Yamaha 2-stroke 50Hp Tuning - Page 2

heffak · 29 March 2018, 21:32

Please Help what 70hp Carbs is best for my 50hp Yamaha?

Roflhat · 30 March 2018, 07:59

Nice work on the exhaust, looks excellent!
I had Yamaha 70hp carbs on my tohatsu 50, the square bowl type. Might depend on your engine, if it’s got round bowls then maybe go for the same in 70hp.

heffak · 13 March 2019, 20:53

Finally I have milled my head.3,5mm

heffak · 13 March 2019, 20:55

The one I will use is the one with 3,5 mm taken off and new squishbands on.

heffak · 13 March 2019, 20:59

More airintake improvements.

heffak · 13 March 2019, 21:01

70 Carbs with 150 Jets and more polishing and porting of intake and exhaust.
Also changed the lower bearing that always is the one most exposed.

heffak · 13 March 2019, 21:13

Now I have tryed my "new" motor and it goes really well but very loud.
It revs 7600 and I need a bigger prop.
The one put on is a Trophy Sport 10/8X15 and its to small.
Anyone out there with suggestions about what to buy?
I was thinking of buying :

https://www.ebay.com/itm/Mercury-25-...1:pf:0&vxp=mtr

I really dont know much about props so please help.
Do you have any thoughts or want to sell please let me know.

Cheers Fredrik

Limecc · 14 March 2019, 00:53

I'm curious why do you believe getting rid of the autolube will save you power? Certainly lots more hassle to premix for an umeasurable gain in hp.
Also isn't it a bit hit-and-miss how the new main jet size was determined? Also never heard any of the 80's two stroke tuning firms recommending removing the reed stops. Important that they are there to prevent metal fatigue - you are on borrowed time.

Shameless sales plug if anyone wants to buy my Yamaha 350 YPVS Stan Stephens Stage 3 kit comprising barrels, heads, 36mm reverse slide TZ350 Mikuni carbs with YZ125 6 petal reed blocks with adaptors and Swarbrick expansion chambers complete with jetting kit and modified airbox and throttle cable then I might be open to offers. I estimate it was good for 70hp about the same performance as my Suzuki RG500. Pipe design (specifically stinger dia and length) controls peak revs, power band was 10K to 13K instead of 6K to 9.5K rpm, welded crank essential. Marine engines are in a very low state of tune in comparison. Seems much tuning knowledge is lost nowadays but us old timers still have it lol.

Roflhat · 14 March 2019, 07:29

Loving your work, the heads look excellent. The cowling vent looks like what I had on my old tohatsu. What sort of speed are you getting with the 15p trophy? I've tried one of them on my 70hp and the tohatsu 50hp, ran well but a bit too much bow lift and not enough speed, decent torque though. If you are running dual stage reeds you don't need the stops, if they are single stage I would recommend leaving the stops on especially at the RPM you're getting now.
Removing the autolube is a good idea, if you are pushing the engine higher than standard it needs more oil for the bearings.

I would avoid Ron Hill props, they are hit and miss, some are good but most are bad. Some just need work but others are so far out they cannot be fixed, different pitches between blades etc. not good quality.
I've got one Forge V1 left I would sell, 11.25x18p 13 spline. Fully blueprinted, heat treated ready to go

heffak · 14 March 2019, 20:27

Thanks Roflhat for your feedback, really appreciate your thoughts.
Your prop looks very nice and perhaps you can make contact and give me your price?

heffak@hotmail.com

The one Im using today is Trophy Sport 15P and my estimated max speed is around 45 knots.
Dont know if my reeds are single or dual stage? Think they are dual but maybe you can tell?
My reeds are Boysen B322 and you can have a look at the pictures.

Cheers heffak

heffak · 14 March 2019, 20:59

Close up second or single stage?
Must be dual stage?

https://www.youtube.com/watch?v=YeR9BMVkjgs

heffak · 14 March 2019, 22:09

After watching this Youtube video Im pretty sure my Boysen Reeds are DualStage Reeds?So no need for reed stops.

Roflhat · 15 March 2019, 07:24

Yes think they are dual stage so you are ok. I've sent you an email just now about the Forge V1, 45 knots is very good for a trophy sport, will be interesting to see what you can do with a cleaver

heffak · 23 March 2019, 22:06

Looking forward to this summer soon I will get my new:

Forge V1 11.25x18p.

berat · 13 June 2019, 09:41

heffak hi,
any new developments? did you figure out to cut rev-limiter?
I've got same type engine 40hp mariner long 2006
I'm having trouble to reduce idle speed. I need to figure it out, gear shifting is like sledgehammer on the transom.

Roflhat · 14 June 2019, 08:06

Idle adjustment is usually a vertical screw on the top carb, just unwind it a bit to reduce idle.
If you are running solid hub props it's best to turn the engine off, put it into gear and then start it again, otherwise there is a lot of force going through the gearbox

berat · 14 June 2019, 09:20

Quote:

Originally Posted by Roflhat

Idle adjustment is usually a vertical screw on the top carb, just unwind it a bit to reduce idle.
If you are running solid hub props it's best to turn the engine off, put it into gear and then start it again, otherwise there is a lot of force going through the gearbox

Thanks Roflhat, i will try that. Also your Thundercat Thread is in my favorite bookmarks. That engine strip down pictures helped me a lot. Mine 40hp mariner 3 carb is exacly same with your previus engine tohatsu.
My prop is quicksilver 12 1/4 x 9", with a Flo-torq square hub, do i need to wory about gear case?
The first owner used this engine on a panga boat but Mine is 300kg fiberglass bass boat style. Thats sure i need a bigger pitch propeler.

Roflhat · 18 June 2019, 20:43

Sorry for the delay, glad you're enjoying the thread!
You're pretty safe with the flo-torq, or any other rubber hub prop although the hub will need replaced more frequently if you're shifting at high rpm. Definitely better to get the idle speed sorted to prevent gearbox wear though

neilharrison_253 · 21 October 2020, 05:21

Quote:

Originally Posted by heffak

70 Carbs with 150 Jets and more polishing and porting of intake and exhaust.
Also changed the lower bearing that always is the one most exposed.

Hi Heffak

Just come across this thread and was a great read. I am about to do a few mods to my 50HMHOS outboard. Keen to understand how the 70 Carbs with #155 jets worked or if you rolled back to the standard carbs. Also, have you done anything else. i.e. Flywheel lightening?

Cheers
Neil

neilharrison_253 · 21 October 2020, 05:23

Quote:

Originally Posted by heffak

Looking forward to this summer soon I will get my new:

Forge V1 11.25x18p.

How did you find this prop. Have looked at them a few times but not seen many comments. Keen to know your thoughts