4000 rpm breakdown????

[perthvert]

Hi peoples, got an old 93 yzf 750, she breaks down @ 4000 rpm, sometimes it will spit an sutter till she breaks free, and off she goes, taken out the exup cleaned greased, no differnce, cleaned carbies, no differnce, fuel pump, seems ok, starts, idles, and once through, (if it breaks through) breaking down stage, it actually goes ok. 37.000 klms on the clock, presume to be actual, so up for major service, so is it timing, valves throttle senser?? what ever they do, battery, seems fine never hurd of charging causing this

When in nutural it will some times rev its tits off at first then will go into breakdown at the 4grand mark, so sounds like fuel BUT????? Help!

[jimmythehat]

sounds spark reated. look at plug caps and coils and ht leads, often the caps break down on these,,

[Openroad]

Hi peoples, got an old 93 yzf 750, she breaks down @ 4000 rpm, sometimes it will spit an sutter till she breaks free, and off she goes, taken out the exup cleaned greased, no differnce, cleaned carbies, no differnce, fuel pump, seems ok, starts, idles, and once through, (if it breaks through) breaking down stage, it actually goes ok. 37.000 klms on the clock, presume to be actual, so up for major service, so is it timing, valves throttle senser?? what ever they do, battery, seems fine never hurd of charging causing this

When in nutural it will some times rev its tits off at first then will go into breakdown at the 4grand mark, so sounds like fuel BUT????? Help!

I agree with jimmythehat but also I'd change the plugs too.

[philyzf750nos]

Hi ive got exactly the same bike with exactly the same problem ive had it in bike shop for about four months, and 700 quid later they gave up, they said it was electrical to start with and two months of investigation later from the so called authorised yamaha dealer found nothing wrong.. then they said it was fuel/carburetor problem and after another two months two cdi units new plugs and a new set of carbs it was still the same and they still wouldnt admit they couldnt sort it so i told them to bring it back and now it doesnt work at all, so much for yamaha dealer..

the few things ive found on the interneck are:

yzf750 tuning story or "Why some it's hard to believe some people."

TECH Notes:

1. Check needle jets for wear!

2. EXUP motor (or similar) MUST be attached or engine will not rev above 4000 rpm

Above quote is here

there's some more links on this website as well, from what ive found you have to make sure the exup valve cables are adjusted properly no more thn 1.5 mm of play and that it is operating properly.

let me know how you get on I still cant get mine going after the shop returned it

Hi peoples, got an old 93 yzf 750, she breaks down @ 4000 rpm, sometimes it will spit an sutter till she breaks free, and off she goes, taken out the exup cleaned greased, no differnce, cleaned carbies, no differnce, fuel pump, seems ok, starts, idles, and once through, (if it breaks through) breaking down stage, it actually goes ok. 37.000 klms on the clock, presume to be actual, so up for major service, so is it timing, valves throttle senser?? what ever they do, battery, seems fine never hurd of charging causing this

When in nutural it will some times rev its tits off at first then will go into breakdown at the 4grand mark, so sounds like fuel BUT????? Help!