revtothelimit - motorbike forum

weeksy wrote: Thu Oct 01, 2020 2:03 pm
IN simple terms, to run with the group, it's pretty damn tough on bikes that are underpowered.

I've no interest in "running with the group", as I said the reason for me being on track is to push my cornering limits, not ride round with my chums.

Tricky wrote: Thu Oct 01, 2020 2:11 pm but a YPVS can still be made to go round corners and get around a circuit at a decent speed without needing expensive special bits

Probably find out next year, as the intention is to use it on track, if it floats my boat more than my FZR400 then the FZR will be sold (well maybe, as selling bikes isn't something I like to do and it's only worth about £1500)

Ace stuff, I like these little bikes because as we get older and slower we can now blame the bike

My CBR500R is 52hp at the wheel but does weigh a fair bit more than the 390 so it’ll be interesting. The Enfield will be mid to high 50’s with the cam and high comp pistons but again weighs more and has a much more basic chassis. I can imagine the ktm and Honda being fairly equal. I’ve never been this excited about a trip abroad before

I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

Nobby wrote: Thu Oct 01, 2020 5:38 pm I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

When you came to see me I couldn't get under 1m dead... it was a bit cold and I'd never been before and the sun was getting in my eyes and, and, and...

KungFooBob wrote: Thu Oct 01, 2020 6:44 pm

Nobby wrote: Thu Oct 01, 2020 5:38 pm I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

When you came to see me I couldn't get under 1m dead... it was a bit cold and I'd never been before and the sun was getting in my eyes and, and, and...

and I still haven't told anyone. But then you were on a bit of a , and in Trickys day, the Track layout was 3 seconds faster.

Couchy wrote: Thu Oct 01, 2020 4:52 pm Ace stuff, I like these little bikes because as we get older and slower we can now blame the bike

My CBR500R is 52hp at the wheel but does weigh a fair bit more than the 390 so it’ll be interesting. The Enfield will be mid to high 50’s with the cam and high comp pistons but again weighs more and has a much more basic chassis. I can imagine the ktm and Honda being fairly equal. I’ve never been this excited about a trip abroad before

Yeah me too, gonna be proper fun , and the first time in a gazillion years that I'm even considering taking a selection of sprockets to a TD

Nobby wrote: Thu Oct 01, 2020 5:38 pm I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

Nah, I never even bothered getting out of bed unless it was torrential rain or snowing - anyway, you're older than me , so it stands to reason you should have been even fasterer than me

Tricky wrote: Thu Oct 01, 2020 6:55 pm

Couchy wrote: Thu Oct 01, 2020 4:52 pm Ace stuff, I like these little bikes because as we get older and slower we can now blame the bike

My CBR500R is 52hp at the wheel but does weigh a fair bit more than the 390 so it’ll be interesting. The Enfield will be mid to high 50’s with the cam and high comp pistons but again weighs more and has a much more basic chassis. I can imagine the ktm and Honda being fairly equal. I’ve never been this excited about a trip abroad before

Yeah me too, gonna be proper fun , and the first time in a gazillion years that I'm even considering taking a selection of sprockets to a TD

Nobby wrote: Thu Oct 01, 2020 5:38 pm I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

Nah, I never even bothered getting out of bed unless it was torrential rain or snowing - anyway, you're older than me , so it stands to reason you should have been even fasterer than me

I'm older than everyone. Guess where I'm off to in the morning ? The weather should be right up your street.
#takesomeextrastrapstotieevertthingdown

Nobby wrote: Thu Oct 01, 2020 6:53 pm

KungFooBob wrote: Thu Oct 01, 2020 6:44 pm

Nobby wrote: Thu Oct 01, 2020 5:38 pm I could get mine around Brands Indy in the 57s and Snetterton in sub 1:20 -

That's unlucky , didn't you ever have any dry races ?

When you came to see me I couldn't get under 1m dead... it was a bit cold and I'd never been before and the sun was getting in my eyes and, and, and...

and I still haven't told anyone. But then you were on a bit of a , and in Trickys day, the Track layout was 3 seconds faster.

Oy! that's not fair, thought that us old has/never-was-beens would stick together!

( Bottom bend was possibly teeny tiny bit faster in the olden days, but that was it- 3 seconds my arse- maybe on a push bike.... )

I’ve been in the classic race shop next door eyeing up race fairings, I reckon the Enfield could benefit from one and a +1 front sprocket

Tricky wrote: Thu Oct 01, 2020 7:02 pm

Nobby wrote: Thu Oct 01, 2020 6:53 pm

KungFooBob wrote: Thu Oct 01, 2020 6:44 pm

When you came to see me I couldn't get under 1m dead... it was a bit cold and I'd never been before and the sun was getting in my eyes and, and, and...

and I still haven't told anyone. But then you were on a bit of a , and in Trickys day, the Track layout was 3 seconds faster.

