tohatsu 50 - yamaha 70 carbs?

[Roflhat]

I'm sure this has been brought up before but I can't find the thread?

Basically I'm wanting to put yamaha 70 carbs on my Tohatsu 50 D2, how easy is it to do? anyone done it? do they require re-jetting?

Thanks!

[Roflhat]

theyre from a 1997 model

[omcstratos]

I don't know if/how they will fit, but you will have to play around with jets with any kind of changes you make to get the most out of it.

[Roflhat]

thanks for the reply, yeh i've heard i'll need to change some of the jets. don't know what to yet though.

[Fast Fred]

they bolt on, main jet, it's been a wile, should have a 130-135 main in the 50hp carbs, 145 for the 70 carbs on a 50hp. you maybe able to lean on her more at 140, but start with 145's

[Roflhat]

Hey Fred, was hoping you'd chime in! ;) Thanks for the advice. I've heard there's some benefit to widening the reed block when going to 70hp carbs?

[Fast Fred]

i set the 70hp gasket on the intake, scribe it on the intake, then use a flap wheel to open it up. i take the time to check that the carbs lines up on the intake, look down the carb with the throttle plate open makin sure no intake is in the way, straight clean shot.

[Roflhat]

sounds good, ill give it a go. Do the stock 70hp linkages work? I've got a fuel pump sorted for them

[Fast Fred]

the gang link matches the intake used, 50hp intake = 50hp gang link.

the yamaha 50 is just a bit smaller, the same jets as above work for 70 carbs on a 50 yamaha, 150psi is the cut off for pump gas, at 180psi on pump she will prelight the fuel,
squish band style is best, positive style is needed to meet the curved piston dome.

nisson , hotsu cranks should be welded, mains and throws, the pigtail on the wrist pin clips should be removed, best clipped with snips for a no heat used removale

[Roflhat]

thanks for the replies Fred! Daft question - what's the gang link?

I've read somewhere that only the round bowl carbs bolt on? these are the square bowl ones (1997) does that change anything?

[Fast Fred]

it's the bar that clips on to the three carbs so the throttle plates move in sync.
as i remember the only one barrel carb that wont fit on the 40/50 power head are round bowl 90hp carbs (round bowl is deeper, so the 90 round bowls wont stack tight enuff to line up on the 40/50 power head.)

[Roflhat]

Ah I see. so because the carbs are stacked closer together I'll need to use different links. Will the ones from the tohatsu 50 carbs work? or can I shorten the 70 ones?

[Fast Fred]

um No, 40/50 hp uses 40/50 link. no matter what factory carbs used.
the link on the tohatsu is adjustable , the sync and link adjustment is not made there on the link. the link is at a set adjustment and unless messed with, need not be messed with.

[Rabbitdundied]

In for later.


Sent from my iPhone using Tapatalk

[Rabbitdundied]

So what is the purpose of welding the crank? Is it because of high RPMs?


Sent from my iPhone using Tapatalk

[Roflhat]

Yeh, the tohatsu cranks aren't as strong as the yamaha 50 ones, so for anything over stock RPM welding the crank is necessary

[Roflhat]

also, does anyone know where to source jets for yamahas? Trying to find a link or something online

[proprider01us]

I got mine at boats.net

also, does anyone know where to source jets for yamahas? Trying to find a link or something online

[Roflhat]

cheers, found this - http://www.boats.net/parts/search/Yamaha/Outboard/1997/70TLRV/CARBURETOR/parts.html
how do you order different sizes of jets?

[Fastjeff57]

You're saying that these built up cranks need to be tack welded so they don't shift?

Jeff

[sabine river killer]

You're saying that these built up cranks need to be tack welded so they don't shift?

Jeff
yes the yamaha cranks as well any multi piece crank done in many engines not just outboards

[proprider01us]

That is correct. Had mine done like this.
You're saying that these built up cranks need to be tack welded so they don't shift?

Jeff

[nhpoplin]

yes the yamaha cranks as well any multi piece crank done in many engines not just outboards

Yea they definitely need to be welded. Twisted my crank in my yamaha 50 over this past weekend. :mad:

[Roflhat]

Yea they definitely need to be welded. Twisted my crank in my yamaha 50 over this past weekend. :mad:

Wow, i was under the impression the yamaha ones were much stronger

[Rabbitdundied]

Educate me on this. When you say weld a crank are we talking spot weld or running a substantial bead? Also does anyone actually lighten their cranks to get more performance?


Sent from my iPhone using Tapatalk

[proprider01us]

Look at post #22, it shows where Tim Kurtz did the spot welds on my Yamaha crank. The cranks are a press fit and could reposition under extreme loads. Spot weld makes sure that does not happen. Don't know anything about lightening cranks, but you certainly can lighten the flywheel to help the crank loads and offer a bit more acceleration. Post #22 is the only picture I took of the crank welding. Hope that helps.

Educate me on this. When you say weld a crank are we talking spot weld or running a substantial bead? Also does anyone actually lighten their cranks to get more performance?


Sent from my iPhone using Tapatalk

[sabine river killer]

4 wheelers too 56739

[Roflhat]

Having problems with the carbs and the throttle setup from the tohatsu not wanting to work together. The way the linkage on the yam carbs is means they're at almost wide open throttle when the tohatsu tiller is at idle.
Took off the carbs to compare, not quite sure how to sort this?
http://i1013.photobucket.com/albums/af256/Roflhat/IMG_2540.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_2540.jpg.html)
The roller on the top LHS of the carb is the problem.
I've tried taking the assembly from the 50 carb over to the 70 but it's much shorter and won't work. Can't see an obvious solution other than welding the 50 setup onto the 70 one?

[Fast Fred]

reshape the throttle cam.

[Fastjeff57]

If you are careful, you can remove the arms and switch them. Epoxy them back on.

Jeff

[88workcar]

You have not asked about your next problem. Fuel pump! The Tohatsu pump is on the carb, the Yamaha is not. You will need a pump, any external vacume style pump. The 70 Yamaha one is a good choice. You will need to tap a hole into the intake and install a threaded hose barb. 5/16 is good. You will need to install one in the back of the pump also and run a little hose from the intake to the pump.

[Roflhat]

This is what I ended up doing: http://i1013.photobucket.com/albums/af256/Roflhat/IMG_2549.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_2549.jpg.html)
Had the engine running on the muffs today, works pretty well. Hopefully get out for a run tomorrow.


You have not asked about your next problem. Fuel pump! The Tohatsu pump is on the carb, the Yamaha is not. You will need a pump, any external vacume style pump. The 70 Yamaha one is a good choice. You will need to tap a hole into the intake and install a threaded hose barb. 5/16 is good. You will need to install one in the back of the pump also and run a little hose from the intake to the pump.

Think I've got this one covered. Bought a Mikuni 35l/h triple outlet fuel pump (one per carb). It's from a seadoo jetski or the like. I've drilled a 5mm hole in the intake and tapped it to m6. the barb for that is the only bit I'm waiting for now. I'll post on here if I have any issues!

[88workcar]

good deal!

[Fastjeff57]

Good work. Having done a few deals like that myself, I can attest how tricky it is to do.

Jeff

[Roflhat]

The barb I was waiting for finally arrived so I got my fuel pump setup.
http://i1013.photobucket.com/albums/af256/Roflhat/IMG_2575.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_2575.jpg.html)
Made up a plate so I could mount the pump using two bolts instead of relying on one.