2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

I will keep the 7 pitch prop for sure, with some more gear and a cooler the rpm will fall below the 6000. My concern was running the motor at and above the upper limit of the recommended band when the boat is lighter. I agree that an 8 prop will be my best bet though, in case I want to shoot for another one. Not sure 1 mph improvement is worth it...

 

[MattFL]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

just don't twist it wide open while you are by yourself.

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

It is that easy!... but didn't come to my mind.
BTW, for how long can I keep the engine at 5-6k rpm, is one hour too long?

 

[MattFL]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

if it is propped correctly, you can spend as long as you want at any speed that is under the maximum. just be aware that the harder you push the motor the less life it is going to give you.

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Thanks Matt!

Which one is the pilot screw on the picture, is it the top spring one?

 

[MattFL]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

I'm not familiar with that particular motor, maybe pvanv can answer for sure. The vertical screw is definitely the idle speed screw so the horizontal screw looks like the pilot screw to me if I were to take a guess.

 

[Sea Rider]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Yep, idle screw is the vertical one, fuel/air screw is the horizontal one, usually comes well factory adjusted. Answering some of your doubts. Your current factory delivered prop is doing fine. If engine has an attached tach, run engine slightly less tham max wot rpm when boating alone.

If you add slight more weight engine will drop at near 6 K. Nobody in their right mind runs wot all the time, full throttle to plane fast, then back up to 3/4, the slight speed top difference it's not worth the extra fuel that engine will burn. 50:1 fuel/oil ratio is most appropriate to run at wot for extended time periods, your spark plugs will thank you.

Happy Boating

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Thank you guys! Does the pilot affect performance and fuel consumption at or close to WOT? Or it has an effect only at low rpm. Sea Rider, I found your post on how to adjust the pilot here: http://forums.iboats.com/honda-tohatsu-nissan-outboards/tohatsu-carb-rich-lean-screw-way-283488.html
BTW, when adjusting the pilot on the water, I saw no change in the rpm at wot even after 6-7 full turns of the screw, so if anything is affected at high rpm, I assume it will only be the fuel consumption. The only adjustment that lead to increasing the rpm slightly, was the adjustment of the magneto position, that gave additional 150-200 rpm.

I have an idling problem now, after cleaning the carb. From what I found in one of the current threads in the forum (Erratic idle), I will first make sure that the float is moving freely and go from there. The motor was idling quite well before I took it apart. Now it misses a lot when at low rpm...

 

[rsnyder518]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

The pilot should have negligible effect on performance and fuel consumption at WOT.

Is it possible that your idle problem is due to the pilot screw adjustments you made? Did you return the pilot screw to its initial setting after you adjusted the 6 to 7 turns that you reference in your post? A mis-adjusted pilot screw will cause idling problems.

 

[pvanv]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Thanks Matt!

Which one is the pilot screw on the picture, is it the top spring one?

Use your Factory service manual as a guide to adjust the pilot mixture. You need a very accurate shop tach, and an experienced ear. BTW... It has precious little effect at WOT... effectively a "drop in the bucket".

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Even after returning the pilot screw close to the starting position the idling problem remained. I hope it is a stuck float as I see sudden increase in rpm or dying of the engine. Will take it apart today.
So getting it right will be tough without the manual and shop tach? Dammit, I don't even have the experienced ear, but what is the guarantee that the shop mechanic has it... I will take a shot. Requested a quote for a manual too. Lets see what they will come up with.

 

[pvanv]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

We usually start with the pilot screw about 2 turns out. Then warm up the motor in the water on the boat under load, and adjust the idle stop screw to specs. Then adjust the pilot mixture until an increase in idle speed... then reset the idle stop to specs... repeat a few times, until you get the idle speed at specs with the stop at the minimum throttle plate opening... then back off the pilot screw about 1/8 to 1/4 turn richer (for stability) and readjust the idle stop to specs.

But you must do this with a good shop tach.

The Factory service manual for your motor is 003-21035-1 SERVICE MANUAL, 1 & 2 CYL, 2-STROKE, $45.00, available from any dealer, including several forum members (even me). Skip the aftermarket manuals, which are too general to be of much help.

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

I very much appreciate that you are sharing this carburetor adjustment information!
I am trying to find general information about carburetors, out of curiosity, to be able to better understand what I am dealing with. Will see how far I will get.

The quote I got is 30% over the price you mention, so I will prefer to buy from a dealer, especially from people who contribute to the forum.

Thanks again!

 

[TOHATSU GURU]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

Smashed,

Where are you located?

 

[smashed]

Re: 2003 Tohatsu 9.8 2-stroke engine - decreasing performance, compression numbers

I am in New Brunswick, Central NJ