yamaha 70 ces

[mobil1]

Just bought an old f4 cat with looks like an almost new 70ces behind it...
Compression on all 3 cilinders are between 175 and 165 psi,
gearcase is mod with nosecone and low water pickup.
Has somebody standard data like compression and squish, timing? I want to find out if the engine has been mod.
Also have the carbs of a 90hp yamaha, to fit these on the engine.
Do you use the the reed plate and reedblocks of the 70?
And what will be the advantage, better pick up and top end?

btw, great forum guys...

Jeffrey

[Carl Kinder]

Hi Jeffrey,
Do you have photo of boat and engine, I guess if its a F4 its one I will know ??
175 psi is the lower side of good if it has 1 piece head. If its got 2 piece head 175 is good.
Bottom cyl is always a little lower cos the oil pump drive is missing.
Good starting point is timing 19 deg, fuel min 98 oct, main jets 165, carbon reads, 10 mm gap. with 1 piece head.
You can go down jet size but beware dont go much past 19 deg with timming.
2 peice head timing 26 deg fuel min 95 oct main jets 155, 10 mm read gap.
If its running 6j2 2 ring pistons keep eye on piston crowns and land between rings. (6J2 pistons BAD batch of piston, most fail, some still turn up as new old stock ! 6H3 work almost as good)
Try to keep max RPM just under 8000rpm !!!! 7400-7500rpm they run and run and run !
Find a good 11 x 19 or 11x20 prop !!!!!!
Fit head temp gauge. lots problems come from "cold seizing" need to get temp in engine with out cooking it !
Carl

[mobil1]

Hey Carl,

thanks for the info.
Have a picture of the boat when i just bought it, original stickers. looks old:)
2 piece head, by that you mean a removable cilinder head?
That is what i have...
How can you see that its 6j2 pistons? is it possible to see true exhaust port or anything?
Can save some time instead of open up the engine...
Do the rings get jammed with these pistons? like merc s3000...
When checking the carbs took a sneak peak @ the reeds, it are carbon ones. Black colour, standard ones?
Only have a water pressure gauge and trim indicator, will see to place a temp. gauge.
Just bought a brandnew merc cleaver 11x22, couldn't test it yet because off the wheater.
Problem of buying a boat when winter starts...

http://i166.photobucket.com/albums/u82/OS-tunnel/F4/SL384492.jpg

http://i166.photobucket.com/albums/u82/OS-tunnel/F4/SL384538.jpg

http://i166.photobucket.com/albums/u82/OS-tunnel/F4/SL384524.jpg

http://i166.photobucket.com/albums/u82/OS-tunnel/F4/SL384528.jpg

http://i166.photobucket.com/albums/u82/OS-tunnel/F4/SL384597.jpg

Grt, Jeffrey

[Carl Kinder]

Looking at your photos, looks like 1 piece cyl head. beware of core plugs in head, they pop out, use plate strips between cyl head bolts to hold them in. watch cyl head bolts (2 washers on each bolt) you can take 1 washer off on bolts you use the core plug plates on. Original bolts was too long !!!. If you deck head check bolt length again. Only use gen Yam head gasket !!.
You can see pistons if you take exh side plate off. 6J2 have 2 thin rings, 6H3 have 2 or 3 thicker rings.
If it has black carbon reads, that was standard for 70ces, check they seat well and no frey on edges, common problem, boyson reads fit, from memory slight mod to suzuki 185 cc reads fit !!!
Rings only jam cos of poor quality of batch of 6j2 pistons, land breaks away near exh port.
Check stat, most have been removed, I think its best if only part removed, leaving a choke in waterway.
How is engine getting water, do you have pick up on bullet ?
Lots had pickups on sponsons feeding into drilled out flush holes on gearbox with original gearbox holes blocked.
11x22 is too big !!!
Looks like engine is flat on transom ?. good starting point for engine height is to have lower gearbox oil plug level with bottom of sponsons, then work from there ?.
Boat looks like old Baracuda ????? prob late eights at guess (no cell).
I would cut the trim tab flush with bottom of cav plate and add a little to skeg
and put steering back to one to one !! and move steering arms to the tiller arm under the engine tray. With the steering arms on powerhead bolts, engine can come loose, also can break mid section ( mid sections are like rocking horse sh*t to find)
Depending on what you want to use it for, lots more you can do !!!!!!!!!!!!!!!!!!!!!

