K & B 3.5 Move from 25% to 50% Nitro

[h20ski]

I'm an newbie. I have a stock K & B 3.5 motor, TS@, Octura 440 and Wildcat 20%. The boat is lots of fun and runs great.

If I want to increase the performance of the boat by running higher nitro, what types of adjustments will need to be made? I know that I'll need to reset the needle valve. Will I also need to adjust the compression ratio with 50% nito. I've tried reading up on squish bands and compression ratio's but I'm a little lost. Everything that I've done so far has been on my own and the guidance of this website. Thanks

 

[Jerry Dunlap]

A TS@?

If the engine is a K&B 3.5ss Gold Head, you might want to check to see if there's a head gasket. If there is, remove it and that will lower the head clearance.

Other than that, I personally think you'd be best off just to work with the hull and prop settings using the higher nitro. If you like Wildcat fuel, I'd recommend the 55% or 65%

JD

 

[h20ski]

Typo Top Speed 2

The motor is an older, stock 8907. Its not a gold head

 

[Geraghty]

Typo Top Speed 2

The motor is an older, stock 8907. Its not a gold head

Open the needle a ton [say a turn and a half to two turns to start] and go run it and find a new needle setting.

When you go to to 60%+ you will need to go a lot richer than you are now.

If you have the tools and know how,set the head clearance at .012".

 

[h20ski]

Typo Top Speed 2

The motor is an older, stock 8907. Its not a gold head

Open the needle a ton [say a turn and a half to two turns to start] and go run it and find a new needle setting.

When you go to to 60%+ you will need to go a lot richer than you are now.

If you have the tools and know how,set the head clearance at .012".

Do you know if there is a previous post or an article on the web on how to set the head clearance?

Thanks

 

[Ronald van Essen]

If I am correct, you need to adjust the angle too. I had to do it on the Villain with K&Bss, just a little negative.

Ronald.

 

[Jerry Wyss]

Do you know if there is a previous post or an article on the web on how to set the head clearance?

Thanks

If you want to set you head clearance, you first have to know what it is now so

you can get to where Rod Geraghty said you need to be.

If you don't have the "tools" as people mentioned to do this job, there is a product called

"plasti-gage" sold by most Auto parts stores, especially NAPA.

Your engine will probably have "high" head clearance as it is, Plasti-gage in the

"Yellow" package will measure from the high 20 thousandths down to 10 thousandths,

"blue" package from 9 down to 4 thousandths.

All you have to do is break off about a "inch and a half" piece, bend it in an "L" shape,

put one end thru the plug hole (with engine assembled) turn the flywheel so the piston

comes up and smashes the plastigage and just measure the "flattened width" with the

scale on the side of the package, or with a set of calipers. Easy and accurate.

I also wanted to say that you can learn how to drive , adjust all the engine movements,

find the right range props and have allot of fun with a mild engine. I did that with a

"piped only" Thunder Tiger, 30% car fuel for two years, all with 23 thousandths headspace.

The last thing you want is a "maximum performance motor" while trying learn all the other

important stuff.

 

[Marty Slater]

hay Rod is this .012'' head clearance good for 60 to 10 percent. or does it change any one why or the other piped or stock

Marty

 

[Mike Larson]

Marty... get the gold head to me, Ive the tool to set it to twelve.... or, ill get it to ya... Throwing a shim in like we did was a band aid fix sunday.. I had no mic to gauge even the thickness of the shim... If, you are dinging plugs as badly as you were on 20 or 30% the motor needed a shim so I gave it to ya......... A performance issue with the clearances,... the motors are all different, I take mine down to 8 if I even feel the need to at all..... All else being equal, and Ill throw this out, the clearance down increases the compression ratio of the motor increasing the chances of detonation, and all other bad things.... other things like timing, etc have to be correct to allow harmony with the right clearance...... Im not Rod geraghty, but, if a motors bitin plugs on 30% somethings wrong, and my first thing is to shim the head, or, I start lookin at bearings..... I ran that motor on rod's boat with the short Irwin pipe and 45% so, if its an exhaust limiting issue from the can you have on it, we may have to change a little..... I stressed sunday I thought it wasnt R'in up like it used to, hence unloading the prop.... Sombody with some motor knowledge jump in, as, Im able to accomplish the task, just need the knowledge to accomplish the goal..... thanks Mike

