yamaha 70 ces

[mobil1]

I want to get the flywheel lightend, and have a few questions about it.
It has 3 rivets in it, when i drill these out will it seperate the ring/gear from the flywheel?
Also my engine has the 6j2 pistons in it, as I have read these are not the best.
How long will these last? Engine has not much hours...

Engine will be ported and 90hp carbs.

http://i166.photobucket.com/albums/u82/OS-tunnel/flywheel_zps67f92ee4.jpg



Grt

[mobil1]

Or if someone can offer me a link to an exploded view of the flywheel...

[mobil1]

To me it Looks like the rivets holds the starter gear in place...
If you have experience with these motors feel free to post...

Im planning to drill the rivets out, machine the starter gear thinner myself.
Then let someone cnc machine circular forms in it to lighten it some more.
Make the rivets self and press it back togheter.

[phillnjack]

so your just going to make it a 90hp then ?
isnt it just the carbs that is the difference in the engines ?

Dont forget when you lighten the flywheel you will need to re-balance with the starter ring back in place.
a lighter flywheel will cause a lot of differences, especially at slower speeds.
if its purely a drag race engine then fine, if you use it for recreation its not a good idea at all.
It would be cheaper for the factory to sell the engine with a lighter flywheel, !!!!!!!!!!!!

i can never understand why people buy new engines that are just big engines with small carbs.
when secondhand yes its fine as the engine will probably never have been tested to its normal limits.

phill

[Fast Fred]

the starter ring is pressed on the hub, the rivets hold the rope ring on . weld the crank or lose the press. the stock high ring pistons are ok, i was not able to get new rings for that piston, once the rings wore out i'd change out the pistons. 17-18deg MAX advance, pull to 7800rpms, not the same as a 90hp powerhead.:cool:

[mobil1]

Got the flywheel back today, shaved 1.2kg of the total wheight.
If you want, it can be more... tomorrow i will balance it.
Also mounted the 90hp carbs on the intake and matched them together.
Soon i will start the porting work.


http://i166.photobucket.com/albums/u82/OS-tunnel/IMG_1057_zpsca112b40.jpg


http://i166.photobucket.com/albums/u82/OS-tunnel/IMG_1070_zpsf203da3c.jpg


http://i166.photobucket.com/albums/u82/OS-tunnel/IMG_1056_zps14d258a4.jpg

[Fast Fred]

brush out the 70 intake to fit the 90 carb base gasket, i'd chuck the choke plates and the reed stops, you will need to make some room for that bottom carb bowl in the tray:cool:

[mobil1]

slowly building further on the engine.
Made a portmap, squish, cc of each cilinder. Determind the height of the ports, compression ratio and now im starting to shave the cilinderhead.
It is a strange cilinderhead, combustion chamber off center.
Don't know the right words to explain bt the ones who are familiar with these engines will know what i mean.
How did you make the shape of the piston dome back in correct place?
I was planning to make center on the mill using the outskirts of the waterjacket.
But the shape is out center.
have the cutting tool as good as possible in the center now, but i'm curious about other experiences.

The 70hp intake is also mod to fit the 90hp carbs.
Tray will be the last thing:)

[Roflhat]

What did you do to make the carbs fit? On mine the throttle roller is on the middle carb on the 90 carbs but the bottom one on the 70. Did you just swap the middle and bottom carbs and the chokes?

[Fastjeff57]

Glad I'm not sitting a few feet away from that potential grenade!

Jeff

[Fast Fred]

i have sat about 3ft away from that style, turnin it into the 8's. only lightened the ring gear. it's when you clean off the alu, on like an OMC wheel, it weakens the hub, lowers the integrity of the G' force thresh hold, or the point at which they come apart.

[Roflhat]

Does the lightened flywheel make a big difference on the CES? I'm going pull start only so I could remove the ring gear completely

[Fast Fred]

just lets it spin up a small small small bit faster, makes it jittery at low speed. ive never ran a 70 hub only, have ran a 50hp hub only, there is some clout to the idea that the ring gear reinforces the hub on that style. ? about 60hp tunnin 7's just the hub was good. more power and turnnin faster i can't say if it would stand up.

