2004 Tohatsu 9.8hp 4-stroke

[gaff756]

I have a skipping/misfiring problem at 1/2 throttle on my Tohatsu 4-stroke 9.8hp outboard. I have changed spark plugs, cleaned carb. changed oil, checked wires but all is to no avail. no power and skipping at 1/2 throttle. what else can i check?

 

[TOHATSU GURU]

Re: 2004 Tohatsu 9.8hp 4-stroke

Using your service manual, you can run the checks on the ignition system.

 

[pvanv]

Re: 2004 Tohatsu 9.8hp 4-stroke

Agree with Elvin. Are there any other symptoms?

 

[gaff756]

Re: 2004 Tohatsu 9.8hp 4-stroke

Okay i have checked the fuel system completely from tank to carb and cleaned. I have good spark at plugs. When running at idle with muffs on it has a skip and will only run 1/4 throttle on boat in water. acts as though its flooding. When WOT only getting 1/4 power. checked prop and its good, no slipping there.

 

[pvanv]

Re: 2004 Tohatsu 9.8hp 4-stroke

In our shop, we would start at the beginning. That would include verifying fuel, ignition, and mechanical systems. A Factory Service Manual will be a wise investment, and your friend. Includes timing and valve lash specs, as well as adjustment procedures for all systems. I will admit that the manual for the 9.8 has a wee bit of "translation from Japanese" problem, but it is very accurate and useable.

If the plugs come out wet, you are likely flooding. But you could need almost anything -- a valve adjustment (or a good de-carbon treatment), cd box, etc, depending on what timing and compression/leak-down tests reveal.

Did it run correctly last season? Did this problem start suddenly, or did it gradually get worse? Is the fuel fresh and clean? Approximately how many hours are on the motor? Do you know the service history? What method did you use to clean the carb? In order to clean these carbs correctly, you MUST soak the carb in dip, not just squirt it out with spray solvent. Did you verify the float height precisely?

 

[gaff756]

Re: 2004 Tohatsu 9.8hp 4-stroke

Thanks for all your input on my problem. The problem started when I took the motor back to the dealer I had purchased the motor from, I had a valve problem where the keepers had come off and dropped a valve. I am figuring by now that the service guy overlooked something. way pass my techinical skills there. I know tohatsu produces good motors but i have had nothing but problems with this one. had gas in oil problems to start with after several trips and dollars later finalil got that taken care of then the valve drops. I try to keep a good relationship with any mechanic but my nerves and dollars are wearing then here. Again thanks for your help here.

 

[TOHATSU GURU]

Re: 2004 Tohatsu 9.8hp 4-stroke

You still need to run the ignition system values so that you can eliminate them as a possible cause. I know you have fire at the plugs, but you may not have the correct fire at the plugs when the problem occurs.

 

[pvanv]

Re: 2004 Tohatsu 9.8hp 4-stroke

I'm with Elvin on this one... Grab a Factory service manual and check ignition component values and compression.

If that checks out, then you can pull the recoil unit abd belt cover off and verify camshaft timing. If indeed a valve was dropped (rare occurrence), the shop may have done a fair amount of mechanical work (head off, replace a valve or 2, etc), and might possibly have missed something simple such as getting the timing belt off one tooth. Quite plausible.

Remember the race car mechanic's mantra for 4-strokes: suck, squeeze, bang, blow. Those are the four strokes (intake, compression, power, exhaust), and all 4 must happen at precisely the right time.

Normally, on a 9.8 that has not been apart, the biggest maintenance things are #1 - dirty carb and #2- ignition. BUT... as this powerhead has likely been apart... not a bad idea to verify timing. Cam/belt timing can be seen from marks on the flywheel and camshaft with the recoil and belt guard/cover off. (two different marks for cyl 1 and cyl 2, info in the service manual). Also... If you have an inductive timing light available (like we used to use on cars), you can check the ignition timing/advance against marks on the flywheel.

Odds are you will find the problem in ignition or compression. If not, and if the timing check gets past your skills, then you will want to chat with your mechanic again.