ESE's works engine tuner

**F5 Dave** · 20th November 2009, 08:22

Interesting article. Gets hard to decipher when they are talking about customer TZs & OW race bikes though.

**F5 Dave** · 20th November 2009, 11:37

ok we are getting waay off subject but I'm learning some history. . .

[from webpage]
The mighty TZ 750

In 1972 . . . .blah blah etc etc.. .
standard. Interestingly, Yamaha claimed the bike had the potential to produce almost 140bhp with TZ350 cylinders fitted.{DT edit;as opposed to it's standard barrels}

Technically, though very similar to the TZ350 motor-wise, it differed in a few crucial areas, these being:

1. The head's squish band was reduced from the 350's 2.0mm to 1mm and it's combustion chamber was made a little deeper so as to keep the compression ratio to 7.3:1.

2. The exhaust port was lowered 1.5mm and four petal reed valves added to help control the influx of fuel mixture from the 34mm Mikuni carbs and to help "tame" the power delivery of this awesome machine , along with an additional fifth transfer port, "inlet" port if you like.

- - - - - -
ok so the premise (and popular story) I was under that the 700s were fitted with TZ350 barrels. That isn't actually true. The TZs were piston ported & the TZs were Reed from the beginning.

So yes those barrels SS posted are entirely likely to be TZ250 as suggested (but could equally be 500).

**SS90** · 20th November 2009, 11:54

Hmmm, lots to catch up on here, but did you manage to find out what year they would likely be?

I was punting on early eighties, but now I'm not so sure!

**TZ350** · 20th November 2009, 16:55

.

If they are TZ250's my guess is they will be between 74 to 82. And as I remember it the first factory TZ500's had piston ports and later reeds with power valves, the later production 500 racers came out with reeds and power valves as std.

The first TZ700's for production reasons had a piston and barrel made to the same dimensions as TZ350's but with reed's. Then they went to bigger pistons and their own new barrels to be true 750's.

Many TZ750 motors and early 700's were fitted with TZ250 barrels and run as 500's in side cars. I have also seen a TZ750 fitted with one 350 barrel and one 250 barrel to qualify for the 600cc postclassic junior class until the rules were changed to limit bigger 2-strokes to 2 cylinders.

I have also worked on the engine of a speedway car that had special home made crankcase plates and four TZ750 barrels and modified RD cases and cranks. This car went like a cut cat. It had a habit of breaking conrods but did not visible slow down untill it had let go at least three rods. The rods would wrap themselvs around the bigend pin. It could go out, break a rod or two and continue competitivly in a race and finish.

.

**F5 Dave** · 20th November 2009, 17:23

Originally Posted by SS90

Hmmm, lots to catch up on here, but did you manage to find out what year they would likely be?

Well I've proved I'm no expert on the matter, but I did stumble across this in the Tips page of the same site/

1. Barrels:
F or G model 350 barrels are best, i.e. 6 port. They are easier to ride.

that was 79 & 80 so not those years is at least certain.

I may become more educated when I get to that chapter as the site seems a bit of a mishmash of info, I'd trust the book as more well researched.

**TZ350** · 20th November 2009, 19:08

.

The last of the 350 barrels were 6 port but SS90's pictures are of 250 barrels. You can tell they are 250's by the thicker cylinder spigot. I am not sure if 250's were ever 6 port, but the last of the conventional twins, the "G" I think had a really wide inlet port and an appetite for pistons and also an odd bore size, slightly bigger. It was possible to mix up the new style pistons and old cylinders then they would seize, it caught a few people out. http://www.tz350.net/tz250page.htm portmap for the TZ250 from 1976 to 1984.

.

**TZ350** · 22nd November 2009, 06:24

I am working on making a copy of the "Darcy" pipe.

Lots of info on pipes at the bottom of the page for the RG500 which could be suitable for a GP125 as there are a lot similaritys between the RG500 and GP125 rotary valve engine.
http://homepage.mac.com/rg500delta/d...pe_design.html

How to go about a graphical analysis of the wave action in the pipe your designing
http://homepage.mac.com/rg500delta/d..._pipe_analysis

Plots of various pipes
http://homepage.mac.com/rg500delta/d...%20designs.pdf

Spec sheet of the Darcy pipe.
http://homepage.mac.com/rg500delta/d...cyPipeSpec.txt

Dyno runs. http://homepage.mac.com/rg500delta/d...cy%20test1.jpg

Chambers, NedKelly and myself with Thomas's help, are working flatout building new pipes, engines with better breathing, diffuser carburettors and tweeking the suspension of our GP's for Taupo. Its just amazing how long it takes to do the simplist things. For the last three months we have been staying back after work most nights and some Saturdays and are still running out of time.

