The bike is happy to rev up to 5k, nice crisp throttle response.  then up to 6/7k it seems to be struggling, keep having to blip the throttle to get it to climb higher eventually it will get to around 9-10k but then misfiring occurs.  any ideas?

1st of all its a kawasaki zephyr 750, had new piston rings, 2nd hand ECU, and airbox filter removed and K&N types fitted.  mileage 30k. 

2nd  i have checked secondary and primary couplings on ignition coils and they match readings in manual.

3rd i have balanced the carbs recently to within a gnats ***** of recommended levels.  carbs have been stripped and cleaned half a dozen times, new inlet rubbers fitted also.

4th plugs are good colour, gapped properly.

My guess would be the airbox and filter?  btw i have just ordered a new complete one off ebay.  but any thought would be most welcome.

wes pu hal

Duke                                                                                                                                                                             

Have you rejetted to suit the k&n's?
If so sounds like the needles may need lifting!                                                                                                                                                                             

Did you set the timing correctly when putting it back together                                                                                                                                                                             

Thanks for replies,  

YID-no, i didn't rejet cos i wouldnt know whether to go up or down, and i am sick of taking carbs off the bike lol, do you not think it would be best just to go back to original airbox? i do tbh.  i mean its only a zephyr-why mess about:)

Wheelbarrow-yeah timing is spot on, i did it myself but got it checked by a garage.  

Just so you know, i bought the bike from a scrapyard, stripped and rebuilt down to the frame-loads of aftermarket stuff,all mods and paint by me and me dad (mainly me, when i could stop dad from messing around with it lol)

wes pu hal

Duke                                                                                                                                                                             

I'd wait & try the new airbox & filter before checking anything else ;)                                                                                                                                                                              

 You sure its not something simple like a airlock or blockage in the petrol tank.
 You could try taking the pipe of a carb and letting the petrol run into a can for a few minutes to see if it slows down or even better if you can take a nut of the bottom of the float bowl, try it on each carb and at least you's know if petrol  getting to them

I'd wait & try the new airbox & filter before checking anything else ;) junction47
=yeah, i think thats best, also hoping to get new twin silencers on it soon (its 4-1 atm, previous owner) then reset and balance the carbs all over again :(
You sure its not something simple like a airlock or blockage in the petrol tank. bikeabill-mmmmm i DID have an inline filter but took it off in case this was causing slow fuel flow, but it made no difference and fuel flow seems fine.  all carb bowls have been checked for fuel, np there, but i haven't checked float height bh.

cheers for comments

Duke

wes pu hal

                                                                                                                                                                             

What speed are you doing when it starts playing up bearing in mind you dont need to thrash it in all the gears as 5k would be fine for changing up                                                                                                                                                                              

Hi jp

this is at standstill mate, not been on the road yet since rebuild.

Duke                                                                                                                                                                             

If thats at standstill revving then hardly any real throttle opening is being used, you would probably still be on the needles not on slides, a coil could be breaking down when asked to run faster.                                                                                                                                                                              

Duke, leave the K&N’s on, leave the 4-1 on, check &, if required, adjust the float heights!!   You say the carbs are well balanced & ign set correctly Good . Now pick up yer ‘Yellow pages’ & find a competent Dyno shop. Tell them you have just rebuilt & have new rings fitted, they can ‘run it in’ on the dyno.   Get them to check and set up your fueling, it IS gonna be all over the place. It should cost you around £60 - £70 Obviously more should parts be required.   Whislt its on the dyno, any other issues should become apparent ... As Harry said, a coil breaking down ????? Or simply carry on with tank off, carbs off, filters off, exhaust off. Change this , change that .. oh , it might be this !! exhaust on, filters on, carbs on, tank on , Know what I’m saying mate,  how long is all that going to take you.   BTW, a 4-1 exhaust is one of the best set ups you can get, (actually it’s a 4 - 2 - 1 but now I’m being picky) The reason being, the pulses from each exhaust stroke helps to pull the next one .. .. and so the cycle continues.                                                                                                                                                                                   

Oh yeah, I was intriuged by 'wes pu hal'  Soooooo   http://www.google.co.uk/search?sourceid=navclient&a...wes+pu+hal     I'm still intriuged !!!                                                                                                                                                                                      

It apparently means "good health" or something close in anglo saxon.

The pu word is sposed to have a carat ^ above it ant sounds like thu; so it comes out sounding like wes thu hal

any clearer:)

wes pu hal 

 Duke                                                                                                                                                                             

Thanks Tony.

i know what you are saying about on/off, on/off etc.

Anyway, got another complete airbox for £25 and the K&N's are going.  I originally thought they would look good, only to discover the outer ones wouldnt fit by the frame AND would be hidden by the side panels anyway.....oooooops.

carbs have been thoroughly cleaned on about 6 occasions, new jets put in (to spec) and now i can do a better job of checking the float heights, so thats the plan there.

The pipes are gonna be changed too.  Don't really follow ur point about exhausts pulses tbh.  The 750 Zephyr should have 4-2's so thats what i'm going for.  The one i got on now is 4-1 (not4-2-1) and the endcan is stamped triumph and is HUuuuuuuuGE.  It really unbalances the bike, seriously.

anyway thanks for thought and advice, nice1.

Duke 

Wes pu hal                                                                                                                                                                             

Well, have put the airbox back to normal, new filter of course, cleaned and checked carburetor (fuel level, float height etc).

Got it running and after a bit (f******* work you stupid F****** T**t) of messin about, got it more or less spot on now, revvin really nice, no pops and getting good revs up to 10k.  Nice.

Thanks for help, all.

Duke