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    • #4810
      Nathan
      Member
      • Topics: 1
      • Replies: 4
      Joined:
      Jun 27, 2020
      @nathan7
      Klerksdorp south Africa
      Comet GT125
      Points: 66

      Good day, I own a 2004 Comet GT125 & I love the bike. That was until the weekend when it left me stranded next to the road!

       

      I was doing about 80km/h when it suddenly died. It felt like I ran out of fuel but without the spluttering & surges. Obviously I checked the fuel lines,petcock etc as best I could seeing it was night time. I tried starting it but it wouldn’t, sounding like fuel starvation. Then after maybe 10 or so minutes I engaged the choke & it started. But sounding rough!!!! I managed to almost limp home,it did exactly the same about 500meters from home,so I just pushed it home. When I did get it going the first time & limped home the bike struggled to increase the revs. It felt like the carbs are blocked/dirty.

       

      The next day it behaved exactly the same: I got it started (but not running as usual) & took a drive. Then same thing happened: cut out soon after starting the ride & after maybe 10 to 15 minutes it restarted.

       

      It looks like it runs when cold & dies when warm. Then restarts when cooled down. Is this possible or am I losing it?

       

      What do you think the problem is? Dirty carbs? Please help,I’m at wits end.

    • #4814
      Nathan
      Member
      • Topics: 1
      • Replies: 4
      Joined:
      Jun 27, 2020
      @nathan7
      Klerksdorp south Africa
      Comet GT125
      Points: 66

      Marcel can you please be of assistance?

    • #4816
      ♠️ MARCEL
      Administrator
      • Topics: 38
      • Replies: 366
      Joined:
      Jun 27, 2020
      @mf448kxn6
      North UK
      GTR
      Points: 4,203

      Usually the bog downs or cutting away means  electrical issue or fuel delivery system.

      Lets deal with fuel first.

      • Go to the rear pump.  Open its metal shield cover.  You will see a glass window inside.  Get CARB CLEANER.   Spray inside through the GOLD PORTS only.  Do not spray inside the GREY port.    Now you must see the particles get cleaned out.   remove the window  (watch the gasket!). Clean the window too.  Dont remove any moving parts of pump.  Clean up and close the pump tight. Fit it back on the bike.
      • Change the fuel filter.
      • Clean the carbs….  see below

      Get compressed air. Open the carb. Clean HARD the Pilot Jets. MAIN jets. And also the *enrichment tube* that is permanent on the carb.

      Then clean every *hole* you see inside the carb hard so all the particles go out. It is crucial.   CARB CLEANER (Liquid) helps also but it is better to use compressed air to blast every tiny hole though!

      Put your carb upside down on a table (floats facing the sky).   Get a ruler.  Start from 0mm on the FLAT EDGE of the carb base (where bowl gasket sits on) .  then make sure all 4 floats are 7mm height.   not less. not more.   this float controls how much fuel you get from idle to top gear. You dont want the carb starving or overfueling. 7mm precisely at the top of the float on your ruler.   or adjust the float metal tangs a little bit! Then recheck.

      Floats all good?.  last mission is to clean the diaphragms at the top (black slides) and search *Slide Mod* on this forum on how to improve the slide needles.

      Now the carb should be really clean and prepared.     before fitting on the bike…. do the following below…

      Go to intake manifolds.

      • Be very gentle. It is very very very hard to get new ones (not made anymore).
      • Remove intake manifolds
      • Check for cracks / damage (vacuum leak!)
      • Check Oring isnt cracked (very important for air leaks too)
      • Clean them. And grease the ORings.
      • Fit them back on the back.
      • Use fresh bolts and washer and tighten (be gentle!)

      We have cleaned the carb.  we have checked the intake manifolds.    put the carbs back.  put the airbox back too. Be gentle as carb intake manifolds will crack open if there is too much weight or pressure on them.

      Connect the fuel pump.  get fresh fuel lines.    get fresh vacuum lines and clamp all lines tight to stop vacuum leaks.

       

      Start your bike. Get CARB CLEANER.  spray the intake manifolds while she is on IDLE.   if revs go up^ = you still have a leak.   fix that area.    if you spray rear manifold and revs go up , investigate rear intake system there as an example.

      Last mission  go to the TANK.

      • If you have a vacuum tap on the tank.   start your bike.  rev up multiple times. You should see fuel gushing down the filter. That means the tap is squirting fuel in to the filter.
      • After a short ride, fuel filter should be FULL if it is a small one.
      • If you have a manual ON/OFF tap on the left side of your bike frame ==> Go under the tap. Open it. Clean the dirt traps inside.
      • If you have a ON/OFF tap that also means your tank has 2 pipes that go down to the ON/OFF tap.    On your tank => remove the spigots that side inside the 2 holes. ((From tank rust or dirt that may prevent fuel coming out of the tank to feed your bike))

       

       

      I hope i have made sense. Try everything i said above. And let us know if there is improvement even if it is small or better. It will respond better when you make progress.

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

    • #4821
      Nathan
      Member
      • Topics: 1
      • Replies: 4
      Joined:
      Jun 27, 2020
      @nathan7
      Klerksdorp south Africa
      Comet GT125
      Points: 66

      Thanks for the advice, you gave me lots to do tomorrow. I’ll report back as requested.

      One last question (hopefully!!!!) please?

      Is it a possibility that the fuelpump heats up which in turn leads to the diaphragm not working properly when the bike reaches normal running temperature?

      That would explain the behaviour of “cutting out” and being able to start again when the bike has cooled down.

      If that IS the case,what would be my best course of action? Replacing the fuelpump altogether or just servicing/repairing the current pump?

    • #4831
      ♠️ MARCEL
      Administrator
      • Topics: 38
      • Replies: 366
      Joined:
      Jun 27, 2020
      @mf448kxn6
      North UK
      GTR
      Points: 4,203

      Sorry i delayed,  to answer you, i would start by fixing the bike using the suggestions mentioned in my past comments.

      The pump sits at the rear of the frame, it doesn’t touch the engine.  Also the bike in your profile image suggests that it’s naked enough to allow enough air flow all over the bike anyways.

      Replacing the pump is usually the last resort, it tends to last a long while when its well maintained.

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

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