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    • #8361
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      Hi all,

      I have just bought a GT650 Comet EFI.   It will idle fine but when I rev it it’s like it will only run on one cylinder and leans right out.

      Can anybody point me in the right direction to start looking?

      Thanks

      Jason

    • #8362
      Simon
      Member
      • Topics: 1
      • Replies: 266
      @syco
      Kent
      Gt250 f1

      Check for any vacuum leaks also clean & check all the sensor connections

    • #8363
      Simon
      Member
      • Topics: 1
      • Replies: 266
      @syco
      Kent
      Gt250 f1

      sorry forgot to say make sure the plug caps are on properly you will be surprised how often they are not.

      • #8367
        Jason
        Member
        • Topics: 3
        • Replies: 28
        @jasgt650
        Canberra, Australia
        GT650s

        When you say plug caps do you mean the spark plugs?  I will start checking all the sensors tonight.  Thank you for the suggestions.

    • #8370
      ♠️ MARCEL
      Admin
      • Topics: 45
      • Replies: 2,098
      @mf448kxn6
      North UK
      GTR

      He also means the “black tubes” that actually connect to the spark plugs deep inside the engine but yes look for;
      – Loose HT wires trying to escape the coil
      – or Loose HT wire trying to escape the black tube  (plug cap as it’s known as)
      – Spark plug is tight in engine and is on the correct torque   (max 15ft lbs on torque wench, engine is aluminium, so threads can still strip due to overtightness)

      Also grab a copy of fresh CR8E plugs (OEM) and use that forever, do not worry about getting “cold” type plugs etc, or adjusting the gaps of the spark plugs. There is other ways to help the bike stay a tiny bit cooler on blazing summer heat.

      // Meditation doesn't mean you have to sit still....

      • #8389
        Jason
        Member
        • Topics: 3
        • Replies: 28
        @jasgt650
        Canberra, Australia
        GT650s

        All great suggestions thank you.

         

        I Have two EFI’s and a Carby 650.  Both EFI’s exhibit similar issues, both have had rusty tanks which I have now neutralized and sealed.  So I have pulled the injectors and sent them for a clean as well.

        I will start on the rest of the checks this weekend.

         

        Cheers

        Jason

    • #8391
      Simon
      Member
      • Topics: 1
      • Replies: 266
      @syco
      Kent
      Gt250 f1

      You have added something to the mix there is every chance that the fuel pump seals have been damaged due to the moisture.

    • #8488
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      So just an update….

       

      I pulled the tank off and bike apart.  I had the injectors cleaned.

      One of the injectors was flowing badly.  When pulled apart they had a lot of rust build up inside the feed caps.

      A hose to the MAP sensor had a split at the top.

       

      I have it back together and it no longer wants to lean out but when riding it feels like it can’t get enough fuel.  Im suspecting that the fuel pump has had it so I have another on the way.

       

      I will update when its fitted to see if this solves the issue.

    • #8494
      ♠️ MARCEL
      Admin
      • Topics: 45
      • Replies: 2,098
      @mf448kxn6
      North UK
      GTR

      You got this! Keep us posted, well done on the diagnosis so far

      // Meditation doesn't mean you have to sit still....

    • #8495
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      Ok Fuel pump replaced with a new unit,  I went with an uprated Kenso unit over the stock.

      Changes in the bike now:

      -Idle is now higher

      -It no longer is leaning out

      -Power appears to be there throughout the rev range.

       

      New issue which I didnt notice before is i have backfiring out the exhaust and  the odd miss.  I suspect that this is plug related so ne CR8E plugs are on their way.  I have also noticed that the coils aren’t earthed to the frame very well so I will clean up the rust and getter a better earth happening.

      The timing is supposed to be set at 5 deg TDC how do I measure this on a bike?

    • #8535
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      Last update for this thread I think.

      Yesterday I replaced the plugs checked the leads and coil packs.

      The plugs were average so replaced with new NGK CR8E

      Leads looked ok.

      The coils and where they mounted to the frame were fairly rusty so I cleaned them all off and re-attached.

       

      The bike now has no hesitation and appears to go through the rev range happily.

    • #8536
      Simon
      Member
      • Topics: 1
      • Replies: 266
      @syco
      Kent
      Gt250 f1

      Great news

    • #8566
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      So I was out riding the other night and only just made it home as it felt like i was riding on one cylinder.

      I had not much spark on the rear cylinder so replaced the coil and it was a little better.

      Checked the TPS and found that the measurements were way out so adjusted to put it back.

      Went for a ride and it lacked pull when I throttled like it couldnt get enough fuel and when i pulled up at lights it would stall.

      I fiddled with the TPS to get it to idle but now has no go above about 5k RPM.

      Anyone have any suggestions?

      Oh and no F1 light.

    • #8567
      Cobra2
      Member
      • Topics: 4
      • Replies: 98
      @cobra2
      Norway
      GT250R efi

      Do you have any way to check; fuel-pressure? (regulator & fuel-filter) , Temp-sensor? , O2/lambda-sensor(s) ?

       

      Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).

      GT125R - sold. New (used): GT250R-efi

    • #8576
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      The only means I have to check the electrics is with a multimeter.

      Just to digress a little, the manual only shows a two bolt TPS and not a 1 bolt.  The pins appear to be upside down on the actual bike compared to the manual.

      The fuel pump was replaced with a new unit.

      https://www.ebay.com.au/itm/164748784383

      The temperature has 3 bars on the dash.  Before replacing the coil the rear cylinder felt noticeably cooler than the front.

    • #8580
      Cobra2
      Member
      • Topics: 4
      • Replies: 98
      @cobra2
      Norway
      GT250R efi

      650Fi -(2009-) sm:

      https://mega.nz/file/vcs1XDyI#NJuh8MykclBv4gAMsVozb-OIPRWDPSCP3tpwPqGg0BI

       

      Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).

      GT125R - sold. New (used): GT250R-efi

    • #8604
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      Thank you

    • #8652
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      Last update on this bike for a while.

      I still had trouble with the bike running.  Most parameters seemed to be in check.

      I managed to borrow a compression tester and got the following results:

      Front cylinder = 150psi

      Rear cylinder = 90psi.

       

      There is no way I will ever get tis bike to run properly with those readings.  I believe 1 of two things has happened:

      1. Because of the blocked injector it has leaned out that cylinder so much it has annealed the rings.
      2. The timing gear has slipped a tooth.

      Only way to find out for sure is to start pulling the engine apart.

    • #8653
      Simon
      Member
      • Topics: 1
      • Replies: 266
      @syco
      Kent
      Gt250 f1

      Could be something as simple as over tight clearance or a valve which wouldn’t be to much of an issue just a bit of mucking about.

    • #8654
      ♠️ MARCEL
      Admin
      • Topics: 45
      • Replies: 2,098
      @mf448kxn6
      North UK
      GTR

      Was the compression also tested when engine was hot warm & full throttle with both plugs out ?

      // Meditation doesn't mean you have to sit still....

    • #8656
      Jason
      Member
      • Topics: 3
      • Replies: 28
      @jasgt650
      Canberra, Australia
      GT650s

      The engine was warm when I did it but not at operating temps.  The last owner complained of it being down on power as well.

      The other possibility is that it has slipped a tooth on the timing gear.  When I get a chance I will pull the rocker cover off and start digging.

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