FWIW - I learned some time ago (in a reply to Jadus' build) that the "32mm seat post clamps for bicycles fit the fork tubes. It made it really easy and clean to make headlight ears with. Cut some ally plate and hand finish with a file and it turns out pretty nice."
Not another bloody SR250?
- Thread starter ManxKat
- Start date
ManxKat
Older but no wiser
Sigh. Perhaps that 535 front end wasn't such a good idea after all (fork tubes are 36mm)!
And a quick test run last night revealed:
- I seem to have stumbled on a half way decent suspension/ ride height set up. It's hardly MotoGP standard but it is predictable and the shocks/ forks work well together.
- I also seem to have lost about 20mph off the top end. Round town it's fine and picks up well but on the open road you get to around 60 and, well, the engine loses all interest in adding much more speed. Given how restrictive the stock silencer was (and the weird internal gas flow it used) that's not entirely unexpected, so there's some dyno time coming to restore the missing mph. A larger main jet beckons.....
And a quick test run last night revealed:
- I seem to have stumbled on a half way decent suspension/ ride height set up. It's hardly MotoGP standard but it is predictable and the shocks/ forks work well together.
- I also seem to have lost about 20mph off the top end. Round town it's fine and picks up well but on the open road you get to around 60 and, well, the engine loses all interest in adding much more speed. Given how restrictive the stock silencer was (and the weird internal gas flow it used) that's not entirely unexpected, so there's some dyno time coming to restore the missing mph. A larger main jet beckons.....
ManxKat
Older but no wiser
The dyno never lies (but it can be persuaded to bend the truth)!
As mentioned earlier, the mighty SR seemed to have lost some top end with the fitting of a new silencer. A thorough going over yielded two interesting contributory factors:
i) there was no tappet clearance at all on either valve but that's not entirely unexpected with a bike that has never been apart for any form of servicing - even the oil drain plug was pristine before I got my hands on it - so those were set to factory spec, and
ii) the speedo was lying! Who would have thought that a cheap and nasty push bike speedo might have been inaccurate? To be honest, it turns out I must have buggered up the spacing between the sensor and the trigger when the original glue gave out and I didn't look too closely at where I put the sensor back. Bottom line was that the sensor probably wasn't picking up the trigger with each revolution of the front wheel and hence the speedo was giving weird readings.
So, with a thoroughly cleaned carb (all jets on stock settings), a healthy compression reading and spot on timing, it was strapped to the dyno to see what the engine could do.
First run was surprisingly solid but, as expected, it was struggling a bit at the top end. We decided to remove the air filter's foam outer cover to see if that improved air flow and another little quirk came to light. Although the foam looked fine where it could be seen, on its inner surface it was badly deteriorated and chunks had been breaking off and heading into the carb - not optimal.
So, what was left of the foam was removed and the dyno fired up again. Bingo! Slightly rich at the bottom end but the exhaust gases were bang on for the rest of the rev range and a maximum reading of 15.5 horsepower! Not bad considering Yamaha quoted 18 - 20 horsepower at the crank when new. What I did find interesting was how little tweaking a healthy engine needed (i.e. pretty much none) to compensate for the stock silencer being replaced with something much less restrictive.
If the dyno printout looks a bit rough that's because it's the "raw" data before the software smooths it all out.
Basically, we're all good so it's time to sort out the headlight and speedo (again) to get the looks nailed before the final beautification process gets underway.
As mentioned earlier, the mighty SR seemed to have lost some top end with the fitting of a new silencer. A thorough going over yielded two interesting contributory factors:
i) there was no tappet clearance at all on either valve but that's not entirely unexpected with a bike that has never been apart for any form of servicing - even the oil drain plug was pristine before I got my hands on it - so those were set to factory spec, and
ii) the speedo was lying! Who would have thought that a cheap and nasty push bike speedo might have been inaccurate? To be honest, it turns out I must have buggered up the spacing between the sensor and the trigger when the original glue gave out and I didn't look too closely at where I put the sensor back. Bottom line was that the sensor probably wasn't picking up the trigger with each revolution of the front wheel and hence the speedo was giving weird readings.