[Hounddog]

In our T850 class racing here in Canada we have several of these motors. One is an out of the box original 1994 version. It was taken down to the crank at the Canadian Nationals in the late 1990's and just passed inspection. I actually contacted UIM at the time because it was so close to failing and this was an out of the box, non blueprinted, totally orignal motor. The reply I got worried me. They basically said that in Europe the inspection process was not a good as the one my motor had. Then a fellow over there sets a world Kilo record in F4 at over 100 mph. When you do the math the motor must have been turning big RPM and a very large prop..much higher than 8000. So there is a bit of history. Now the questions.

[1] by the colour of the motor [dark blue] this a one of the early versions. Yes there were two separate spec sheets. The later one is the Yamaha grey and the cowl has the checkerboard on it. My motor has 150 lbs compression. How do you legally get to 175 lb plus?

[2] an 11 x 20 prop or an 11 x 22 prop turning mid 7000's with a 1.71 ratio gearcase , jacked to the moon is not going to run 80 mph in my book. Then there is the 100 mph run. There must be a a trick.
How do they do it?

[3] I purchased a legal pure race 70CES long block from Sweden. It was no where close to legal by the UIM rule book. The motor was ported, the block decked, the head cut and the crank lightened. Question is: How would this motor pass inspection. I must have never been looked at.

The reason for the post is to point out to my fellow Canadian T850 racers that the 70CES motors they are using are closer to the UIM specs and don't go out there and modify your motor when T850 is a stock class.

Don Whittington

[Carl Kinder]

Don,
I understand some of what you say,
I have opened new "out the box" Yamaha 70ces and the porting in some places can be very close to each side of UIM spec. But I think this is more to do small production runs of the motor and the hand finishing of the guy cleaning the castings on production line !.
Not sure you can rely on colour on paint to gauge age ? most have been about a long time. some are dark blue some are grey some are green some blocks had no paint !.
If you take the head vol down to UIM limits 175 psi is not high, I have seen several with well over 200psi.
After any work to cyl head, must use 99 oct 100 oct fuel, keep eye on piston crowns/ jetting
As for engine stripping here in Europe, in the past it did get a little lax !. but then the rules on blending got "clarified"!!!!!. . lots of the old pre "clarified" blocks got dropped from World championships, Still get to see a few,,but most the fast guys are running "clarified" blocks !
Some of the old blocks got closer to F3 than F4, and some of the fuel made your eyes water !!.
A good well built motor will run at 8000rpm, no problem, but when you get much higher reliability is not so good.
But on the back of a non cell old'ish boat 7500rpm, it will last all season.
In race conditions 11x19 or 11x20 is ideal keeping the RPM in the safe side will give you 80 ish mph.
If you are looking for any Yamaha 70 ces engines or parts or props, We have some quick stuff 2 x WC 2009, 2011.
I can find lots older non "clarified" stuff it it helps !

[Hounddog]

Thanks Carl, that does make sense and matches motors I have seen over here. What could of happened was the powerheads go to an engine builder and he matches the porting on all three cylinders. Since the the porting in each cylinder is varied, the engine builder matches to the best ported cylinder and ends up with a motor way out of spec.
I can see a 70 CES on a tunnel hull turning 7500 rpm. On the T boats we're in the 6600 to 7000 rpm range. Most T boat yamaha racers I have spoke to over there run in this range.
We have lots of Yamahas running over here. E-mail me your list of parts and I will post them on our race site.

[Carl Kinder]

What rules do you run to for engines , do you run 60 or 70 gears ? Are you looking for complete engines or just powerheads Let me know whats good for your racing and I can find Good, fast motors.
The Yam 70ces has been about a long time, most have seen a lot of racing, All will have been moded in some way or another, some will have been done by someone who knows what makes a motor go fast, Lots will have been copys done in a shed by someone with grinder and a shaky hand. Old engines never die they just get moved on !!

[Hounddog]

Carl, this thread is getting off topic, so I will send you a message.
Don

[Carl Kinder]

Sorry Jeffrey, Don you are right !, it has gone a little astray.

I think try what you have see how it goes first. Then if you want to go faster, start with the prop before you start on your engine !.

I have seen lots of Yams with lots of mods that make them slower !!!!!

