help modding a 40hp twin yammy

[serious3]

lads i'm looking for a bit of help and advice on a few simple mods i can make to my 40hp yamaha twin (6E9 model). ive had a root around the "normal" outboard forums and the advice is always "if you want more power buy a bigger motor" thing is i'm unemployed so thats out the window!
the motor is on a zapcat (thundercat, dux hammerhead type) and all my mates have the ubiquitous tohatsu 50.
i'm not after huge power id just like it to rev quicker and harder and get a few extra horses, i was thinking of lightening the flywheel for starters then maybe a set of reeds, possibly dumping the choke flaps and upping jet sizes slightly. has anyone else any ideas that can be done on the cheap by a reasonably competant man in a workshop?
thanks in advance!

[DeanFHobart]

Mill the head to get more compression and increase the ignition timing before top dead center for starters. Use a little more oil.

And as you said.... lighten the flywheel some. Balance it.

[serious3]

hallelujah!! a reply to my question that doesn't start with "trade your motor" .... she's running at 135psi at the moment. how much is the norm for milling the head? presume a couple of thou would do it! i'll start with the flywheel tommorrow after i've been out playing and got a base line figure on the gps. thanks for the reply and keep em coming!!

[byrdsperformance@tds.net]

If your saying a couple as in removing (2) thousand's ,
it wont be worth the time an gasket's.:eek:

[serious3]

so how much would you remove then? :)

[curbman]

take 8 to 10 thou

[88workcar]

I would go thirty thousands right off the bat. But before you do anything check the clearance that you have right now. Make sure the head is bolted on with a used gasket and insert a piece of soider in the spark plug hole till it reaches the side wall of the cylinder. Then slowly turn the flywheel by hand till it compresses the soidier. The remove it and mic. the smashed spot to see how thick it is. This should be kept around .030. Any less and you will get into trouble.
Those carbs are plenty big on that engine, but mic them too, the backside, let us know. The reeds stops can be spread open also. If it is the same block I have a few 2 cylinder 60 powerheads here.

[fs5]

so how much would you remove then? :)
i dunno about the twin cyl 40hp,but over here they skim .060 off the 50hp 3cyl motors.probably best to stick with 88workcar post ,you can always skim it a bit more.

[serious3]

now were getting somewhere! thanks lads! erm daft question 88workcar what do you mean by mic? think that i'm losing something in the translation this side of the atlantic.....!!!
i was actualy thinking about removing the reed stops altogether

[byrdsperformance@tds.net]

:)These are mechinist's type mesureing tool's.
You will need one of these to check solder or clay once it's squishied out.

[serious3]

ah (light bulb goes on) mic as in micrometer!!!! i'll pull the carbs during the week and measure the bore size and post up jet sizes etc. while the carbs are off i'll look at the reed stops as well.

[byrdsperformance@tds.net]

It's a good time to install composite reed's .
Steel reed's can break an have resulted in some wiped out engine's.
Composite reed's are some performance gain an safer .if one break's.

[Ballistic]

i dunno about the twin cyl 40hp,but over here they skim .060 off the 50hp 3cyl motors.probably best to stick with 88workcar post ,you can always skim it a bit more.

workcar's point is the way to go.. .060inch? I wouldn't dare to take that much off.

[OUTBOARDER]

Are you allowed to run a low water pick up? go there first and get a clever from Ron Hill.
cyl head is most cost effective first mod, usually, most outboards are made to run third world low octaine gas. remember cylhead geometry, cooling,ign timing and jetting must be all taken into consideration along with a half dozen other things.

What are the rules?

A two cylinder will never make as much power as three cylinders unless you add a expansion chamber and port it until you can here chinese comin out of it!

Once again what are the rules?

[serious3]

with the standard 15p mariner/yammy ali rabbit ear prop i was doing a gps speed of 45.9mph, not bad for a 40hp twin i think! going to borrow a semi cleaver type and see what she does then!

[OUTBOARDER]

with the standard 15p mariner/yammy ali rabbit ear prop i was doing a gps speed of 45.9mph, not bad for a 40hp twin i think! going to borrow a semi cleaver type and see what she does then!

Get a low water pick-up so you can raise the motor, several mph gain..
Do have rules, and picks?

[88workcar]

way back in the day I have shaved .120 and just grinded where it touched on a 3 cyl 40. On my 90 we have cut .250 but that is with a machine shop cutting new squish in it afterwards. What boat is it on put up a picture, that is great speed.

