KR-1S.co.uk Forum

TwoStroke Institute wrote:

mj43 wrote:

TwoStroke Institute wrote: I call it 'closing' because of closing the resonator, you could say opening the sub ports.
I meant the original curve posted.

The curves exhibit the characteristic flattening in the power curve around 8K that happens when the power valve opens the sub port (KIPS). It might be only one cylinder is opening? I did have a KIPS linkage come off once in a race and there was a noticeable drop in power - pulled in as not worth carrying on.

Same thing happens with Aprilia 125's with a solenoid PV, it's the on/off, yes/no, open/close nature of this type of PV. The Aprilia is sensitive down to 100 rpm , the further you get away from optimum the bigger the dip.
Varying the resonator volume might ameliorate the effect. I have a plan to make a 2 stage or a variable volume resonator(but a variable length pipe works the best)

I don't see the sense in machining of the top of a cylinder , looses the power stroke and worse it's irreversable.

this reminded me of a problem I had on my last ride out with my home made links. Suddenly my engine was making much less power and didn't feel like wanting to rev as before, but everything else was normal and it didn't feel like the engine was going to let me down completly soon. So after a couple of miles I stopped (where it could be done safely, that's why I didn't stop immediatly) and after just looking at the engine for a bit, I found that the right powervalve of the right cylinder had "changed direction" : because of the design (a small error on my part probably ) the valve has passed it's endpoint and was now working the other way if you know what I mean. Just pushed it back and everything was fine.
So yes, one powervalve (especialy one with a resonator chamber) not working correct makes a big impact

after my bike only making 42bhp at the last meeting, i stripped it down, changed the outer two crank seals, fitted a new gearbox shaft and bearing, fitted KR1S expansion chambers, fitted KR1S CDI, alligned the powervalves, put it on the dyno to find it still smokes like a trooper, drinks gearbox oil and only makes 40bhp at the back wheel - ARSE!

time to get all dirty (again) fit another engine - back later

It might be drinking gearbox oil from the centre crank seals Tricia? The balance shaft runs in gearbox oil so it could be coming in from there. Especially as the centre shafts are made of chocolate.

Good luck!

Dan

which engine was that you were trying?

just put the road engine back in, started up ok, ran for a while, then the water pump pipe o ring failed and had to take the side casing off.

Shit luck or what

that's rubbish, but I think you should stick with that "road" engine for this weekend.

right, made a new gasket, installed a new o ring, put it together, ran it up to temperature and all runs ok - no leaks, Yay!
cases are flowed, but the head and cylinders are standard. Think I might leave it as is though.
Off to the dyno again tomorrow, hopefully see more than 42bhp.
Incidentally, I'm running 35:1 oil (motul 800), is that Ok?

Even with a stock top end you should be seeing mid 50's on the dyno which is a vast improvement.

I too run Motul 800 at 35:1.

Look forward to some more positive news tomorrow, fingers crossed

How did it fair today?

put some new fuel in today, started it up, warmed up, shut down.
Put the seat on so that I could put it in the van, tried to start it - wouldn't start. Checked plugs, bright spark - Check, smelt the plug, fuel getting in - Check. Basically no matter what i did it wouldn't start. Took the carbs off, cleaned them out, blew them through with an airline, put them back on...kicked it over...it fired once and stopped and wouldn't start again.
whipped off the 35mm carbs, put the 28's on....first kick, it starts.
Put it together, load it in the van, take it to the dyno.
Putting out about 48hp at the wheel and lean in the midrange and about 13.5:1 at 11k running 140 mains. Didn't have any 142.5's but did have some 145's. Did another run, peak power down about 0.5hp, but a little rich at the top.
So, basically, 48hp is better than yesterdays 40hp and 6hp up on the first meeting - so that will have to do, not the mid 50's I would have hoped.
Would be better off racing my NC30 which is making 59hp (running lean)

Putting out about 48hp at the wheel

I may be way off the mark here, so I apologise but........

Isn't horsepower only part of the equation? It was something that Maccas mentioned in one of his posts about shaving a few grams here & a few grams there & I questioned why, to which Janbros replied something like 'a few grams off each component adds to a greater weight loss on the whole'.

And then there is aerodynamics, the Kr1 fairing is essentially late 80's tech, so I assume, way behind when it comes to 'cutting through the air'

And even with the little I know about race bikes, the one thing I do know is out & out power does not make a good race bike but driveability does.

Please feel free to shoot me down but if you don't ask, you don't find out.

Plus I have to ask, why are you using 35mm carbs?

Power isn't everything that's for sure, but to put it into perspective, you're racing other machines with anywhere from 60-70bhp, you want to be somewhere close to everyone else.

You need a complete package in racing to be competitive and all the other bikes will also be in good shape suspension wise.

Even with the best chassis, if you're 12bhp down on the least powerful machine, that's 25% and it's going to be a struggle.

Fortunately Brands indy is quite flowing, so that will help a bit.

Sorry you're not getting as much out the engine as we hoped, but I'm sure you'll feel an improvement and make the most of it.

I'll come find you after qualifying, good luck.

I totally agree that it isn't all about peak power, but it gives you a good indication that the engine is working well. One of my best seasons was on a TZR250 in the supersport class, simply because the TZR had a massive midrange that I could exploit.
I would say that my bike is pretty aerodynamic as it uses an RS125 fairing which is nice and curvy.
BTW - I'm not using the 35's as I couldn't get the engine started with them on, so I switched back to the 28's.

Mainly miffed that the crank I sent to BDK for a full rebuild came back with leaking middle seals (it cost a lot of money)

Are you two racing at Brands this weekend,

I'm not, just going down to see Mick Stokes of the 2-stroke GP series and also give our scooble some moral support.