[Fast Fred]

:cool:

[mobil1]

it's ok, more to read...
I dont' want to start tuning the engine, just determine of the engine has mods or not...
And keep the engine safe, it's not for racing. just pleasure...
I'dont know the history of the boat and engine...
The guy i bought it from, bought a big warehouse that was gone bankrupt.
The boat was in the deal...
Sat 8years in storage before i bought it...
Placed a new battery, cleaned the fuel thank, replaced the worn fuel lines and primerbulb.
Checked the carbs but they where drained,good thing! Impeller was in good condition.
I thought that in the picture engine is completly trimmed in, I can give it more neg trim if needed...
Yes, water pick up is in the bullet.
A guy who i spoke to said it was a barracuda to, indeed no cell.
Hope the prop will run fine. If not, mod it...

[Fast Fred]

the nose cone pickup will push the core plugs out of the head. should have a 000 serial number on the case. 17deg advance is good on the stock ces head. you should weld the crank. 90hp carbs make it go, 160 main jet:cool:

[Fast Fred]

oh, the tuna, it's chrome plated steal, they rot off fast, best to have it copied in stainless is nice, alu' works:cool:

[mobil1]

so i better check each time the core plugs, is there a way to secure them better?
Only drived the boat once with to small prop, i think i had then about 15psi water pressure...
Is the crank that bad? and what do you need to weld?
Will take a look at the tuner when i take the block of the shaft.
When searching for info over the yamaha ces, found alot of your posts fred...
Seems you have alot of experience with this motors...
Why should it have that serial nb on the case?
To fit the the 90hp carbs on the 70hp engine, i assume you make the holes off the reed plate bigger?
no Further suprises when mounting the carbs?

Its difficult sometimes with these technical terms:)

[88workcar]

I think you will be quite happy with this rig just the way it is. I wonder how it ever made it sence all this stuff is wrong or going to break as soon as you try to use it. I am baffled.If you ever need 90 carbs which I don't think you do, I have about 30 sets, just let me know.

[Hounddog]

I thought I would post rather than e-mail several people and go back and forth.

I can only relate to my experience with the motor and how we would inspect any motor racing in T class in Ontario Canada.

First there were two UIM inspection sheets numbers 398 and 435 [I think there the numbers].
There are two different blocks. You can tell the later block because it has the mounting blocks for the newer style ignition. The one in this thread is the older block.
The original motor does not have 90 hp carbs. It has the older style 60 and 70 hp small carbs.
The crank, rods and pistons weight 1000 grams
Based on the original Specs from Japan the motor is 70 hp at 6400 RPM.
The compression is 150 psi.
The horsepower curve drops quickly after 6500 rpm. The motor will turn 8000 with very light load. The igniton is a weak link to run the motor a very high rpm over long periods of time.
The bell shaped short tuner helps to get higher rpm on a tunnel, but the stock tuner has more torgue and is equal or better on a V bottom.

The designers in Japan copied the OMC Stinger. The gear case is 1.71 ratio on the CES and 1.76 in the OMC. They both are 15 inch mids, off centre chamber heads, The horsepower curve is raised from 70 hp at 5500 to 70 in the yamaha at 6400 and 75 plus at 6000 in the OMC. Based in prop shaft HP the OMC is a little stronger. The big reason is the weight of the rotating assembly The yamaha is very heavy.
You pin or weld the crank on a CES or any modular crank in a performance application because they shift out of phrase. That changes the timing.

Racers in Europe motors pass inspection. That is their inspection and their business.
In T Class here we decided on a maximum compression rule of 160 psi. The motors are stock and run on pump gas, not super stock. Inspection is first fault, easiest first. Visual is first, next is compression. If it reads over 160 psi your out.

Can this motor run over 100 mph in the kilo on a F4 tunnel? Not in my opinion unless it was on a trailer pulled behind a car.

[ima75man]

if racers spent more time on props and setup, they would be faster than most racers modifying their moters.

[FrenchPhil]

Well, it did in at least once in 1992 - 101.93MPH - UIM record. Since the motor is no longer legal in European/World class races like Rouen, there's probably good deals to be made.


Can this motor run over 100 mph in the kilo on a F4 tunnel? Not in my opinion unless it was on a trailer pulled behind a car.

