I have a mid 1980's Kawasaki Ninja 750, variously described as either GPZ, GPX or ZX as model prefix.
It was imported from North America, and shows the tell-tale differences to be found inHaines manuals.
However, it has also been restricted to 6000 revs under load.
Once you get there, in any gear, the motor feels as if it's hitting the rev limiter, although it redlines on the tacho at 12000 when you run the bike in neutral or with the clutch held in.
We've taken the carbs off and there were no inlet rubber restrictors, we've set the valves at the proper gaps according to Haines, there's a weird vacuum-operated exhaust-emission thing on top of the engine that's bizarre but operating properly.
Other than that, we're not too sure what's going on.
I was wondering if anyone on your side of the Atlantic (we think the bike's from California but it could be anywhere in the US or Canada) knows how such bikes are restricted and if so how they are de-restricted.
The engine should be able to pull strongly throughout the rev-range, but i'm only getting power in the bottom half, which hampers overtakes and motorway cruising. Also, it's only doing 30mpg rather than the 40-45 that it should be capable of.
Id really appreciate any help offered.
Thanks, Merry Christmas and a happy new year to all you and yours, wherever they may be.
Al.
American 750 Ninja Restriction?.
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Posthumane
- Elite
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- Location: Calgary, Alberta
Thanks for the reply.
I think you might be onto something there.
A few days ago, the bike spluttered to a near-halt after a trip down the motorway. Revving at standstill is fine, but when you get under way it feels like there's no fuel getting through, like you're almost out of petrol.
So, it would seem as though the coil and ignition are about to get a going over.
I think you might be onto something there.
A few days ago, the bike spluttered to a near-halt after a trip down the motorway. Revving at standstill is fine, but when you get under way it feels like there's no fuel getting through, like you're almost out of petrol.
So, it would seem as though the coil and ignition are about to get a going over.
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Tarheel365
- Regular
- Posts: 40
- Joined: Tue Oct 19, 2004 12:28 pm
The spark seems strong on all 4 to the eye, although i don't have a multimeter.
The carbs have been taken apart, thoroughly cleaned and reassembled.
It has Keihin flatslides, and they're opening and shutting just fine.
Having borrowed a set of mercury guages, and someone who knows how to use them
the carbs have been balanced.
The tank vent pipes are fine.
Thanks for the input though
The carbs have been taken apart, thoroughly cleaned and reassembled.
It has Keihin flatslides, and they're opening and shutting just fine.
Having borrowed a set of mercury guages, and someone who knows how to use them
the carbs have been balanced.The tank vent pipes are fine.
Thanks for the input though
Hey, i've got the same problem with my bike (same make/model zx750F1 / 1987), i had replaced all the worn carby internals with new OEM ones and installed a dynojet kit, and now it has issues going over around 6k-7k rpm.
What was your outcome? i'm about to borrow a carby synch tool from a neighbour, but thought i'd ask how you went anyhow.
Cheers,
Mike
What was your outcome? i'm about to borrow a carby synch tool from a neighbour, but thought i'd ask how you went anyhow.
Cheers,
Mike
Wotcha.
Still no joy here i'm afraid.
I've changed the coils and CDI ignition unit, and that didn't change it. I'm wondering if mine, which was destined for California, doesn't have a massively detuned engine, in line with their draconian emmissions laws and speed limit. It won't do more than 90 no matter who's riding it or where.
I can get it to make power allthrough the rev range in 1st and second; it pulls up to the redline.
It's just in 3rd to 6th that it's sluggish over 70 and won't do more than 90, regardless of revs.
I don't know why yours would stop at 6k. Does it pull in first higher than that?.
It's buggered itself electrically somehow now though. Misfiring like it's running out of petrol, only it's not.
I've tried carb-icing additive, changed the coils and cdi, as i said, new spark plugs, ht leads...
I think it's going to have to go to the garage for sure this time.
Good luck with yours. If i find anything new, i'll post here for you.
Still no joy here i'm afraid.
I've changed the coils and CDI ignition unit, and that didn't change it. I'm wondering if mine, which was destined for California, doesn't have a massively detuned engine, in line with their draconian emmissions laws and speed limit. It won't do more than 90 no matter who's riding it or where.
I can get it to make power allthrough the rev range in 1st and second; it pulls up to the redline.
It's just in 3rd to 6th that it's sluggish over 70 and won't do more than 90, regardless of revs.