 

[Jerry Wyss]

" I stressed sunday I thought it wasnt R'in up like it used to, hence unloading the prop.... Sombody with some motor knowledge jump in, as, Im able to accomplish the task, just need the knowledge to accomplish the goal..... thanks Mike "

Well I'm not RodG either, but, it would be helpful if you could blurt out which specific motor

your running. Then somebody on here may have measured that engine and could even

have it in a Engine Analysis Program (or similar) and could tell you where to go.

What Your doing is "shootin' duck's in the dark". Yes, you can "over compress" and see a loss

in performance with the same prop you used before when it ran good.

Guessing, can be endless but knowledge can lead you to a solution and "searing" performance.

 

[Geraghty]

Marty... get the gold head to me, Ive the tool to set it to twelve.... or, ill get it to ya... Throwing a shim in like we did was a band aid fix sunday.. I had no mic to gauge even the thickness of the shim... If, you are dinging plugs as badly as you were on 20 or 30% the motor needed a shim so I gave it to ya......... A performance issue with the clearances,... the motors are all different, I take mine down to 8 if I even feel the need to at all..... All else being equal, and Ill throw this out, the clearance down increases the compression ratio of the motor increasing the chances of detonation, and all other bad things.... other things like timing, etc have to be correct to allow harmony with the right clearance...... Im not Rod geraghty, but, if a motors bitin plugs on 30% somethings wrong, and my first thing is to shim the head, or, I start lookin at bearings..... I ran that motor on rod's boat with the short Irwin pipe and 45% so, if its an exhaust limiting issue from the can you have on it, we may have to change a little..... I stressed sunday I thought it wasnt R'in up like it used to, hence unloading the prop.... Sombody with some motor knowledge jump in, as, Im able to accomplish the task, just need the knowledge to accomplish the goal..... thanks Mike

A motor not "R'n" up doesn't necessarily mean you have a motor problem especially if you were running an "X" series or Prather prop.Those props need to be up on the tips to "R".Raise the motor 1/16" and see if the motor will "R".Any motor has to be high enough for any prop to un-load and "R".

In your case,with the motor eating plugs,and if the deck was set at a reasonable height,I would guess you have something else wrong in the motor.Like the man said,I would suspect the bearings but a leaky PTO will act the same way.I would also check the obvious like are all the powerhead screws tight.K&B 3.5 outboards,on occasion, like to loosen the front housing screws.I have also seen K&B crankcases with hairline cracks just under one of the motor mount lugs or at the bottom of the crankcase right on the casting parting line.

I set all head clearances by motor application and the proper compression ratio for that application.That approach comes from years of emperical testing,lost races,broken parts and several hundred "sit-down Bon Voyages" in a retreive boat.

I don't set CR's by the % of nitro in the fuel I am using or if the motor is piped.In the big scheme of things,choosing a CR using that criteria is a waste of your time and resources.Maybe after you learn everything there is to know about props,set-ups,pipes,bottom blue-printing,hydro-dynamics,driving stratagies,etc,etc,etc,you may want to launch a test effort as to how different nitro fuels and oils respond to different CR's.

A standard water-cooled K&B 3.5 sets at .012".A Gold head 3.5SS will set at .010" for equal compression ratios.That will set the CR's right at 9.7/9.8 to 1.

Thats a great number for "any" outboard application.

Rod Geraghty

 

[Marty Slater]

thank you for coming back

30''JD wof new boat this year

KB3.5ss outboard stock i think

Mark S cut an cupped X440

25%fuel

prop shaft maybe 3/8 above sponson bottom [higher then i ever used before]

is there a head clearance that is good to start with or does it change with fuel pipe

Marty

 

[RodneyPierce]

thank you for coming back

30''JD wof new boat this year

KB3.5ss outboard stock i think

Mark S cut an cupped X440

25%fuel

prop shaft maybe 3/8 above sponson bottom [higher then i ever used before]

is there a head clearance that is good to start with or does it change with fuel pipe

Marty

I set all head clearances by motor application and the proper compression ratio for that application.That approach comes from years of emperical testing,lost races,broken parts and several hundred "sit-down Bon Voyages" in a retreive boat. I don't set CR's by the % of nitro in the fuel I am using or if the motor is piped.

