68mph - 82mph Lumpy! - Between 68 & 82mph my Z1000 is lumpy as old porridge

[The Doony]

Hello. I've had some ongoin issues with my carbs but mostly things are quite good now.
Not that the bike's been out much over the past few months, been doing quite a bit of tidying up.
Anyhooo, between 68ish and 82ish MPH my Z1000 is as lumpy as old porridge, however if I open the choke fully it smooths out a treat. Not being too clever with these things how can I sort this problem?
The carbs have just been balanced by my local garage at a cost of ?47...! I don't much feel like having to fork out for that again anytime soon.

Any suggestions please?
Thx.

[Pigford]

Hello Doony,.. if she runs better with choke out, must be running weak. You can remove float bowls, check jets & float heights and do a visual on needle wear etc without disturbing slide/balancing. Was bike ok before carb balancing? Assuming float heights are OK,run at 68mph+ try holding on minimum steady throttle...... then whack her open for a few seconds and slowly wind her back. If she gets better as you close throttle, definitely running weak. This could be several things (air filter replaced OK? air leak on manifold rubbers? Needles adjusted wrong during carb set-up.. on to high a notch?). Check main jets right size and clear. Carbs may need a good clean (sonic) if been standing for more than a few months, previously.

[The Doony]

Hi,
Thanks for the feedback.
The carbs were stripped completely and rebuilt prior to balance. The float heights were supposed to have been set by another garage, the needles, jets etc were cleaned and checked over and all seemed ok. The bike was running like a dream prior to rebuild, whereupon all gaskets were changed. The reason for the strip was to clean the exteriors and change gaskets as there was a small weep from one of the carbs (which is still there).
If I get to around 68 and pop the throttle open she excellerates fine, she's only lumpy if I'm just trundling along between the speeds mentioned.
What about adjusting the mixtures, would that help?
Also, one of the garages cleaned the air filter, could it be that it's now letting too much air through?
Cheers
A.

[Pigford]

Try this, Copy and paste:
http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

You should be able to isolate part of carbs causing problems?

[The Doony]

Thanks again,
Read but not completely understood. Am I right then in assuming that the mixture screws will only really have an effect at idle to 1/4 throttle?
So this is not going to remedy my problem.
From what I've just read, engine speed has little to do with carburation, but my problem only occurs between the speeds mentioned.
I'm sure I'm being a bit thick for you here but I'm certainly no mechanic and I ain't loaded either, just a Z owner that wants to get his bike running properly...I'm afaid I need an a, b, c, approach.

[Pigford]

A)Pretty sure you can discount electrics.... they usually breakdown under load, and as runs nice with WOT, must be OK. (Wide Open Throttle)!
B) When cruising at 70mph, throttle will probably be open 1/4?? or 1/4 - 1/2??? Sound like a blocked pilot jet?
C) If running good on more open throttle, main jetting OK!
Again, all this assume rest of fuel system OK!

(Edited by Pigford at 9:40 pm on April 17, 2006)

[The Doony]

OK, thanks.
I'll get the bottoms off and check the pilot jet, I can remove this safely without adjusting balance me thinks.
It's only likely to be dodgy on one carb though, is there anyway of testing for which one....or is it just drop all the bottoms and see?
Seriously, big thanks for the help.
A

[Pigford]

The best way is to just whip em off and give all of 'em a good blow!!!!!????? The balancing will not be effected. This is quite easy to do and a quick way of finding out if it helps or not! Might be worth using a good filter in the fuel line to eliminate rust & dirt contamination. This can be a big problem with any 'older' bike!

[The Doony]

I'll give it a go and let ya know.
TTFN.

[DogsbolloxofZ1B]

A few other things to check.

1) HT caps are screwed into fresh copper, chop 1/4" off
each HT cable splay Cu strands & screw back in.
2) Valve clearances & timing set correctly.
Points/condensors OK?
3) Clean the plugs & take it for a 10 mile spin at the
speed you have problem wiv, remove plugs & they shoud
all be a nice chocolate Brown, if Black/sooty or
white/Grey OR plugs are different colour to each other
you need to do all of what the guys previous have said.
i.e. Go back to basics & check the carbs over again.

Good luck.

Mike

[Rickman CR]

Keep carbs on the bike but disconnect air filters. Run the bike and one by one block off each carb air intake with a bunched up rag, Keep it fairly high revs to stop it stalling. This creates massive pressure throughout the carb jets and airways and tends to clear them out. Its a bit rough and ready but it can work out ok with minimum strip down.

No? Ah well strip the feckers down and blow through the airways with compressed air. I'll put the kettle on whilst you think about it...

[Rich]

and look for blocked holes in the emulsion tubes while you have the float bowls off.

[The Doony]

Hi again,
Well, I adjusted all mixtures, found that the manifold clamps were a little loose so tightened, took it for a blast and in the main I think things have improved.
I'm not sure if there's still a little fluff every now & then but there's so much buffeting and wind noise over 80 I can't be sure at the mo.
I'll have to do some more test runs.
Thanks for the input....

[Pigford]

Check the manifold rubbers for cracks... if originals probably perished!!!

[Daximus]

This sounds very familiar.... had similar problems with mine and of course spent loads on the carbs. Then I bought a set of taylor leads.....Problem solved....now swear by them. Fifty quid wasn't much considering how much i'd already spent and it was just fab taking her down the road and descovering that suddenly it was a different bike to ride.