[serious3]

ill be out later and ill get pics then for you, there are no rules as i'm not racing!

[serious3]

one thing i do think i have to change though, i think i have too much positive trim on the motor as flat out she was starting to ventilate, i'm gonna try a 3/8th shim in the motor clamp at the top of the transom, it might loose me a mph or two but will save me over revving. according to the prop calculator over on i**ats i'm pulling 6300rpm with that prop at that speed

[88workcar]

there are no rules as i'm not racing!

This how I like it LOL

[serious3]

few pics of the boat! its about 13feet long and 7 feet wide and wieghs about 220lbs they are rated for up to 70hp:eek:
and for those that want more info
http://www.zapcat-racing.com/Home.aspx ( if i cant/shouldnt post links please feel free to remove it!)

[88workcar]

You need a cleaver and a low water pickup. ASAP!!!!!

[microbream]

so how much would you remove then? :)

to give you an example i took 1mm (40 thou) of my twin cylinder, this increased the compression from 115 to 190psi. I run 95 octane at 30:1 and she runs hard!!

Two strokes are all about the squish clearance, my initial squish was 2.2mm, it is now 1.2mm, i could have got it down to say 0.8mm but it is risky when you take into consideration all the engine tolerances. IMO 200psi is as high as you want to go, this is what mx bikes have and run hapily on 95 octane.

seriously it is a quick cheap mod that you can feel.

look up these guys as well they know all about thundercats!
you will find many are running rons cleavers and topping 100kmh!

http://www.thundercatinflatable.com.au/forum/

[serious3]

You need a cleaver and a low water pickup. ASAP!!!!!

your preaching to the converted! trouble is i reckon there are only maybe 15-20 low water pick ups in the country and the smallest would be on a 175merc, as for finding a small cleaver or semi cleaver forget it!!

[Ballistic]

to give you an example i took 1mm (40 thou) of my twin cylinder, this increased the compression from 115 to 190psi. I run 95 octane at 30:1 and she runs hard!!

Two strokes are all about the squish clearance, my initial squish was 2.2mm, it is now 1.2mm, i could have got it down to say 0.8mm but it is risky when you take into consideration all the engine tolerances. IMO 200psi is as high as you want to go, this is what mx bikes have and run hapily on 95 octane.

seriously it is a quick cheap mod that you can feel.

look up these guys as well they know all about thundercats!
you will find many are running rons cleavers and topping 100kmh!

http://www.thundercatinflatable.com.au/forum/

Are you sure? 190 sounds a bit much for just 1mm off the head...

Serious3.. I know you don't wanna hear it.. but get a 3cyl Yamaha or Tohie and spend some money on that to get it modded. I think putting money into this engine is just throwing it away.
http://www.youtube.com/watch?v=ASnj4l3NliE

[serious3]

sensible head says do just that! BUT there is a little bit of me that gets a kick out of modding something like my twin, i can get the head skimmed for very little and lightening the flywheel and balancing can be done by me, besides that i'd love to see peoples faces when they cant shake me off! if i can get a s/s prop that i'm happy with then i reckon 52-55mph is possible with the few mods i can make and still keep it reliable!

[microbream]

Are you sure? 190 sounds a bit much for just 1mm off the head...

Serious3.. I know you don't wanna hear it.. but get a 3cyl Yamaha or Tohie and spend some money on that to get it modded. I think putting money into this engine is just throwing it away.
http://www.youtube.com/watch?v=ASnj4l3NliE

yeh 185-190 is what it puts out, maybe i took off a tad more like 1.5mm
all depends on the cylinder stroke and bore to how much you will gain.

Probabaly the safest method is to measure the squish height and machine enough off the head to acheieve around 1mm, the comp you will get is the comp you will get
but remember both cylinders may not be identical so check both

[serious3]

well after some delay i took off what i could from the flywheel last night and it weighed in at aboult a pound!! seems small but should make a bit of a difference. picked up a ballistic prop as well, semi cleaver type 15p 10.25" dia. i should be out saturday morning if the weather holds so i'll post up some figures then!

[serious3]

can anyone recommend a set of reeds for this motor? (6E9) ive had a look around but cant seem to find any?

[Lil' Blue Rude]

Chris Carson probably makes a set of reeds for it.

[serious3]

Chris Carson probably makes a set of reeds for it.

spot on thanks!! just emailed him so we'll see what the response is!

[serious3]

well chris has reeds for me so ill order them on payday (next thurs) and we'll see what happens!