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Discussion Yamaha SRX250 Specifications

Discussion in 'Yamaha 250cc Singles' started by Mike Fulcher, Apr 19, 2018.

  1. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Awesome build, I have one of these, I love it, but there is very conflicting engine power specs out there.
    Most say only around 17-18 BHP, that is, Excuse my Kiwi accent (bull ****) I used to race, 30 years ago an NSU Max 250 that I had extensively modified & ran it on methanol, that old 250 single OHC 2 valve engine produced around 28 BHP
    I believe these twin cam 4 valve engines produce more like 32 BHP @ around 11-12000 RPM
     
  2. Andych

    Andych Well-Known Member Premium Member

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    Hi Mike, yep, it is a great little bike but you are way off on the HP figures.
    Factory specs are 17hp for the 51Y and 16hp for the 3WP due to minor cam changes to give it a little more torque.
    As you said, you had a methanol fueled heavily modified NSU that produced 28Hp and it was most likely super peaky and would not survive on the street.
    These have a lowish 10:1 compression, very mild cam specs and redline around 10000 rpm as well as a damned big counterweight for smoothness and that sucks power as well.
    You need to remember that the FZR250 4 Cylinder engines that scream to 19,000 rpm at 12:1 compression are 45hp when brand new
    Remember, these are a docile, light weight “ urban” commuter. It is after all a production bike designed for someone of a max weight of 90kg.
    Poor thing has a shock coming when I get on it.
    The TT350 is rated at 31hp and that is what mine will end up at more or less.
    And these figures are engine hp.
    Depending on how it all goes I may end up putting mine on the Dyno when finished, just to see.


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  3. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    The late 80's XT250 4V engine same as mine has 27hp at the engine @ 9000rpm, peak torque is 15.9ft/lb @ 7000rpm,
    Doesn't have electric start though
     
  4. Andych

    Andych Well-Known Member Premium Member

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    Maybe it does but anyone can look at the published specs for the SRX250 and see it is 17hp.
    Pretty sure if Yamaha had a more powerful engine they wouldn’t have rated it nearly 10hp lower.


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  5. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I wonder what the difference's are though, it's basically the same engine
    Camshaft's maybe, the XT only has 9.5/1 compression too.
     
  6. Andych

    Andych Well-Known Member Premium Member

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    I cant actually find any specs on the 4V XT250.. the 2V XT250 shows as 22HP with a single 28mm carby.. the TT250 is a 4V but again I couldnt find any HP specs on that but it did have a 30mm slide Mikuni for carburetion..
    I am guessing the big difference will be the carburetion as the XT350 and the TT350 use the same basic carby as the SRX just that it is a 24mm rather than a 22mm. They show as 31HP.. but we are talking off road bikes vs a City commuter.
    In the end it really doesnt matter.. mine will be a hybrid of sorts and no doubt it will have more power than the original.. :)
     
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  7. Andych

    Andych Well-Known Member Premium Member

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    So... just to add to the confusion... I did manage to find the specs for a 4V 1984-87 XT250 and it is 27hp. Interesting that the engine is for all intents the same apart from the electric start but the differences are in the Carby and the ignition by the looks of it.
    When comparing part numbers etc through Megazip the XT is certainly jetted up quite a bit from the SRX, meaning potentially there is quite a bit of power to find in the SRX... but the SRX has an "igniter" where the XT250 has a "control unit assy"
    It would be interesting to find out what the differences are.
    I should compare the XT250 with the TT350 carby and see what differences are there as there is very little difference between them in stated power... torque will be different though.
     
    Last edited: Apr 20, 2018
  8. Andych

    Andych Well-Known Member Premium Member

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    Interesting comparing the XT250 and the TT350 (XT350 is a later model than the TT) in that the carbys are certainly a different size, not that I can confirm XT250 size but the jetting is vastly different in some aspects.
    Main jet on the XT250 is a 130 but on the TT350 is a 122... Pilot Jet is 40 on TT350 but 38 on XT250 while on the other carby (secondary??) the main jet is the same on both... all very confusing.
     
  9. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Look I beg to differ, All the big 4 Jap motorcycle Co, produced their own version of these sport high performance single cylinder DOHC 4 valve engines, all around the same time 1984-1987
    Suzuki NZ 250, Honda CBX 250 RS, Kawasaki BR 250 & these Yamaha SRX 250's.
    All of them produced over 30hp.
    Check this web site www.autoevolution.com
    Most of the figures you can upload on these SRX 250's are ridiculous, ie: the same website www.motorcyclespecs.co.za
    Rate the commuter Yamaha SR 250 SOHC 2 valve engine produing 21hp @8500RPM
    Come on, a DOHC 4 valve quad port twin choke engine producing only 17hp?
     
