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Rev's slow to come back down 1.8 CVH Zx6R carbs
mikeb - 20/3/17 at 09:45 AM

Any suggestion why under zero load the rev's on my 1.8CVH take a little time to come back down.
I'm running zx6r carbs with Nodiz ecu, on a blip of the throttle it responds well just takes a couple of seconds for the revs to come back down to idle?
It's on standard jets (i've bought some 1.6mm to go in) with the idle screws 2.5 turns out.
It also bogs down underload after about 3.5k but assuming the jets and a rolling road would sort that.

Thanks

M

redturner - 20/3/17 at 10:03 AM

Sounds like you are under jetted, stick the 1.6s in or maybe some 180s.....

Slater - 20/3/17 at 11:14 AM

Have you got a throttle return spring fitted? Often needed for bike carb set ups.

Link to post

Norfolkluegojnr - 20/3/17 at 11:48 AM

quote:
Originally posted by Slater
Have you got a throttle return spring fitted? Often needed for bike carb set ups.

Link to post


Yes, this. Having fitted two sets of bike carbs, both needed additional springs to help them close.

mikeb - 20/3/17 at 12:19 PM

I've got the extra return spring on the pedal end, the zx6r's seem to snap shut very well, so don't think that the problem.
I've seen teh zx6r also have adjustable needles, i've not found that adjustment yet, anyone know where its adjusted and the effect of adjusting over bigger jets ?

Would the jets affect the return to idle?

[Edited on 20/3/17 by mikeb]

CosKev3 - 20/3/17 at 12:40 PM

The additional spring needs to be in the carbs, not the pedal.
Even though they do seem to snap shut my experience with the R1 carbs is you need a additional return spring on the carbs as on the bike they use twin cables

Norfolkluegojnr - 20/3/17 at 12:49 PM

quote:
Originally posted by mikeb
I've got the extra return spring on the pedal end, the zx6r's seem to snap shut very well, so don't think that the problem.
I've seen teh zx6r also have adjustable needles, i've not found that adjustment yet, anyone know where its adjusted and the effect of adjusting over bigger jets ?

Would the jets affect the return to idle?

[Edited on 20/3/17 by mikeb]



easy way to check - rev it and close the throttle by hand, on the carb.

if its that, you wont get the slow rev drop issue, if you still do, its something else

SJ - 20/3/17 at 01:00 PM

quote:

I've got the extra return spring on the pedal end, the zx6r's seem to snap shut very well, so don't think that the problem.
I've seen teh zx6r also have adjustable needles, i've not found that adjustment yet, anyone know where its adjusted and the effect of adjusting over bigger jets ?

Would the jets affect the return to idle?



I have Zx6R carbs on my Zetec & they work really well. The needles are adjustable by taking the carb top off and moving the circlip that holds the needle in either up or down. There are 3 or 4 grooves I think.

The effect of the needles position is on mid throttle mixture. At WOT the jet size determines mixture. At idle it is the pilot jet and float height, and everywhere in between it is a combination of the jet size and needle height.

Mine needed an additional spring on the carb to return quickly, though I don't have a spring at the pedal end.

Stu

mikeb - 20/3/17 at 01:27 PM

Thanks Stu, thats really helpful.

I'll pop the tops off tonight to see if I can adjust, handy for IVA to if it fails emissions!

r1_pete - 20/3/17 at 01:46 PM

Not that familiar with 6R carbs but done plenty of 9R and zzr carbs, while you're in there check the slides are nice and free and not sticking.

mikeb - 20/3/17 at 01:54 PM

any tips if they are a sticking a little?

kingster996 - 20/3/17 at 08:18 PM

Carbs being out of balance can cause the revs being slow to drop too.

r1_pete - 20/3/17 at 08:35 PM

If they are sticky, a good clean, and polish any rough areas with something like solvol autosol, Ive used T Cut with success too, but clean any residue away, both autosol and T Cut are abrasive enough to cause wear if left.

[Edited on 20/3/17 by r1_pete]

scudderfish - 20/3/17 at 09:53 PM

quote:
Originally posted by mikeb
I've got the extra return spring on the pedal end, the zx6r's seem to snap shut very well, so don't think that the problem.
I've seen teh zx6r also have adjustable needles, i've not found that adjustment yet, anyone know where its adjusted and the effect of adjusting over bigger jets ?

Would the jets affect the return to idle?

[Edited on 20/3/17 by mikeb]


The throttle cable always needs to be in tension. Imagine you had no spring at all at the carb, the spring on the pedal would be trying to push the cable which will just bend and buckle wherever it can.

r1_pete - 20/3/17 at 10:04 PM

But you do need some slack to enable the throttle lever/cam to home on the tickover adjusting screw, under tension it will lift off, or be slow to settle, usually 2-3 mm at the cable stop is the norm.

[Edited on 20/3/17 by r1_pete]

Tatey - 21/3/17 at 06:04 PM

They other thing to look for is an air leak, I have had one on my ZX6R carbs. The way to check is with some WD40 or other suitable flammable spray and spray all around the carbs to see if the revs rise.