Johnson "70mod"

[LittleCharger]

I measured also heads from 30 to 34 and my small chamber 21.
That 190, is ex port in stock timing? I have chamfer, 1.382 from deck.

My motor feels real good when running even its quite worn. White one when bored and built with new pistons 5 years ago wasnt nothing like this now. Think that crank psi isnt the hole truth as you go on higher rews. Big part of the story is scavening and how it works.

I think Ill try little more ign timing when go out next time. A degree or two. IMO my previus PH wasnt up to task, not even if I had limiter taken away, because it was just under that and was hitting occasionally.

Be careful on the timing, the 56er typically does not like more timing, if your looking for top end you don't want more timing

[hupiveneilija]

Okay, thanks! Maybe I leave it 17* where it is now.
If I get more prop somewhere then perhaps with lower rpms.

Think I concentrate on cooling to adjust it little warmer on speed but not much. Reliefvalve spring needs slightly more tension so pressure goes up a bit and flow little less water through block.

Btw looked inside of a plughole and there seems to be pretty much flowmark on piston, so it is on a rich side wich is good.

[zul8tr]

throttle open or closed dont make any difference at cranking speeds, air comes straight back in from exhaust anyway.
ive often measured compression with and without fully opening the carbs and it dont make any difference.
I have even put a plate over the intake to seal it just to see what happened, no difference at all.. there is no explosing sending hot exhaust out in a hurry.
and obviously no one way vale closing the exhaust port, so it realy dont make a difference.
but do it what ever way you want, as long as you get the reading with it cold with no oil or fuel dumped in the bore to give a false reading.

on a 3 cylinder I always double check if its been left a while, but with this just having the pistons and rings out it will not be any sticky rings.

but be good to see how high or low it is.

and to see how high the rpm is , then can get an idea of how long the motor will last..

Probably so for max pressure for electric start engines but I like to see and record all rope overs (no electric starter on my jobs) to judge how pressure builds especially 1st pull and full open matters here and is they way I do it to keep consistent results.

[LittleCharger]

Okay, thanks! Maybe I leave it 17* where it is now.
If I get more prop somewhere then perhaps with lower rpms.

Think I concentrate on cooling to adjust it little warmer on speed but not much. Reliefvalve spring needs slightly more tension so pressure goes up a bit and flow little less water through block.

Btw looked inside of a plughole and there seems to be pretty much flowmark on piston, so it is on a rich side wich is good.

Forgot your were at 17 you could go back up to 19, just wouldn't add any timing past that.

Fat is good til you get everything else dialed in then you can work on jetting

[hupiveneilija]

Forgot your were at 17 you could go back up to 19, just wouldn't add any timing past that.

Fat is good til you get everything else dialed in then you can work on jetting

I thought so also that 19* isnt too much, might be better down low for going on plane. I dont touch jetting at all for now. Maybe little fatter for middle jet is what to do.

[LittleCharger]

I thought so also that 19* isnt too much, might be better down low for going on plane. I dont touch jetting at all for now. Maybe little fatter for middle jet is what to do.

raising timing to 19 would help bottom end

[filthy phill]

I think the low compression is simply because the chambers have been made far too deep.
to be 21cc and made deeper they must be tiny diameter
just shaving the normal heads raises the compression, but making the cups deeper seems a bit strange for someone wanting top end speed and power.


the chamfer on the exhaust ports is correct, everyone puts chamfer on the top of the ports.

what is the new tacho your going to use ? how many rpm is that 10,000 rpm ?

LittleCharger
what is the cc of your heads now ?
and did you shave a lot off or fill the chambers with a bit of metal then machine them to get the smaller area.

when you measure the cc of the head do you fill it upto the chamfer on the head or include the chamfer with plug in ?
I am thinking to include the chamfer on the head with plug in tight ?

I need to find out what the cc of my heads are.


anyone know best way to take th bolts out of a motor that has never been apart since made in 1990 and used in salt (

[filthy phill]

on the cylinder head chamber sizing this is what I have always known.

this is from just one 2 stroke tuning page from Apilia, and they know a little bit about 2 stroke race motors !!!
same thing on every 2 stroke bine forum around. and go karts.

Cylinder-head shape also affects the powerband.
Generally speaking, a cylinder head with a small-diameter, deep combustion chamber and a wide squish band combined with a high compression ratio is
suited for low-end and midrange power.
A cylinder head with a wide, shallow chamber and a narrow squish band and a lower compression ratio is suited for high-rpm power.

so I am not understanding why this was done for a outboard 2 stroke that wants high rpm to go fast.

[hupiveneilija]

on the cylinder head chamber sizing this is what I have always known.

this is from just one 2 stroke tuning page from Apilia, and they know a little bit about 2 stroke race motors !!!
same thing on every 2 stroke bine forum around. and go karts.

Cylinder-head shape also affects the powerband.
Generally speaking, a cylinder head with a small-diameter, deep combustion chamber and a wide squish band combined with a high compression ratio is
suited for low-end and midrange power.
A cylinder head with a wide, shallow chamber and a narrow squish band and a lower compression ratio is suited for high-rpm power.

so I am not understanding why this was done for a outboard 2 stroke that wants high rpm to go fast.

Should I take it away of my engine because originally it was ment to be on bone stock fishing motor and make it more powerfull and crispier throttle response on midrange under 6000rpm? In a real life boating.
I know what it was made for before I got my hands on it. Saddly it works on my case too although its in a wrong use in my hands.

Phill You have to open your mind a little bit, not everything go by the book. There are people who are curious to try different things. Even here where hell freezes over.

That tachmeter for 8k I purchased yesterday dont work on my motor. Its propably for newer motors, cant adjust it 3cyl 2stroke. Have take it back to shop.

[filthy phill]

it is not a case of not trying things out, it is a case of a very well tried and proven thing over and over again, small combustion chambers do not give high speed power,
that is fact proven by major race teams and major engine tuners. and dont forget a race team dont even care what happens to the motor as long as it wins and last
till end of race.

smaller chambers Will give more low speed power/torque call it what you like. would be good for say water ski-ing or wake boarding as the speed is slow.

your small chamber head is not what has given you more rpm, that was the raised exhaust porting and the no limiter electrics..

shame about the tacho, what make is that one ?