[Hounddog]

Well, it did in at least once in 1992 - 101.93MPH - UIM record. Since the motor is no longer legal in European/World class races like Rouen, there's probably good deals to be made.

Yes Sir, it's in the book and thats a 2 way average. Doing the math he turning a 26 pitch prop at over 8000 RPM from a 70 hp motor.

[FrenchPhil]

Wonder how much HP they actually had...

[Hounddog]

Phil, welcome to the How did they do it with a stock 70 CES Club. There are many of us in the club. No other F4 has ever tried to beat it.

[DoktorC]

The horsepower curve is raised from 70 hp at 5500 to 70 in the yamaha at 6400 and 75 plus at 6000 in the OMC.

Other than the head and tuner what else did they do to the CES to raise the peak power 900rpm? I have a tough time believing that by adding 60+psi of compression and a tuner that you still have 70hp IF you start with 70hp....and those two mods raising the power curve seems odd without raising the port timing.

[Fast Fred]

pull one washer out of the head bolt set, cut and drill a piece of alu' to cover the head, about an 1/8 thick, bolt that down on the head, it will keep the core plugs in the head. cuzz of the stock class they, the factory, can only use stock parts, with no mods, makes it only a matter of time for the power head. anyways, the flaws are, the crank press on the top pin sucks, it will come apart and cut the top of the cases off .the wrist pin clips need to have the tail cut off, they vibrate and jump out, then the pin drops in the port, boom. the squish band is negative, should be re-cut then you can lean on it. i remember my first one she was the bomb, stretched that crank out second ride, still had them 70hp carbs on it, put them on a 50hp. told ya about the tuna,:cool:

[Hounddog]

Other than the head and tuner what else did they do to the CES to raise the peak power 900rpm? I have a tough time believing that by adding 60+psi of compression and a tuner that you still have 70hp IF you start with 70hp....and those two mods raising the power curve seems odd without raising the port timing.

DoktorC they did basically the same as OMC. If you compare the normal 70 hp 49 motor with the longer tuner and head to the stinger style tuner, head and larger carbs in OMC's case. The shorter tuner will change the power curve of the motor. The shorter tuner will require more RPM to attain the same horsepower. The timing is the same. In many cases the yamaha engine builders will run less timing. say 17, especially if they have over 150 psi and a modified head. That is the reason they run the larger 90 carbs. The motor will run too lean with the smaller carbs.

Racers are always looking for an edge. The 70 CES in pure stock form is an excellent motor with very few problems. It is when the racer thinks they are smarter than the person or persons that designed it, they run into problems. Soon as you alter one part of it you end up altering another part because of a problem you created by altering the first part. It is from trial and error that mod engine builders learn. I bet except for a few, racers who have done their own mods do not have as good a motor as one totally stock.

[Fast Fred]

Hounddog is right on the OMC copy thing, a bunch of Mod 50 in it as well. the other way the factory insured a short life span for the motor was the ces piston, it's got a high ring and it's way thin, the only way to get a new set of rings or pistons was in a new power head. stock is the only size for that piston. all the things mentioned is how the factory assured it would sell motors. other than the 90 carbs the mods are "stay alive" mods:cool:, it's a fun moda, take it out, try to keep it under 6500rpms till you get a good feel for it, if you bust it, you can find all the facts you need to fix it hear. my first one, after i fixed it by doing all the thing said hear, raced by my self and others, she is still out there today, scarin the crap out of all that see her.:eek::cool:

[Hounddog]

The T850 UIM records are fine in my view. The kilo is 66 to 67 mph and every few years a racer has tried to break the record. In Canada our yamahas run the same as the UIM boats speed wise. Modified Yamahas on our V hulls have not yet shown to have any advantage over a stock yamaha. They all run the same. Lots of mid range and then flatten out right at 65 mph. It is only on the tunnel where the mods appear to help. Fred's comment in the post above makes sense to T boat racers. Our motors in stock form run below 7000, so we do not have the problems the F4 racers get.

Now if you want to talk about a motor which you can really get to go on a tunnel. Think 60D. I bet most know little about them. They raced in Japan with close to mod 50 performance out of a small 2 cylinder 80 to 90 hp at 7500 rpm.

