Another Track Day

I did 2 x 20 minute sessions on the bike at Hampton Downs on Wed. March 20th.
The bike ran well and the 41 tooth rear sprocket was perfect in terms of just reaching 12,000 rpm at the end of the main straight. Very enjoyable!
Paul seemed to think that the bike didn't sound all that crisp anymore.
I was clocked at 1 min 22.4 seconds for a lap.

I did 1 x 20 minute session on the blue fairing NSR250 that is shown in some of the pics on this blog.
It is an MC21 engine in an R2j frame running PGM-1 ignition. (no battery required).
I was pleased to be able to notice that my bike was noticeably quicker than the blue bike.

I want to pull the heads and barrels of my NSR and maybe give the barrels a very light hone and fit new rings.
I also want to get the thing on a dyno, and get a horsepower reading.
This will have to wait though as I have other priorities.
Am heading into winter now, so,..   may go into hibernation for 6 months.

A look up the exhaust ports

I took the pipes off to have a look up the exhaust ports.
OK, well this doesn't look the best.
I did have a few high speed "clutch in" moments during the first 300kms.

I am fairly sure that this was due to the petrol tank breather not working properly.
This meant that a slight vacuum built up in the tank and hence petrol flow into the float bowls may have slowed down to a dribble or less and resulted in a lean condition after a while at high revs and max throttle.

I fixed this problem before my first track day and it seems to be running pretty good now at prolonged high revs/throttle.

Sadly it seems that the LH Cylinder in particular may have come quite close to seizing at some stage?
I am hoping that it will survive the next track day. Then I will pull the heads off and check this out properly.
Looks like I will probably be taking the barrels off as well.
Bloody fuel tank breather!!! Argh.

RH Cyl

LH Cyl

RH Piston

LH Piston

Scorchers

41 tooth Rear Sprocket

In order to get the gearing right for Hampton Downs racetrack, it seems that gearing of 15 tooth front, 41 tooth rear is going to be about right.

I ordered a couple of 41 tooth rear sprockets from TYGA Performance.
Including freight they cost NZ$179 or approx NZ$90 each.
I ordered them on Friday and they were at my door 8:30am Tuesday, from Thailand.

The TYGA 41 tooth rear sprocket weighs 293 grams Made from a type of aluminuim called Duralium? and anodised for hardness.
The standard Honda 42 tooth rear sprocket weighs 830 grams.
So, a nice way to save half a kilo.

When I went to fit the sprocket I found that my 110 link chain was too long and I had to shorten it to 108 links.

110 links works for 15/42,.. just. If things wear/stretch a bit, there is little or no adjustment left at all.
110 also works for 16/42.

Link Plates, Gear Shaft Extender, Radiator Bracket

Today I fitted the "compromise" rear shock Link Plates. (see previous post)

I also fitted a proper gear shaft extender so that the gear change mechanism no longer rubs on the frame.

I also fitted the little bracket that bolts on to the bottom head and holds the bottom pin of the radiator.

"Compromise" rear suspension link plates fitted 01

"Compromise" rear suspension link plates fitted 02

 I plan to do another track day in approx 10 days so it will be interesting to see if I notice much difference.

Rear Suspension Link Plates. Part 3

Yesterday, a couple of friends and I played around fitting different link plates to an MC18 R2j.

We compared the link plates by measuring the distance from the centre of the rear axle to the centre of the bolt that holds the rear fairing on just behind the riders seat.
18 " rear wheel.
Bike standing under its own weight.

The standard link plate measured 478mm
The standard link plate turned to have the "F-->" pointing up measured 488mm
The Compromise plate measured 504mm
The HRC plate measured 521mm

So very basically:
The HRC plates raise the ride height by about 43mm
The compromise plates raise ride height by about 26mm

The HRC plate makes the bike "look" way better in my opinion. However, the rising rate becomes pretty stiff pretty quickly. Great for the track, but perhaps a bit much for the road?

The compromise plate probably actually is quite a good compromise for road riders that want to do the odd track day. But it is very simple to change this part anyway.

See previous posts:
1) http://edetuckracing.blogspot.co.nz/2011/11/rear-shock-link-plate-options.html
2) http://edetuckracing.blogspot.co.nz/2012/11/rear-suspension-link-plates.html

MC18 R2j with HRC link plates (521mm) on right.

I recently put the "compromise" plates on the R6k and the distance from rear axle centre to rear fairing mount measured 521-2mm. About the same as the R2j with the HRC link plates.
I guess the subframe/geometry differs slightly from R2/4j to R5/6k.

Track Day

Yesterday I attended a twilight session at Hampton Downs racetrack.
I did three sessions out on the track at 15 minues each (22 km each)
Standard jetting except for 125 mains, plus 2 x ø20mm holes in the side of the NSR250 airbox.
0.8mm squish. 12.8cc combustion volume (to the top of the spark plug hole)
Running 95 RON and oil pump set to standard (approx 37:1 ?) on Castrol Power1 TTS fully sythetic oil.

The bike was slightly under geared for the track with standard gearing (15F 42R)
Speedo indicated approx 195 km/h at approx 12,200 rpm just before braking at the end of the straight for turn one. It was pretty difficult to take in these numbers with turn one looming :-)
Rear wheel circumference of 2010mm.

Plug chop photo below:

It actually looks slightly whiter in the photo than it does in real life, (on my computer).
I think that's about as lean as I would ever want to go.

I was typically changing gear at approx. 11,500 rpm.
Slight issue at very small throttle holding constant speed through sweepers.
[more to come]
Overall,.. extremely happy with it.
So cool to finally get my knee down on my own NSR250 again. (20 years later)

Oh, and also, the day before, I played around trying to calibrate the TPS.
But I didn't have any proper information to go by.
Calibrate TPS. <<== click here.
Perhaps someone can tell me the correct way to calibrate the TPS?

I put on the old damaged original fairings for the track day:

The screen is the one that came with my Chinese fairings. It doesn't really fit properly.
It distorts into a sort of "high rise" screen when forced to fit.

I ran out of time to play around with the different rear shock link plates.

Air Correction Solenoid - Air Filter

Today I decided to prise apart the little air filter that supplies air to the Air Correction Solenoids when they open up to allow for extra air flow into the carbs to correct for the effects of the power jets kicking in.

This is a little part that never seems to get much of a mention and is largely ignored I guess?
Probably because nothing ever goes wrong with it.

There was a small build up of lint on the side of the filter connected to atmosphere, but basically it was OK.
I was just curious to see what it was made up of more than anything else.

As can be seen in the picture, there are 2 circular filters. One is paper like, the other is kinda like synthetic wool or something?

In any case, it was easy enough to blow air through the filters, so I guess they are fine.