tohatsu 50hp timing and carb setup - Page 2

Locozodiac · 10 May 2015, 03:47

Hi Commando.

Some issues :

Ignition coils can fail at any time, will give trouble at idle, fast idle or through the entire throttle range. Coils have 3 conditions, works good, is kaput or has intermitent heating failing issues, which is the most difficult to troubleshoot. Buy a spare ignition coil and swap between 3 cylinders, one of them is kaput, can't have 3 down coils at same time.

Main Jets for 50D2 carbs are 132 for upper and middle and 135 for lower carb. Slow Jet are 80 for all 3 carbs.

Although you can have all 3 carbs adjusted to 2.5 turns from lightly seated, it's no indication that engine will rev smooth, will need to have a musician ear for carb tunning while playing with mixture screws. Tunning with a set of 3 led vacuum gauges is more precise.

You can play with all the props you want, what you should't do is having a standard engine revving higher than its factory wot stated 5850 rpm with any chosen prop. That's the max rpm the engine was designed to run at. If it were a new engine and breaking it due to overreving forget all about Tohatsu warranty.

According to TT factory a TT installed on a 3 cylinder engine will not read accurately, are just intended to work well on 1-2 cylinder engine.

Happy Boating

Roflhat · 10 May 2015, 08:30

The tiny tach works fine on 3 cylinders. Just about everyone with a thundercat has a tiny tach. You just have to put it to the right setting (120 degrees from memory).

As for the RPM range, it's true for most boats you don't want to go over the rev limiter. And you don't want to on a tohatsu unless the crank is welded either. But the powerband goes well beyond the 5850 limiter, you can prop it to get a WOT of 6500-6700. The engines powerband continues fairly flat upto 7k rpm. I've attached a file (hopefully) of a dyno test carried out in the US.

But I wouldn't go snipping the rev limiter without welding the crank first

Locozodiac · 10 May 2015, 16:19

Roflhat,

See a Yam 70 on your avatar, what happened to your extremely modified Toahtsu 50 HP, engine pulled a rod through crankcase ?

Happy Boating

Roflhat · 10 May 2015, 19:26

Quote:

Originally Posted by Locozodiac

Roflhat,

See a Yam 70 on your avatar, what happened to your extremely modified Toahtsu 50 HP, engine pulled a rod through crankcase ?

Happy Boating

haha not quite

It's running really well, still have it. Mine is fairly tame to what some guys overseas are building believe me. There's a guy in the states with a turbocharged slowhatsu 50!
Been searching for a yam 70 short shaft for years when this came up for sale last year.
You can expect to see some mods on the 70 too

Commando C2 · 12 May 2015, 22:38

Where on the carbs would I connect vacuum gauge pipes? I have a carb balancer for a motor bike which shows vacuum so wondering if I can use it to tune carbs.....

Locozodiac · 14 May 2015, 02:23

Will need to modify carb's manifold, that's remove, drill a hole side to each carb, install a small plug to close hole after tune up.

You can find on the market led light vacuum gauges that comes in 3 or 4 led sets. Will need to ballance all 3 cylinders at same time untill all 3 lights are even.

One vaccum is good for a 1- 2 cylinder one carb engine, it's more complicated to fine tune 3 individual carb separately.

Happy Boating

Commando C2 · 22 May 2015, 21:07

Took the boat out this week on the river.
It ran well, accelerated ok from idle and trolling, by that I mean it didn't cut out or bog.
It still feels a bit chuggy when pulling away compared to my race tuned tohatsu 50, but this could be down to the standard reeds in the mariner.
I did 3 things to the engine but can't be sure which one worked.

Did extra earth wires between coils and to earth.

Made idle timing 3 atdc as it was about 5 btdc, and syncd carb links

Put pilot screws to 2.5 turns out.

Commando C2 · 22 May 2015, 21:10

Clocked it at about 44 mph running at about 5500rpm
Plugs a little bit oily but knew that the premix in tank was a bit rich as ran out of space in tank when filling so could have put 4 more litres in to make it 50:1

Last question. With the pilot screws. Which way to turn to o to make mixture weaker, and which way for richer ?

Thanks all.