Tohatsu 50 outboard questions

simzpilot · 18 July 2017, 10:15

Hi All, I have a Tohatsu 50 outboard on a SIB and I have the following scenario that I would appreciate your help an advice with

(1) Engine struggles to start and requires a lot of warming before it will run
(2) Engine appears to misfire at low revs but runs well once engine revs are up

Engine is 2003, new plugs fitted, runs in freshwater. I cleaned all carbs last season. Engine compression is around 130 on each of the three cylinders (I will test again this week for sure).

watersidemat · 18 July 2017, 20:03

The timing rods all set to correct length. Carbs balanced and set to service manual measurements?

Bigplumbs · 22 July 2017, 08:05

Is it a 2 stroke or 4 stroke

The Black Pig · 22 July 2017, 14:52

Spartacus is your man he should be along shortly

simzpilot · 22 July 2017, 21:12

@Bigplumbs - It's a 2-stroke...
I went through a full set up today from original factory setting and following all the settings advised in the factory service manual. It is running a lot better now and it may be down to a number of issues such as timing at idle/carb balancing, bad earth. I also noticed that she was fitted with NGK plugs that were B8HS-10 instead of the correct BR8HS-10, which I gather may affect idling. I have her much closer to where I want her now and changing the plugs next week may solve the final piece of the pie.

Always welcome to hear any other experienced advice as it is always appreciated. Let me know your thoughts folks.

The Black Pig · 23 July 2017, 05:29

Quote:

Originally Posted by simzpilot

@Bigplumbs - It's a 2-stroke...
I went through a full set up today from original factory setting and following all the settings advised in the factory service manual. It is running a lot better now and it may be down to a number of issues such as timing at idle/carb balancing, bad earth. I also noticed that she was fitted with NGK plugs that were B8HS-10 instead of the correct BR8HS-10, which I gather may affect idling. I have her much closer to where I want her now and changing the plugs next week may solve the final piece of the pie.

Always welcome to hear any other experienced advice as it is always appreciated. Let me know your thoughts folks.

Hopefully this is of use to crack the NGK code

https://www.ngk.de/en/technology-in-...-the-ngk-code/

On the heat rating if you go either side( drop or increase ) of the standard manufacturers recommend heat number you can adjust the running to suit

This has worked for me

spartacus · 23 July 2017, 07:01

Quote:

Originally Posted by simzpilot

Hi All, I have a Tohatsu 50 outboard on a SIB and I have the following scenario that I would appreciate your help an advice with

(1) Engine struggles to start and requires a lot of warming before it will run
(2) Engine appears to misfire at low revs but runs well once engine revs are up

Engine is 2003, new plugs fitted, runs in freshwater. I cleaned all carbs last season. Engine compression is around 130 on each of the three cylinders (I will test again this week for sure).

Tohatsu 2-stroke mid sized engines are a bit of a dog to start from cold in my opinion. Once they get going they'll start on the button from warm.

One thing I would check is the butterfly choke behind the air-box on the top cylinder. I've seen them sieze before restricting operation. Not sure if your 50 is manual pull or electric? Pre-ignition choke on remote if electric is important as you should hear the butterfly choke open with an audible click. Fuel bulb should be rock hard. Turn over the engine with wet or contaminated plugs and you risk burning out the starter motor, so short bursts of 2-3 seconds with choke out until it splutters into life.

The spark plugs and condition of HT leads could be your possible misfire issue. Fit the right NGK plugs as mentioned. Always use a little marine grease on the thread (and I can't emphasise this enough), and do not over torque the plugs when seating or you'll strip the threads. Plugs should be dry. If they're wet, or have any electrode contamination, just dry them off with a rag and use a little soft bristle copper wire brush to remove any carbon surface deposits.

Hope that sorts things.

simzpilot · 23 July 2017, 21:39

Thanks everyone for the advice. Some really good check points here. Will get through them all this week and advise when done

simzpilot · 24 July 2017, 07:23

Some interesting data for the NGK plugs for this engine from the link sent by @ The Black Pig
NGKBR8HS-10
B=14mm thread size
R=Resistor type (important for this engine)
8=heat rating (range is from 2 ‘Hotter’ to 13 ‘Cooler’)
H-12.7mm thread reach
S=Firing end type (Copper core centre electrode)
10=spark plug gap (1.0mm)

simzpilot · 27 July 2017, 08:52

@Spartacus @watersidemat @The Black Pig @Bigplumbs
Quick question on carb balancing
So, I have the correct plugs fitted and torqued. All static adjustments made to the factory manual settings and air/fuel screw adjustments done (also idle done). The question I had is can only static carb balancing be done on this engine or is there a process for dymanic balancing using 3-way vacuum gauges or Uni-sym with the engine running?

watersidemat · 27 July 2017, 12:45

Have you seen the dangar marine videos on you tube he does one on balancing carbs and will explain it better than anything I can type. I just ran my engine unroll warm then adjusted mixture screws and idle speed to the point it sounded right.

simzpilot · 27 July 2017, 15:32

@watersidemat, Yes, I saw these videos but I don't see the same ports/connectivity and adjustment on the Tohatsu 50 to use the dynamic balancing rig. I may be missing this completely so happy to stand corrected if someone can advise how to do this on the Tohatsu 50.

watersidemat · 27 July 2017, 15:35

The dynamic balancing is way beyond me. I also looked for said ports and drew a blank so as above, just adjusted mix screws, timing rods and idle to get it running smooth.

Roflhat · 27 July 2017, 16:07

Dynamic carb balancing on 2 strokes is quite difficult from what I hear, I just undo all the linkage screws and set them so the throttle flaps open together evenly

Bigplumbs · 27 July 2017, 16:59

Quote:

Originally Posted by simzpilot

@Spartacus @watersidemat @The Black Pig @Bigplumbs
Quick question on carb balancing
So, I have the correct plugs fitted and torqued. All static adjustments made to the factory manual settings and air/fuel screw adjustments done (also idle done). The question I had is can only static carb balancing be done on this engine or is there a process for dymanic balancing using 3-way vacuum gauges or Uni-sym with the engine running?

I am afraid that is beyond my knowledge

Dennis