tohatsu 50hp timing and carb setup

Commando C2 · 25 April 2015, 22:35

Hello boaters.

I have a tohatsu 2 stroke 50hp 3 cylinder, on a zapcat.
Its actually mariner badged with gas tilt but identical engine under hood to my second engine which is the tohatsu badged m50d2.

Had some trouble with low speed, would bog down or stall when going into gear and pulling away. Would have to rev engine in idle let revs drop, bang it in gear and rev up quick to stop it stalling.once goin it planed but was lacking and wouldn't go flat out.

Engine was fine for about 45 mins before this started. Limped back to slipway, then few mins later gave it a blast and it seemed fine, got 40mph out of it.
Next day, lumpy low down to start but after an hour was ok.....? Annoying as can't trust engine without finding fault.

Need to check timing and carb jet sizes etc.

I cleaned the carbs months back and left them dry. Emptied fuel tank and lines, put in fresh fuel and measured oil exactly. Plugs new too. Coils all same resistance,, Thought it would run fine.

Any help or thoughts would be great
.thanks

Looking for a manual in any links or contacts or info, clymer, seloc, etc would be good.

spartacus · 26 April 2015, 08:09

I had a similar issue myself with a M60/70C outboard. If you've checked the carbs and they are spotless, ensure the butterfly choke operates properly. They are known to seize. The carb pilot screws should be adjusted too. Think it's one and a half turns out from lightly seated.

Scribd do some fairly comprehensive service manuals which should help you. There is one manual by Adrian Peterfi (1992-2000) that will include your model. Don't worry about the date.

Also, Roflhat on here knows the M50d2 like the back of his hand. You could PM him.

A1an · 26 April 2015, 09:22

Thinking logically it doesn't sound like a timing issue, if it was it wouldn't run fine one minute then rough the next then back to fine. That goes for jet sizes too, they are all a constant.

Sounds more like fuel related problem to me, when did you last drain fuel tank and carbs?

Commando C2 · 26 April 2015, 09:47

Thanks Spartacus, I will look out for those manuals. I have heard some of them aren't accurate so don't want to end up making engine worse.
It is an ex rnli engine but has been owned by someone else since should have been setup properly just depends if previous owner tinkerered with it.

Will be pulling the carbs off anyway first.

Anyone know jet sizes? Akin last time I cleaned carbs there is a small rubber bung over the needle jet so can't understand how it gets to suck up fuel from float bowls?

Commando C2 · 26 April 2015, 09:50

I drained and cleaned the tanks a few days before using.the carbs got cleaned 6 months ago and not started or filled so carbs dry.
That's why I was expecting it to work.

Just want to check timing to cover all bases as the idle timing could be out.

Roflhat · 26 April 2015, 10:33

I had a similar issue, took me a long time to figure it out as it sounds like a fuel problem. Must have cleaned the carbs 10 times before I checked the coils. For me the engine would idle fine and rev in neutral, then bog as soon as you put it in gear and wouldn't rev properly at all. Turned out to be a bad coil, try taking the lead off each cylinder individually and see if they're all firing, the coils on the 50's are notoriously unreliable. In zapcat racing they're now allowed to swap tohatsu 70 coils, no performance gain just reliability.

I would doubt it could be the timing, I've tried all the settings possible without modifying the timing linkage arm and the engine idled fine with them all, the range is between 18-22 degrees at WOT I think? There's really no reason to adjust the timing beyond that

The D2's has 132 main jets if i remember correctly, they can be swapped out for 125's with slightly retarded timing but the gains are debeatable...

Let us know how you get on

spartacus · 26 April 2015, 14:34

Rule out fuel related issues such as primer bulb (these can fail prematurely). Use Quicksilver part, not cheap EBay rubbish), fuel reservoir filter on engine, and fuel pump isn't leaking (worn diaphragm).

Commando C2 · 26 April 2015, 16:43

Good info thanks. Will see how the carbs look.
I have some spare coils from my other engine that is running sweet so might swap them out. Going to add additional earth strap between coils too.

I did pull the plug lead off number 1, then start it and it felt the lead had a spark, then did same with other 2 so if one was down and one taken off it surely wouldn't start on one cylinder.?!

I think its not coil related as I was getting 40 mph out of it once it got planing....a duff coil normally shows up at top revs.

