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Author Topic: Yamaha SR250 Power and Temperature Testing  (Read 23866 times)

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #40 on: Aug 31, 2016, 05:28:51 »
So it looks like the figure of 20hp that is published, posted and discussed everywhere is very much a 'claimed' figure from Yamaha.  Typical.  I have never seen an SR reach that in a test.  The highest I have seen is actually one of these Spanish ones above - where they got 16hp (yes, at the wheel).  But still, most have shown a rear wheel hp figure of 13 something with a crank/flywheel power of 17-18hp.

Torque seems to be quoted at between 1.4 to 1.7kgm which is 13.7 to 16.7Nm.  This is similar to the Australian and Which Bike tests which got a figure of 12.3Nm.

Interestingly, with one of these Spanish tests, they obtained a rear wheel figure and a crank/flywheel figure so you can calculate the power train loss into a percentage.  I will use this to calculate the flywheel power after my own tests.

So from 18.2hp at the flywheel, to 13.6hp at the wheel, a loss of 34% has occurred.  Is this correct?  13.6 x 1.34 = 18.22

There is one other factor to come into play here and that is the metric horse power vs the imperial horse power - which is perhaps what Yamaha would have used in any promotional material.  A metric horse power is 98.6% of an imperial horsepower - not much, but would add up.

Anyway, the output perhaps depended a lot on the specific year model and the country to receive that model. 


Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #41 on: Sep 01, 2016, 11:46:08 »
The bike is real fun to ride with these mods!  Only thing is, it's not getting full power down because the clutch is slipping BAD.  I expected it but didn't think it would be this noticeable.  But I think this means the mods must have worked well?

Probably a good thing, then I got to check out some of the insides of the engine and change the oil and filter again.

A great thing I discovered when replacing the clutch was that with this header installed, you don't need to remove it to get the clutch side cover off like you do with the stock exhaust  ;D  Saves some time and hassle!

You can see the old clutch coming out and the new one in place with the new stronger (4mm longer) clutch springs.

While I had the cover off I also checked to see the crank shaft roll pin mod had been done - yep!  Pretty stoked to see that, this means the head has hopefully never been starved of oil.

Out for a test ride after was amazing!  Bike hooks up pretty nice and hauls :)  Cant wait for the testing now, I am sure it is going harder.

Offline sbruton

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #42 on: Sep 01, 2016, 12:06:43 »
Following. 

I haven't heard about the "crank shaft roll pin mod"... I guess it's time to do some searching!  This may be something I'll need to do to mine.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #43 on: Sep 02, 2016, 05:46:57 »
I haven't heard about the "crank shaft roll pin mod"... I guess it's time to do some searching!  This may be something I'll need to do to mine.

It was an issue where the head did not receive enough oil at low rpms.  This guy on another forum puts it better than anyone I have read/found:

''Fix was to put a roll pin in the crank snout to restrict flow to the big end hence increase flow to the head. I flat track mine 6-10k rpm so I don't bother. Problem generating bulletin was no doubt riders who slogged around all day at low rpm with dirty 5W-20 Penzoil. Regular top end inspections show no lack of lubrication whatsoever.''

Cory Rich

I have tried to dig up the original bulletin but can't find it anymore.  The topic was discussed a bit here:  http://www.thumpertalk.com/topic/513561-tt250-and-xt250-hot-rod-project-need-group-buy/

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #44 on: Sep 02, 2016, 06:04:27 »
Its all go!  Got some testing done this afternoon which is real exciting.  I talked to a few people and decided that the best plan of action would be to test the bike first with all the performance parts on and see what power it makes, if it makes good power, then it is worth it to continue testing.  If it doesn't, then I can stop and walk away with my tail between my legs BUT save a lot of money!  With testing like this you pay per hour and it is not cheap.  Plus with all the parts to test and optimise, it's looking like it'll be a few days... 

Then after the testing of the parts is complete/optimised carb settings etc, I will put all the stock parts back on the bike and put the carb back to factory settings and do a couple of final pulls to get a base figure to compare to.

Well everything started well - 20rwhp on the first pull!!!  Fucking stoked.  Actually quite shocked.  The tuner I am working with thinks there is easily more because the lambda was showing that it was running very rich right through the rpm range.  If that is optimised, there will be more power  ;D

Then things went a bit south...  The clutch started slipping!  Again! From 5000 rpm onwards the revs build really fast and power drops off.  Damn.  So that was testing for the afternoon done.  We ordered some 10% stiffer clutch springs from an RD350 and hopefully they will arrive tomorrow morning ready to install and continue testing.


Offline sbruton

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #45 on: Sep 02, 2016, 13:50:27 »
It was an issue where the head did not receive enough oil at low rpms.  This guy on another forum puts it better than anyone I have read/found:

''Fix was to put a roll pin in the crank snout to restrict flow to the big end hence increase flow to the head. I flat track mine 6-10k rpm so I don't bother. Problem generating bulletin was no doubt riders who slogged around all day at low rpm with dirty 5W-20 Penzoil. Regular top end inspections show no lack of lubrication whatsoever.''

Cory Rich

I have tried to dig up the original bulletin but can't find it anymore.  The topic was discussed a bit here:  http://www.thumpertalk.com/topic/513561-tt250-and-xt250-hot-rod-project-need-group-buy/

I found the bulletin online the other day and will look into this further.  If nothing else I will check mine to see if its one of the models that were fixed at the factory and perhaps open up the engine and check the top end.

Good info!

Thanks.

Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #46 on: Sep 02, 2016, 14:18:41 »
I found the bulletin online the other day and will look into this further.

You did?!  Where?  Care to share?  ;)

Offline sbruton

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #47 on: Sep 02, 2016, 14:42:00 »
Yeah.  For sure!

http://www.thumpertalk.com/topic/888480-81-xt250-oil-flow-to-head/

This is the copy I have.  It's not very good but gives the general info,


Sent from my iPhone using DO THE TON


Offline JadusMotorcycleParts

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Re: Yamaha SR250 Power and Temperature Testing
« Reply #49 on: Sep 03, 2016, 06:20:07 »
Got the days testing started by replacing the clutch springs.  The guys in the shop said the orange Barnett springs were shit - even though they were longer, they were too weak and too thick (in wire thickness), so when compressed, they bound up.  They were also too large in diameter (they suspected because of the thick layer of orange paint, duh!) which made them large for the holes in the clutch basket, meaning that they also bound in this way as well.  Worthless.  Anyway, we installed the new stronger springs from an RD350 and even added some 4mm custom spacers to the springs that they cut on a lathe. 

During this process I asked them about the oil being synthetic and the slippage etc.  They were pretty much like, 'thats rubbish, what a load of bollocks' but in Swedish.  They said that just with the extra power I would need the stinger springs anyway and the stock ones were probably already light from the factory - being a 250 for beginner riders having a softer clutch action etc.  They also though it was strange that the SR250 only has 4 clutch springs when a lot of other bikes from the same era have 6...

With those installed we started testing and no more slippage!