First Tohatsu motor 9.9HP

[andreipou]

Put top arm back to 72 mm.
Had to extend lower arm from 75 to 77 mm to achieve +22 to -3 degrees.
Put stop screws as you said.

First pic is max open throttle.
Second is max closed. Roller is still sitting on low step of the cam

 

[gman2692]

My motor looks just like that and is 9.9b2. Mine is 1986 if that helps you in any way

 

[Sea Rider]

Where did you got the measurements for both horizontal and vertical arms ? Clarify : did you played with stopper A to achieve 22 deg as posted, or achieved that seeting playing witht he vertical arm ? this is important to know.

Seems you got both cam/carb's roller settings mixed up. In pic 1 the carb's pawl needs to sit flat against the base as seen in second pic, post 60, once there and without releasing the pawl located on the metal plate extreme readjust the roller arm screw for the roller to sit against the high hill cam portion and that's with throttle grip set to max throttle. Something like this, this cam/roller synch pic corresponds to a 9.9 D2 motor : Is the cam same as yours ?



Once there, when returning the grip to min throttle, should see the roller stopping at the beginning of the cam, that's where the carb works on its own, readjust and report...

Happy Boating​

 

[andreipou]

My motor looks just like that and is 9.9b2. Mine is 1986 if that helps you in any way

Do you have any manual that covers B2 model?
I wonder if older B2 model has differences that cause all this headache.

 

[andreipou]

I got measurements from the manual (pic 1 & 2), but it does not cover B2 model what could be the problem. I was not able to locate B2 manual.

I had to play with arm length to achieve -3 to +22 range. It is as much as tiller arm can rotate in both directions now. Stopper screws are not even needed really.
With default arm lengths range would be 0 to +20 only.

My cam looks differently (pic 3).
Do you mind posting side pics of carb showing throttle and cam position with tiller to max and tiller to min?

 

[andreipou]

My motor looks just like that and is 9.9b2. Mine is 1986 if that helps you in any way

gman2692, if you do not have B2 manual do you mind checking what is the range of timing marks from MIN to MAX tiller turns?
Is it -3 to +22 ( see pics from SeaRider post #56) how to check it?
Also, what is the length of vertical and horizontal linkage arms measured from center of the pivot balls?
If you can post side pics of carb showing throttle and cam roller at MIN and MAX tiller twist it would be great.
I am getting impression that B2 is not 100% the same as later models, therefore it is difficult to figure out those things.
Tnx.

 

[Sea Rider]

Sorry, as stated I'm not familiar with the 9.9 B2 obsolete model. Need to know what the factory specs are for both arms to achieve a spot on time advance/carb synch, surely differs much from the later 9.9 models. The posted pic seen on post 63 shows max timing advance along max cam advance achieved with throttle grip fully turned to max, the pic seems to correspond to a 9.9 D2 model ?

Happy Boating​

 

[andreipou]

Going back to this project:

Is there anyone with manual for M9.9B2 out there?
Or actual M9.9B2 working motor?

Also, I have an impression that 2002 Nissan NS9.9B2 is the same motor. Maybe, it will help to find the info for mine.

 

[Sea Rider]

As of now, is the motor currently running ? As long the right side of the cam is not pushing the white roller when at min throttle grip as to start to open the butterfly a bit not an issue, while there the motor works at idle/ralenti provided that both mixture and idle scews are well adjusted to. Those Nissan 9.9 are same rebadged Tohatsu...

Happy Boating​

 

[MattFL]

Going back to this project:

Is there anyone with manual for M9.9B2 out there?
Or actual M9.9B2 working motor?

Also, I have an impression that 2002 Nissan NS9.9B2 is the same motor. Maybe, it will help to find the info for mine.

Check manualslib.com, sometimes you have to search a bit but they have a ton of manuals.

 

[andreipou]

I put this on hold hoping that I find manual for B2 model and it finally happened. I got original M9.9B manual (pic1).
Still not B2 what means maybe not 100% exact, but definitely better that D2.
As I suspected there are differences for B model in some important settings:

1. Idle speed for B is 1000-1100 rpms against 800 rpms for D2 (pic 2). That explains why I was not able to make it to run on "low". Even now when it is finally running it is, 1200-1300 rpms. If I try to go lower it stalls randomly.

