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Click on these links for a "hot lap" of the TZ350 and 250 Website:                                     

TZ Performance.

     We need input from all you TZ owners who have modified their bikes.

Picture: Brazilian based Bob Keller aboard his TZ350F recently at Hengelo in the Netherlands. (John Valster)

Come on, spill the beans and tell us all what you've done to your bike to make it just that little bit faster than your competitors.

Brand new TZ suspension setup guide ... click on this link.

   A look at the TZ250 C...... from a personal viewpoint:

I have left mine basically stock for now, it goes well enough for me, but what I have done is run my TZ250 motor through my MOTA software package to see what improvement in power output, in theory, I can achieve through modifying a few aspects within practical and monetary limits.

     Below is the power graph of a theoretical comparison between the horsepower and torque outputs of my stock TZ250C motor and a modified version called "TZ2P57RE".

     I have had comments about the peak power being produced at 13,000rpm, which sounds high I admit. I think it all comes down to the initial measurement of my motor, maybe I mis-measured something slightly. ( I can't imagine what since I spent so much time doing it !! ) I'll muck around with exhaust tuned lengths and other stuff one of these days and see what happens.

     The modifications chosen were:

1. An expansion chamber constructed out of 0.8mm plate with the dimensions below.
2. Exhaust port raised 1mm.
3. 18 degree static ignition advance
4. 11:1 Air fuel ratio

Click on this thumbnail image to see the "cutting list" for the chambers used in the "TZ2P57RE" dyno run.

Please note two things:

1. This is the best theoretical output I could achieve. I did some 50 odd different runs, altering all sorts of things such as port heights, air/fuel ratios, ignition timing, chamber shapes. This one, "TZ2P57RE" was the best.
2. You should ignore the actual figure for the power output and concentrate on the improvement. No doubt some owners will have had their 250C's on the dyno and be thinking: "Mine put out more power than that". Remember, this is theoretical, the figures depend on how accurately I measured my motor. The increase is the important factor here.

Side note:  Have you ever played around with a 2 stroke tuning software package? They are so much fun !! Check the "Reviews" section for a short review of MOTA if you're curious.

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http://www.strappe.com/plugs.html  is a link to a reproduced article about spark plug reading copied from Cycle magazine in 1977, written by Gordon Jennings.

TZ 350 jetting advice   from Kerry Wilton:

"We use different carb internals, and the 350's pull much better from low down on 38mm powerjets:

Needle:      6DH7  (A standard Mikuni needle)
Needle Jet: Q-4
Pilot Jet:    75

Need to make sure the float needle jet ( or "needle and seat" ) is good condition, or the results will be a waste of time - have seen a TZ where the owner was using the amount he opened the fuel tap to regulate fuel to the carb, as he hadn't figured out the needle was stuck open!"

Jetting advice link.

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Click here for a new article about early TZ carburetors from Nick Parkyn.

Click on this link to view a good, basic article on tuning the carbs of a 2 stroke motorcycle:

Remember:  You'll be leaving the TZ350 and 250 Website if you go there and will have to use your "back" button to return.

Click here to view top speed calculation charts for old TZ's !!

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Picture at left is an interesting method of achieving better performance from your twin cylinder bike, in this case a 1972 Yamaha TR3.

Back in the early seventies,  Rob Hinton grafted a third crankcase chamber onto the ignition side of a stock TR3 bottom end, then bolted an additional TR3 cylinder on to create a 520cc triple.

This was a modification done by quite a few riders back then, mainly overseas.

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Click here to view TZ750 Porting information and experiments !!

Front Disc Brakes.    by Kerry Wilton.

When I was the 19 year-old ‘budget-racer’ (read ‘poor’) of a nice little TZ 250C, I high-sided it in a spectacular manner, smashing the front master cylinder.  “Bother”, I thought, as a new TZ twin-outlet master cylinder would no doubt break the bank.  “Aha!”, I thought; the RD350 street-bike (of which there seemed to be a lot about then) has a single disc and the calliper looks the same, therefore the master cylinder from the RD 350 must be the same ratio as the TZ.  The RD master cylinder is different looking (same make), but would surely work! 

