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(93)750ss Help Needed With Poor Running And Cut Outs

Discussion in 'Supersport (1974-2007)' started by BeardedDuke, Apr 10, 2017.

  1. Morning all, new member here

    Right so last week I picked up my '93 750SS the first few days I had with it were awesome. Until the other day it started cutting out on me. It seems to be after it's had a chance to warm up and when it starts cutting out it continues about every 500m. Sit at the side of the road for 5-10mins start it up and continue.

    Things I've done/checked

    The fuel tank breather hose was blocked so unblocked it and added a new filter.
    Changed the spark plugs out for iridium plugs.
    I've got some ca cycleworks ignition coils on the way

    The couple of things I've done so far seem to have helped slightly (it starts up sooner after cutting out) but not cured it. Any help would be appreciated
     
  2. Are you sure you've fully sorted the breather problem??
    Is the non return valve working properly and in the right way round??
     
  3. Hi, yes I believe the breather is working correctly. The old non return valve was shot so while waiting for a new one to arrive I replaced it with an nitro car fuel filter I had laying around. While not ideal the tank can breathe without getting crap in it from the hose.
     
  4. How warm was it?
    These bikes suffer from carb icing below about 10 degrees.
    That could fit.
     
  5. It is only around the low double figures at the moment. I had considered that so I have some sikolene pro fst on the way also. Having said that I've just remembered that the last time I filled it was with standard unleaded not super like the tank before. The problems have been happening since I last filled.
     
  6. Could it be water in the fuel??
     
  7. I'm going to be draining the carbs on my day off tomorrow. Hopefully a few of my new bits n bobs will turn up too. Have a day of tinkering
     
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  8. It won't be the difference between super unleaded and unleaded but it could be contamination.
     
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  9. It really does sound like a blocked breather, but you appear to have that covered.

    Another option is something floating around in the tank that’s covering the outlet then floating away when the engine stops.

    Yet another is the vacuum hose to the fuel tap getting sucked flat because it’s deteriorated or been replaced with normal hose without the correct strength to deal with a vacuum.

    I’d drain the float bowls out first though to see if there is any contamination, either water or solids.

    Nasher.
     
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  10. The breather isn't a non-return valve - it needs to suck air into the tank easily to avoid a vacuum (which you may be getting), but release a build-up of pressure from the tank.

    There aren't many on the market that do that - the OEM one has a little arrow on it - it should point away from the tank, IE, forwards.

    The stub pipe on the tank that the breather connects to is prone to getting blocked with paint and rust - try running strimmer 'wire' through it.

    There is no vacuum hose on a carbed SS fuel tap - it is a continuously pumped system.
     
  11. I agree it sounds like fuel starvation, iridium plugs can also be hit and miss in these bikes
     
  12. Oops, yes sorry, getting confused with my M900, and haven't got anywhere near plumbing up my Mongrel SS yet.

    Nasher
     
  13. could be inline fuel filter/tea bag filter blocked as no-one likes to do this job*. Does fuel pump tone sound the same when the motor cuts out or is it labouring/stopped even? - easier to hear with fuel cap carefully opened.

    *Many threads on here covering this operation, if you do it, you can 'externalise' the inline filter for easy checking/replacing in the future.
     
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  14. Well I've ruled out ignition. New coils came and fitted still have the Same issue although it is running slightly better as the coils that were there were definitely not a pair.
    I've drained the carbs and there was a little bit of contamination so I hoped that fresh fuel in the carbs would also help. No.
    I've now discovered that I have oil fed warmers on my carbs and I've read that expansion can be an issue if these are left on when it's warm. Anyone able to tell me the tap positions?
    Guess I'll be looking into the fuel system next. Swap out the filter and pump.
     
  15. Oil heaters sometimes work, sometimes don't - mine did.

    Tap lever across the bike (Lever towards the carbs) = Heaters On
    Tap lever parallel with the bike (Lever Forwards) = Heaters Off

    BTW draining the carbs may not be enough - if crap has got into the pilot circuit it could also cause problems, particularly as it affects rpm from idle up to 2500 - 3000. The main jet doesn't come into play until above those revs.

    However, I am of the opinion that your problem is breather related unless as Chris says the filters are blocked. Try doing 5 miles carefully with the fuel tank cap partly open.
     
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  16. Take the breather pipe off you can run it without to test, also open filler and blow through the small pipe where the breather attaches at the front, you should be able to blow air into the tank but not lots.
     
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  17. Yup have done this, breather is definitely clear. I'm starting to suspect the fuel filter. Had a good run on it this morning but it wasn't until I hit the dual carriageway and sustained 70mph consistently that it started to burble and then cut out. Which to me suggests fuelling.
     
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  18. Thanks for all your help guys. Culprit was a fuel tank that probably hadn't been drained in 23 years. 3 litres of scungey petrol removed, new pump and filter and we're back up and running. Looking forward to leaving the car at home tomorrow
     
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  19. Glad you got it sorted
     
  20. :upyeah::Cigar:
     
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