[Roflhat]

Ok, I'll probably leave the flywheel for now. What gains are there with the 90 carbs? I've got a set of round bowls which I can put on but I don't want to lose any bottom end

[Fast Fred]

90 carbs need a welded crank, round bowls need a hole in the tray to fit, air box, choke plates, reed stops go in the trash. the intake needs to be opened to the size of the 90 carb base gasket, 8-9hp gain, pull the 165 mains out of the 90carbs pull the 160's in out of the 70hp carbs put them in the 90 carbs. you won't notice any low end loss, make new throttle cam.

[Fast Fred]

there is a shim plate on the intake, it needs it or the crank will hit the reed blocks and she will lean out and Boom,

[Roflhat]

Thanks Fred,
Sounds like a decent gain from the carbs. I had a look at them and it looks like the mounting bolts are different patterns? It doesn't have an air box, I'm getting some velocity stacks for it. The reed stops are still on but I'll remove them when I put in the CCM reeds. Not sure about the choke plates, I quite like having chokes. Do you swap the throttle roller on the 90 carbs? Mine have it on the middle carb whereas the 70 is on the bottom carb. Do you just swap the carbs and chokes about?

Thanks for the tips on jetting and the shim, saves a lot of hassle! Have you got any photos of your throttle cam?
I'm getting a billet head for it with positive squish, think I'll leave the ports alone for now. The crank will be getting welded at the same time

[Tiller guy]

Thanks Fred,
Sounds like a decent gain from the carbs. I had a look at them and it looks like the mounting bolts are different patterns? It doesn't have an air box, I'm getting some velocity stacks for it. The reed stops are still on but I'll remove them when I put in the CCM reeds. Not sure about the choke plates, I quite like having chokes. Do you swap the throttle roller on the 90 carbs? Mine have it on the middle carb whereas the 70 is on the bottom carb. Do you just swap the carbs and chokes about?

Thanks for the tips on jetting and the shim, saves a lot of hassle! Have you got any photos of your throttle cam?
I'm getting a billet head for it with positive squish, think I'll leave the ports alone for now. The crank will be getting welded at the same time

All of the throttle shafts should interchange. I just went through this with my little Yamaha.

[Roflhat]

All of the throttle shafts should interchange. I just went through this with my little Yamaha.

Excellent thanks

[Fast Fred]

just a 70hp gasket set, on the rings, the stock ces pistons run a thin ring high up close to the crown, never could order them rings. on the ces head, with a nose cone on a tunnel inflatable it will push the water plugs out of the head, i would take the extra washer off the head bolts, make a cover plate for the head (same thickness as the washers), that keeps the plugs in.

[Roflhat]

just a 70hp gasket set, on the rings, the stock ces pistons run a thin ring high up close to the crown, never could order them rings. on the ces head, with a nose cone on a tunnel inflatable it will push the water plugs out of the head, i would take the extra washer off the head bolts, make a cover plate for the head (same thickness as the washers), that keeps the plugs in.

Cheers Fred,
yeh ordered a gasket set today, tried to get the rings but they are discontinued with no equivelent. Have you tried Wiseco pistons in it?
I was thinking about getting a LWP nose cone. I'm getting a billet cylinder head made by TSR, will i still have to make a cover plate?

[Fast Fred]

ya always used wiseco's, in every thing. would have to see the head. carefull not to bottom out the head bolts and or to short is also a problem i've seen, eather one strips the case, torque on the head is like 18lbs i'm thinkin.

[Roflhat]

Cool thanks.
Here's a couple photos of the head -
http://i1013.photobucket.com/albums/af256/Roflhat/IMG_8686.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_8686.jpg.html)
http://i1013.photobucket.com/albums/af256/Roflhat/IMG_8687.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_8687.jpg.html)
It comes with new bolts too, custom stainless ones.

