Tohatsu 15 D2 Sluggish Acceleration

[SoggyPaws]

I have a 15HP M15D2 2000 Tohatsu that I bought used, and it had been stored for a good while before I ever cranked it up.

Now that I have commissioned it, it runs fine, EXCEPT in the acceleration from idle to planing speed. Most of time, it is sluggish and pings during acceleration. Once it finally gets up on a plane it seems to run smoothly and at full RPM.

I have the factory service manual for an M15B2, but the Japanese/English translation is so poor that I'm having trouble understanding the timing section.

So far I have done the following:
- Changed to new spark plugs
- Dismantled and thoroughly cleaned the carbuerator and fuel pump
- Replaced the fuel pump diaphragms
- Changed to a new fuel tank with brand new high-test fuel with carefully measured TCW3 oil mixture
- Inspected all the hoses and wires and fittings on the motor
- Checked compression, and it is at 135 psi on each cylinder
- Verified there are no fuel line air leaks
- Made sure air vent on tank is open
- Checked and cleaned fuel filters
- Adjusted the pilot screw to 2 full turns out
- Verified that the cavitation plate is roughly even with the bottom of the hull

The motor is on a 10.5-foot Rigid Inflatable, and a previous 1984 Tohatsu 15 ran well on this same boat without the acceleration problem.

I am currently looking at whether the propeller is the right pitch (mine is model 8.5) and trying to determine what the timing arrangement should be.

Regarding the timing, it appears that the Top Dead Center (TDC) should be one long tic mark aft of the forward end of the Advancer Link Rod B (according to figure 10-11 in the service manual). My magneto coil plate, which has the timing marks, has a down arrow in place of one of the long marks, in the same location as shown in Fig 10-11, so I believe this to be indicating TDC on my engine.

But I can't tell what the timing setting should be for wide open throttle. Both the diagram (Fig 10-12) and the words are very confusing. There are no numbers and no TDC indication on Fig 10-12. It looks like the wide open throttle settings should be about 3 1/4 long tic marks BTDC. Anybody know if this is correct?

Anyone have any other ideas/suggestions/hints that might help me.

I am in Guatemala and don't have easy access to a service center.

 

[TOHATSU GURU]

Re: Tohatsu 15 D2 Sluggish Acceleration

The 15D2 is set at 25 degrees BTDC and 3 degrees ATDC.

Follow the steps below.

1) Set the throttle at WOT

2) Adjust the timing link so that the full open mark is even with the crankcase mating point

3) Set the stopper bolt so that the advancer arm just barely touches the wide open point on the stopper bolt at WOT

4) Now set the throttle at dead slow

5) Set the stopper bolt so that the full closed mark is lined up with the crankcase mating point when the advancer arm touches the stopper bolt

6) Adjust the nut on the advancer arm so that it is firm , but not overly tight

7) Go back and clean the carb again as you have a 90% chance that there is still an obstruction in it somewhere and this time set the screw at 1 1/2 and adjust from there

8) No step 8

9) Repeat step 8

 

[SoggyPaws]

Re: Tohatsu 15 D2 Sluggish Acceleration

Many thanks Elvin! That info was enough for me to sort out the timing and get it right on. I also spent some time adjusting the pilot set screw and talked to a dealer who indicated my prop (8.5) is the standard prop mid range prop sold with the these engines. And then I looked at the carbeurator throat with the air intake housing off during acceleration in order to ensure it was getting a significant increased spray of fuel as I turned the throttle up. It was.

However, none of these things had much effect on the sluggish and missing problems during acceleration. It still seems to run smoothly during idle and once it settles out on plane. I now have the carbuerator and fuel pump back off and am going through them carefully one more time. So far no indication of dirty fuel or other problems. I'll finish up with that tomorrow morning.

In the mean time I'm looking at other possible causes. I understand from talking with a local cruiser/former outboard motor dealer that sometimes the CDI module can cause erratic behavior such as this.
--Do you have any experience with that and do you think it would be a possibility?
--If so, are you familiar with the procedure for testing the module?
--There is a troubleshooting table in my M15B Service Manual. However my module is newer and has a different stock number than the older module that the manual applies to. So I'm wondering if the troubleshooting multimeter readings would be the same.
--Any other thoughts that I haven't looked at yet?

Thanks again for your help.

Dave
SV Soggy Paws
In Guatemala

 

[TOHATSU GURU]

Re: Tohatsu 15 D2 Sluggish Acceleration

Do you have any experience with that....Yes
And do you think it would be a possibility....Possible, yes. Likely, no.
If so, are you familiar with the procedure for testing the module...Yes and you will need a current manual to get that procedure as I cannot provide it to you.
There is a troubleshooting table in my M15B Service Manual. However my module is newer and has a different stock number than the older module that the manual applies to. So I'm wondering if the troubleshooting multimeter readings would be the same...Nope
Any other thoughts that I haven't looked at yet...Clean the carb again. Then pop one of the sparkplug leads off while the engine is having its problem. If it does not die you know that the other cylinder is working. Then do the other one. If both are working you have a 99% chance that the problem is fuel system related. In the end you are going to have to get a manual for your model engine.

 

[SoggyPaws]

Re: Tohatsu 15 D2 Sluggish Acceleration

Recap: I have a 2000 Tohatsu 15D2 with sluggish acceleration, located in remote regions of the Caribbean (no dealer nearby). Have 15B2 service manual and 15D2 owners manual. Have been working on this problem for about 6 months with no success.

Since my last posting, I have done the following:

- Disassembled, soaked and blown-out the carbuerator thoroughly (twice), once with a very experienced outboard mechanic looking over my shoulder.

- Changed the spark plugs for brand new plugs per Tohatsu specs (B7HS-10)

- Checked and adjusted idle screw setting and ignition and carb linkage settings (by an experienced mechanic with my 15D2 manual)

- Tested all the coils for resistance with a digital multimeter, with the following results:

Ignition coil: .3 Ohms between terminal and ground, open between high tension leads

Exciter/trigger coil: 168 Ohms between red lead and blue lead. Open between red lead and ground, and open between blue lead and ground.

In my manual (15B2) pg 43 Figure 17-10 shows #3 and #5 as separate items, an exciter coil and a trigger coil. But my outboard only seems to have one coil, with only the red and blue wires going to the CDI module.

Are my readings normal, or do they show one of the coils defective?

Anyone have any new suggestions???

Note: I bought my engine used. My serial number is 44005. If anyone has access to the Warranty Database for Tohatsu, it would be interesting to see if there was ever a warranty claim for this motor for a similar issue.

 

[TOHATSU GURU]

Re: Tohatsu 15 D2 Sluggish Acceleration

Until you get the correct service manual I can't help you.

 

[gabriel]

Re: Tohatsu 15 D2 Sluggish Acceleration

I started to have the same problem. I bought the book read from cover to cover worked on my OB (1990 25 inch 90HP NISSAN) chapter to chapter when I got to the oil Adjustment and set that to what it had in manuel, Sluggish acceleration was gone.