Motor idles smooth but shakes and will not accelerate

[SALTY7S7]

Hi All,

I'm hoping someone here can help me out, as I am a newer boat owner and do not have much experience with outboard motors. I have a 70hp TLRC that has been giving me issues. She idles fine and sounds fine, but once I open the throttle she shakes violently and will not accelerate. The engine starts right up every time and does not stall, I just can't accelerate or get on a plane.

I am thinking it might be an issue with fuel delivery. The prop is not damaged and not tangled. There are no leaks in any of the fuel lines as far as I can tell. Before this issue, I would typically run the boat at least 1-2 days a week, so it is not bad fuel. I use startron with every fill up as well.

What are your thoughts? Could this be bad plugs or fuel filter/fuel pump?

[pstephens46]

Think I would be checking spark on all cylinders first.

You may want to verify the alarm works also. Pull the safety lanyard and try to crank. Alarm should sound.

[SALTY7S7]

Thanks for your suggestion pstephens. I am planning on changing the plugs first since they are cheap and easy to do.

Also, the alarm does sound when the lanyard is pulled.

[pstephens46]

Get a tester and make sure they are firing at the problem point. Testers are not very expensive. Cylinders not firing can create quite a shake...

Could be fuel, but rule out spark first.

[SALTY7S7]

I will check the compression and let you know how it looks.

Thanks

[Floatober]

That's how my 90 feels when temp alarm is going off...

[SALTY7S7]

Quick update. Checked the spark plugs, and they look oil fouled. I also tested the compression in each of the 3 cylinders three times each. The top cylinder averaged 95, the middle averaged 98 and the bottom averaged 88. From what I know, this is an OKAY. I'm guessing I could have a bad seal. I'm going to replace the plugs and see if she runs well, then I will know for sure.

Floatober, I have never heard the temp alarm go off before. Are you suggesting a bad water pump or impellar?

Thanks again guys, I do appreciate your advice.

[pstephens46]

Somebody else want to take a turn here?

[ausnoelm]

I'm guessing I could have a bad seal. I'm going to replace the plugs and see if she runs well, then I will know for sure

Not too sure which seal you are suspecting?

[SALTY7S7]

I was thinking maybe bad valve seals or rings. Also, I have NGK plugs that are recommended per my owner's manual. If they are oil fouled, could this be an issue with too much oil being released?

I was thinking maybe the carbs were not adjusted correctly, but she ran fine for months. I would think if they were not adjusted correctly I would have issues right off the bat.

Could it possibly be a thermostat issue?

[99yam40]

Bad stats could mean motor is not geting up to proper temp.
fuel does not burn properly if too cold

[SALTY7S7]

Thanks for the suggestion 99. I will take a look at the thermostat later today and see what it looks like.

[Captn Dave]

Somebody else want to take a turn here?

Maybe one of these days he will actually check to see if each cylinder is getting spark.