Messages

1

Tech Talk / Re: So what is the story with lowering transfer ports?

« on: April 22, 2019, 10:11:35 pm »

I have recently seen some two-stroke cylinders, and read some tech documents that show lowering the bottom edge of the cylinder transfer ports, below the top edge of the piston crown at BDC, some up to 6mm lower!!!

l'm guessing the only benefit to this is more exposure to a cooling flow from the air/fuel coming up the transfers, and/or maybe a more upward blast as the piston gets towards BDC?

Can anyone offer me some ideas here? :-)

I wouldn't be copying that.  Some tid bits from the documents still hold true . Piston crown is the hottest and the more slowly exiting cool intake charge that contacts the piston crown the better. With a single exhaust port the intake charge sitting in transfers is not going to start moving until BDC when the lowest pressure is in the exhaust . Be interesting to look at the next few years to see what changed

2

Tech Talk / Re: PVL ignition, too little or too much advance?

« on: April 02, 2019, 08:46:57 pm »

Depends how many winds in the stator that determines how much advance and retard it has over the static timing you give it.  They are well past their use by date. Just be thankful you never bought the digital

3

General Discussion / Re: All electric soon ?

« on: April 02, 2019, 08:44:10 pm »

 Not so long ago around the turn of the last century the automobile was begining to become common place, I'm sure there were many that said they will still be riding on a horses back etc etc etc. Are there still horses around now? If there are horses what are they mainly used for now?

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Tech Talk / Re: Exhaust port height on Piston-port 250 ?

« on: January 16, 2019, 11:51:42 pm »

Hey Chaps  :-)

I purchased a ported barrel for a Yamaha DT1MX, I'm concerned that this porting could be too radical.

This is a piston-port 250 with a bore/stroke of 70x64, much the same as early KX250, TM/TS250, & CR250M.

The distance from the top of the cylinder to the top of the exhaust port is 36mm, stock on these cylinders is 39mm.

Does anyone have experience to say if this is in the ballpark?

Regards, John.

Whats the rod length?

5

Tech Talk / Re: Smart carburettor

« on: December 10, 2018, 10:00:08 am »

http://www.pbase.com/jdjetting1/metering_carburetor_dyno_comparison&page=all

Thanks for finding that, the differences in all those runs look to be nothing more that run to run variations, the only run that was any different was torque from a Lectron.
50% improvement on emissions is impossible from a carby on a 2T. If you ride where there was big elevation changes the smart carb or Lectron/EI would be worth a try

6

Tech Talk / Re: Smart carburettor

« on: December 03, 2018, 10:23:17 am »

AS there is a broad base of knowledge on here whats the opinion of these?



https://www.enduro21.com/index.php/40-general/3751-first-look-smartcarb-a-smart-look-at-the-carburettor-problem

https://technologyelevatedco.com/smartcarb/

Snake  oil from a snake oil salesman. Other than altitude compensation does nothing that the carb you get with your bike. Not many race tracks (even Spa or the Nurburgring) have big enough changes in altitude to affect the jetting.  The "inventor" run away at a rapid rate when he was required to turn up with his carby at a dyno with a extremely well tuned RS 125 for a back to back test.

7

Tech Talk / Re: Wiring loom re-wrapping?

« on: December 03, 2018, 10:12:36 am »

You can buy non-adhesive loom tape or cloth tape on ebay, plastic over braid with heat shrink  works well or plastic spiral wrap. I normally go non adhesive tape and spiral wrap where the loom will be attached to the frame

8

Tech Talk / Re: Fuel tap

« on: November 08, 2018, 09:40:39 pm »

Would a 10mm bore be big enough on petrol Walter? These are awesome no poofy on/off tap just in is on out is off   https://www.vfv.com.au/8-15-2018-0-8590.html

https://www.vfv.com.au/8-15-2018-0-8608.html

9

Tech Talk / Re: Needle jet shroud height changes? Mikuni VM38.

« on: October 25, 2018, 11:22:07 pm »

What made you think to do that Baz? So does the shroud reduce the drop in pressure over the needle jet, so by you cutting it, you increased the vacuum (reduced atmosphere pressure) to eliminate a lean stumble?