[Fast Fred]

stainless is weak, grade 2, the stock ones are chrome plated steel, grade 5. the stainless bolts will react with the alu' and weld them self's together, = snap. nice lookin head, should be good to go, if the squish is pos', then you can lean on the main jet size.

[Roflhat]

stainless is weak, grade 2, the stock ones are chrome plated steel, grade 5. the stainless bolts will react with the alu' and weld them self's together, = snap. nice lookin head, should be good to go, if the squish is pos', then you can lean on the main jet size.

Ok, I may just run the stock ones then thanks. Yeh it's got positive squish, on the tohatsu 50 there was around 1000 rpm gain.
I'll try the 160 jets in the 90 carbs first and see how it goes from there. Have you got any photos of your throttle cam for the 90 carbs on the 70?

[Orion Racing Team]

cool man

[Roflhat]

Do you get any smaller gearcases for the 70ces? Was looking at bass or SST lower units, the 70 one seems fairly chunky

[Roflhat]

Anyone have experience testing different CC head chambers on the ces?

[Fast Fred]

yes, what are you lookin to do?

[Roflhat]

yes, what are you lookin to do?

Hey Fred,

after all round power, engine is ported with 90hp carbs. The TSR head ive got has removable chambers so I could draw up some new ones and have them CNC'd
I've heard 34cc is decent, TSR tells me the ones I've got are 37cc but it's only at ~135psi with that head

[Fast Fred]

factory CES is about 28cc, the head is porous so it maybe more or less, you are about at the end of pump gas at 28cc or 150 -155psi. there is no gobs of hp there, helps the snap on the low end

[Roflhat]

I run super unleaded here in Scotland, 97 RON

[Fastjeff57]

That's not thrifty! I thought Scots were thrifty?

Jeff

[Roflhat]

haha, its hard to go fast for cheap!

[Fastjeff57]

Someone once wrote: "Racing costs money. How fast can you afford to go?"

Jeff

[filthy phill]

97ron is roughly 92 usa octane the best stuff to get over here on the cheap is Tesco momentun 99. that gives about 95 usa pon.
Shell V-Power Nitro + 99 and Tesco Momentum 99 are the highest of the octane at roadside pumps (apart from the gas station outside donnongton race track) with bp coming close,
but most people say the Bp is not as sharp as the other two.
shell and Tesco both claim 100 ron , but again this would realy be about 95 in the usa, so still realy not high enough for high compression motors.
the old shell stuff was ethanol free, but both Tesco and shell now have about 5% plus other additives to boost octane.

avgas is the best stuff, but it is way way too expensive to play with in the uk, we cant afford those prices..

ROFL have you found any improvement running the 97 super unleaded over the cheap stuff ? any results would be good to know.

[Roflhat]

Someone once wrote: "Racing costs money. How fast can you afford to go?"

Jeff

Always liked that phrase, the costs seem to increase exponentially the faster you go, I only paid £750 for the engine, the porting + other mods were £1200


97ron is roughly 92 usa octane the best stuff to get over here on the cheap is Tesco momentun 99. that gives about 95 usa pon.
Shell V-Power Nitro + 99 and Tesco Momentum 99 are the highest of the octane at roadside pumps (apart from the gas station outside donnongton race track) with bp coming close,
but most people say the Bp is not as sharp as the other two.
shell and Tesco both claim 100 ron , but again this would realy be about 95 in the usa, so still realy not high enough for high compression motors.
the old shell stuff was ethanol free, but both Tesco and shell now have about 5% plus other additives to boost octane.

avgas is the best stuff, but it is way way too expensive to play with in the uk, we cant afford those prices..

ROFL have you found any improvement running the 97 super unleaded over the cheap stuff ? any results would be good to know.

There's only 1 fuel pump on the island that sells super unleaded, I think it's BP. Since I've had the Yamaha I've always run it so can't say what differences/gains there are
On the old thundercat forum there was a guy who had a motor that ran on avgas, must be serious compression