Commando C2 · 26 April 2015, 16:48

Will check fuel pump and primer bulb. I did have a look at fuel filter while on river and filter was full all the time so to my knowledge this shows the pump is ok as fuel pulled through constantly.

Damn engines.....why can't it be simple to find problems...

1eyedjim · 26 April 2015, 18:23

Had the same issue when I got my zapcat

Fuel pump needed rebuilding and carb adjustment screws needed removing and cleaning as was seized in

After this it runs bang on and flys

Commando C2 · 26 April 2015, 20:16

The pilot screws on each carb were only 1 and 3/4
Turns out. Would this make a big difference to the idle speed pull away?

Also last time a took carbs apart there was a small rubber bung over one of the jets, but can't work out how the fuel gets sucked up. On my motorbike carb the jets need to be open to suck fuel.

Baffling.

Roflhat · 26 April 2015, 21:32

Quote:

Originally Posted by Commando C2

Good info thanks. Will see how the carbs look.
I have some spare coils from my other engine that is running sweet so might swap them out. Going to add additional earth strap between coils too.

I did pull the plug lead off number 1, then start it and it felt the lead had a spark, then did same with other 2 so if one was down and one taken off it surely wouldn't start on one cylinder.?!

I think its not coil related as I was getting 40 mph out of it once it got planing....a duff coil normally shows up at top revs.

if you can try taking the spark plug boots off while it's running, makes it easier to tell if it's firing on that cylinder, just be careful of shocks

My tohatsu amazingly would run on 1 cylinder, not too happily of course...

When I had that coil issue, it was intermittent, sometimes at WOT the dodgy coil would suddenly come to life. With the aftermarket coils I've got now the only issue I had was a corroded earth, just needed cleaning up with sandpaper and then some vaseline.

Saying that the other weak link on a tohatsu 50 is the fuel pump, again I've replaced mine with an aftermarket part from a jetski. Original required 5 rebuilds in one summer, poor quality part and that's with 2 fuel filters

Roflhat · 26 April 2015, 21:34

on a probably unrelated note, 40mph seems a bit slow? What propeller have you got on it?
With a stainless 15p bunny you should be getting around 46/47 with a zapcat, maybe 48 with a thundercat. Or get an 18p prop and you'll be closer to 60mph

Commando C2 · 26 April 2015, 22:06

Its a 15p prop semi cleavr type for Zapcats.
I thought 40 was pretty good. I was against a tidal flow of about 6 knots at least and had about 35 kgs fuel in front of boat and a 10ft surfboard strapped across the bow .
I like the sound of an 18 pitch prop though.

Will check all the carb and fuel pump and other recommendations this week.
What make coils do you use now rolfhat?
Thanks all for your help.

Roflhat · 27 April 2015, 09:19

Ah ok, so you're probably at ~ 40 knots ish top speed, thats decent.
i generally keep all the weight, fuel tank etc. as far back as I can unless I'm in big waves with just myself onboard.

Here's my tohatsu 50 build thread on here - http://www.rib.net/forum/f50/my-thundercat-61912.html
They're nakuru motorbike coils, there's been a couple of discussions about them on here since as well.
Once you start with cleaver props and chasing numbers you can't stop

Commando C2 · 27 April 2015, 16:52

Thanks Rolfhat, will try to the plug cap removal next time I get to tinker.

I keep the fuel at the front to make more room for passengers at back and so front is weighed down a bit as some times boat is driver only and some waves to get back through.

There was no link to your thread in last post
Was there meant to be? Would be interested to read that .
Thanks

Roflhat · 27 April 2015, 21:47

link works on my computer? try this - http://www.rib.net/forum/f50/my-thundercat-61912.html

Commando C2 · 28 April 2015, 22:59

Enjoyed looks through your thread..thanks

Roflhat · 29 April 2015, 16:24

cheers, check out Thundercat Inflatables Forum as well. A massive amount of info on there. I'm Roflhat on there too

Commando C2 · 06 May 2015, 10:55

Have set pilot screws to 2.5 turns out.

Wot timing is spot on 20 btdc
Idle timing was about 5 degrees btdc and offer to be 3 atdc so adjusted the stop.
Carbs all open at wot.

Just need to water test it in next few weeks.
Installed a tiny tach to help with max rpm and idle speed.