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Author Topic: Yamaha SR250 Power and Temperature Testing  (Read 23854 times)

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #50 on: Sep 03, 2016, 06:43:15 »
Once testing was underway we started by testing the short bell mouth and played around with that for a while.  That needed an increase in main jet up to a 135, which was kind of expected.  We also optimised the pilot circuit - going up a couple jet sizes and dialling in the adjustment screw for a perfect idle and crisp throttle response off idle.  It made awesome power - got up to 21.5hp and torque was around 18Nm.  Was pretty stoked with that!

It felt like we could have optimised the jetting a little more but I figured it was worth trying the other length intakes at that point before going too far down that road.  So we bolted up the longest intake, the one that was supposed to give the 2nd harmonic.  Whoa it pulled hard!  Torque ran up to 24Nm in the midrange!  Haha.  But power sank to 18.5hp because it just wouldn't rev out past 7000rpm, it got waaaaay too rich.  I got really excited at this point because I felt the potential.

For the next couple hours or so we changed the carb settings about 10 times and just could not get it right.  We tried moving the needle position, different air jets, different pilots etc (all one at a time of coarse).  We finally got the bottom end and midrange right but we it was still running rich up top, even after going way down to a 105 main jet - apparently this happens with long intakes, the tuner said he sees it all the time.  We got power back up to 20hp while maintaining the good torque but it still wouldn't rev higher than 7000 because of the rich condition.  At this point I decided to give up on that length intake thinking it would be too tricky to get just right and also, slightly impractical for real world riding (it sticks quite far back into the frame triangle, a little too close to the rear wheel to be able to have a large air filter on it.

So it was on to the middle length intake, the one tuned to give the 3rd harmonic from 7000 to 8500rpm.  This felt good right away.  Power was back up to 20 and torque was also at 20, which felt like a good balance/compromise.  Lamba showed a lean condition pretty much from 3000rpm to the top, to be expected with the small main jet.  Before the day was done we bumped up the main to 110 and did another pull.  Lamba showed some weird peaks and troughs so there is plenty of work to be done, but power was back up to 21 and torque still at 20, so this is what we will continue to optimise tomorrow. 

Btw, this was a very fun day!   ;D

Offline sbruton

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #51 on: Sep 03, 2016, 11:22:32 »
Excellent stuff!  Such an efficient way to tune carbs.  I'll be doing plug chops until I'm blue in the face...

I'm too cheap to book dyno time!


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Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #52 on: Sep 08, 2016, 05:33:12 »
I'll do a proper write up of the final day of testing soon.  I can say that we did end up getting 22.5hp with the best set up and an almost completely flat torque curve - the other guys were shocked.

So yesterday I got out and went for a bit of an early Autumn ride and man, it rips!  Could do with some good tyres and a little better suspension now! This thing is fun in the twisties!  ;D

Offline sbruton

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #53 on: Sep 08, 2016, 11:44:31 »
That's excellent news! 

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #54 on: Sep 12, 2016, 05:15:15 »
Final day of testing...

We started off where we left off the day before, trying to optimise the medium length runner.  We found that the pilot jet and the adjustment screw were still giving the correct mixture (from the previous tests/settings) up to around 1/8th throttle so we didn't touch that any more throughout the day - it remained consistent.  We did up the air jet though believe it or not, contrary to what I would have thought would have helped.  We went up 4 sizes right away just to see if it had any affect and it smoothed out lambda over most of the rpm range.  I'll get to more of an explanation (or at least, my thoughts) on that in another post.

We then kept trying to raise the the needle - one step at a time to bring lambda down at around 1/2 throttle because it was running too lean there in the middle, but still rich up top (like 8000+).  This didn't seem to help all that much, so we went back to the middle position and decided to increase the main jet again to see if that would help the midrange lean condition.  Straight away it was better, almost spot on.  BUT, it still ran way rich (like in the 10s) after say 8500rpm.  At this point we realised that our power curve had already been dropping off by those rpms in all our other tests anyway, so we decided to leave it rich there as some kind of over-rev/rev limiter function.  So if you are winding it out, you run into a pretty heavy rich condition after 8500rpm and don't really damage anything, power just falls off and the engine hesitates slightly, at which point, you should upshift haha.  You should have already upshifted though because peak power is around 7700rpm. 

The last thing we did was a final power pull without the lambda system installed (sometimes the tube in the exhaust can affect back pressure and the exhaust pulses).  This confirmed we had the settings right cos power was pretty much the same, if not a fraction more.

Then, as an experiment, we did a few pulls with me holding various thickness rods (starting with a screw driver shaft) right across the opening of the exhaust silencer.  Apparently a cylindrical object provides the same resistance regardless of exhaust flow?  Or so the guy explained.  What we discovered was no change in power at all.  He then said that this means the exhaust design/resistance was spot on because it didn't get better/produce more power or torque with more resistance.