Oy! that's not fair, thought that us old has/never-was-beens would stick together!

( Bottom bend was possibly teeny tiny bit faster in the olden days, but that was it- 3 seconds my arse- maybe on a push bike.... )

"Graham Hill Bend" was flat out from Druids all the way to Surtees on a 250 , whereas now it's on the brakes , down 1* and accelerate out. That stretch could also now be a smidge longer.
I could ask around this weekend , but when I start up about the good old Days , they look at me like I'm some kind of old c#$t
* or 2 depending.

Harry wrote: Fri Oct 16, 2020 4:36 am This is my LC curve.
Standard bike with matched/balanced pistons and a power dynamo ignition - but other than that it's a standard engine.

The peak figure was 45.5bhp @ 9248rpm - but as you can see after 8,000 not much is happening, mostly because of restrictive exhausts.
I reckon 45bhp for a standard bike is very good on an LC, it was previously 39bhp but the NOS barrels, balanced and matched pistons, plus a magic ignition gave it 6bhp.

I think the bendy frame would let it down in a race against the KTM, but it would be fun.
(I was only ever a mid-pack club racer and these days I'm a 'go steady because no one will pay the bills if I'm knackered' racer.
I'd have a go, but I reckon a lack of skill on my part and a superior frame/engine/suspension on Tricky's bike would see him winning.

I reckon if you put two identical riders on the bikes then the KTM would win, easier power, less fickle delivery to the back wheel and a more taut modern set-up.

That's proper funny how the power goes up a cliff I have never ridden a proper 2 stroke (only mopeds) but I imagine this is the power band people speak of...

45 bhp from a stock LC is good, the Yamaha press bikes made 43 when dyno tested by Motorcycle Mechanics (became Performance Bikes in 1985) they tested a YPVS at 49 bhp.

I think the KTM will be faster round a track, I think a stock Yamaha R3 would be faster round Cadwell than a YPVS, just because the chassis is a lot better, I'm more interested to see how the engines compare, if a modern 4 stroke single can make similar power to a two stroke of a similar capacity, especially the torque, my 1991 FZR400 makes more power than my YPVS, but it does it at 15000 rpm not 9000 rpm, the YPVS has far more torque than the FZR

A well sorted YPVS, or TZR250 for that matter will smoke a standard 390 in a straight line, at least one without a fairing- I did a few TDs on my 390 Duke, and at Rockingham there were a couple of YPMs, both 3MAs, one of which I had real good fun with in one session, every single lap he would breeze by me on top speed 3/4 way along the front straight , but having said that, my last 390 would just about break 100mph on the clock flat out with chin on the tank, a decent LC or TZR has 20mph on that
The new baby , being an RC390 does of course have a fairing, so am pretty sure that will help a good bit at these power levels, and am also hopefull of a few more hp at the top end with the airbox and exhaust mods, and who knows whatever else

Having said that, I've not done anything with this one yet, but for interest, and comparison with Harry's graph, this was my 2017 390 Duke after a morning on the Dyno fiddling with the fuelling and ignition maps.
The line that says "all stock" isn't in fact all stock, it was with Powertronics developed generic map for the 390 on there- all stock it was peaking at just about 39hp, with a very jaggedly curve and AF very lean

My old 400cc Honda CB1 with 33bhp restrictor washers in could crack a tonne, so I'm a bit surprised a much newer and more powerful bike struggles to.

It was only dragging my 17 year old 10.5 stone arse around TBF.

The KTM probably has a more truthful speedo than the CB1
For reference my standard 250LC scraped an indicated 100, my 350LC with Microns indicated 115 with no problems, YPVS 350 with Allspeeds indicated 120, with a stage 2 Stan Stephens tune about 130, I think the speedo only went to 120 or 125, and with Lomas pipes probably about 135, it has to be remembered that in 1983 when the YPVS was first made the only bikes that genuinely did more than 135 straight off the showroom floor where the Unitrak GPZ1100 and the CB1100R, I don't know about the CB but the YPVS could easily out corner the GPZ.

My very tired 1986 TZR250 did about 105mph, but it handled really well.

