biketofish Posted December 19, 2007 Share Posted December 19, 2007 hi all just spent some hard earned money on a 1990 xtz 750 and all seemed well initially (great fun bike ) starts fine but after 10 mins or so of riding perfectly on the 3 occasions i have riddden it , closed throttle going into corner and serious misfire has started and continued all the way home . bike ticks over ok but blipping throttle on and off eventually just coughs and dies . any advice will be greatly appreciated filters are new , have plugs to fit tomorrow. regards martin Link to comment Share on other sites More sharing options...
mr benn Posted December 19, 2007 Share Posted December 19, 2007 plug, cap or coil breaking down when it's hot? Link to comment Share on other sites More sharing options...
yoda Posted December 19, 2007 Share Posted December 19, 2007 Check the above but I think it might be a sticking carb float. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted December 19, 2007 Moderator Share Posted December 19, 2007 hi all just spent some hard earned money on a 1990 xtz 750 and all seemed well initially (great fun bike ) starts fine but after 10 mins or so of riding perfectly on the 3 occasions i have riddden it , closed throttle going into corner and serious misfire has started and continued all the way home . bike ticks over ok but blipping throttle on and off eventually just coughs and dies . any advice will be greatly appreciated filters are new , have plugs to fit tomorrow. regards martin Poss fuel starvation, check the pet cap has air vent unblocked and tap has no crud in it which would then point to crud in the carbs blocking main jet. you don't say which cyls go off, or is it random? Link to comment Share on other sites More sharing options...
mr benn Posted December 19, 2007 Share Posted December 19, 2007 kinked or trapped vacuum or fuel hose? Link to comment Share on other sites More sharing options...
biketofish Posted December 27, 2007 Author Share Posted December 27, 2007 hi thanks for the advice , have replaced plugs , checked coil and leads/caps for resistance readings and seem fine . pump operating as it should , went out last night and it ran superbly well for about 15 mins !! and after blasting down a long straight in top gear closed throttle and was back to cough splutter pop. then started the bike this morning and it ran one 1 cylinder all the way to work? plugs are dry and sooty and so are my hands any other ideas would be greatly appreciated and thanks to the helpers so far martin Link to comment Share on other sites More sharing options...
yoda Posted December 27, 2007 Share Posted December 27, 2007 Whilst you were in the arms of morphius, the Yamaha gremlins crept in and wrecked havoc with your bike. Now go and do the rest of what you were told. Link to comment Share on other sites More sharing options...
mr benn Posted December 29, 2007 Share Posted December 29, 2007 what he said^^^^^^^^^^^ did you know the bike has 2 fuel taps? the one on the right often gets blocked with crud as most folk only use the one on the left. how do you know the pump is operating as it should? does the bike run ok on prime? could be a split fuel tap diaphragm. have you checked that the fuel and vacuum hoses are not kinked or trapped? have you tried to run it with the fuel cap open? could be a split carb diaphragm. Link to comment Share on other sites More sharing options...
ozzyfzr Posted December 31, 2007 Share Posted December 31, 2007 I'd also drain the float bowls and check for water! def sounds like fuel starvation!!! Link to comment Share on other sites More sharing options...
johnthunder Posted April 1, 2008 Share Posted April 1, 2008 The reason for this is your carbs. The carbs have a tube in them called an emulsion tube. On large cylinder bikes the vibration from the engine pulling in the fuel makes the needles in the carb vibrate inside the emulsion tubes causing them to become oval. This then lets in more fuel and makes the bike run rich, this is why you have soot on your spark plugs and soot on your hands. Check your rear indicators too, I bet they are covered in soot. So, how do you cure this. You need to buy a new set of emulsion tubes and needles. These are available in kit form for this purpose as its quite a well known fault. It will cost you about £50 for the parts, once you have done this job, its quite a good idea to balance the carbs too. You will need some vacuum guages or you can make a manometer for free using some tube and a bit of oil and wood. After this your bike should run sweet. Mine had the same issue. The bike will run fine while running cold, and as soon as the bike is warm you will get really crap performance at low revs from it running too rich and choking the bike. Link to comment Share on other sites More sharing options...
khblue Posted April 9, 2008 Share Posted April 9, 2008 Hmm, this sounds familiar. I've just posted a very similar problem. I'd expect the kinked hoses and blocked air vent in tank to produce too weak mixture or just cut-out but not sooty plugs. The oval needle sounds far more convincing to me (not that I know much). Why would that only cause a problem when hot though ? Would be good to know if that works for your xtz before forking out another £50! Ta Kevin Link to comment Share on other sites More sharing options...
khblue Posted April 9, 2008 Share Posted April 9, 2008 Would be good to know if that works for your xtz before forking out another £50! Ta Kevin FFS 4x Emulsion tube + needle = £169.20 inc VAT I think the bike is worth about 20p more than that. Anyone do these as pattern parts ? Link to comment Share on other sites More sharing options...
khblue Posted April 9, 2008 Share Posted April 9, 2008 I spoke to these chaps: http://www.nrp-carbs.co.uk/ Apparently the XJ doesn't suffer from the vibration issue, more for V-twins like yours. However, I've probably nuked the rubbers in the carbs by using Redex, (which may have sunk to the bottom of the tank and gone through undiluted), Quick Start spray, and Carb cleaner through the air intake ... oops ! All part of the learning curve. Kevin Link to comment Share on other sites More sharing options...
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