This was on a Friday and I had a flight to catch to London at 3pm so by the time we got everything fine tuned with this set up, there was no time to put all the stock parts back on the bike to do the comparison run.  One of the guys was like 'why do you want to anyway, you already know the results of others and just use that baseline'.  I wasn't satisfied.  But the place was fully booked for the next 4 months so I guess I'll have to go back another time  :(  All in all, quite satisfied with the results though!

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #55 on: Sep 12, 2016, 05:28:39 »
Here is the dyno graph print out I got.  They told me I shouldn't show anyone the carb settings because its my IP haha.  I'm not too worried because it turns out that these settings wouldn't really work with any other set up.

I did however put a pen over the 'magical' length of that intake bell mouth though  ;)  This is the length I will use to make a production run of parts for a kit.

Speaking of which, the intake system I tested was made up of a couple of pieces - so I could test the different lengths.  No I have that length decided, I am designing the final one for further testing - see 3D printed prototype.

Also, with the money I had set aside to make a production order, I decided to buy another SR instead to do some final testing!!!  Haha.  I'll just have to take some pre-orders or something to come up with the money later if all works out well.  I figured it would be a good idea to do a comparison with a bone stock bike to either confirm or deny the results I got on the first bike.  So what better bike to do it with than the re-released SR250 Classic.  This is a '96 model and none of these actually ever made it to Sweden - I imported this one from across the bridge in Denmark.  So to my knowledge, it is the only one of its kind in Sweden!

I am glad I got this bike because it turns out there are some slight differences, so I will be making sure everything fits both models.  First thing I checked was the ignition system - yep, different brackets.  So I'll likely have to design a new system for these bikes to advance the ignition.  Fun times though!  :D

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #56 on: Sep 12, 2016, 05:48:47 »
Back to the dyno results.  The guys were quite blown away with the flat torque curve - it sits above 20Nm of torque from 2500rpm all the way to 7500rpm.  Apparently this is quite uncommon so I asked them why.  They said it is because of the low state of tune of the engine haha.  Meaning it was not peaky in anyway and it responded well the the exhaust and intake designs, but probably wouldn't make any more power until head work was done. 

They also said I could probably ignore the final peak in the graph as there is sometimes weird characteristics when the engine starts stumbling up the top there.  So I took that advice and made my own pretty graph with smoothing and eyeballed the curve to come out at 22.1 something rather than the 22.71 listed on the original.

When we first rolled the bike onto the bench and did the first pull, I had some form of the kit installed (exhaust, ignition and short bell mouth) and it made 20hp, then 2.5 days later and after a lot of testing, it was making a little over 22hp, thats a 10% increase in power for just swapping intake length and optimising carb settings.  I can't wait to find out what stock makes!  Will also be cool to see if the orange bike makes 22hp with the kit installed.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #57 on: Sep 12, 2016, 06:07:58 »
Just thought I would point out that this SR250 now puts out almost as much power as the new SR400s haha.  But weighs a good 35kg less!  Torque is obviously better from the 400 though but still  ;D

http://www.cycleworld.com/2015/12/10/2016-yamaha-sr400-standard-motorcycle-dyno-run-video-and-performance-chart/

Offline Eleganten

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #58 on: Sep 12, 2016, 17:33:22 »
That's insane! Very impressive numbers you got there! How can the SR400 only put out 22-23 HP? On paper the SR500 puts out around 34 HP (24 kW). Wonder how much mine will put out after the re-bore to 90 mm.

Do you know a good place around Malmö or Lund that dose that?


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Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #59 on: Sep 13, 2016, 04:45:59 »
That's insane! Very impressive numbers you got there! How can the SR400 only put out 22-23 HP? On paper the SR500 puts out around 34 HP (24 kW). Wonder how much mine will put out after the re-bore to 90 mm.

Do you know a good place around Malmö or Lund that dose that?

Well the new SR400s are choked up both at the exhaust and the intake to reduce noise and control emissions.  So with similar work to them that I have done to this bike, they would probably make more like 28hp.  But yeah, the original SR500s made more power than any of the 400s have.  That figure of 34 HP though, is that 'claimed' or tested?  Big difference  ;)

All depends what combo you end up with on your bike.  The bigger piston will certainly help, but better head flow (bigger valves, more cam, a little porting) would bring out the true benefits of a bore increase.

I have heard and read many times that to achieve 100HP/Litre is really impressive for any air cooled bike, so for an SR500 to make 50HP, you would be doing very bloody well.  Its totally achievable, but would take a lot of quite involved work.  Same goes for the SR250 (239cc), you would be killing it it you got it to make 24HP with the stock bore.

Yeah, onto recommendations...

You got Malmö Motor Renoverring:  http://www.mmr.se
I have heard both good an bad things about them, you should speak to them and get a feeling for yourself.

Then I just got a tip from an old colleague of mine about this guy:  http://www.hedstromsmotor.se/index.htm
Basic website but apparently he has a lot of skills, knowledge and expensive/good equipment.

Obviously he's not in Malmö but it could be worth just sending up your jug to him for boring?