Not Reving up properly - no top end power

[phase83]

Hi All,

Im new here and in desperation of finding the answer to my ZXR problems.

I have owned the bike for some 7 years now but has been stood up in a damp garage for the last 5 and im itching to get it back on the road.

Its now insured and ready to go to its MOT but when revving it seems to get to around 8,000 RPM and then not go any further. A few pops from the exhaust and a little white smoke (Definitely not loosing water or oil tho).

Things I have done to try and rectify the problem:

1. Strip carbs and cleaneb everything. (Copper had gone very dark brown, clean as best I could with carb cleaner, reset Air/Fuel mixture to factory)
2. New oil, Air Filter and Plugs
3. Checked coils are strong (Nice white/purple spark thats reached over an inch.)
4. Re-checked carbs and choke not stuck open
5. Checked fuel flow and fuel pump operate well (Filter definitely not clogged)

After doing all the above the problem was exactly the same as before.

However after re-install of carbs I had a bad overflowing problem on either carb 1 or 2.

I readjusted the float levels and that seemed to fix it. However reving was still not getting up there.

Im bypassing the tank and using a dummy tank, but im sure that doesnt really matter.

The airbox never seemed to sit well against the carbs and is a pain in the a*se to get on.
Would a little air leak here really have that much of an affect?

I does sound VERY load and rough when you give it a handful.

Any help would be greatly appreciated.

PS, its a 750 not a 400, hope its still OK to post in here

Chris (Phase83)

[Jeppo]

An airleak does cause a bit of roughness. Does it tick over smoothly? If not that can indicate an airleak.
If i were you I would try a fresh tank of fuel if you haven't already, and maybe some redex to flush the system.

[lewisdale]

exactly what i was going to say definatly use fresh fuel and im sure a airleak could do this, if my airbox isnt on properly it will idle fine but as soon as i give it some revs it pops and bangs, shoots flames etc and wont go no highter than about 8k so get the airbox properly fitted

[phase83]

Thanks for the speedy responses!

Yep used a new jerrycans worth of premium unleaded.

It idles perfectly and even starts off the button with no choke or throttle (Once warmed up).

Even when I had the air-box totally off it idled just fine?!?!?!
I was thinking an electrical problem like timing not advancing, but you have me thinking now it may be the fuel/air mixture?

What do you all think?

Thanks again for the replies, most appreciated

[phase83]

exactly what i was going to say definatly use fresh fuel and im sure a airleak could do this, if my airbox isnt on properly it will idle fine but as soon as i give it some revs it pops and bangs, shoots flames etc and wont go no highter than about 8k so get the airbox properly fitted

Ah could be the airbox alone then...

I have tried pushing the air-box on tight whilst trying to rev, but didn't make any difference. hummm...

[lewisdale]

mines the same, ticks over fine with no airbox just pops n bangs and does the same as youres, airbox on its fine, so try the airbox first

[phase83]

mines the same, ticks over fine with no airbox just pops n bangs and does the same as youres, airbox on its fine, so try the airbox first

It is actually on, just one of the rubber mouths wasnt put back on properly sometime in its past and warped/bruised the rubber so one is extreamly hard to get to fit perfectly. The old problem of pushing the bottom of the carb openings on, the pushing to get the top to sit in and the bottom pops out.

It was running brilliantly when I first had it and it had the same problem with the air-box back then so I still think it may be something a little more menacing. Im just hoping its not a CDI or Pick-up coil....

[lewisdale]

did you check the gaps on the plugs? checked the leads and caps arent perished/split/cracked?

[phase83]

did you check the gaps on the plugs? checked the leads and caps arent perished/split/cracked?

All spot on unfortunately... Thanks

[lewisdale]

tell you what i would do, put it all together properly, throw some redex in the fuel like has already been said and take it out for a good thrashing and see if it clears

[phase83]

tell you what i would do, put it all together properly, throw some redex in the fuel like has already been said and take it out for a good thrashing and see if it clears

Will do exactly that....

Thanks for all the help everyone.....

[lewisdale]

ok mate let us know how you get on

[motoxxx]

you havent unpluged your spedo have you?

i found when i removed my spedo it would not rev over 9k.

[phase83]

you havent unpluged your spedo have you?

i found when i removed my spedo it would not rev over 9k.

Its a mechanical spedo on my bike. Its lighting up when the lights are on so im prety sure theres no loose connection, is there something else in the spedo unit I dont know about?

[motoxxx]

not the speedo cable, if you removed the spedo and left the wires disconected it wouldnt rev past 9k...wel on mine anyway