So, with a thoroughly cleaned carb (all jets on stock settings), a healthy compression reading and spot on timing, it was strapped to the dyno to see what the engine could do.
First run was surprisingly solid but, as expected, it was struggling a bit at the top end. We decided to remove the air filter's foam outer cover to see if that improved air flow and another little quirk came to light. Although the foam looked fine where it could be seen, on its inner surface it was badly deteriorated and chunks had been breaking off and heading into the carb - not optimal.
So, what was left of the foam was removed and the dyno fired up again. Bingo! Slightly rich at the bottom end but the exhaust gases were bang on for the rest of the rev range and a maximum reading of 15.5 horsepower! Not bad considering Yamaha quoted 18 - 20 horsepower at the crank when new. What I did find interesting was how little tweaking a healthy engine needed (i.e. pretty much none) to compensate for the stock silencer being replaced with something much less restrictive.
If the dyno printout looks a bit rough that's because it's the "raw" data before the software smooths it all out.
Basically, we're all good so it's time to sort out the headlight and speedo (again) to get the looks nailed before the final beautification process gets underway.
Attachments
This is really cool! Pretty much backs up the results I found with two different stock-ish SR's (plus over 20 hours of testing). But I also took a closer look at the air-fuel ratios too (down there at the bottom of your graph) and even that is spot on to what I found.
Now to test some Jadus performance parts
;D Bikes looking great btw. I might be a little biased though
Now to test some Jadus performance parts
;D Bikes looking great btw. I might be a little biased though
ManxKat
Older but no wiser
OK, the Yam has been stripped and parts scattered all over the place for chroming, painting and welding.
First major reassembly were the forks. I took 25mm out of them by shortening the springs and machining up 25mm damper rod spacers. As I've mentioned earlier, these forks are off an early 535 Virago and if you're considering a similar exercise it's worth checking that the damper rod spacers don't cover up the rebound bleed holes (hence the spacers were actually made into two halves) - later forks may have different internals.
Next up was the engine which now looks a little tidier than the crusty lump that was prised out of the frame. After an internal health check didn't throw up any horrors, some external bling was applied in the form of a good polish for the outer cases, a finned oil filter cover and some really nice valve covers from Jake at Jadus.
Next stop: a freshly repainted (and pruned) rolling chassis.
First major reassembly were the forks. I took 25mm out of them by shortening the springs and machining up 25mm damper rod spacers. As I've mentioned earlier, these forks are off an early 535 Virago and if you're considering a similar exercise it's worth checking that the damper rod spacers don't cover up the rebound bleed holes (hence the spacers were actually made into two halves) - later forks may have different internals.
Next up was the engine which now looks a little tidier than the crusty lump that was prised out of the frame. After an internal health check didn't throw up any horrors, some external bling was applied in the form of a good polish for the outer cases, a finned oil filter cover and some really nice valve covers from Jake at Jadus.
Next stop: a freshly repainted (and pruned) rolling chassis.
Attachments
ManxKat
Older but no wiser
OK, I'm calling this one done (at least from a visual point of view, there's some carb fettling needed and the speedo to be calibrated but otherwise it's finished). The original brief was to turn an SR250 into something that looked like it rolled off Yamaha's production line in the late '70's or early '80's - I think it's pretty close and, anyway, it's certainly a whole lot better looking than what I started with! For me, that's a win.
If you're remotely interested, the build includes:
535 Virago front end – chromed mudguard, forks shortened 30mm, speedo drive blanked off, top yoke reworked to lose the stock "wings", satin black paint
Triumph T140 headlight, aftermarket brackets
Aftermarket clock, idiot lights and indicators
RD 250 bars (I think)
SR 250 controls (shortened throttle and clutch cables)
Stock tank – lowered with a Jadus kit
Jadus valve covers
Aftermarket oil filter cover
Jadus side panels
Jadus seat and rear frame loop
LC 250 tank and side panel badges
Reprofiled chainguard
Aftermarket silencer/ stock downpipe
Hagon shocks - 30mm over stock
Delugged frame, side stand extended 25 mm to avoid unsightly droop when parked
Aftermarket rear light
Time to go and get it filthy.
