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Carboned Throttle valve/butterfly

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Ice-Eyes, Jan 17, 2008.

  1. Hi all.
    I have just purchased a 1985 Suzuki GSX 550 EF, at the bargain price of $650 and in condition good enough to ride away!!!
    First things, I did were replace plugs, oil, oil filter and air filter.
    Bike was idling badly (if at all) when cold, the choke is not reliable, and when warm still has no power below 3500RPM. Apart from these issues all was good until I decided to try adding some carb cleaner to the fuel.
    The morning after, my bike would not start, and no fuel was getting to the engine.

    So, next step is to find a friend with more mechanical smarts than me, then remove the carbs, to clean the jets and float chambers.
    When we reach this stage you can see carbon buildup on one of the 4 Throttle valves. Before I reassemble the engine is there anything I should be worried about, or anything I should do?

    Thanks in advance, and glad to be with you all on the forums!
  2. Sounds like it might be worthwhile having the valve adjustment checked. That could cause carbon to blow back onto the throttle butterfly, and a loss
    of power at low RPMs.
    While you're in there, clean the spark plugs too. I think you're on the right
    track with carb cleaning.

    Add an in-line fuel filter to prevent more crap from getting into your
    carburettors in the future. Every bike should have one, almost none
    of them do. **EDIT** Do not install your own on a Fuel Injected bike.
    Most fuel filters bought over the counter are not suitable for Fuel Injection.
    Fuel injected bikes usually have a special high-pressure filter installed
    at the factory.
  3. On the contrary most bikes do, I believe, have a fuel filter. It is a strainer in the tap, or sometimes incorprated in the fitting which bolts to the carb body - some dellortos do this.

    Since most bikes are still gravity fed, you cannot use a traditional, paper-type filter as used in cars. These are too restrictive and will reduce your fuel flow, leading to lean running and possible engine damage.. If you can get a strainer-type, in-line filter, you could add one.

    Best plan is to clean the tank and always fill from a reliable, high-volume servo.


    Trevor G
  4. True but it is such an ineffective filter that I don't count it. I call
    it a 'strainer' which gives a better idea of its abilities. :grin:
    Dellortos I couldn't talk about, I only ever worked on
    Japanese (and German EFI) bikes.

    I have had varying results with paper type filters on bikes, but I have
    always had good results with the sintered metal (metal sponge) type
    and with the metal mesh type. Most bike shops will sell either sintered
    or mesh type filter at $5-$14.

    While I think of it, as a rule
    inline filters will NOT be suitable for EFI bikes
    especially if placed AFTER the fuel pump (which is sometimes in the tank).
    There is too much pressure and the filter could
    explode or crack, leaking fuel and causing a fire and/or crash.
  5. After checking valve clearances, do a compression check on all four cylinders. You might have dodgy rings on this cylinder, or all the ring gaps could, by mistake, be all aligned together. (Some people claim this is important.)

    I think the condition of the spark plug could also be a clue if this cylinder has a problem. If the inlet valves are too tight (not enough clearance) or the inlet valves on this cylinder are slightly burnt because of this, that will cause some back leakage of combustion gases. This is, I think, the most likely cause.


    Trevor G
  6. Thanks for the suggestions, the fuel was clean, the filter on the tank was clean. One of the jets in the carb was blocked, but the resivoirs were pretty clean apart from a few waxy crystals. So for the moment we'll not worry about that.

    Carbs back on, and it started up ok, warmed up a little, but wouldnt idle, she died and wouldn't start again. Decided that while we're dead and checking things to check the compression, and valve clearance. (You said it!)
    Valve clearance seems close enough. Unfortunately compression seems to be bad all round, WS manual suggests 10~15kg/cm2 (140~200 PSI). From memory the carboned cylinder was under 50PSI, Best was ~100PSI, and the other 2 were between these values. We added a little oil down the cylinders and re-checked compressions, now from ~120 to ~170 PSI. Seems like I'll need to replace the rings.
    With the original cost of the bike so low I'm reluctant to spend much money, any suggestions on what I should try?

    I'm a little tempted to tune as best I can and just run her till she dies.
  7. Pull the cylinder head. You will need a new gasket at least.

    It is quite possibly a burnt valve. You won't know until you try. It might have happened previously and been overlooked for the same reasons you are thinking.

    All the best

    Trevor G
  8. Thanks for the support Trevor G

    I'm becoming sorely tempted to attempt a top end rebuild, but i'm a little concerned about ensuring I have everything needed for the job, and yes, I have no idea about the cost.. but a full gasket set was about $220 on ebay, and I can only guess at the price of rings and new valves if they are required. If I put in new rings I have some people saying I should get it re-bored and new over-sized pistons, and others just say to replace the rings and drop straight in.

    Can you maybe give me a list of parts I'll probably require, and maybe an estimate on prices for all these parts? or do you know a supplier with good prices who ships to SA that I might call?
  9. Rebuild it. The GSX550 is an absolutely cracking bike. You won't find a faster, better handling air cooled middleweight.
  10. Just get a top-end gasket kit, so that if you pull the head and decide it's not worth doing, you can at least put it all back together and run it again.

    Otherwise it just becomes another dead-end project to rot away in your lounge room. Hey, I'm not suggesting your place is a mess ;-)

    I'm betting on a valve job, although the fact that the compression came up with some oil in the troubled cylinder suggests it could be rings.

    It is probably one of these, if valves are OK:

    1) Cracked or broken ring(s)

    2) Stuck ring(s) - gummed up and partially seized in piston

    3) Circlip or similar dropped out of gudgeon pin recess, scoring cylinder wall

    4) Rings all rotated so that the gaps are in line (should be staggered).

    Once you have the head off you will be able to see if there is damage to the cylinder wall without going any further. If no damage, and valves are OK, you will either need to pull the cylinder assy off to see what is wrong, or just put it all back together again.

    Get a base gasket as well as the top-end kit, and everything is sweet. :) Don't worry about other parts until you know what is wrong - you can always put it all back together again and put it in the NR Classifieds with "top-end overhaul" or "new gaskets fitted". ;-)

    You would need a rebore (=bigger pistons) only if the cylinder wall is damaged. A competent shop can measure the pistons and the cylinders to check the wear. If you get this far, make sure you leave rings on pistons - they don't like to be disturbed or put back in the wrong order or on the wrong pistons.

    Let's know how you go.


    Trevor G

    PS And listen to PatB also :)
  11. Update for you all

    Hi again, been working slowly and impatiently to get her back on the road, top end came off with minimal effort, but the process of getting the correct parts has been slow.

    So far I've replaced one inlet valve, re-machined 2 more, and lapped the rest, had the cylinders trued and honed.

    Everything else been cleaned up pretty well, and now just waiting on the correct rings from my supplier, I got the wrong ones!

    Now it's just playing the waiting game to see if I break and buy a 2008 Ninja 250R before my replacement parts get here!
  12. Re: Update for you all

    Thanks for reporting back! :)

    Glad you can still get the bits.

    It took me just 3 weeks to get GN250 valve spring seats from Japan to rebuild my Moto Guzzi V65 Lario.

    All the best

    Trevor G