New 9.8 Tohatsu wont rev out

[steelstrings]

I am running in my new Tohatsu 9.8 4-stroke and notice when increasing the throttle past half way, no increase in boat speed or revs occurs. It starts easily (electric start) and seems smooth at low to middle throttle. I'm running it on an 18ft displacement lapstrake (clinker) glass hull (but don't suspect prop size being the cause). I have checked throttle linkage and it seems to be synchronized correctly - i.e. full throttle at the helm lines up with WOT at the carb body. Checked plugs: slightly oiled at edge but otherwise good tan color.

Also notice puff of smoke each time I start or restart it. It has not been transported wrong side up - checked oil level was over filled - drained and refilled to mark - still smokes at startup. Is the smoke just a part of running in new engine? Are these issues linked or can anyone suggest solution?

Thanks!!

 

[pvanv]

Re: New 9.8 Tohatsu wont rev out

Get a shop tach on the motor to see what RPM you are getting at WOT. Which prop are you running (different props come "stock" depending on shaft length). It would be best to achieve almost 6,000 RPM at WOT. Is there any change in the "note" of the motor above 1/2 throttle?

Fill oil to half way on the dipstick until the motor is broken in. Do not run synthetic oil. Use 10W-30 FC-W rated oil. That will help the puff at startup.

 

[steelstrings]

Re: New 9.8 Tohatsu wont rev out

Thanks for the speedy reply.

There is no change in engine note when throttle changed from half to full throttle - nor does it sound as if it is flooding or bogging down. I have brought motor back to dealer who is going to test it for me - but he doesn't have a tacho....

He thought it might be water/dirt in the fuel - but so far I have only just ran about 1 tank full of fuel through and I am always careful to use good funnel with strainers etc.. so I am not convinced this is the issue. Also I drain the carb after each use (4 times so far)

Is there any possibility valve clearances could be too tight?
Any possibility that initially running engine too full of oil could have cause bore glazing or premature ring wear?
You say fill oil to only half way on dip stick until fully run in - once run in, do I top it up to top mark or always run it at half mark?

Thanks again!!

 

[TOHATSU GURU]

Re: New 9.8 Tohatsu wont rev out

Is there any possibility valve clearances could be too tight?

Always possible, but I would bet it's not the problem.

Any possibility that initially running engine too full of oil could have cause bore glazing or premature ring wear?

Nope

You say fill oil to only half way on dip stick until fully run in - once run in, do I top it up to top mark or always run it at half mark?

Tough call. I generally tell people, who do a lot of idling, to fill it halfway up the hash mark. If you tend to run WOT a lot then the top part of the hash mark would be correct.

Just keep in mind that you will gain fluid in the crank case over time so periodically check it and drain it.

 

[pvanv]

Re: New 9.8 Tohatsu wont rev out

And if your dealer doesn't have a tach, they should get one. They can order a decent one from Tohatsu America.

 

[reddogg]

Re: New 9.8 Tohatsu wont rev out

My father has an 09 9.8 tohatsu 4 stroke and he had a similar experiance with his. Turned out to be crud in the jets. The mechanic said that these tohatsu's have really small jets and are easily cloged. $100 carb cleaning and she runs like a top. We changed the fuel filter under the hood and added one in line between the tank and primer bulb. No problems since, starts first pull or crank every time now.

red

 

[pvanv]

Re: New 9.8 Tohatsu wont rev out

All EPA-rated and CARB-rated small OB's, of all brands, have very lean mixtures. On carbureted motors, that is achieved by using relatively long, narrow, high velocity passages in the carbs. (as opposed to the relatively short, wide, low-velocity passages of the motors of yesteryear). These passages are more vulnerable to minor varnishing that would not have been noticeable in older-style carbs. That, coupled with poor fuel, which leaves more deposits as it evaporates, results in more varnishing, which results in poor running. The solution is the same as it always was: Run the carb dry at the end of each day so that the fuel does not sit in there and evaporate. It was a good idea years ago. Nowadays, it's critical.