Annaz Posted August 21, 2013 Report Share Posted August 21, 2013 I've got four hot pipes, so firing on all 4 cylinders, runs fine on tickover, if I rev it up it acts like there's a rev limiter cutting in at 3000. The smell of fumes suggests it's rich but I haven't touched the carbs so I'm pretty confident it's electrical (also I have been fooking around with the electrics) I have eliminated the possibility of the cdi, coz I tried another one. Maybe it could be the rectifier? The bike is a YZF750 and it's almost 20 years old so the wiring loom will be a tad unreliable I suppose but what can I do to work this out via elimination? I've also checked the pulse jobby that picks up off the crank and that is fine. I am confused.com! Link to comment Share on other sites More sharing options...
BudgetBoy Posted August 21, 2013 Report Share Posted August 21, 2013 umm check vac hoses for leaks.. 3000rpm is when the slides start to lift in the carbs and thats my thinking.No vac no lift.. Or a diaphragm could be split,stuck/blocked jet.. Link to comment Share on other sites More sharing options...
trackdaybob Posted August 21, 2013 Report Share Posted August 21, 2013 umm check vac hoses for leaks.. Beat me to it Link to comment Share on other sites More sharing options...
Annaz Posted August 21, 2013 Author Report Share Posted August 21, 2013 umm check vac hoses for leaks.. 3000rpm is when the slides start to lift in the carbs and thats my thinking.No vac no lift.. Or a diaphragm could be split,stuck/blocked jet.. With the tank and airbox off the slides move evenly when revving, maybe I should take the carbs off and check the inlet rubbers and suchlike? Link to comment Share on other sites More sharing options...
ronenige Posted August 23, 2013 Report Share Posted August 23, 2013 Is this whilst riding it , or just revving it up on the bench with the airbox off ? Link to comment Share on other sites More sharing options...
Annaz Posted August 23, 2013 Author Report Share Posted August 23, 2013 It's with the airbox off or on, tank off or on. It was fine till I started messing with the electrics. I re-routed some cables and fitted some koso clocks (which work fine apart from the rev counter not operating) I took the carbs off today to check them out and can't find anything wrong there. It feels like there isn't a strong enough spark to ignite the extra fuel when revving, It feels like a rev-limiter is kicking in, with lots of backfiring etc. Next thing on the list to look at will be the plugs and ht leads. I've tried disconnecting the clocks, tried a different cdi. I'm almost out of ideas Link to comment Share on other sites More sharing options...
Beanerno1 Posted August 23, 2013 Report Share Posted August 23, 2013 Have you try'd re fitting the original clocks?,, did the yzf have a speed limiter?, some jap bikes have a speed limiter, that run from the clocks "usually a resistor" and should you remove the clocks will not run properly. Link to comment Share on other sites More sharing options...
Annaz Posted August 23, 2013 Author Report Share Posted August 23, 2013 Have you try'd re fitting the original clocks?,, did the yzf have a speed limiter?, some jap bikes have a speed limiter, that run from the clocks "usually a resistor" and should you remove the clocks will not run properly. I did try to refit the original clocks and couldn't get the old rev counter to work for some reason? If it is a resistor in the rev counter how the hell would I get around that? Link to comment Share on other sites More sharing options...
Beanerno1 Posted August 23, 2013 Report Share Posted August 23, 2013 You'd find the appropriate wire at the loom and run it to live with a resister in line, but you need to undo what you did with the clocks and start again, you might just have a faulty spark plug, but as you've changed something you may be running round in circles for some time.. Link to comment Share on other sites More sharing options...
Annaz Posted August 23, 2013 Author Report Share Posted August 23, 2013 Going around in circles is becoming a way of life in my shed! I wired the new clocks into the multiplug from the old clocks so, in theory, if I borrowed some standard clocks I could just plug them in to test. There is a yellow striped pulse wire from the cdi that triggers the original counter, I suppose that would be the one to fit a resistor to. I'll give it try anyway. Cheers for your help Link to comment Share on other sites More sharing options...
kwakbiker Posted August 24, 2013 Report Share Posted August 24, 2013 Have you trapped a breather or the fuel hose from the tank? Link to comment Share on other sites More sharing options...
Annaz Posted August 24, 2013 Author Report Share Posted August 24, 2013 Have you trapped a breather or the fuel hose from the tank? I don't think so. I've got the carbs off at the mo to check and clean the floats, jets etc so it'll go back together properly. I took the old tacho to bits and found a little circuitboard in there and then it dawned on me that I rode the bike with no clocks at all last time I went out so it's looking unlikely that a resistor is the problem. So I'm taking out the plugs next and checking all that out. If that proves to be ok I'm going to have to go through the loom with the test meter! Link to comment Share on other sites More sharing options...
Boozybloke Posted August 24, 2013 Report Share Posted August 24, 2013 The rev counter is broken and sticks at 3000? Sorry, not helping really... Link to comment Share on other sites More sharing options...
Gregorious77 Posted August 24, 2013 Report Share Posted August 24, 2013 Has it got a throttle position sensor? if so that would be my guess. Link to comment Share on other sites More sharing options...
Annaz Posted August 24, 2013 Author Report Share Posted August 24, 2013 Has it got a throttle position sensor? if so that would be my guess. There is no throttle sensor. I'm convinced it's electrical though. Fucking about with electrics = electrical problem Link to comment Share on other sites More sharing options...
Annaz Posted October 26, 2013 Author Report Share Posted October 26, 2013 Just to update, the problem is fixed! It turned out to be the exup servo motor. I had removed it and the bike had gone into limp mode. I had tried refitting it as part of the diagnosis but I didn't realise you have to disconnect the battery in order to reset it..DOH!! Link to comment Share on other sites More sharing options...
lorenzo Posted October 27, 2013 Report Share Posted October 27, 2013 So, after months of faffing around, it turns out you needed to switch it off and on again. Should've asked somebody in computing. Link to comment Share on other sites More sharing options...
Annaz Posted October 27, 2013 Author Report Share Posted October 27, 2013 So, after months of faffing around, it turns out you needed to switch it off and on again. Should've asked somebody in computing. Yep it's hilarious, someone even suggested it Ha! Link to comment Share on other sites More sharing options...
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