Tohatsu 18hp dies under load

[Peter16]

]i have an 18hp tohatsu that has no balls up top and dies significantly at higher rpm. approx 3k.

i have included a video which may help. i was thinking electrical before but their seems to be some nasty sounding knocking going on.

This is what it was pushing. I was unable to plane, just kept on plowing through the water
http://i263.photobucket.com/albums/ii128/mercury16_2007/IMG_1395.jpg

spark test was fine. compressions were 140psi. Im doing a carb job on it now just for good measure.
Does it on ear muffs, in the water and in a bin.
0:14 i believe some knocking is evident. fairly certain its not exhaust noise. sounds quite mechanical.
0:19 you can hear it start to die. (as i described)
0:29 its very evident.

 

[pvanv]

Re: Tohatsu 18hp dies under load

I take it this is an M18 2-stroke, possibly an E2. Sounds like you may be running out of fuel. While you have the carb apart for its 4-hour soak in carb dip, be sure to inspect or repair the fuel pump section on the side of the carb as well.

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

If you throttle any engine at neutral without load, funny sounds you will hear. When engine "dies", stops and must do a re start, or misses but does not stops ? Clean tank interior, remove pickup elbow, remove and clean small filter located at bottom, before placing back, blow air through lower hose while pushing metal ball at elbow, sometimes small debris can be captured there limiting fuel delivery, check pump diaphragram conditions, if severely balloned, cracked or dried up, time for new ones, clean carb and big filter well.

If having same sympthons after previous check work, try a new gas hose, with use, E gasolines, small rubber o'rings inside fuel connector's extremes wears off, doesn't seal properly, lets air in and engine misses specially when giving juice 1/2 to wot. If all mechanical issues are ok, you have Exciter Coil, CD or Ignition coil electrical failure.

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

The issue has been resolved.
after reassembling a nice and clean carbie the results were still the same.
i pulled the flywheel off and their was quite a bit of rust on the stator and magnets. I gave it all a good clean. the timing base was a little sticky so i free'd that up as well and the motor is performing as it should.

Thankyou for you're suggestions.

 

[Peter16]

Re: Tohatsu 18hp dies under load

aaaand its back. ive used it twice since it was "resolved" only for an hour on 2 separate weekends. went to use it yesterday and it just wouldn't rev.
back to the drawing board...

 

[pvanv]

Re: Tohatsu 18hp dies under load

The issue has been resolved.
after reassembling a nice and clean carbie the results were still the same.
i pulled the flywheel off and their was quite a bit of rust on the stator and magnets. I gave it all a good clean. the timing base was a little sticky so i free'd that up as well and the motor is performing as it should.

Thankyou for you're suggestions.

That motor does not have a stator. Rust on the exciter and or magnets will not inhibit the electrical characteristics of the ignition system, unless really "growing a beard". Look through the entire fuel system again, and run the ohm meter tests on the ignition components.

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

I would start by changing 2 new 1.0 mm gapped brand new plugs and carb intake manifold o'ring before diving into electric components, sometimes does miracles....

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

where can i find the readings and tests to perform on the motor?

edit- found the specs primary and secondary coil, cd unit, exciter coil and pulser coil. i will go through the fuel system again

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

When you say just wouldn't rev, is it at all throttle settings ? Does the engine die when giving juice at 3/4 to wot ? You need to have a proper meter that reads DVA volts to troubleshoot, one thing is reading Ohms with any meter at rest other reading DVA electric factory parameters while cranking or while engine on.

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

at idle it sounds just "ok"
1/4 throttle still ok.
1/2 throttle you will occasionally hear a miss, any higher and its constant spluttering and coughing.

It has new plugs set at the correct gap. fuel filter is clean. diaphragm fuel pump is sound. the carburettor is clear. I am ordering the o-ring you mentioned now.

I have a proper DVA meter for the weekend. I also have a hard copy of this
http://issuu.com/cdielectronics/docs/troubleshootingguide

although not all the wire colours match.

