Yamaha 660 what mods can be done

[Cyclops Hammer]

what mods can be done with out a major overhall to the engine , i know big bore kits and all that can be done, but im looking for an easy mods that not so drastic and that will yield a few extra Hp.

[basser23]

Three words: Exhaust,cam,carb...at least a re jet..
Pure bolt on stuff really..
Chip

[MSW]

Do many people do the cam? I've done the header (tunebike), can (holeshot), and carb (tunebike), but it still feels like there's a little something missing. Anyone want to share their experiences with a more radical cam w/out any further internal mods?

Gracias.

[OLDMTNCARVER]

Your intent, without getting into the motor is what lead me to my demise.
First an exhaust and at the same time a jet kit...
If you're a carb expert...enjoy yourself, good luck...
I just purchased a set of carbs that are stock to get back to reality.
The originals got a Dyno jet kit installed after an M4 exhaust. I never tried the stock carbs with the exhaust as I was in a hurry to get the 01 Baghira ready, to go with friends, to Laguna Seca for the weekend watching races. The shop that dyno'd their installation (great improvements-wide open, it runs like a raped ape). In the traffic, HELL, DOESN'T RUN!!!
My advise, get an exhaust and install it. Before you install a carb kit RUN IT WITH THE EXHAUST BEFORE ANYTHING IS DONE TO THE CARBS. Then take the bike to a shop that KNOWS THE CARBS AND THE ENGINE! AND TRY ADJUSTING THE CARBS WITHOUT ANY JET KIT DRILLING, GRINDING OR WHATEVER !!!
If your thinking of cams consider the cost of the crank cleaned up, after market rod, piston, rapor quad head (ported with valves and cams installed) and be done with it. You'll likely want a custom exhaust as well
Threads have shown small end rod failure after time or mods.
I'm going back to stock, except for the exhaust. I intend to a build the head then buy a rod and piston and do it right the first time and not build it to blow up after 100 miles. I want to improve all that I can and keep the reliability.
Wishin you the best,
OMC
PS I'd advise a talk with the folks at bikeworx. I've heard nothing but good.

[Bill Jurgenson]

I don't know what some of you have done, but I do have some experience with the xtz engine, both the 4 I call my own and those I have built for customers and/or friends.
First, I have never had a small end failure, never ever. If some one has had that, then something was seriously amiss and not caused by any hanky-panky with such trivial mods as are being discussed here. more like elcheapo oil, even cheaper filters, too seldom changed, above all: not allowing the engine warm up properly and also wide open trottle at low revs! More that almost anything else, Thumper style driving ruins the xtz engine straight away. It is not a thumper.

That said unless you are seriously into making noise, forget about the exhaust if you have a Skorpion. For top end and within anything even approaching street legal noise limits, the stock L&W cannot be bettered. True, it is heavy but it will outlast you and the bike several times over. Replacing the can only gets you more noise. Some cans like the BSM actually deliver less performance. Of those I have dyno tested, only the BOS gives significant gains - in noise too. 108db in out of the box so-called E4 trim. Any mods to the exhaust demand as a very first move larger headers. For the Baggi there are a couple of aftermarket kits but here,too, I have seen at least one that returned significantly less performance than the original system. It just looked cooler. For the Skorpion there is next to nothing until you go full race. Occasionally you can garner the Remus Cup system or the 2-2 system from the Replica. Both have the same larger 32mmID headers and both do improve performance. Here is the Cup system mounted on my toy:



Both the Tunebike and the Dynojet kits do improve performance a bit. Bernd's (tunebike) is better thought out, but the most important part of his kit is the spacer for the membrane. Reducing the lag between both carbs improves performance a bit, too ,but also makes it less drivable. Don't worry about too lean jetting; the stock 165 on the right side is way too big to begin with and the reason why the Skorpion gets such poor mileage. It is standard Yamaha practice to jet too rich as one(poor) method of avoiding engine failures and lawsuits.
If you want serious improvements, you have to go to a different carb.
The easiest way is to mount the Mikuni TM34-65 such as is offered for the Raptor.



Even on a stock engine, this returns really significant performance improvement and also better mileage. The mod is simple to do as well and in the Skorpion can be integrated into the original airbox so well, that even experts don't notice.