    Last edited: Apr 20, 2018
  10. Andych

    Andych Well-Known Member Premium Member

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    The problem is Mike... the SRX250 is classed as an "Urban Sportster" it is not a sports bike.. A light weight nimble commuter that has good torque and a 6 speed gearbox to offset the lack of power.
    If you look at what I put up regarding differing jetting etc between the XT250 and the SRX250 you can see that "in standard form" the SRX is tuned more for torque than for power 17hp @ 10000 rpm and 17.3lb/ft at 8500rpm vs 27hp@ 9000 rpm and 15.9lb/ft at 7500 rpm.
    The Carbys are different.. jetting is different, CDI is different as they are both tuned for different applications. their overall gearing etc is also matched to their purpose...
    As for the SR250 specs... have a look at what else it says... it runs a single 34mm Mikuni carby.. and the SR250 is a highly sought after bike because of the performance and good looks... the SRX250 is a somewhat runt of the litter that didnt sell well because it was underpowered compared to other equivalent bikes... It was even worse in the USA when they had to throw SMOG gear onto it...
     
  11. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Well the ones they sold out here in NZ must be way higher specked because mine goes like a scolded cat.
    Did you check the autoevolution web site?
     
    Last edited: Apr 20, 2018
  12. Andych

    Andych Well-Known Member Premium Member

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    Sorry Mike but there is only one specification... other than the TC in the USA that has the smog gear on it... plus "goes like a scalded cat" doesnt actually relate to HP figures... plus.. yours has been modified / Cafe'd and unless you know exactly what has been done you cant relate it to a Standard bike that has all the fairings, Air cleaner etc. They may well have changed the gearing on yours etc..
    I did check that site but there is nothing on there regarding SRX250 so I dont really know what you were referring too.
    If it is HP ratings of other bikes of the era... I am not really interested... all I am interested in is building this little bike the way I want.. :)
     
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  13. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Have a look at this, by the way, look I'm not trying to discredit you OK, your rebuild is awesome.
    Just, I would like to know where you got those low hp specs from. The SR 250 is the low spec SOHC 2 valve Commuter not these high spec DOHC 4 valve SRX 250- 10.000RPM + screamers.
    You talk about carbs. or some of your readers do, these engines used a twin throat carb which gave the excellent low down torque plus when the secondary throat was actuated gave an awesome top end performance as well.
    You haven't ridden the bike yet have you? I think you will be very pleasantly surprised.
    Then again you have increased the size of the engine.
    O well as they say all the best of British.
    Cheers
     

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  14. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    That is the earlier 1984 SRX250F, Andy's is a SRX250T

    My XT250 has the TeIkei Y22PV YDIS carby same as the SRX250T,
    main jet is a 122 standard but i had to swap mine for a 120 as it was too rich @100km/h
     
    Last edited: Apr 20, 2018
  15. Sue Booth

    Sue Booth Dragon3961au

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    So I own an SRX250 1984 model what is & how do I find out the difference between the F & the T


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  16. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  17. Sue Booth

    Sue Booth Dragon3961au

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  18. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  19. Mike Fulcher

    Mike Fulcher Active Member Premium Member Contributing Member

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    Hey Guys this discussion has probably gone on for too long, sorry about that, but I thought at least someone would realize that a SOHC 2 valve engine would produce nowhere as much horsepower as DOHC 4 valve engine unless the engine was suffocated with legal or pollution or registration restrictions.
    Keep up with that great Resto job, you are obviously a perfectionist.
    Love the progress pics.
     
  20. Andych

    Andych Well-Known Member Premium Member

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    Mike... just to put an end to this once and for all... The info I had was from several sources.. apparently they were all wrong... I deferred to our resident SRX250 archivist (@2valve ) to see what info he had and also did some other research because there shouldnt be that much disparity in the figures.
    Gary (@2valve ) provided me with 2 interesting pieces of info... A comparison spec sheet and an in depth Road Test which has detailed specs....
    I also found specs on Webike that corroborated those figures and also showed the SRX250 3WP (japan bike only) to be at 27PS, not sure what they changed but my memory tells me the cam timing was slightly different but as you cant buy cams anymore it doesnt matter.
    So Mike... apologies... I was wrong :)

    Oh yes... for clarity... there is no difference in engine specs between the T and F models.. it is just the difference between the naked bike and the one with the fairing... the belly-pan was an option.

    Now I might ask our Lord & Master (@GreyImport ) to drag all this stuff out of my project thread and into a seperate one... :)
    Comparison 250's.jpg Road Test SRX250.jpg
     

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