.

**koba** · 22nd November 2009, 18:32

Originally Posted by TZ350

I am working on making a copy of the "Darcy" pipe.

Lots of info on pipes at the bottom of the page for the RG500 which could be suitable for a GP125 as there are a lot similaritys between the RG500 and GP125 rotary valve engine.

My MB100 runs a right rear RG500 Pipe. (I think) It goes good, Having a guess at what to do I was going to add a wee bit in the belly section to bring the revs down a wee bit but I may have another plan now.

I drew it up and overlayed it on a drawing of the RM125C Pipe as provided in A. Graham Bells book and it was VERY similar except the RM had about 18.75mm more in the belly section...

**TZ350** · 23rd November 2009, 18:23

.

Motor number two with reduced crankcase volume, opened up transfers, bigger inlet tract, race style forged piston, RGV250 rod kit, KX80 ignition, 24mm diffuser carb and the good old faithful copper head.

Pic-01 engine number two.
Pic-02 24mm diffuser carb
Pic-03 piston with the transfer widened and a small boost port in the back
Pic-04 cases with the bigger inlet tract and opened up transfers
Pic-05 KX80 ignition, fixed point, hope to change this for a suitable retarding unit later
Pic-06 opened up the transfers with the port roofs Devconed to a higher angle on the front transfers and flat at the back

I have tried to incorporate all those ideas put forward by SS90, F5_Dave, Speedpro, Sonic_V, K14, Buckets4me, Bucketracer, Sully60 and others recently. I am hoping for the same power, but at lower rev's with a wider power band. Looking forward to getting it on a dyno soon.

Now to start assembling the RG50 engine.

.

**TZ350** · 27th November 2009, 21:16

.

Thanks Sonic_V I have just realized that there is a very interesting source of technical info on Kart engines. Its the homogolation tech sheets from the

"COMMISSION INTERNATIONAL DE KARTING - FIA"

Here's one that has chamber dimensions and drawings of the ports for the engine in the first picture.

http://www.ak-racing-shop.de/ak-raci...%2030-M-09.pdf

.

**bucketracer** · 28th November 2009, 06:42

.

Handy crank angle to piston position calculator

http://www.torqsoft.net/piston-position.html

.

**bucketracer** · 28th November 2009, 22:31

.

Ok here is one for you TeeZee

The 125cc Parilla Sudam engine is an amazing engine package. This engine built as an open with dual carbs and stroked crank is capable of a reliable 55+ horsepower.

http://buller.net/cat--125cc-Parilla...eng_sudam.html

.

**TZ350** · 29th November 2009, 06:46

Originally Posted by bucketracer

.

The 125cc Parilla Sudam engine is built as an open with dual carbs and stroked crank capable of a reliable 55+ horsepower.

http://buller.net/cat--125cc-Parilla...eng_sudam.html

.

Thanks for the tip. I looked the engine up. Bored+Stroked = 130+cc and running on methanol = 55+Hp at the crank.

From what I can make out the standard 125 version on pump fuel is in the low/mid 30's for Hp.

Very encouraging though, because it means that air cooled 125's can make much more Hp than I thought.

People had been telling me the thermal limit of an air cooled engine on petrol is in the high 20's well it looks like we can go to 30's OK.

Very exciting............BIG rwhp here we come..

.. FXR's.....get a

and

while GP125's come

.

I already have the copper cylinder head and barrel cooling to do the job and am getting the retarding ignition thing worked out.

Plus some other ideas like bronze clutch plates and a gear box oil cooler so I can really cane it coming out of the corners.

By following Sonic_V's tips we have been able to greatly increase the air flow through the regulation 24mm carb.

So it might be possible to make a F4 GP125 with a mid 20's rwhp setup for long tracks, too late for the Taupo TRRS this Xmas but maybe for next time.

Next year looks interesting already, the promised land beckons.

.