An alternative the works pretty well is Galen Miller's Bikeworx kit - if it is still available.



If you are talking Skorpion, the very first move toward better performance is getting better lighter wheels such as those from the SZR or even better, a TZ250RR 3MA. But even the mudane wheels from a venerable Suzi 500E are much better. Lots of possibilities here.
Then change to a shorter final drive ratio, for the Skorpion from 15/39 to at least 15/42 or even better to 16/46. Along with this have the CDI modified (tunebike for instance) or as long as the engine is more or less stock, use the CDI from the TDM. Do not, I repeat, do not go to a 14tcog unless you want to seriously damage the layshaft. And when you do change the ratio, get the best chain you can such a a DID 520 3ERV. Standard type sealed chains use up to 2hp just for themselves, 2 hp you don't have to give away.
These mods will give you significantly more performance gain that the simple engine mods without so much as touching the engine.
My son's completely stock Skorpion Sport but with SZR wheels, 15/42 and TDM CDI ran a clocked 160kmh although the engine was the 35hp version for beginners. The same bike, same completely stock engine, went to 190kmh after TM34/65 were mounted. I rode it from Milan to Turin (250km) at that speed most of the way (8000rpm) without blowing the engine or even damaging it. As said, completely stock, no Carillo, no forged piston, no tuning cam, no nothing, not even larger headers.
If and when you have done the important chassis mods, you can think about doing something to the motor.
The list here is long, the cost no limit. Up to about 60hp, it is relatively easy and also not very expensive. The toy shown above has 59hp at the rear wheel. still running the original stock crank, conrod, valves and guides and that with over 80000 km = 50000mls. Beyond 60, every hp costs real money and lots of headaches and setbacks. been there - done it. I raced these things. My racing engine has almost 80hp at the rear wheel. Has never blown the small end, either, but that engine does have a Carillo, JE, etc, etc, etc and a one-off in-house built crank and hours and hours of thought and much more work.

there is, BTW, no point specifically getting a Raptor head (5 valve), cause it is identical to the xtz head. the new 4 valve XTZ engine is entirely different and most parts are not interchangable. Its crank does not fit and it has a different ignition, too.the idea of putting that engine in the Skorpion could be enticing if you can get a wrecked new-model XTZ to scrap. Otherwise, far too expensive. All the serious contenders on the ESA circuit using the XTZ engine are all using the old 5 valve engine. Still. the days of the big bore are numbered on the track.The minomonos are the future. Bikes built from a Honda RS125 production racer or something similar with a Yamaha or Honda 450 cross engine, suitably modified for track use and delivering @ 60hp and that in a bike that is hardly able to meet the minimum weight of 95kg. Add to that the small front area and low profile and the big ones just haven't the slightest chance except perhaps at Monza or Hockenheim where they can use the extremely long straight to their advantage. Tunebike Bernd has built himself with the Husky engine as special based on a Mito.



without the fairing of course.

It weighs about 120kg with half full tank. Don't have any dyno details on it yet but Bernd guesses about 70hp. My racer weighs 125kg ready to race with 80hp rear wheel. Some claim 85hp but I only believe Martin Sweet about the Slipstream. Pami claims 104hp for his BMW/Rotax. Daiber has about 90hp in his oneoff one of a kind radial valve 800cc engine with Apfelbeck head:



don't even think to ask what this thing has cost!
Sorry off topic.

Check out the archives of all the 660 relevant forums. There is an awful lot on the subject.

[MSW]

Bill,

You just made my head explode. I learned more from reading your last post than everything I've read on every MZ board in the last year.

When I said it felt like there was something missing with the tunebike header and carb mod and Holeshot pipe, it really feels like it's in the carb. I'm going to have to look into those Mikuni carbs. Do you know approximately what the Mikuni set-up would cost?

Also, you mentioned that the Mikuni set-up would work well with the stock Skorpion air-box. Do you know what kind of air-box/filter mods I'd have to do to fit that to a Baggy?

Huge thanks for the very informative post.

