Exhaust smoke after throttle shutdown

[z1000puddin]

Guys,
I had a hundred or so miles on my 1075 zed. yesterday.

My mate following noticed that there was smoke coming from the exhaust when the throttle was shut-down. Noticeably when it was getting a good thrash.

The bike has new MTC piston & rings
28mm carbs with 112.5 mains & 17.5 pilots.
Open ally trumpets


Intend getting it dynod, but I am concerned about the smoke - Should this happen on a rebuilt motor ??

Or should I carry out a compression test. ?

The bike starts & idles well, pulls well although it may need a jet up one or two.

.The bike has done a couple of hundred running in miles.

Stu

[Charlie]

How much smoke and what colour is it ?

[ZedHead]

Blue smoke on over run. I would suspect valve oil seals.

[chrisu]

http://z1ownersclub.co.uk/forum/viewtopic.php?t=25536

[jimmock]

Blue smoke on over run. I would suspect valve oil seals.

I agree,

on over run it must be stem oil seals and/or guides.

[z1000puddin]

Thanks guys,
I will get the compression check - just for my own reference.

I whipped out # 2 plug just to check - pic below - does this show a bit lean ?

[paulmceleney]

no that what everyone want there plugs to look like that is the best

[KeithZ1R]

Feck me the mythical "straw coloured plug" save it for posterity

[z1000puddin]

So you would not advise messing about with the 28mm carbs then.

I thought my current set up of the mains @ 112.5 & pilots @ 17.5 was standard.

And as I have 4-1-2 underseat exhaust, open velocity stacks & andrews 2X Cams - I thought I would need to up jet.

Stu

[paulmceleney]

Try 130 main jet this will make a difference
it will run better more power I have a under seat exhaust on my z1000 rebored to 1075 gas flowed head z1r cams 33 smoothbore carbs was running 28 mm carbs and 130 jets there is not much difference between z1r carbs and smoothbore carbs in power

[z1000puddin]

Thanks Paul,

The 28mm carbs I have on are from a Z1B.

Do you think I need to go up as far as 130 on the mains ?
It seems a real big jump.

Stu

[paulmceleney]

yes I ran 150 in my z900 which was a bit to big it still pulled well plus 50 to the gallon went to Germany with the 150 jets in but 130 should be spot on then adjust the air screws even moving them 1mm can make a difference just a little each time

[z1000puddin]

Paul,
What would you suggest for the pilots ? Keep these @ 17.5 ?
What needle position should I set at ?

Thanks in advance

Stu

[paulmceleney]

I would just change the main jets the pilot jets in my carbs which are 33 smoothbores are 17.5

[ZedHead]

How much smoke and what colour is it ?

I would go back to this before deciding to play with carbs. Blue = Oil, Grey/White =Rich mixture which, looking at your plugs, I would say is not your problem.

I am not sure if leaking oils seal will show on a compression test? The blue smoke on over run is usually due to the increased vacuum when the throttle is shut off sucking oil passed leaky seals on the inlet side.