If you're remotely interested, the build includes:
535 Virago front end – chromed mudguard, forks shortened 30mm, speedo drive blanked off, top yoke reworked to lose the stock "wings", satin black paint
Triumph T140 headlight, aftermarket brackets
Aftermarket clock, idiot lights and indicators
RD 250 bars (I think)
SR 250 controls (shortened throttle and clutch cables)
Stock tank – lowered with a Jadus kit
Jadus valve covers
Aftermarket oil filter cover
Jadus side panels
Jadus seat and rear frame loop
LC 250 tank and side panel badges
Reprofiled chainguard
Aftermarket silencer/ stock downpipe
Hagon shocks - 30mm over stock
Delugged frame, side stand extended 25 mm to avoid unsightly droop when parked
Aftermarket rear light
Time to go and get it filthy.
Attachments
ManxKat
Older but no wiser
Settle down boys and gurls, it's tech time!
OK, there's now about 100 miles on the Yam since it was completed and I'm pleasantly surprised by how well it's all come together. The ride is on the firm side but that's my preference - the shortened forks are now running the stock capacity of 10 wt oil and they cope really well with everything the crappy Manx roads can throw at them. The riding position does encourage a bit of a slouch but it's not uncomfortable. Oh, and having a disc up front rather than a weedy single sided drum makes stopping a much more relaxed affair.
More importantly, an afternoon at the dyno has yielded some very interesting results – the attached printout shows the final outcome (the previous run is also on the graph, it’s the one in blue).
Using a Jadus intake kit with a 120 Main jet, 50 Pilot jet, stock downpipe and a silencer that's probably as restrictive as the stock item it's created a whole different feel to the bike from about 5,500 to 7,000 rpm and, at 6,500 rpm, there’s a genuine 15% power hike (from 14 bhp to 16 bhp) which just it makes it so much easier to ride. I’m never going to be troubling R1s but I now can hold gears rather than jump up and down the box to keep a constant speed up hills. I'm still playing with the needle position but the stock setting seems to work best for slow speeds around town.
My dyno guru reckoned that with a less restrictive downpipe and/ or silencer a 115 Main jet would work well and see the mid-range power increase carry on to the red line.
With a 17/ 43 sprocket set up the theoretical top speed is now 84.6 mph but I doubt I’ll get anywhere near that given it (together with me board) makes a house brick look aerodynamic!
The only issue was that all my cheapo, made in China LED idiot lights failed within five miles. Who would have thought that £1.25 items (with free postage no less) might not have been top quality? Sturdier items have been ordered.
So that's it, project successfully completed, thanks for checking it out.
OK, there's now about 100 miles on the Yam since it was completed and I'm pleasantly surprised by how well it's all come together. The ride is on the firm side but that's my preference - the shortened forks are now running the stock capacity of 10 wt oil and they cope really well with everything the crappy Manx roads can throw at them. The riding position does encourage a bit of a slouch but it's not uncomfortable. Oh, and having a disc up front rather than a weedy single sided drum makes stopping a much more relaxed affair.
More importantly, an afternoon at the dyno has yielded some very interesting results – the attached printout shows the final outcome (the previous run is also on the graph, it’s the one in blue).
Using a Jadus intake kit with a 120 Main jet, 50 Pilot jet, stock downpipe and a silencer that's probably as restrictive as the stock item it's created a whole different feel to the bike from about 5,500 to 7,000 rpm and, at 6,500 rpm, there’s a genuine 15% power hike (from 14 bhp to 16 bhp) which just it makes it so much easier to ride. I’m never going to be troubling R1s but I now can hold gears rather than jump up and down the box to keep a constant speed up hills. I'm still playing with the needle position but the stock setting seems to work best for slow speeds around town.
My dyno guru reckoned that with a less restrictive downpipe and/ or silencer a 115 Main jet would work well and see the mid-range power increase carry on to the red line.
With a 17/ 43 sprocket set up the theoretical top speed is now 84.6 mph but I doubt I’ll get anywhere near that given it (together with me board) makes a house brick look aerodynamic!
The only issue was that all my cheapo, made in China LED idiot lights failed within five miles. Who would have thought that £1.25 items (with free postage no less) might not have been top quality? Sturdier items have been ordered.
So that's it, project successfully completed, thanks for checking it out.
