GPZ900R flat spot on acceleration??

[Gosling1]

a good carbie balance will get rid of that inconsistent idle.......

and if the cam-chain has not been changed recently ( or since 1984 ) - a new one makes *all* the difference.

[phear8me]

yeah i know itll get rid of the inconsistancy ..... one day


lol and i dare say its the same cam chain seeing as it was in storage for 10yrs before i got it but it goes away once up to temperature

i got excited last week as it clocked over 50thousand ks lol whick means ive done 20k in less then a year

[callanan]

hi guys , my very first post lol. had same problem with my gpz908 r .here we go get this. iI f you engine has over 80,000 on it more than likely the diaphram slides are worn out . the diaphams are about $ 175 ea. ======= go to the wreckers and get some cvk 36 ' s off gpz1000rx. exact external dimensions but 2mm bigger id. and about $ 200---- $ 250. I spent 12months trying 2 find dis lean spot. & thats wot fixed it in the end. some fotos of a gpzzzzzzz scooter will b next, if i have the skills

[lauriep]

update.
raised the needles by another washer (so now two washers) approx a good 1mm in height (they are thin washers!)
idle mixture screws out 3 turns.
running about 90% good.
then discovered that fuel tank is now not venting properly, I think may be fuel cap vent system?
riding with fuel cap open and now bike is a little on rich side low down.
Wish I found this out earlier!
I am going to wind the idle mixture screws back to 2-1/2 turns, fix the venting and see how it goes but I think I have it 95% good (to my standards, but maybe 99% for some others?).
Evident now that next, if I really want to be perfect, is to get a carby balance.
But not necessary as it now pulls throughout the range (just a little uneven at idle).
but mind you it will idle as low 800rpms ok, if you want, so no real issues.
I think with the K&N air filter and the rear baffle removed from the mufflers, it needed the middle range to be richened up a little (ie. the washers).
So now all good and as far as I am concerned the project on this baby is now coming to an end.
I have spent $4k on parts alone on this (twice what I expected) so now time to move on.
Its all A1 Mechanically, should last for a long time before anything should need doing I would think.
Pretty much got the bugs out of it, and happy to now pass it on to someone else.

tis was a sad day when the bike left home on its way to a new found owner and pad.
she will be missed.

thanks
Laurie

[bonester]

My GPZ900R has a flat spot, particularly under load 3-4k. Runs well elsewhere. Gos do you reckon cam chain makes a huge difference on these????? Mine has 164000km on it as far as I can tell. Half way along the ratchet tensioner I put in it in the 1990s but the marks on the cams are a little out- suggesting worn chain. Ideas? Ta

[bonester]

Found this on Z Power site:

The GPZ was fitted with a set of four Keihan CVK34mm carbs, which were normally excellent in operation, but it was noticed that sometimes there could be a slight hesitation at low engine speeds, a bit like the lag that we used to get on the injection models. Kawasaki decided to modify the needle jet holder allowing more fuel to pass through it. The new part number for this holder was 13091-1347.
This went some way to eliminate the problem but some owners were still complaining of flat spots at around 3,000 rpm and erratic tick over. Inspection of the carb diaphragms verified that they could twist in the carb bodies so Kawasaki modified them and fitted them under warranty to all affected bikes. All new bikes after frame number 015192 had these modified parts fitted at the factory. If you need to check to see if yours was done, there was a blob of white paint on the left side of no.1 carburettor.

Sounds just like my bike.My carbs are off maybe an 86/87 model. Have to look here.

[bonester]

Found this too:
The bike did have a bit of a misfire/flatspot at 3000rpm, but I put that down to the old Lazer exhaust can that it had on when I got it, as there was no baffle in it to speak of. When I took it to DynoTorque in Birmingham for him to try and sort out the 3000rpm glitch he opened up the airbox inlet a bit, which helped. He said that the can was a real problem, as it was so free flowing there was no back pressure, and he had no end of trouble pin pointing what exactly the problem was.

[bonester]

Found the problem for future reference. Someone on the net mentioned the seal on the airbox door. Made a new one out of foam and banged it on. Runs like a dream. Easy.