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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 31651 times)

Online JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #230 on: Feb 18, 2019, 10:17:22 »
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.

Very true.  Unfortunately I can't see another way to increase trail without compromise.  There is one option left and that is to design some custom triple tree clamps with less offset to increase trail.  Because the rake/caster is actually pretty good.  But then if I am designing custom triples, I may as well install a modern fork.  And I really don't want to do that!  Maybe I should look into an anti-dive system  ;D

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #231 on: Feb 27, 2019, 16:03:14 »
And now for something completely different...  I was/am not planning on spending much time on styling/finishes on this build as I did with the last build.  But that doesn't mean it won't look cool, just a little more function over looks.

Anyway, I was going to go for a completely raw, materialistic look - all aluminium parts bare aluminium, all metal parts rattle canned black and then I was going to strip the tank, brush it and have it clear coated for a nice raw look - see attached.  However I recently got inspired by a customers bike in Poland (the SR was a Police bike there for many years  ;D ).  His bike had the original tank in white and it had gained some really nice patina - the typical collection of grime around the filler cap, a few scratches and dings, then this really nice yellowish brown in some places where fuel had been spilled on it and it had weathered differently there.  This gave me the idea that perhaps I want to keep the original paint - it is kinda cool after all, in brilliant orange.  Plus it has a really stylish 'SR' on the sides.  Then I would reuse the stock headlight too, which also has some nice patina.  I then looked at one of my favorite bike books for some inspiration and yes, I really like the rough, old bike look - check out the cool Nougier Four.  Yes, I will need to 'cheat' in some places for some parts that are new, but I won't do anything special with them, just leave them uncleaned and unpolished and let time do it's work.  What are people thoughts on this idea?

It also leaves me with a dilemma of how to remove the one massive dent in the middle of the tank while retaining the paint... Anyone tried one of these kits?...


Offline advCo

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #232 on: Feb 27, 2019, 16:23:38 »
The dent puller should work since its not bad and really no hard creases. You can also try a blood pressure gauge from the inside, inflate it to pop out the dent.

Offline wozza

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #233 on: Feb 27, 2019, 17:12:49 »
The cheaper kits dont really work on fuel tanks as the metals a little to thick...have tried and failed....

Offline advCo

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #234 on: Feb 27, 2019, 17:32:27 »
You can also try getting a lever in there and pushing it out from behind. If you try this be sure to put a cushion on the end so you don't put a fresh crease in the metal from the back side.

Offline zap2504

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #235 on: Feb 27, 2019, 23:31:16 »
I tried a very similar hot-glue-gun-bridge device (Ding King brand) and it was so-so. Am following a guy on YouTube (Sweet Project Cars) and he had a couple episodes on using a slide hammer with hot-glue plastic pads. Was so impressed I got a set, but have not gotten around to using it. Many of the kits on ebay include hand or bridge pullers, but the slide hammer and plastic pads looks to be the best option.
I ended up doing the Virago 750 headlight mod to the OEM SR250 headlight ring to get a H4 replaceable bulb (we only got the weak sealed beam headlights in the USA). I think that had I to do it over, I would go with a 5 1/2" LED light assembly (think Daymaker).
« Last Edit: Feb 27, 2019, 23:35:00 by zap2504 »

Offline Brodie

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #236 on: Feb 27, 2019, 23:36:58 »
Crusty but trusty. I have quite a few bikes like that.
I'm not sure, but don't ask Brodie.

Way to many build and half done projects to list here.
Sr250, Gs750, Z50A, XV1100, A10, Z160A.

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #237 on: Mar 03, 2019, 12:36:07 »
Crusty but trusty. I have quite a few bikes like that.

Haha I love it.  Exactly.

Thanks for all the tips and info!  I'll give the slide hammer version that zap mentioned a go.  Makes good sense!

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #238 on: Mar 03, 2019, 12:48:06 »
I posted something on Instagram a couple of days ago about a header extension kit I am thinking of producing.  It lifts the silencer up to a 20 degree angle (matching the pillion peg bracket angle) to get more ground clearance and give a bit of a more sportier appearance.  It will clamp onto the existing Jadus header (or possible even the stock header).

For this build, I plan on using this extension to weld in a vacuum pick up for a PCV system.  On the third photo you see where the battery is positioned under the swing arm (the Jadus triangle tidy kit puts it there).  But for this build, with the elimination of the electric starter, the wire harness can be much simpler and therefor the battery too - so I have bought a 4 cell Antigravity instead of the 8 cell and the small battery will now sit under the seat in the electrics tray.  This then leaves space on the Jadus battery bracket for an oil catch can for the PCV system.

I have read a bit about this in Graham Bell's 'Four Stroke Performance' book and have a pretty good idea about how I will do it.  I have also read a bit online where people have had success with this system with thumpers - to combat the huge pumping losses.

Here is a great bit of info from zap a while ago in this very build thread:

'One thing to suggest to your list of engine mods is thinking about pumping losses. There was an article by Dave Searle in Motorcycle Consumer News about this a couple months ago. Thumpers are notorious here because they don't have other cylinders working together to offset the crankcase pumping action. Many builders just vent their crankcases to look "cool" but it really doesn't do anything to decrease pumping loss (just keeps oily junk out of the carb like an oil catch can would); I got a Krank Vent off evilbay to experiment with creating a partial vacuum in the crankcase instead of trying to get all that air in/out of that skinny hose outlet (still planning). Krank Vents are a 1-way check valve and seem to be very popular with the H-D crowd as they reduce crankcase pressure and keep gaskets from blowing. My thoughts are that the engine will pump through the Krank Vent a couple times until the partial vacuum is created, then no more pumping.'

Does anyone have a link to that dudes build thread where he made a similar system for an LS650?  (must be huge pumping losses in a 650 thumper!).

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #239 on: Mar 08, 2019, 07:16:34 »
Since I sorted the frame geometry/suspension set up (rear shocks ordered, more on that later), it was time to sort out the riding position.  The clip ons are not sitting 100% correct but pretty close.  They will drop about 20mm once I trim the top triple clamp.  But I will leave them there above the triple clamp rather than moving it down to between them.

So with the bars relatively set, the biggest task was to get the footpeg position right.  Which sounds pretty straight forward, but with not wanting to use the stock position (too low, too little ground clearance cornering) or the stock rear passenger peg position (too far back, too high, just awkward), I need to draw up a custom bracket.  But where to start?  I made a simple plywood template with a bunch or known/measured hole positions relative to the stock footpeg bolt positions.  After a a lot of playing around and 3 prototypes later (third proto printing now), I am pretty sure I got it right.  You can see the development in the images.  I wanted to get a comfortable position when crouched (and also aerodynamic-ish) plus a decent leg position when stopped at traffic lights etc.  This also worked out nice for a visual position with my knee right on the side of the tank where it should be.  To test all this I set the camera up on a tripod with a timer and took a bunch of shots with all the different positions - so I could study them and compare.  Don't laugh, I felt as ridiculous doing it as it looks haha  ;D

You can also see how much ground clearance there is at full lean (yeah right!!! haha).  The exhaust silencer will most likely be the bigger problem now, rather than the footpegs/my feet.