Slow tohatsu 50 (zapcat)

Allye · 22 March 2020, 18:12

Hello all,

Firstly thanks for the information this forum has provided for me, I’ve been a reader for years!

To the point. Got my first zapcat with the standard tohatsu 50hp, first launch last week and it’s really down on power. Will rev up freely in neutral, once in gear it really struggles along, Ive been helming 30hp RNLI Inshore rescue boats for nearly 10 years so I know this should be a fair bit quicker for comparison!

Ive rebuilt the fuel pump and upgraded the coils for the naraku items, fully serviced new plugs, fresh fuel, good even compression across all three, had a boyesen read stick on the air box so assume it has those. Re launched today and no difference. So time for a carb rebuild I guess? Will I need a gasket set or do they come apart without damaging gaskets? Any other advice appreciated.

Thanks in advance,

Ali

spartacus · 22 March 2020, 21:33

Not aware of gaskets being on the carbs? Yes old fuel can get gummed up, but be careful when stripping down. I stripped the carbs on my Tohatsu MC60 three times without success. Eventually put it in to a marine engineer who effectively reset all settings.

On a power trim and tilt engine, then the butterfly valve behind the airbox can stick. In addition, if you're using after-market fuel connectors, then check the 'o' rings as they are known to dislodge and restrict fuel. Genuine Tohatsu only. Also check the primer bulb. Can get brittle or hard with age and diagraphm can restrict flow. Genuine Tohatsu or Quicksiver only.

Good call on the fuel pump. You can rule that out by running in neutral and premoving pump from engine block.

Lastly, check electrical connections. Tohatsu bless them (as with all outboard manufacturers) use non-tinned wiring. Not unusual for electrical gremlins as the wiring is oxidised or even broken causing intermittent issues.

You can check spark individually to rule out HT leads.

Allye · 23 March 2020, 09:41

I’m assuming the carb has gaskets internally? Manual tilt engine. I was considering bypassing filter and quick release to rule that out, may grab another primer of the chandlerys are even open! Fuel filter looks to be clean though.

Roflhat · 23 March 2020, 12:45

Try priming the fuel pump as you're going along, that will rule out the fuel pump.
Worth putting earths between all the coils, even the naruku ones sometimes miss. If you can, get the carbs ultrasonically cleaned, on my 70hp I cleaned them 10+ times they were spotless but still wouldn't run properly. After an ultrasonic clean it ran perfect

Allye · 23 March 2020, 12:51

Thanks for the reply, had all three apart and seemed annoyingly clean really, only slightly residue. Took the reed block off too, all seemed as it should. Reassemble it all, last thing was to check the fuel filter, loads of odd white gunk at the base. Disassemble all the fuel lines and looks like it has deteriorated internally and was clearly blocking it near the quick release. I’ve got a spare bulb and line which I’ve put on (spotless inside) ran it up and it started with way less choke required and revs much more freely. Get it out again this afternoon and see how she goes!

I have to say looking at the lines they looked quite new so it was the last thing I thought of. Lesson learnt!

Allye · 23 March 2020, 13:26

Quote:

Originally Posted by Roflhat

Try priming the fuel pump as you're going along, that will rule out the fuel pump.
Worth putting earths between all the coils, even the naruku ones sometimes miss. If you can, get the carbs ultrasonically cleaned, on my 70hp I cleaned them 10+ times they were spotless but still wouldn't run properly. After an ultrasonic clean it ran perfect

Also did you get my PM? Not sure it’s working, is there rules with new members sending PM’s?

valvebounce · 23 March 2020, 15:06

Have you tried the vent in your tank cap filler?
Even a partially blocked vent will cause a vacuum in the tank.

Locozodiac · 23 March 2020, 16:18

Is the motor running tha factory delivered prop which is ? state diam and pitch ? What's the max wot revs achieved with said prop af full throttle grip ?

Happy Boating

Allye · 23 March 2020, 17:45

The plot thickens. Numb nuts over here had previously pulled both top plugs and not the bottom one. Blast down the river today with a max speed of 29mph, bottom cylinder plug is untouched/brand new! Idiot. Checked all the wiring, re did some connectors. Shared earths around, tried old coil, no spark. Assume the CDI is dead? Strange for it to fire 2/3 signal wires. Prop is a 15’ stainless one they race with.

Roflhat · 23 March 2020, 18:13

Yeh got your PM, replied
try swapping the coils over to eliminate them, can also be the pickup coils beneath the flywheel, CDI don't usually go wrong

Locozodiac · 24 March 2020, 16:51

Quote:

Originally Posted by Allye

Prop is a 15’ stainless one they race with.