2. Advance link rod B length adjustment is different also (pic 3) and nowhere in the manual I found specs on adjusting link A what makes it difficult to understand how it is supposed to be.

4. Pic 4 contains values for ignition timing adjustment and they are different for model B too. But, it shows that there are two types of magneto with different settings, and nowhere it says how to determine the type of magneto. I got better running with values for Type 2, but again it was just guessing.

5. Pic 4 also contains value for initial low speed needle opening, but again is shows 2 different carb type, so I am not sure which one I have. But, difference is only 1/8 turn, so it really does not matter I think.

My cam has no marks mentioned on Pic 3 (Fig 10-9), so I am still not clear how to properly adjust throttle opening points.

After all this experimenting I have following:

1. Motor is hard to start with choke off, but with choke on it starts with half of pull, but I have to push choke off immediately, otherwise it stalls almost right away.

2. It runs 1200-1300 rpms on idle as long as I want.

3. When I put reverse gear on it is ok and keeps running.

4. Wen I put forward gear on it tries to stall in 50% of cases and I have to give some more gas with tiller handle and go back to low and then it runs.

I can tell now that I got this motor working, but it still needs fine tuning because not everything is perfect. Just need to find what to do.

Any thoughts?

Tnx.

 

[MattFL]

It sounds like you're down to tuning. I would go back over all the basics. Make sure the valves are properly adjusted, overly tight valves can cause idle problems. Also make very sure the pilot circuit in the carburetor is spotless. Sometimes there are tiny holes that need to be cleaned. If the pilot circuit is plugged or partially plugged, it won't run until you open the throttle enough that it start using the next circuit. My guess is this is the most likely problem. Also double check the timing while you're at it.

 

[andreipou]

It sounds like you're down to tuning. I would go back over all the basics. Make sure the valves are properly adjusted, overly tight valves can cause idle problems. Also make very sure the pilot circuit in the carburetor is spotless. Sometimes there are tiny holes that need to be cleaned. If the pilot circuit is plugged or partially plugged, it won't run until you open the throttle enough that it start using the next circuit. My guess is this is the most likely problem. Also double check the timing while you're at it.

What valves?

 

[MattFL]

What valves?

Ha! Oops, tired brain, forgot we were talking about a 2-stroke. But valves still apply, check out the reeds (reed valves), stock ones are usually metal, make sure they're not bent or dirty and that the surface they seal against is clean and flat. The rest still applies I believe. Also play with the idle fuel mix a little bit. Some carburetors have an air screw (turn-out to go leaner) and some have a fuel screw (turn-out to go richer), I'm not sure which that motor has, but try both directions a little bit to see if it helps. How is the compression? Low compression can also affect idle.

 

[andreipou]

I took 12 semi-V aluminum rated for 10 HP on home lake to see how this motor runs for the first time.
I am used to 6HP on this boat, so when I hit FAST I almost fell of the boat.
It flies!
It does try to stall when I put on gear, so I have to add gas to keep it running, but on this motor tiller has only 3 positions: SLOW-START-FAST.
All my OMC motors have SLOW-SHIFT-START-FAST. Very easy to figure how to shift.
With Tohatsu I twist tiller between SLOW and START to shift because it stalls if it is on SLOW and as I mentioned before it idles a little high, so it is somehow rough on shifting because of high rpms. My concern is that I kill gears this way.

This motor still needs some tuning, but I am not sure in which way. The manuals are terrible comparing to OMC ones. They give just few basic things, no details. I guess they want only professional mechanics to work on their motors, not the amatures like me....

 

[andreipou]

I think this will be the last post on this super long thread.

I got carb off again, disassembled it as much as possible and cleaned every hole and passage I could find. I did find 2 microscopic holes I did not see before.
Then sprayed, blew with compressed air.
Also, rebuilt fuel pump just in case.
That was obviously what was missing for this motor.
After some adjustments motor starts with half pull, idles nicely at 1000 rpms, switches gears smoothly, accelerates and slows as it is supposed to.
I think this motor is done.
It was interesting experience with something new.

Thanks to everyone who helped in this experiment.