There yah go marty, read the above there.

 

[Marty Slater]

thanks for highlighting that for me Rodney but i think you should have highlighted it a little far down :lol: the Gman also said for water coled .012 an for air coled.010 i think that is the answer i was looking for

Marty

 

[RodneyPierce]

thanks for highlighting that for me Rodney but i think you should have highlighted it a little far down :lol: the Gman also said for water coled .012 an for air coled.010 i think that is the answer i was looking for

Marty

Marty, read abit closer, you asked if it changes with fuel or pipe, Mr. Geraghty states that he doesnt determine compression based on pipe or fuel. he bases it on an individual motors specs if you will :lol: :lol: :lol:

 

[Marty Slater]

oh i see you mean like water or air cooled for KB3.5 :lol:

Marty

not trying to reinvent the wheal just trying to get a base line for 3.5 KB outboards for fun running you know

Marty

 

[RodneyPierce]

oh i see you mean like water or air cooled for KB3.5 :lol:

Marty

not trying to reinvent the wheal just trying to get a base line for 3.5 KB outboards for fun running you know

Marty

you know I am all about reinventing the wheel man! I think a few of your boats run great! That green one with the KB yoru working on now needs a little help, but im sure it will be rocking again also here very soon. Let me know if you get out in the garage here this week sometime, as i got a few things I need to do on the villain... Like replacing that bottom motor plate that i ripped off, and plugging that hole in the side. Also was gonna see if you had some thin aluminum from yoru favorite collins store, and beef up this transom with it.

 

[Ronald van Essen]

Also I did go from 25% to 50% nitro, ( just for your info, 50% nitro is about 100 dollars a gallon overhere).

Yesterday used a quater of a gallon, without improvement on performance. On 25% the Villain/K&Bss flies, just over 40 mph and nice and steady.

50%: did some engine changes, opened up the needle a lot, no more dying out ( to lean) on the water; nice pickup on the throttle. Raised the engine just a tiny bit more, adjusted the angle etc.

The only thing I didn't touch was the shims. There is one just under the head, and one under the sleeve. I don't have equipment to measure the clearance or squisband.

I made one change at a time and the prop is the grim1440. Checked for leakages on fuel lines etc.

Any suggestions????

Btw: does starting the outboard engine gives you an idea on the correct setup of the engine?

Ronald.

 

[Jerry Wyss]

Well Ronald, I don't know K&B 3.5's very well but your right, more needle (out) with

the extra nitro. Nitro creates oxygen when it burns, so balancing with more fuel is the

right direction. Another way to get more fuel in there is to trade "Less water for more fuel".

Pinch the water flow down and you can open the needle some more.

Just so you can understand the principle,, Full water flow forces you to lean the needle to

heat the engine up enough for a good rate of burn so everything runs right.

Cut down the water (will heat it up) which forces you to balance it with more fuel, giving

you more power, more lubrication and an engine that has swelled properly to give a better

piston /sleeve fit (more efficient compression). Try it.

 

[Ronald van Essen]

Well Ronald, I don't know K&B 3.5's very well but your right, more needle (out) with

the extra nitro. Nitro creates oxygen when it burns, so balancing with more fuel is the

right direction. Another way to get more fuel in there is to trade "Less water for more fuel".

Pinch the water flow down and you can open the needle some more.

Just so you can understand the principle,, Full water flow forces you to lean the needle to

heat the engine up enough for a good rate of burn so everything runs right.

Cut down the water (will heat it up) which forces you to balance it with more fuel, giving

you more power, more lubrication and an engine that has swelled properly to give a better

piston /sleeve fit (more efficient compression). Try it.

Jerry

Thanks, but the K&B ss is aircooled.

Ronald.