Carb Problem

[AussiXS11G]

irish....they were all new plugs.....
pete - i am going down that road as you read this...

[petejw1966]

bryan, put it back the way u had it,
and run it with the bp6's pugs. 

[pgnz]

that puts another spin on it, 1 & 2 both rich as hell,  # 3 and 4 look OK-ish ,  #4 looks a brand new plug and it'll take a while to colour up,  if the bike  was running fine previously with clean plugs then changing jets or fiddling the needles ain't the right cure,  If it suddenly started playing up then it'll be electrical(pick-up coils/coils ignition plugs leads etc,,), or crap in the carbs/fuel system or possibly air leaks in vac hoses

[AussiXS11G]

ok - checked fuel levels - it seems that 1 and 2 are too high (level with top of float bowl) while 3 and 4 appear a little low.......yet the floats are all at 22mm
I found a split in the line leading to 1 and 2 and this may have leaked into the air box ....maybe....
I agree about the short single line and will braze a "H" piece with a large bore to replace this
I found that without joining L and R fuel taps the R side of the tank dried out before the L, hence the setup...
these are BS36 carbs.....reassure me that the float levels are checked thus...

Tilt the carbs so that the floats just flop over towards and into the carb body.
Tilt just enough to touch and close the float the float valve, but...
Do NOT compress the float valve spring when measuring (only exception is 95-97 zx6r)

[Miti]

hello Miti and thx for the advice...
seems strange that the machine ran well for 60km at various speeds under my test conditions. The problem started when I stopped at the first set of lights after the country roads.

this is the fuel line setup - fuel filters are now in the two horizontal lines above the carbs. not much opportunity for a kink I reckon. I have run this setup for the past 4k km.

the carbs are BS36 units - the info I have for fuel level is 4.5 to 5.5mm below joint - I will measure this in the next half hour and get back,

I appreciate that you've put quite a few km in with that setup, but I'm not keen on the single line section... I've had fuel starvation snags on my own XS and I know that the correct fuel line and routing is VERY important...

My own preferred routing is:

LH Tap - Short section of fuel line - fuel filter (horizontally mounted above #3 & #4 inlets - Long section of fuel line, all the way around #4 inlet then up between #3 & #4 carbs, into the Tee Piece.

RH Tap - Short section of fuel line - fuel filter (horizontally mounted above #1 & #2 inlets - Long section of fuel line, all the way around #1 inlet then up between #1 & #2 carbs, into the Tee Piece.

I always use reinforced fuel line too... The single skin neoprene stuff is just way to "kinky" to try to plumb in a Sport with Octy fitted...

That said... After seeing your setup, I think I'd be checking all the lines for blockages... Especially those concerned with #3 and #4 carbs

HTH

Miti

[excess.11]

thanks for the advice guys....
I have set the float levels, dropped the needles one knotch....
balanced and then no 2 carb decided to overflow into the airbox....
working atm - so tomorrow .....carbs out -AGAIN-
getting good at it tho....

Bryan....what was the outcome of the overflow into the airbox ?
Has the problem that caused this been found and rectified?

[AussiXS11G]

hello Miti and thx for the advice...
seems strange that the machine ran well for 60km at various speeds under my test conditions. The problem started when I stopped at the first set of lights after the country roads.

this is the fuel line setup - fuel filters are now in the two horizontal lines above the carbs. not much opportunity for a kink I reckon. I have run this setup for the past 4k km.



the carbs are BS36 units - the info I have for fuel level is 4.5 to 5.5mm below joint - I will measure this in the next half hour and get back,

[Miti]

Hi Bryan;

Looks like two different snags there mate...

#1 and #2 are clearly too rich... The very dark deposit around the base of the plug thread is oil being washed off your bores by the fuel-rich mixture...

#3 and #4 are clearly fuel starved...

I suspect that you've introduced a kink in the fuel line to carbs #3 and #4 and that they're hardly getting any fuel at all.  I'd check for this first.

A float height of 22mm should have the float valves closing nice an early, but there's no replacement for an actual fuel level measurement (clear fuel line up the side of the float bowl).

If you've the earlier carbs with the 10mm headed drain plug, you could "knock up" an adaptor to fit the float bowl... Old pozilube 2-strokes had small banjo-bolt feeds for the 2-stroke lube injection... One of those (bolt and banjo) will fit neatly into the float bowl and the tube end of the banjo fitting connects into a clear pipe as if it was designed for it... 

If you've the newer float bowls with the cast drain spigot, the fuel line slips straight on (and off sometimes - beware..!!)

A fuel level somewhere near 3mm below the joint twixt carb body and float bowl is what you're looking for.

Also... When adjusting the float height tab:  Double check that the spring-loaded plunger in the float is moving up and down properly and that the tab is acually pressing against this plunger all the way through the range of movement... I've had probs where the tab was fouling the body of the inlet valve and, although the float height measured correctly, the valve wasn't being held closed properly...

HTH

Miti

[AussiXS11G]

fuel filters are brand new today.......

[excess.11]

How are the fuel filters you installed?
Can you bypass them or replace?

[AussiXS11G]

this is the latest......
Floats set at 22.0mm
main 140
pilot 45
needle at second from top
checked compression too... 1 175, 2 175, 3 170, 4 180
Went fora 60km ride .......runs nice - still a slight hesitation at abt 6-7k revs.....
then 5 km from home running rough - like on 3 cylinders.. thought a carb was was flooding.....
here are the plugs....1 to 4 - L to R







WTF? 
I will have a look in the morning... 

[AussiXS11G]

thanks for the advice guys....
I have set the float levels, dropped the needles one knotch....
balanced and then no 2 carb decided to overflow into the airbox....
working atm - so tomorrow .....carbs out -AGAIN-
getting good at it tho....

[pgnz]

nah, just check the carbon deposit around the rim,  they're reading slightly on the rich side, they can be leaner but  those plugs are reading pretty much perfect if they were checked quickly after running 5th gear any revs over 4000.   that's the mainjet circuit and it's sweet.  just slightly on the rich side,  one size down on mainjet would  likely be pretty revvy and  best top speed and best acceleration

  bottom pic 2nd plug from right lightly richer than the rest probably the merest touch of the float.   If plugs were checked after running round town and idling for a while they're still looking primo and not overly rich.     if you ran the bike in the stumbling zone for a while then checked the plugs on the side of the road you'll know if it's too rich the plugs'll be black and sooty running below 4000 revs,  a drop of the needles might fix the stumble if that's the case

[steptoe]

my 5 cents,, pot one is getting pretty close to what you want, but still lean, the other 3 are lean by some,
the ceramic center needs to be a touch darker, and all 4 tabs are showing a white colour,

seems like that trip up still has to happen,

lift your needles 1 groove first and see what happens

[petejw1966]

i know ur bikes got some mods,
but theres really no need to run a colder
plug unless maybe ur in the middle of a very hot
summer and running it at high revs,
it might not solve the carby problem if there is one,
but plugs are cheap and it wont hurt any.