Close the higher the shroud the richer the mixture will be ie increases the pressure drop around the needle. The lower the shroud the less fuel is drawn from the float bowl. 4T engines don't really need the shroud as the engine always has a good strong pressure signal, the shroud helps the weaker signal of a 2T.
You'll try a Dellorto one day and get to use either a 3,4,5,6,7 or 8mm high shroud independent of the jet needle/atomiser 

10

Tech Talk / Re: Curing handlebar vibration.

« on: September 17, 2018, 10:38:51 am »

But doesn't balancing a crank on a single cylinder only smooth it out at a particular rpm? So either side of that rpm it will vibrate?

Surely the manufacturers know the weight of pistons/rods/used rpm to get it correct in production?

Yes that is correct, however there are a few other factors the angle of the cylinder, closer to 90deg verticle the higher up the rpm scale the vibes move to closer to 90deg horizontal the lower down the rpm the vibes move to. That should dovetail with the balance factor ie big bore should mover the vibes up to 8-9000rpm and a 85cc down to 5-7000rpm 125cc cylinders are tilted forwards more than big bores

Tungsten is far more dense than lead and should stop 80% of the vibes at the bars, the most effective is to rubber mount the front engine mount(s) and the head stay, so the engine can move slightly in the vertical plane. They are the damaging vibrations and the ones you feel the most. The vibrations sap energy and concentration from riding.

Manufacturers aim to sell new bikes and curb warranty and liability claims :-)

11

Tech Talk / Re: Running Hot .

« on: September 17, 2018, 10:26:47 am »

That sucks Iain, if the engine is over heating (a cheap laser temp gun makes diagnosis easier) and the jetting doesn't go blubbering rich at the same time you must be very lean to begin with. Jetting will get richer with heat.

12

Tech Talk / Re: Suzuki ts/tm 250 road racer

« on: August 02, 2018, 10:47:04 pm »

Unless your a masochist with a big wad of cash and immune to disappointment, starting with a T250 or RD 250 is a better idea. If you dare to be different and want a engine that makes really good hp a rotary valve Kawasaki engine is the place to start.

13

Tech Talk / Re: Alluminium disc rotors, your thoughts?

« on: July 18, 2018, 12:24:45 pm »

Hey Guy's,

l've been thinking of making an alloy rear brake disc for either my dirtbike or roadracer. l don't use a rear brake overly hard; vertially never on my roadracer, plus l don't like a savage rear brake.

l was thinking that alloy might have a lower friction coefficient plus be much lighter (less unsprung weight and all that), yeh it would wear out quicker but eh?

Idea's on what grade alloy; less chance of shattering or warping?

Aluminium discs are plasma sprayed  I *think* Zanzani were the first to do that on the Kobas bikes early 80's ........................but local hot shot Aaron Morris who picks up a few rides with the French R2CL team in France (Le Mans24h and Suzuka) told me after 2 or 3 hours the rear brake goes metal to metal, they don't change it because of the time it would take at a pit stop and it feels just like you put a valve spring between the lever and m/c

14

General Discussion / Re: Chinese are coming along

« on: February 25, 2018, 10:52:39 am »

DT motor is a gem was just let down by running gear. The Chinger suspension won't be the best but nothing that can't be fixed. For sub $8k you get a lot of bike, great features billet hubs, servo power valve 6sp with balance shaft will make the motor as good if not better than the DT.
Can't wait to have a look inside the engine.

15

Tech Talk / Re: Need help with 240 volt tig welder selection please

« on: January 31, 2018, 07:29:56 pm »

You will need a 15 Amp plug and a dedicated 4mm2 circuit unless you like running out to the power box a lot. Plenty of people file the earth pin down so it fits in a 10amp GPO but normal wiring is only 1.5mm2

Don't know who wired your place Lozza, but power is run in 2.5mm2 cable, good for up to 20A.

A typo  ................ still need a stand alone circuit and might as well do that properly with 4mm2 and a 15A plug.