[Hounddog]

Now if you want to talk about a motor which you can really get to go on a tunnel. Think 60D. I bet most know little about them. They raced in Japan with close to mod 50 performance out of a small 2 cylinder 80 to 90 hp at 7500 rpm.[/QUOTE]

In early 90's they raced a mod class in Japan. Simple rules, motor had to be 2 cylinder mods unlimited. The boat was a tunnel about the size of a Sport C [13']. Boat, motor and driver approximately 500 to 550 lbs. They used 15 inch mids. Suzuki and Yamaha were strong in the class. Yamaha used a motor similar to the 48,55,60 mariner/yamahas.
The yamaha was a 60D.Great motor to mod, Steel crank, twin carbs, light weight etc. The motor is basically 2/3's of the 90 hp Yamaha. They we getting big horsepower and 100 mph speeds. Very dangerous in a 13 ft boat. Take a look at the exhaust chambers on a fishing model of this motor, you can see they likely made expansion chambers in the race version that fit inside the mid.

Yamaha did send me a spec sheet to modify my 90 yamaha and said the motor would make 120 hp and last. I gave the specs to Jon at Hydro Tec. He said there was no way the motor would make 120 hp by those specs and only 150 lbs compression. He built the motor and phoned me after having the motor on the dyno, he called to tell me it didn't make 120 hp. It only made 119.6 hp at 6500 and over 100 hp at 7500. He then asked if it was OK if they used the specs for other customer motors. He has and I still have my motor 10 years later and it still has not broke. I only use this as an example to show the knowledge yamaha had about these motors and Yamaha said they were not into outboard race motors.

If Yamaha and Suzuki ever decided to go and build race outboards, Mercury better move aside. Look what happened when they got into motorcycle racing.

[Fast Fred]

how can i gets a copy of them 90hp specs Hounddog ?:cool:

[88workcar]

how can i gets a copy of them 90hp specs Hounddog ?:cool:

I remember seeing you offer info for a price Fred!

Mine turned 7400 and never broke, Hydrotec told me after quite a few converstions that they believe mine made more that theirs, and that they did not know what they could do for me. I tried hard to spend money there.

[Hounddog]

how can i gets a copy of them 90hp specs Hounddog ?:cool:

Fred, since Hydro Tec is in the engine building business they likely wouldn't give you the spec sheet unless they did the work. I think they have the only copy. I know several other guys got more horsepower, Steve Cooler for one. He was in the 130 hp range as I recall, but did have issues with blowing head gaskets. Popa Sam can build a mean 90 for sure.

Just to get back to the original thread. A racer e-mailed me askng me why having 200 lbs compression as a problem. It makes power!
My answer is: It will get you more power off the dock. It hurts you top end wise because the motor is actually fighting itself because of the added compression at the high RPM, so it slows you down. It also results in a much shorter engine life, especially if you running stock parts. It is one reason why the Yamahas break a lot of parts. It is also why I find it difficult to believe you can get 200 lbs compression legally in a stock 70 CES and if you could, It would slow you down. Again just my opinion.

[lcp]

hounddog, any idea how can i keep in touch with steve cooler?regard Mr Lo.

[Carl Kinder]

I would just like to stop the thinking!! that the Yam 70 is a weak engine if you carry out any work to the engine. This is not true. We race every Thursday evening (20 weeks) plus a National series plus World series !!. Rouen the engines race for 24 hours ! and the same engines are still racing several years later having covered many 24hour races.
The biggest problem is the engine is getting old !.
Old engines dont die, they just get moved on !!
In 1990 Yamaha changed the spec of the Yam 70ces (modified cyl head, 2 ring pistons,carbon reeds etc)
Some original engines had update kits fitted, some are still racing now.
Enforcement of UIM rules has had its ups and downs over the years !. So you find several different levels of legal !!!!!!!!, depending on when the engine was raced.

The fastest and most reliable engines in the World championships are to UIM spec.

On a tunnel boat its a big difference between a engine made to UIM spec and a out of the box motor (speed, not reliability)
In the 25 plus years this engine has raced most things have been tried.

Old engines never die, they just get moved on !!!!

[Fastjeff57]

Just curious, but how flow effective are the stock reed systems in 70 hp Yamahas? I adapted a set of them on my Merc triple and--though they look kinda small--I assume they must flow pretty well for these motors to perform that well. (The same reeds are used for the 90 hp Yamaha, by the way.)

Jeff

[Hounddog]

hounddog, any idea how can i keep in touch with steve cooler?regard Mr Lo.