[Bill Jurgenson]

good to know you are talking about a Baggi.
It is always a good idea to start off stating which bike you are talking about.

the baggi airbox is considered (e.g. by Bernd Lischo) to be better than that of the Skorpion at least.
On the carb side, the mods are the same as the Skorpion: simple replace the left bellows with one the larger one for the right side, cutting the hole in the airbox larger to fit. done.
bernd uses a soft baggy foam airfilter like those used on cross machines. Otherwise, there is not much you can do.
In general, the frequency of a box is dependent on its capacity but also on its orifice. Enlarging the intake hole will lower the frequency and this can be easily done is such a baggy faom thing is used. Lowering the frequencyis similar to enlarging the box and both bring the box closer to the resonance desired or such a large diplacement. For some strange reason, all of the MZ airboxes are too small, even that of the 1000. SR racing developed a new exhaust for the 1000S along with a modified airbox and remapped chip and together that brought a gain of 5hp and, much more important, got rid of the hole just below 3000, making it unrecognizably drivable. In a word, they got rid of all the problems the (German) press keeps bitching about.
HeInz Weber http://www.mz-heinz.de/ spent a lot of time with the RT125, even building a one-off of his own with 170cc which went like a bat out hell. He found a couple of airbox mods (additional holes in the right places .i.e. lowering the frequency) that brought real improvement. With these and a much shorter final drive ratio and removed limiter, his stock RTs for customers run over 140kmh with no trouble all day long. Putting on a slightly larger flatslide...
Oh boy!
b

[claytonb]

hi Bill,
I was following your interesting post but got lost on the frequency and airbox. What frequency are you talking about?

BTW i own a baggy...is it the TM34-B70(as seen in the pic) or the TM34-65(as written in the post). Are these as standard on any bikes? You said that it will increase performance and mileage so its ideal no?! does it run well at all engine speeds?

Clayton

[Bill Jurgenson]

Frequency, i.e. the resonance within the box. it should be low enuf for the gas pluse to profit from andabove all not at odds with it.
The lower the better for our purposes, because the gas pulse frequencies can then be overtones (upper partials) of the fundamental.
Also the reason why the exhaust of such a lager capacity single has to be long, and ahy so much effort and experiment goes into making really good tuned 2-stroke exhausts, altho they are not compatible with what we need. Different ballparks.

TM34-65 or 70, the second figure is the distance center/center between the two venturis. 34-70 is too wide really, but it can be forced into the rubber mounts. The 65 fits better. In my own experience, everything works better with such a carb; starts better, idles better, uses less gas, performs better.

I know of no stock bike using this carb or such from Keihin either.
A very few extra hot models from Kawa like the KR750RR used Keihin FCRs back before injection.

[Cyclops Hammer]

Where can i get this filter kit ?

[Bill Jurgenson]

it is not a filter kit. The K&N filter is specifically one for a Harley.
What you see, as I said above, is the Bikeworx kit. It adapts a MIkuni TM42 (yes 42mm venturi) to the xtz engine and is specifically for the Skorpion. If it will fit the Baggi, I don't know. It includes the plainly visible manifold, the filter, the battery box which is necessary since the original airbox must go, and all the installation hardware including the gas cable. Galen will also supply the Mikuni TM42 if you want, or you an get it yourself as I did. The kit is well done and complete. And it works, too, very well - as long as you have a low restriction can like the Holeshot. I used it with the BOS and with a Remus GP on the road. With a civilized can, I could not get the jetting right at all, and no one I know using the kit has been able to, either. The problem is the drop in manifold vacuum at low to mid rpm caused by a restrictive can. The 42mm venturi is just too large for that. It would probably be possible with TM40, however.
For more detailed information, you'll have to call Galen:
(978) 897-0044
http://www.bikeworx.com/

[ZzerO]

bill

is the mikuni tm 42 the same carb as the hsr 42? because on ebay they are called the same sometimes, and they aslo look the same. and 90% of them came of a harley... is this the same carb?

and whats the difference in power and trottle control with the tm 34/65?
greetz

[basser23]

Z,
According to what I've seen the HSR42 is the carb used in the kit from bikeworx.
I think the kit is still available.
Chip

[OLDMTNCARVER]

Bill,
Dang it, I own a Baghira and if you're going to help guys like me get this stuff figured out you'd better get one too!
I can't tell you how much I appreciate the information and experiance that you bring to this forum!
Highest regards,
Robert

[Bill Jurgenson]

tm42 and HSR 42 are the same thing.