The factory wot rpm range for that motor is 5200-5800 rpm. The max top spped of 29 MPH was achieved with the motor running at which max wot revs ?

29 MPH is a very poor top speed, my 450 Rib with 1 up powered with a standard 2 stroke Tohatsu 18 HP motor does 21 MPH running at its full 5800 wot rpm on flat calm water cond.

Happy Boating

Allye · 24 March 2020, 17:05

Thanks for the help. Yes I’m well aware that’s a low speed I was just pointing it out to prove the lack of power. No idea what the RPM is nor will I be running any kind of tach.

New CDI is on its way so hopefully that’ll make it run on three! Not that anyone can launch for the next few weeks.

Locozodiac · 25 March 2020, 01:24

When the motor runs strong again, install an induction tach on the tiller armas in picture and check what's the max wot rpm achieved. Can play with less prop pitches for motor to run towards its max wot rpm range, can go 5% beyond the max wot rpm range for motor to run safe.

If everyone else runs a 15 pitch prop doesn't mean it's the correct prop for your set up, worse if it's not known at which max wot revs is the motor running specially when racing. Motor height, trim, deck load distribution accounts for rpm reduction if not working spot on on any boat.

Happy Boating

valvebounce · 25 March 2020, 11:18

Quote:

Originally Posted by Locozodiac

When the motor runs strong again, install an induction tach on the tiller armas in picture and check what's the max wot rpm achieved. Can play with less prop pitches for motor to run towards its max wot rpm range, can go 5% beyond the max wot rpm range for motor to run safe.

If everyone else runs a 15 pitch prop doesn't mean it's the correct prop for your set up, worse if it's not known at which max wot revs is the motor running specially when racing. Motor height, trim, deck load distribution accounts for rpm reduction if not working spot on on any boat.

Happy Boating

I wish I had seen that,I bought a taco last year that you have to find a spot to fix it on.

valvebounce · 25 March 2020, 11:29

Bought an 18hp motor with a 9.25X11" prop on it.The boat wouldn't plane or reach the WOT of the motor.Changed it for a 9"X9" prop,and it got on the plane and reached the correct WOT,no problems.
Like has been said,every boat is different,and needs the correct prop.

Allye · 25 March 2020, 12:00

I’m fairly well up to speed to pitches and the effect they have on the boat. My zapcat is purely leisure and will rarely go out twice with the same crew or weight, it’ll be toe surfing, pulling ringos, pub trips, solo blasts, dive boat, surf helming and so on. 15’ is a good all rounder and it’ll be rarely driven at WOT for long periods of time. What I’m saying is as long as it gets about as it should I won’t be chasing 100’s of rpms or 1/2 knots.

valvebounce · 25 March 2020, 12:40

Quote:

Originally Posted by Allye

Hello all,

Firstly thanks for the information this forum has provided for me, I’ve been a reader for years!

To the point. Got my first zapcat with the standard tohatsu 50hp, first launch last week and it’s really down on power. Will rev up freely in neutral, once in gear it really struggles along, Ive been helming 30hp RNLI Inshore rescue boats for nearly 10 years so I know this should be a fair bit quicker for comparison!

Ive rebuilt the fuel pump and upgraded the coils for the naraku items, fully serviced new plugs, fresh fuel, good even compression across all three, had a boyesen read stick on the air box so assume it has those. Re launched today and no difference. So time for a carb rebuild I guess? Will I need a gasket set or do they come apart without damaging gaskets? Any other advice appreciated.

Thanks in advance,

Ali

My first thoughts would be a fuel supply problem.It's amazing just where crap will lodge in a carb.
The results you are getting could also be a flooding issue.
Carb primers,float sticking etc.

Allye · 25 March 2020, 15:10

Did you have a read of the thread? CDI is dying and only firing on 2.

valvebounce · 25 March 2020, 16:19

Quote:

Originally Posted by Allye

Did you have a read of the thread? CDI is dying and only firing on 2.

My apologies,I must have missed that bit

Locozodiac · 25 March 2020, 19:44

If you don't want to have said tacho permanently installed assumig it's for a central console installation, install longer cables that protrude out cowl as to hold it with your hand, conduct a water wot test, depending on the wot rpm achieved, prop the motor right to rev at max 5800 wot revs with you alone, once there can throttle to the rpm you feel comfy with.

If you don't intend going that way, will never know what you are going to miss....

Happy Boating