Sorry, I can't help you. I know he sold his FV 90 yamaha to Ernie Brown and I believe Erinie sold it to a fellow on this site. It was a green SSV hull number 27 if my memory is right.

[Fast Fred]

well lets see, never did lose the press on a 40-50 hp yamaha cranks, no matter how bad it was beat on, you can stuff it at 8000 , if you don't empty the foot she will just keeps goin.
maybe thats not a good comparison , could look at the Stinger, not known to lose her press.

anyway the Factory puts a ton of R&D in, not to mention we can see the history of how that info performed, port maps like the 19-s, the 60DES, SST60, they have value cuzz they are tryed and true, you know it worked, time after time, record after record .

so check this, " i have a port map for sale" ,,,, or,,, "i have a port map for sale, it has the Kilo record, and the marathon record " witch one you guna pay for. that is not to say the first port map offered was not the same or better.

oh, until they start given away free samples at the bank, i expect to have to pay. not sure if that was a Question in there.

185psi seems to be the number Hounddog.

[Hounddog]

To get right back to the original post and offer the fellow some suggestions:
Since you do not know the history of that motor, do the basic initial checks
- clean the carbs
- check the reeds for damage
- re do the fuel pump and check the fuel lines
- drain and check the lower unit
- replace the water pump
- look inside and mid and check the tuner... is it complete?
- put fresh fuel in and flush out the fuel lines
- start it up.... how does it sound..is it smooth?
- check the compression is it in the 150 to 180 range, are all cylinders equal?
- go out and test it. If it turns the props you have in the 7500 range...
LEAVE IT AS IS!

[Fast Fred]

thinkin theres a new set of plugs in that spring make reddy list, maybe wave the grease gun at it,

[mobil1]

Have already done all the things in the list, only not checked the tuner...
But i took a sneak peak in the cilinders before i bought it, togheter wit the compression test. An i could see the marks of honing in the bores.
So the engine doesn't have that much run hours
Replaced the plugs by iridium ones,
Drove her once, with a to small prop, everything was ok.
Wheater has been to bad to test the cleaver.

All i asked was a little bit of info from these engines so i can check if the engine is mod...
And some info from the problems i could encounter trying to fit the 90hp carbs that i have laying arround from a blown engine...
If i have them, why not use them...
Technical aspect is not a problem, i am a technician...
And see ALOT of tuning on both s3000/F1 and the sterndrives.
So if i ever feel the need to do some porting and others, that won't be any problem.

grt

[Fast Fred]

there is two styles of 90hp carbs, the square style fit right on, the round style you need to change the screws in the top of number 2 and 3, number 3 needs some room between the tray and the bowl, if you don't want cut the tray, you can sand off the bowl and just get it.
i liked the round style best.:eek::cool:

[Roy Hodges]

Can you tell me what's the dif in weight ,between the running POWERHEADS , of a
75 hp 49 in OMC ;and a 90 HP yamaha ? It seems to me that a sport E boat or a mod 50 boat , with a stock 90 yammy powerhead on a sport E tower &lower unit ,with nose cone & low water pickup would be the cats pajamas !

[Fast Fred]

from shippin them out i know a Stinger, in full dress is right about 100#, the 90 was feelin like about 140# when i pulled her off, what's up Yard Bird:cool:

[mobil1]

there is two styles of 90hp carbs, the square style fit right on, the round style you need to change the screws in the top of number 2 and 3, number 3 needs some room between the tray and the bowl, if you don't want cut the tray, you can sand off the bowl and just get it.
i liked the round style best.:eek::cool:

I have the round style, as i remember.
What do you do with the electric choke, does it fit the 90 carbs?
And the rods connecting the throttle levers of the carbs, do they fit?
The boat and engine stands in winter storage, so i can't check anything...
Trying to work everything out before the season starts so i can mount them fast...

regards

[Fast Fred]

on the 90hp power head, you want the carb studs in the intake. choke, remove choke plates, toss them out. 70hp gang linkage works on the 90carbs. thinkin you my have to cut the tray.
you want to open the intake so it is the same as the 90hp gasket, i cut 1/3 off the reed stops. you will need a new throttle cam. no air silencer,

[Fast Fred]

:cool::eek::cool:

[Fast Fred]

and one more:cool:

[mobil1]

thats clear...
Now waiting for better/hotter weather. First test with the 70carbs and cleaver.
The i will try the 90hp carbs.

