'88 ZX-4 Flatspot at 4k rpm

[imthatguy]

Hey guys,

haven't posted on here in awhile! Never did get my issue sorted with the ZZR400, ended up taking it to a mechanic. Turned out to be some very burnt valves.. :facepalm:

Anyway to business! In the mean time Ive bought a 1988 Kawasaki ZX-4(G F3 blablabla) which runs like a stabbed rat except for a very annoying flat spot at aprox 4-5k rpm. Because its normally being driven on the edge it doesn't really matter once the bike is upto speed but taking off from the lights etc is pretty annoying..

Without getting flatsides for it (which I can do for a cool $2600..) is there anything else i can do to get rid of this? Ive been told its basically wear and theres not a lot I can do about it (by Gorge at motorcycle doctors in Auckland).

[Akzle]

a 25 year old raped ass 4hunnit 4pot.

Carb tune. Rebuild.

[Drew]

Air leaks around the carb boots on one or both sides.

Can of engine start sprayed around then while running will test. If the revs climb when you spray, you've found your leak.

Could be any number of things though.

[imthatguy]

a 25 year old raped ass 4hunnit 4pot.

Carb tune. Rebuild.

Hahaha thanks for your always helpful input Akzle ;) Its only done 20something k's, and the previous owner was a lady who only occasionally used it on weekends - its hardly been raped..

Also before I brought it, it had the carbs completely reconditioned and balanced so I really doubt thats the issue.. I did consider raising the needles a bit but I think that would just migrate the issue further up the rev range which would be even more annoying..

[imthatguy]

Air leaks around the carb boots on one or both sides.

Can of engine start sprayed around then while running will test. If the revs climb when you spray, you've found your leak.

Could be any number of things though.

I really don't think its an air leak, Ive delt with those before and this doesn't feel like that - its just a flat spot at almost exact 4k, doesn't show up anywhere else in the rev range really.

[imthatguy]

Hey guys,

haven't posted on here in awhile! Never did get my issue sorted with the ZZR400, ended up taking it to a mechanic. Turned out to be some very burnt valves.. :facepalm:

Anyway to business! In the mean time Ive bought a 1988 Kawasaki ZX-4(G F3 blablabla) which runs like a stabbed rat except for a very annoying flat spot at aprox 4-5k rpm. Because its normally being driven on the edge it doesn't really matter once the bike is upto speed but taking off from the lights etc is pretty annoying..

Without getting flatsides for it (which I can do for a cool $2600..) is there anything else i can do to get rid of this? Ive been told its basically wear and theres not a lot I can do about it (by Gorge at motorcycle doctors in Auckland).

I should have mentioned this is wear in the emulsion tubes, the engine itself runs mint and when last checked about 5k ago all the clearances were well within tolerances etc..

[F5 Dave]

So check the plugs, if they are dark the emulsion tubes, or often just a couple, are worn making adjustment pointless.

Non std pipe or filter and I'd be experimenting with thin washers under the needles.