine. I was shown this by the guy I've had work on my Evenrude. LW.

threeCs Loc: Allen Texas

First of all I am not an expert outboard motor mechanic. I have read all post so far and here is what my approach to solving the problem would be.( I don't know about any senors so will not address that)

If it will not come up to rpm, I suspect the prop is okay.

1st. verify that flywheel has not spun causing motor to be mistimed. Remove number I spark plug and insert a pencil in opening and turn motor until the pencil does not move outward any more. Check the pointer on flywheel is pointing at the TDC symbol. It it isn't the shear pin in the flywheel as sheared and motor is out of time.

2nd verify that fuel is present at carburetors in volume enough to fuel carburetors. You can do this by checking the output pressure of the fuel pump. Don't know what Yamaha should be but I suspect around the same as OMC. Max is 2.5 pounds.

I have never experienced spark plugs and wires causing a motor to backfire through carburetors. Backfire is caused by improper timing.

3. If the motor is in fact having carburetors blown back rather that backfiring then the thing to check is the reed plates

Difference be backfiring and blow back is easy to determine which it is.

Backfiring usually has a sound as the gas is being ignited and some smoke.

Blow back will not necessary had a noticeable noise but you can feel the fuel spray at mouth of carburetors

I guess to sum it up. Backfiring is timing and Blow back is reed plates.

I hope this may help you in some way

wd4ity Loc: Middle Georgia, Forsyth

I wouldn't use a pencil in the spark plug hole to check the position of the piston. I work on motorcycles and I had a guy bring a bike to me that had a broken pencil in the cylinder. He was checking the ignition timing on his bike. I had to pull the head off the engine to get the broken pencil out. I'd use a plastic or cardboard drinking straw. They'll bend but they don't break.

hookemjim

Make sure you didn't spin the hub in the prop. Did it once when I hit something. Put motor in gear and see if prop will spin with a little pressure. Easy fix if thats the proplem. But my lower then went my next tournament.

Huntm22 Loc: Northern Utah. - West Haven

So much help - so little time. Thus should help you get to the bottom of the problem.

wd4ity Loc: Middle Georgia, Forsyth

If the prop was slipping on the hub the engine would rev up but the boat speed wouldn't increase. Similar to a slipping clutch in a truck. If the engine is not spitting or sputtering then I wouldn't suspect a fuel flow or ignition problem. If it's sensor problem it could be a low oil sensor, water pump flow sensor, or an overtemp sensor putting the engine in a "limp" mode if the RPM won't come up. I don't know what kind of safety sensors that Yamaha puts in their engines. If none of those conditions exist then it could be a bad sensor. If the engine is a two stroke model with an oil injection system they usually have a sensor and an alarm the sounds if the oil level in the oil reservoir gets too low.

threeCs Loc: Allen Texas

I agree, plastic rod or plastic straw would be a better choice but I have always used a pencil because that is the way my Dad taught me. Old habits are hard to break LOL

Huntm22 Loc: Northern Utah. - West Haven

Its kinda hard to teach old dogs new tricks but now days we can learn better ways to do the old things. I struggle with too much change when it has worked for decades. I try to learn something new every day and sometimes it is only changing how I used to do something. Now with that said.... on to more honey do’s.

Lowescatfish18 Loc: Wesley Chaple florida

Sounds to me your power head is going I would some to check this out before you go out .

Dwallace7718 Loc: Cookeville TN

Not no expert here on outboards but I would probably check coil output. One bad coil could cause this same problem