Thanks for the info, looks neat on the pics.

[Fast Fred]

a good place for a half set of 250hp carbs, be on the front of the 90hp:eek:

[sharpeye Mike]

Hey! We should start a thread on the mighty 90 Yammy......Well not me but maybe one of you connoisseurs, it seems to me that theirs lots to say about this motor. :)

[mobil1]

Still bad weather over here but drove the cat 2 times last month.
First time was good, acceleration ok. Top speed fast!
After that run checked the plugs and the where on the lean side, to lean for pleasure so i richend them up one size.
Following time on the water acceleration was bad, difficult to pick up rpm's after a turn.
The cleaver i bought is a size to big, think i need a 11 x 20.
With the 11 x 22 i was turning arround 6400 rpm.

[Hounddog]

If your turning 6400 rpm with a 22 pitch. You will only gain 300 to 400 rpm dropping down to a 20 pitch. With a 1:71 gearcase You are far away from the normal 75 mph to 80 mph speed the F4 fellows run and no where near the 100 mph record. Maybe your boat is heavy.

[mobil1]

but acceleration will be better, enhough i hope...
Boat is light, didn't wheight it but can lift the back alone.
Also have to watch my step while boarding or my foot makes a hole in the deck.
It will be my driving probably, only used to v-bottoms...:D
Also i'ts difficult to watch rpm, the gauge sits between my legs just in front of the seat.
So when i'm givin WOT and trimmed out, I'm not keen to look down...
You can feel good when you are trimmed to make it fly, boat picks up some rpm's and accelerates once more...
Then you need to keep it like that:rolleyes:
Still learning to drive this boat and get the feel for it, so it will become better, faster in the future. (i hope)

Exact speed i don't know,
When i was driving, they where training for waterski. One boat, 21foot with 300xs i tryed to follow once.
I could follow him, the distance between us stayed the same.
Don't know of he was giving it all...

[Fede 97]

per yamaha top 700 \ 40 hp

[Fede 97]

57423

[Fede 97]

57424

[Fede 97]

57425

[fast213]

fede these attachments dont work I am very interested in 90 yamaha mods

[kellytheaker]

I happen to be reading this since all I could find was a 97 yamaha 75 and I could sure use some help bringing a bit more power out of this powerhead . I understand it has same block and such as the 85 and 90 so please forward what you need to do to make this 75 improve its baseline to the 90 specs . Thanks -

[coleindustries]

I happen to be reading this since all I could find was a 97 yamaha 75 and I could sure use some help bringing a bit more power out of this powerhead . I understand it has same block and such as the 85 and 90 so please forward what you need to do to make this 75 improve its baseline to the 90 specs . Thanks -

I cut and pasted the below info form somewhere on the internet, but it seems plausible. If you want to be sure, trawl through one of the online parts websites like megazip or boats.net or see what parts numbers change per year.
The carbs are exactly the same, it’s a common myth that the 90 has different carbs from the 75hp. The jetting is different but the venturi are the same. The physical differences are the 75hp had a low compression cylinder head and restricted exhaust tuner. 80hp had high compression head, restricted exhaust. 85hp low compression head, unrestricted exhaust. 90hp high compression head, unrestricted exhaust. The later 75hp may have had the high compression head fitted

[kellytheaker]

I appreciate the reply - still working on figuring this out . The carbs - square vs Round bowl is another question but possibly the square bowl are just on the premix motors like the 85 and such .
Another issue I have heard is when removing powerhead to do the exhaust tuner - the bolts are usually snap off . Hopefully when I do the changes to the tuner I can get them out reasonably with heat .
I cut and pasted the below info form somewhere on the internet, but it seems plausible. If you want to be sure, trawl through one of the online parts websites like megazip or boats.net or see what parts numbers change per year.
The carbs are exactly the same, it’s a common myth that the 90 has different carbs from the 75hp. The jetting is different but the venturi are the same. The physical differences are the 75hp had a low compression cylinder head and restricted exhaust tuner. 80hp had high compression head, restricted exhaust. 85hp low compression head, unrestricted exhaust. 90hp high compression head, unrestricted exhaust. The later 75hp may have had the high compression head fitted