I'm not expecting great things from the YPVS I've got now, I weigh 35% more than I did when I had the last one, so I'm expecting a top speed of about 110mph, and I won't be surprised if that turns out to be nearer 100mph

Julian_Boolean wrote: Fri Oct 16, 2020 12:07 pm ........
I'm not expecting great things from the YPVS I've got now, I weigh 35% more than I did when I had the last one, so I'm expecting a top speed of about 110mph, and I won't be surprised if that turns out to be nearer 100mph

Bring it to Porto and give it a proper run out

(probably advisable to pack a few spare pistons too- i's a long main straight there )

Time for a bit of an update.
Work for me over the last 6 months or so has been fairly hectic, and that coupled with a fair bit of domestic stuff including buying another house has meant that the little RC has had nothing done to it since I bought it, apart from being started every couple of months or so. I’m now in the new (to us) house though and starting to get my bikes and tools etc over here so last night I managed to get some garage time.
First thing for attention is the suspension, and I started at the rear, as the easiest first.
The standard RC390 shock is perhaps the poorest quality fitted to any non-Chinese tank badge production bike. It is completely devoid of any (compression or rebound) damping, has a non-linear spring, and absolutely no form of adjustment possible so it has to go.



As mentioned previously I have a decent nick OE R6 shock here, which although undoubtedly nowhere like leading edge and knocking on in years, has had very little use and is the same eye-to-eye length as the standard RC390 unit, uses the same 10mm mounting eyes, and will hopefully provide a decent starting point.
As standard, however, it’s a well under-sprung at 93N/mm for someone of my size on the RC, so a new 105N (educated guess) spring was purchased and fitted.





The spring swap itself is a straightforward affair, (assuming of course that you have a pair of suitably sized spring compressors, which I do), and the actual shock swap itself on should be just about as simple as it can be on this one , as there is no linkage involved, and the mounting eyes are both reasonably easily accessible.
The task was however complicated somewhat by the previous owner’s love of Loctite- decent thorough chap as he obviously was, he's replaced most of the little cheesy KTM bolts with stainless button heads and loctited stuff that doesn't need it, and in fact there is good reason not to.
It was a fecking right pain in the arse on the hugger and chainguard bolts- the issue is they screw into those horrid little U-clip captive nuts, which just twist and deform with the amount of effort you need to break full power Loctite.
Anyway, eventually, I managed to get enough of them out to get to the shock mounts, and the “ new” R6 shock is now in there.



Needs a little shimming on one of the mounts, and the shock reservoir fouls the rear brake reservoir but neither of those are biggies and will be easily sorted. Not got as far as measuring and trying to set sag yet, but from a highly scientific sit and bounce , the first signs are 105N spring is probably about right and it feels good.

The big question I’m still mulling over at the moment is what to do with the front, which as it currently is, seems significantly under-sprung- hard to know RE damping at this stage but they are budget-level forks and un-adjustable so as they are, the options are, in order of ascending cost:

• New springs more suited to my weight and intended use, and perhaps different weight oil- this will cost me £270ish installed from a specialist such as SSR or approx. £100 in parts if I do it myself. May possibly improve things but is never going to be great and still won’t leave me with any adjustability without strip-downs to increase pre-load or change oil weights.

• A second-hand set of Cup forks- these look pretty much identical externally but internally they’re not. Fully adjustable, these retail for £1400, but can be had on the SH market from time to time for £600-ish. Still a big chunk of change on a £2k bike, but chances are prices may come down as the 390s don’t seem to be the bike to be on in SS300 these days

• Cartridge kit with springs etc. SSR are coming out at £700-800, more than a SH set up cup forks and more than I want to pay on this bike, but of course there’s the confidence that with this route the forks are going to be in top condition when they go in, always a risk going SH

Am still thinking it over, and ’ll decide over the next couple of weeks or so.

As for other stuff, I’ve got it booked in at my dyno place end of next week. A serious family illness there means that unfortunately I’ve got to drop the bike the day before and I’m not going to be able to stay there and be part of it whilst it’s all going on this time, which is a disappointment, but they’re good guys and won’t affect the end result.
Anyway, watch this space for much excitement - exciting dyno graphs with massive power to follow in the not too distant!

Knowing how you want to ride it along with how long you'll usually keep bikes, it would make sense to me to go with the Kit forks, mostly because they should be good and should also have a residual value if you sell the bike.

weeksy wrote: Wed Feb 17, 2021 9:16 am Knowing how you want to ride it along with how long you'll usually keep bikes, it would make sense to me to go with the Kit forks, mostly because they should be good and should also have a residual value if you sell the bike.

Cheers and yep, my current thoughts too