I don't know why yours would stop at 6k. Does it pull in first higher than that?.
It's buggered itself electrically somehow now though. Misfiring like it's running out of petrol, only it's not.
I've tried carb-icing additive, changed the coils and cdi, as i said, new spark plugs, ht leads...
I think it's going to have to go to the garage for sure this time.
Good luck with yours. If i find anything new, i'll post here for you.
This is probably a dumb idea but have you checked the fuel filter? Also I had a smaller bike doing the same thing even after cleaning the carbs. I put new main jets in and problem solved. It doesn't take much to clog them a little.
Your bike should easily go over 90 mph. The emissions things do not affect things near that much.
Your bike should easily go over 90 mph. The emissions things do not affect things near that much.
I would be the old, slow guy. Just let me know where you are going and I'll try to get there before you leave.
Well i have fiddled with mine a *LOT* and have found that it is still behaving badly.
I replaced all four emulsion tubes as i figured they were shot ($160AUD later....) and then it started behaving quite badly like it was having a huge problem, coughing and spluttering like anyones business. It turns out someone in its past had replaced the stock N53L needle with a N53I needle and put 105 sized mainjets in instead of the 112's it was specced to run.
Anyhow i replaced the jets with 110's and then 112's to see if that'd fix the problem, but unfortunately no luck with that. So i bought a 2nd hand bank of carbies to try and replace bits off of that onto my bike. I replaced the sliders (which were in better nick than mine) and put their needles in (a N31L, which i cannot fathom WHY it is in there anyway...) and it still ran like a dogs breakfast.
So off i go and think, stuff it, i'll sort it once and for all. So i bought a dynojet kit for it, put a stage 2 in it as i have a formula 1 full system on it (a stage 1 is 105 main jets, stage 2 is a 118 main jet, stage 3 is a 136 main jet, all of these main jets have a deep head on the jet to stop frothed fuel getting into the circuit), other things that installing a dynojet kit requires you do is replace the needle with their one, drill the air bleed hole on the carb slider with the supplied drill bit and put their springs in instead. I replaced a couple of electric bits that were a bit shonky in the contact area.
But it beats the HELL out of me wtf is wrong with it having issues at going above 1/2 throttle or so. i get to about 6krpm, and then the sucker just bogs down, goes stuttery and becomes more recalcitrant the further open you twist the throttle.
Which brings me to where i am now, im going to try a carb synch to see if that steadies the low end stutteryness. But still im stuffed as to wtf is up with the top end.
oh and r.e. fuel filter, it was a bit bodgy before i put one on. and the filter expands to about an inch at the filter element, so it shouldnt be restricting fuel flow too much.
I replaced all four emulsion tubes as i figured they were shot ($160AUD later....) and then it started behaving quite badly like it was having a huge problem, coughing and spluttering like anyones business. It turns out someone in its past had replaced the stock N53L needle with a N53I needle and put 105 sized mainjets in instead of the 112's it was specced to run.
Anyhow i replaced the jets with 110's and then 112's to see if that'd fix the problem, but unfortunately no luck with that. So i bought a 2nd hand bank of carbies to try and replace bits off of that onto my bike. I replaced the sliders (which were in better nick than mine) and put their needles in (a N31L, which i cannot fathom WHY it is in there anyway...) and it still ran like a dogs breakfast.
So off i go and think, stuff it, i'll sort it once and for all. So i bought a dynojet kit for it, put a stage 2 in it as i have a formula 1 full system on it (a stage 1 is 105 main jets, stage 2 is a 118 main jet, stage 3 is a 136 main jet, all of these main jets have a deep head on the jet to stop frothed fuel getting into the circuit), other things that installing a dynojet kit requires you do is replace the needle with their one, drill the air bleed hole on the carb slider with the supplied drill bit and put their springs in instead. I replaced a couple of electric bits that were a bit shonky in the contact area.
But it beats the HELL out of me wtf is wrong with it having issues at going above 1/2 throttle or so. i get to about 6krpm, and then the sucker just bogs down, goes stuttery and becomes more recalcitrant the further open you twist the throttle.
Which brings me to where i am now, im going to try a carb synch to see if that steadies the low end stutteryness. But still im stuffed as to wtf is up with the top end.
oh and r.e. fuel filter, it was a bit bodgy before i put one on. and the filter expands to about an inch at the filter element, so it shouldnt be restricting fuel flow too much.