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Help Problem cold starting SRX250

Discussion in 'Yamaha 250cc Singles' started by GeorgeT, Aug 16, 2021.

  1. GeorgeT

    GeorgeT Active Member

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    I am having trouble cold starting my SRX250 1984. If I use a couple of squirts of VIP it starts no problem and seems to be running as it should albeit a bit slow to come back to idle when the throttle is released. I will check the spark plug tomorrow and have ordered a couple of new ones anyway. The slow return to idle is a bit puzzling and sounds like there could be incomplete fuel burning, i.e., the mixture is too rich. Any ideas out there? I know my BMW airheads were very temperamental when the plugs got a bit long in the tooth. The slow return to idle is definitely not mechanical as the throttle is functional rapidly as it should.
     
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Slow return to idle is usually a lean condition. Check for air leaks.
     
  3. 2valve

    2valve Well-Known Member

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    I had the same issue with mine also on a cold start up , but when warmed up started brilliant.
    There is a small O ring on the choke side , that was M.I.A. Should have taken picture's for future info.
    Pretty sure that Oigy purchased new inlet's , no harm in checking on that.
     
  4. GeorgeT

    GeorgeT Active Member

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    I have since removed the spark plug that definitely appears to have been operating under a lean condition. I had a similar situation many years ago with a car (HQ Holden). That turned out to be something stopping the base of the carburettor to mount properly on the inlet manifold. Intuitively, this motorcycle situation seems to suggest a problem with the ignition timing, i.e., failed pick-up coil maybe. I haven't as yet been able to get to that unit wiring to check the resistance etc.
     
  5. GeorgeT

    GeorgeT Active Member

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    Once the engine starts the choke seems to be working, i.e., the rpm increases without any additional throttle.
     
  6. jmw76

    jmw76 Well-Known Member

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  7. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    If I remember correctly the PO had the engine running ok but it was low on compression, hence a newer barrel with new rings. Air leak is certainly a better option to look for initially... spray some WD40 around the carby and inlet manifolds with it running... that will tell you if you have vacuum leaks.
    If your old HQ did a similar thing and it was the base gasket on the inlet manifold why would the bike issue be similar but have an ignition timing issue?
    Most of the time these sort of things are simple to sort out as long as you dont overthink them... try the simple steps others have outlined first.
     
  8. GeorgeT

    GeorgeT Active Member

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    Yeah, on further thinking I feel it probably does not relate to an ignition timing problem but a vacuum leak problem. My intention today is to do exactly what you are suggesting, i.e., spray around the carby and especially where there is a vacuum tube fitted into one of the boots between the carby and the head. The tube has been fitted in what seems to be a non-factory way and is sealed only by some sort of adhesive, to the rubber boot. The HQ problem was definitely a leakage problem that I cured by using a better gasket arrangement. This problem may seem different because it is a single cylinder trying to start cold while a vacuum leak exists?
     
  9. 2valve

    2valve Well-Known Member

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    Hi George.
    The O.E inlet manifolds fitted with the spigot are N.L.A. and has been for a long time I'm afraid.
    So the XT / TT 350 manifolds are used and then you have to install a spigot on the R/H inlet.
    Also check the vacuum hose make sure it's a tight fit on the inlet manifold spigot and fuel tap spigot , if there not sealing , this can cause issues on start up / running.
    Not sure if you've noticed , but the fuel tap has a prime position for start up and then a on position after start up.
    The markings on the fuel tap are small though especially the arrow on the fuel tap handle is even smaller again.
    If you need anything copied out of the owners handbook , just ask.
     
  10. GeorgeT

    GeorgeT Active Member

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    I did a little checking today and did not seem to get any noticeable surging by spraying VIP starter product while the engine was idling. There was a slight change around the fuel tap area. I also checked the resistance of the pickup coil. The works manual says 10 ohms + or - 15%, mine reads 98.3 and a couple on eBay are 100 & 103 ohms? Not sure why they are different from the manual, including mine?
     
  11. jmw76

    jmw76 Well-Known Member

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    Change when spraying fuel tap area???
    An air leak at the vacuum operated petcock maybe?
     
  12. GeorgeT

    GeorgeT Active Member

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    There does seem to be a problem with the vacuum-operated petcock but definitely not the only problem. Today I actually blocked off the vacuum connector on the secondary carby's inlet boot to the cylinder and yes the engine ran better but still would not cold-start? I ran the engine by not exploiting the vacuum to turn the petcock on, i.e., I ran the engine in the reserve position that works without the vacuum connected?
     
  13. GeorgeT

    GeorgeT Active Member

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    Where exactly should the small o ring you mention be? There is no mention of it on the choke itself in the workshop manual.
     
  14. GeorgeT

    GeorgeT Active Member

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    Still having trouble with the cold start. Yesterday I checked the coil resistance given the coil appeared non-standard as it did not fit the bracket on the bike. The result was primary coil + 2.7 ohms, secondary = 17.4 ohms (incorrect). The secondary coil should be 13.2 K ohms. I had the correct one so installed it. Sure enough, the bike runs much better at a spark plug gap of 0.0276" (recommended), but still a problem starting cold. The other anomaly is the pick-up coil. The manual says 10 ohms while the installed one is 98.3 ohms and any I have found secondhand on eBay also say ~100 ohms? Could anyone that has the same bike please check the resistance of their pick-up coil? It is a simple task, the connector is accessible under the rear of the tank, i.e., RW/GW plug.
     
  15. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Just measured mine and it reads 97.2 ohms


    Sent from my iPhone using Tapatalk Pro
     
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Cold start: Full choke and no throttle.
    I would not waste time looking at the ignition. If that was the problem, it would be the problem everywhere. Check the choke circuit for any blockages.
     
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  17. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Not sure which manual you are looking at but the SRX repair manual I have shows very different to what you have.
    B62CCC9B-B516-415B-906D-D996E4D221FC.jpeg
    The cold starting issue will be to do with the carby.... all you are doing at the moment is chasing ghosts.
     
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  18. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Just reading this... Reserve doesnt bypass the vacuum operation of the petcock... ON and RES both use Vacuum operation for the petcock and in normal situations it is fine (if you have sufficient fuel in the float bowl for the bike to start) while troubleshooting use the PRIME position as this allows fuel to flow without vacuum from the manifold.
    To ensure you dont have any issues with the Petcock or the filter screens in the tank try starting it (with new fuel) from a remote container. This eliminates all of the tank, filters, petcock etc so it is just the carby you need to concern yourself with.
     
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