Another quick (?) carb question :) Now sorted :) :)

[JohnC]

OK, decided to be a naughty boy today (no MOT yet) and take my poorly running Z out for a quick spin, in the hope that I could resolve what I'm sure is a carb problem (should be getting them ultrasonically cleaned soon anyway).

My new Dyna HT leads arrived this morning and were fitted. No difference - number 2 cylinder / pipe (not heating up as much as 1,3,4 as before).

So I took the VM29's off, checked all the float heights again, all were bang on at 23 mm as per spec. Took out all the pilot jets, all seemed fine, even swapped them around just to be sure and all were as per spec 17.5's.

Blew the airline through everything, checked the needles and needle heights, all looked fine as per spec.

Put everything back together and took the bike out for a run, both urban and down the by-pass.

Bike runs like a dog around town, tick over hopeless, seems to go up and down and revert back to about 2000rpm even when I adjust it down to 1K once warm.

Slight backfiring, not a lot, but periodically, and mainly on the overrun.

Seem to run OK when giving it the rubber welly, but doesn't like a steady throttle. Pulls like a good un' when going for it. Hunts at 60 - 70 mph.

Brought the bike back to the garage, did a quick water splash and pipe 2 is just the same, water vaporizing on contact but with some water lingering. All other pipes water dissipating like mist, gone as soon as it hits the pipes.

Took filters off, strong suction when placing my hand over all the carbs but less so from number 2, suction never the less but not as strong as the others.

Question (short one lol Would the carbs simply being out of balance cause this sort of prob? Statically balanced and checked again as 1.5 mm high this morning.

Is there some other reason the bike would run so poorly at low revs / tickover that I'm somehow missing?

Would a slightly dicky / sticky valve cause this even after a negative leak down test?

Would ultrasonic cleaning clean something that could cause this that I cant clean manually with carb cleaner?

Clutching at straws guys, bearing in mind shims OK, leak down test OK, spark OK. I've replaced everything I can prior to whipping the bloody head off :/


John

[lude]

leaky carb to head rubber ?

[JohnC]

Tried that lude m8, even put a tiny smear of RTV Silicone Permatex Ultra Copper on the inlets. Checked by spraying the rubbers with carb cleaner when the bike was running, no leaks. Rubbers are brand new as well so still have the raised lip, swapped them about this morning as well and checked every vacuum take off with no joy.

J.

[z1bman]

remove the pilot jets & squirt some wd 40 into the pilot passageway in the carburettor it should come through a small hole in the throat of the carburettor underneath the slide any wd 40 left in the passageway indicates a blocked carb. have you removed the main jet holder/ emulsion tubes & cleaned the holes

[FOZ1A]

John, 17.5 pilots are too small, std is 25, I run mine on 20's as 25's are too rich.

foz

[ZedHead]

Defo sounds like carbs. I would get hold of a vacuum balancer and see what you have.

A couple of good links to look at. Note the mention of an extra vent on some VM29 carbs on the wired george link.

http://www.z1enterprises.com/Z1CarbGuide.aspx

http://www.wgcarbs.com//index.php?optio ... =Itemid=85

Good luck with this we are all scratching our heads with you

[JohnC]

FOZ1A, I thought 20 -25's were for the later VM29 Smoothbores? Perhaps they are a bit small for my bike with a 1075 and 4 - 1 etc? Worth a try but I doubt this is my main prob :/

John

See below from Jeff:

Jeff.Saunders - 23-12-2004 at 08:18

http://www.z1enterprises.com/catalog.aspx?pid=KPCF3

The float needle valve on the Mikuni VM29 29mm smoothbores is not common with the Mikuni carbs Kawasaki put on the KZ650 / KZ900 / KZ1000.

The 29mm smoothbore needle valve assembly has the provision for a small inline filter to stop crud getting into the float chamber (a really nice idea).

There are still a moderate amount of parts available for the 29mm carbs - but not everything.

Float height is 23mm.

These carbs do not have an overflow, so if you do have a float valve sticking, or you set the height too high, the gas will flow into the engine...

Here's the typical 'stock' setup from Mikuni

29mm smoothbores Z1 / KZ900 / KZ1000
Main Jet 120
Air Jet 0.9
Needle Jet O-6
Jet Needle 5DL31-3
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 17.5 or 20.0 (or 25 in the later versions)
Air Screw setting 1 1/2 turns out

[JohnC]

z1bman, yes did that this morning everything seemed fine, no blockages

[oldzed]

Hi John.

just to check . It was no1 cylinder that was cold last week.
It only ran when we increased the vacuum by partially blocking the carb inlet.

Is that one now running ok ?

just curious

craig

[z1bman]

have you tried swapping the coils over ?

[Rich]

Your pilot jets are too small at 17.5, go to 20 or 22.5, as said 25s are too big, run 1 to 1 1/4 turns out on the air screws.

[lude]

you probably done this already.....
VM CARBURETOR DISASSEMBLY /
INSPECTION / ASSEMBLY
http://www.marclatulippe.com/ManuelShopMotoneige/Polaris/Polaris%202007-2011/2007-2011%20IQ%20Service%20Manual%20Chapter%2004%20-%20Fuel%20Systems.pdf

Does it run properly on number 1 from cold with choke on, ie just let it tick over ?

[tricky]

hi john, have you done a fuel service level check?
in my experience float hights mean jack, also what was your procedure for mechanicaly balancing the carbs? tricky.

[JohnC]

Hi Tricky, no I haven't done the float height fuel service check, I'll order up a spare drain screw from Allens Performance so that I can drill and tap it for checking the fuel level.

I balanced the carbs by using a small 3 mm drill bit and just made sure the drill bit was a sliding fit on all carbs. (I said earlier 1.5 mm but it was actually 3mm). I received this advice from Pigford on here, he thought anything between 3 - 7 mm is OK. It does say 1.5 mm 'slide cutaway' on http://www.z1enterprises.com/Z1CarbGuide.aspx, not sure if this is an indication of static height for balancing or that it would really show up as the problem I'm having. What do you think?

When I took the bike for it's MOT yesterday (20 mile ride) it seems the low to mid range is where the bike is worse, it hunts between 2 - 4K rpm. Once I hit 5000 rpm (70moph) the bike goes like stink and pulls like a train. The bike also doesn't like to hold tickover much under 1.5K rpm but that could because I've not fully set up the air screw properly due to the other problems. It does seem to be getting a bit better the more fuel that I get through the carbs. Perhaps all they need is a good ultrasonic clean and a full balance with gauges, hopefully!!

z1bman swapped the coils and made no difference, coils are fresh out the box new 3ohm from Dyna. The coils are definitely not wired as per Dynas instructions but the bike has been running fine for years with the current setup.

I'm also going to order up some 20 & 22.5 pilot jets just to see if this helps any.

lude thanks for that link, great find and I'll give it a good read. As oldzed who was helping me out said earlier it's actually only No 2 that's not getting quite as hot as the other pipes. Make no difference regarding whether it's on or off choke, i.e. warming up or fully warm.

Zedhead cheers m8, no extra vent of vacuum take off on my VM's.

Craig (oldzed) has offered to loan me his carbs while mine are being cleaned so hopefully this will say one way or another if the carbs are the main culprit.

Update: Allens Performance reckon my problems are the pilot jets, they say they just chuck them straight away on old VM carbs for my new ones, so here's hoping.

[steve bowdler]

http://www.ebay.co.uk/itm/KAWASAKI-Z900 ... 2c700a4dcb