 

[pvanv]

Re: Tohatsu 18hp dies under load

Also verify link (timing and sync).

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

Depending on how old that horse is and if the timing and syc have not been played with and now out of adjustment, all electric parts are working properly, change head gasket. Clean well crankcase and head walls from old gasket remains and follow bolt torque sequence, torque to 30 NM. Seems when engine heats up, there's small water droplets leaking through gasket into cylinders producing constant sputters at higher rpm's than idle.

If opting for that procerure could take advantage to decarbon piston heads and head interior with Power Tuner or equivalent, just apply a generous amount of PT, let soak for at least 15 minutes, with old toothbrush, brush off, repeat if needed. Will need to buy a new engine base gasket too. And one thing is testing on a barrel, other at sea at wot...

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

replaced that o-ring and did another carbie job while i was at it. no change. :facepalm:

how can i check the timing?

I will take the powerhead into work next week. I will need oxy to get the head bolts out.

The starter motor died last week and im tired of pull starting it. where do you all get your aftermarket starters from?


EDIT- is the float level adjustable on these? how so?

 

[pvanv]

Re: Tohatsu 18hp dies under load

Grab a Factory service manual (available from any dealer, including me), and you will see the procedure to check/set timing and float height. In brief, the float should be parallel to the casting when you invert the carb body and allow gravity to draw the float towards the top.

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

The float on this model is non adjustable, it's all plastic inside, if float valve maintains a sharp point on upper tip it's good, if worn or deformed, change it alone or with float if you preffer. Does your motor have the white or black hard plastics that holds/secures both rods in place ?

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

Grab a Factory service manual (available from any dealer, including me), and you will see the procedure to check/set timing and float height. In brief, the float should be parallel to the casting when you invert the carb body and allow gravity to draw the float towards the top.

That is how i would normally adjust them but this one looked non adjustable which Sea Rider just confirmed. It sits at quite the angle.

Does your motor have the white or black hard plastics that holds/secures both rods in place ?

I dont know what you are referring to here?

 

[pvanv]

Re: Tohatsu 18hp dies under load

That is how i would normally adjust them but this one looked non adjustable which Sea Rider just confirmed. It sits at quite the angle.

If you invert the carb and the float is not parallel, something is off. You can change to a new float and needle, or, with CARE, you can gently remove the float, heat and re-shape the arm on the float, and then reinstall it.

I think Luis was referring to the "rod snaps" that attach the choke and throttle rods. If they are too sloppy, you may get uneven RPM due to the throttle plate being unsecured.

 

[Sea Rider]

Re: Tohatsu 18hp dies under load

Thanks Paul for the term correction, if upper bolt joint and cap which holds upper horizontal rod, both rod snaps mounted on advancer arm, lower cable pin & rod joint that holds vertical rod have excesive side play you could experiment rpm fluctuations due to magneto plate miss behaviours. With old or very used motors it's mandatory to change all these sliding parts if wanting precise and uniform acceleration through all throttle range.

If your engine happens to have brass upper bolt joint and lower cable pin which wears out fast if not lubed or already worn out with excesive side play, replace for same new stainless steel ones. Apply a proper amount of grease to every sliding part before assembling back. Parts will slide better and last much longer.

Happy Boating

 

[Peter16]

Re: Tohatsu 18hp dies under load

I will check how much play their is tomorrow. Iirc they are plastic.

i pulled the powerhead off and took it into work. Every head bolt requied oxy acetylene to remove. only one snapped which is pretty good considering.

The head is clean as a whistle. this is a good indication of water ingress is it not? the pistons also show a lot of signs of being "steam cleaned"





while its all apart im doing the exhaust plates as well.

Thank you very much for this on going help.

 

[pvanv]

Re: Tohatsu 18hp dies under load

Definitely looks steam cleaned. Try a new head gasket and you may be OK.