More Hp Out Of A 40 Yamaha

[j nye]

Guys Im New On Here But Injoy All The Info I Get Just By Reading Your Treads Theres Not Much Info About Hp Outboards Out There Unless I Had A 2.5 Merc. My River , Boat Or Walet Wont Hold One Of Them Bad Boys No Way.i Dont Race Well Not Apba Anyway We Race All The Time .see I Need To Get Ahead Of My Buddys We All Have 40hp Yamahas On Wood Strip Boats 13.5 Ft Long Most Are 38inchs Wide With 3/8 Inch Concave Bottoms About 63mph On Strait Smooth Water And About 45 Through A Very Curvey River They Are Blast To Run . Tiller Handle , Merc Chopper Props 10-1/4 X 18 Pitch, Boat Weights About 220 Dry. I Have 50 Hp Carbs And A 50 Hp Exhaust Tuner . And Yes The Gray Wire Is Cut Any Help On Port Work Or Cylinder Head Work Would Be Appreciated I Have Extra Blocks Heads, Carbs, And Cranks To Work With . Please Help Or At Least Tele Me What Not To Do With The Port Work. Thanks J Nye

[Fast Fred]

finger ports will make more HP, 70hp carbs, bring the boost port up. NOS.
best not to mess with the exhaust hight, bullet nose cone, surface the prop:cool:

[j nye]

I Know About Them Finger Ports Put One In A Yamaha 40 And The Main Jet Size Went Up From .055 To .068 And Had Trouble With The Top Piston Burning Did Everthing I Knew To Stop It But I Got Tired Of Burning Pistons. It Worked For Top End That Thing Would Hall. Hey Whats The Boost Port Is That The Intake Ports. And If So How Would You Shape Them Bad Boys. What About The Exhaust Tuner Or Do I Just Leave It Be. Ihave A Hydro Tect Race Head Also But The Water Pump Pressure Went Down When I Ran It That Thing Is For Comp Use Only , What About The Stock Head Do I Cut It Or Not And If So How Much Cranking Compresson Do Like To See. I Saw That Motor You Bilt On That Voodoo Boat Man Looked Like It Would Hall Buggy Is That A 50 Or 70 Or Some Of Both Thanks Jnye

[Fast Fred]

ok, lookin through the exhaust port into the cyl, on the Yama we got three intake ports, two side tranfurs and one (in the middle of the side tranfurs) boost port. the boost opens later than the side transfurs, escavate it up to the same timein as the side tranfurs, leave a small shelf at the top so the charge rolls out,

:cool:

[j nye]

Thanks Fred Hope This Puts Me Ahead

[quty06]

same motor with you, but never seen an exhaust tuner before.
appreciat it if you can share a pict(s) with us.

[quty06]

Hi j nye

result on your port project? any improvement

[Fast Fred]

gots a 40-50hp case set, i needs to look it over , if it checks out, i'm guna port it up. she will need to be bored, i could have it bored and the pistons fitted, or you could have that done ware you are.

let me know if this works for any body hear.:cool:

[yamonster]

These pics are from 89 - 90. My 40 ran 74mph on radar. I did not know near what I know today. Yes you can make a 40 fly.

[yamonster]

I had a light flywheel, port work, shaved head, cut reed cages, fiber reeds, 50hp tunner modifide, 70 carbs, low water pickup, the prop was a merc chopper 24p that was cut down to 11" and made to resemble a yamaha race wheel. I dominated the waterways around my area. Even came out 3rd place at the draggs in the V4 class out of 6 boats.

[quty06]

89 - 90 you had it that year, and i just goin to make it this millenium era! (20 yrs later)

BTW nice & good speed also.

[Phil McDaniel]

J, Before offering you some info. to help, I need to know 2 things. What type ignition(pack,stator,etc) are you running and where are you from?? Phil

[Mark75H]

He's in Texas :)

[yamonster]

Just keep in mind that set up, and props are more important than th HP numbers. All the basic stuff works well on that engine. Give us all the details of the whole rig.

[markt111]

I had a light flywheel, port work, shaved head, cut reed cages, fiber reeds, 50hp tunner modifide, 70 carbs, low water pickup, the prop was a merc chopper 24p that was cut down to 11" and made to resemble a yamaha race wheel. I dominated the waterways around my area. Even came out 3rd place at the draggs in the V4 class out of 6 boats.

I love reading these old posts, I am picking up a 1992 Yamaha 40 for my Minihawk tonight,

it should be a good upgrade from the 25 Merc!!