Drained carbs.. LOTS of air from one?

[Shifty]

Hey guys

ZZR250 is & has been great, but idle (1300 +/- 100 rpm) changes from time to time being anywhere from 900rpm to over 3000rpm (!). It also has a flat spot just off idle and sometimes when you start to open the throttle from a cruising speed. It's not something that's bothered me much but I'm starting to notice it a little more and I'd rather fix it now than when it leaves me stuck on the side of the road in a few months time.

Not knowing a lot about carbies, the first thing I set about doing tonight was avoiding the job. After thoroughly degreasing the engine I decided to actually look at the problem.

Again, I don't know a lot about carbies so the second thing I did (after avoiding the job!) was to drain them. So I set the fuel tap to PRIME and hooked up a clear hose & bottle ($8 Repco brake bleeder kit FTW!). The right-hand carb didn't show up anything unexpected... it just drained out nice clean looking fuel with the occasional small air bubble.

When I repeated the process for the right-hand carb there was heaps of air, it looked like about a 60/40 mix of air and fuel coming down the hose.

Suggestions as to what the problem is?

Also, I assume the next thing to look at is balancing the carbs... apparently I need some vacuum gauge. I'm a bit scared because a mechanic once made a big deal about it... but is it really as simple as running the engine with two vac hoses hooked up to a gauge and turning the screw until it reads zero?

[Daisy]

Ummm, air goes up - fuel goes down ...
Did you let them drain or did you suck it out?

To balance them you could get two gauges and adjust the balancing screw until they read the same.

[Shifty]

Ummm, air goes up - fuel goes down ...

True to a point, but the same as bleeding brakes the I would expect that air would come down the line if there's enough fluid coming down the line under pressure.

The first carb this was the case, lots of fuel and just the very occasional air bubble slowly working its way down the line. As soon as you close the drain plug any air bubbles still in the line climbed back upwards.

With the second carb though, heeeeaps of air seemed to be pushing down the hose... in fact as I think about it, it is almost as if the fuel was "glugging" out like if you turned a bottle of water upside-down... so with that carb maybe there was bugger-all fuel coming out and as such the air was climbing the line making it look s like lots of air was coming out?

That being the case I'd like to change my question to "why is more fuel coming out of one carb than the other?"

Did you let them drain or did you suck it out?

Drained. Just set the tap to PRI, opened the tap and the fuel poured out...

All a learning process for me, I've done all sorts of shit but it's mostly been with EFI cars so this stuff is a little new to me despite it's old-school-ness.

[Daisy]

Shit in the carburettor. *
There's probably muck in the bowls. I had a set off the other day and one of the drain holes was almost completely blocked with this rusty brown stuff.










*Do not try this.

[Shifty]

Hah, I received that joke once too.

OK so I'm trying to decide if there's actually really a problem or if I should just HTFU and put up with it. Maybe I'll get onto some vac gauges and balance the carbs and see if that makes any difference... then if not look at the awful job of taking the bastards off and giving them a cleanout.

[mike-s]

Take the carbs out, take the bowls off, check for shit in them, if theres none, perhaps do a bit of poking around, take the main jet (and idle, if removeable) check for crap, if any, soak in carby cleaner (spray doesnt cut it, a good 12+ hour sock and then clean is what you need)). remove the diaphragm off the top, watch for the spring, pop the emulsion tube out (the brass tube the needle inserts into) by pushing it out with a chopstick or something from the needle-side (usually they are held in by the main jet being screwed in place) check that for crap too and soak and clean if you can (this is the main area where shit can accumulate and clog a carby), reassemble, remembering to keep everything labelled and seperated per-carby. now all you'll have to do is a resynch of the carbies, which you were planning to do anyway.

Just bring some beer along and make it a bit of an event

[edit] do NOT get carby cleaner on the diaphragm or any other rubber bits, it WILL destroy the rubber, and the diaphragms are NOT cheap to replace, you have to buy the whole sodding slider with the disphragm as a unit and not just replace any shot rubber :-\ [/edit]

[jl4049]

Your idle speed moving around like that is generally caused by carbs out of balance or worn needles and/or emulsion tubes. How many k's? I have seen needles worn out in 10,000 k's!

[Shifty]

10,000km? You missed a zero, friend.

I don't think I want to know about this problem... emachizzit for a mechanic to remove/rebuild/refit & balance the carbs?

[jl4049]

No I have seen carb needles start to show wear, and emulsion tubes starting to go oval in 10,000k ( Racing with no aircleaners is no help!). As for price for a strip clean and rebuild, you should be able to do most of it yourself, however if your ike me and lack time to work on your bike most of the time, A dealer will prbably charge 350-500 depending on how many parts (carb parts arent exactly cheap) Probably less if the carbs only need a clean out and balance. (200 or so for that)

[Shifty]

I knew you meant 10,000km.... I was saying that mine is 100,000km!! I think it's showing 97,000ish.

$500 is a lot to spend on a $1000 bike... I might just sit on my arse and see if it gets worse or not

[jl4049]

ahh I see. Ir's a pretty easy job to whip the tops off the carbs and slide the diaphragms, slides and needles out and have a good look at the needle in the light, if one side is really shiny and slightly unrounded, theres your problem, if someone lives near you with a few skills, might be a good time to put some beers in the fridge and get someone round for a look, and give you a hand to clean/balance the carbs, cos it really is a pretty simple job.

[Shifty]

OK cheers, I'll see how energetic I feel

PS: I notice you're from Sale... me too, once upon a time.

[Shifty]

Just called Kawasaki... price on a pair of new needles and something else was $200. I kinda tuned out after the $200 thing....

[Shifty]

Ok well it died when Dale was riding it the other day, juuuuuust got in the driveway and it conked out.

Started with simple things first, disassembled & cleaned out the fuel tap which had a bit of crap in it. That may/may not have been the problem bu when I put it all back together and left it on 'prime' for 30 seconds or so it fired first go and has been fine ever since. Hmm....

[Shifty]

Ok well couldn't get it running so the carbs came off last night.

Started pulling them apart and noticed heeeaps of crap in one of the float needles, so it was leaking. Gave it a good degrease and hit it with some compresssed air... fingers crossed! I got the bike back together but I didn't have the keys with me (bike is not at home) so I'll have to head over tonight to see if it's a goer or not.

Unortuantely it's ben a bit hit & miss though so I've lost a little confidence in its reliability.... a week of riding it trouble-free o work should get me back on track