Sooo, after rebuilding a second-hand RD master cylinder, I fitted it to the 250C.  Presto!?  Well, not quite.  The TZ C front brake had been sort-of wooden feeling before (a Lockheed calliper was fitted – more on this in a minute) and felt like granite now, but I put this down to a short riding lifetime on a diet of drum braked-British bikes (on which the drums didn’t work too well as they needed sorting properly..) and a similarly wooden-feeling disc brake on my Ducati 450 Desmo.  The 250 would give no indication of imminent front wheel lock-up other than the squealing of the tyre.  I should have fallen off it more often.

Anyway, I suspected that the TZ master cylinder may not have been the optimum size (9/16 inches = approx 14.2mm), and that the RD item was probably a ‘fitting of convenience’ for Yamaha – it was 5/8 inches = 15.875 mm), and probably also used on bikes with twin discs.  What I didn’t realise was that the Lockheed calliper fitted to the 250 has smaller pistons than the Yamaha item, and therefore should have had a master cylinder even smaller than stock – and here was me fitting one that was bigger!  No wonder the brake didn’t work! Still, I knew something wasn’t right, but didn’t know where the reasonable limit was, in terms of master cylinder size, nor what alternative sizes were available.  Besides piston rings were more importantt.

So, how to work out what’s required for feel and performance?  Kevin Cameron’s book ‘Sportbike Performance Handbook’ gives some good guidance, as do several other articles around the place, including one by Michael Morse (of Vintage Brake, USA), and some work by Gerald Douglas.   I shall attempt to roll them into one here.

Lets’ start with some numbers:

Lockheed calliper piston diameter:                    41mm

Yamaha TZ/RD calliper piston diameter           48mm

TZ master cylinder diameter:                              14.2mm

RD master cylinder diameter:                             5/8”

Required ratio of calliper to master cylinder ratios is around 27:1.  Get towards 20:1 and the brakes are ‘wooden’, though the lever is firm.  Much more than 27:1 will result in a excessive lever travel and brakes that are overly sensitive.

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Have a look at the following chart:

Single Disc, Twin Piston Callipers

The figures with the red are close to the recommendations.  From the tale above we can see that the standard TZ  master cylinder (close enough to 14 mm for the demo) with the standard TZ calliper gives a ratio of  23.5 – near the bottom of the acceptable range.  This deteriorates to 17.2 with the Lockheed calliper – which fits with the lack of feel problem experienced on the 250.  This became even worse (13.3) with the RD master cylinder.   The little 450 Desmo master cylinder was probably around the same poor ratio as the TZ.  Conversely, my current TZ350F with a 14 mm master cylinder and a standard calliper is good, proving the original set-up.

The next table is for the twin disc arrangement.  Proof that it works is the excellent feel and power of my 750B front brakes with an 11/16” master cylinder and two standard callipers:  30.2.  Lever travel is acceptable, though you really wouldn’t want any more.

Twin Disc, Twin Piston Callipers

Go on; put your bikes figures into the tables and see where the ratio falls.  How does what is recommended relate to your bikes’ front brake feel? 

Thanks go to Kerry Wilton for this excellent article on brakes performance. ( Where would we be without you mate !! )

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A link to an interesting page about master cylinder ratios: http://www.vintagebrake.com/mastercylinder.htm

Click on this link to read an interesting story on running and maintaining a TZ350

......and here's another excellent article written for us by Paul Collins, full of tips etc.

Click here to view a list of over 100 magazine articles written about TD, TR, TA and TZ Yamahas over the years around the world.

Please note: These are not articles available for download or purchase. Simply a list of the ones you might like to try and track down yourself over eBay or whatever.

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      03/23/08 10:24 AM +1000                                                         

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This Website and it's contents © Greg Bennett 2002 unless otherwise indicated.