Hey all, long time no speak, dont really get free time at work anymore, but there we go!

Decided to balance my carbs this weekend as they needed doing, so i whip off the tank, plug in the gauges and start her up...

the first three carbs were fine, but the 4th wasnt showing any vaccum at all, so i tried to balance the 3rd and 4th carb (as there are only three adjusting screws, on of each pair of carbs then a screw to balance the two) and suddenly the 1st and 2nd started to be ajusted, any way to cut a long story short i managed to get 3 carbs running fairily similarly, but it runs worse than before, looking to strip down the carbs in 2 weeks time, but its running so badly while idling, not while its running...

anyone have an idea what i could find when i take the carbs off?!

Have you done a compression test?

You will prob find that your carbs are now way out of balance, as the first 3 are trying to make up for the 4 one.

Did you try to swap the gauges about to check it was not a problem with the gauges?

When I couldn't get my carbs balanced I found it was because I had splits in the diaphragms, so I had to replace them.

I have no idea what type of carbs your bike has or whether it might have this problem but I just thought I'd offer my experience.

I'd check the compression and the valves.




My thoughts exactly. A very simple test would be to stick your finger on the pipe you attach the vacuum gauge to. You'd feel the vacuum sucking on your finger.



I had a split diaphragm on a Z250 and I remember lifting the slides up and seeing if they both take the same time to drop when you let go of them. The one that had a split dropped like a stone.

Just took the tops off my carbs and the splits were easily visible, each one had a split about threequarters of an inch - no wonder it didn't accellerate very well!

Sorry I havent replied sooner, The bike runs well over 3k rpm, so i dont think its a diaphram or else it would be spluttering all over the place? not carried out a compression test as i ran out of time, I am hoping its an air blockage/leak somewhere along the line, just going to take the carbs off, give them a good clean and put them back together again, hopefully that might help!

What's the condition of the plugs when you do a plug chop? (ie warm it up, put a few revs on to the point where it plays up, hit the kill switch, then check the plugs) - that should tell you if any of the cylinders are running rich or lean, could be a float is sticking at lower revs?

I dont think its fuel, as before I started fiddling with them they were OK. I know the bike is now running rich, but I have had to to stop it stalling every time it idles, will be a right pain in the arris to get right again though :( Just have to wait and see i think - thanks for you input guys

Ok well i decided to try and balance the carbs and blocking up the carb/fuel tank breather (as advised on this forum somewhere), I managed to get them balanced pretty well, and it was running nicely for about 5 miles, then it went back out again just as bad if not worse..

what on earth could cause this?!?! Going to strip down the carbs next weekend, its a pain through because i do 500 miles a week on it in central london, its not very plesant!

Just one more thought; have you checked for air leaks between the carbs and the cylinder head?

at the Inlets, I have thought about that, but will check when i take the carbs away, i definately think its an air leak, because the revs change at idle, just a matter of where is the air leak and can i fix, or do i need to replace!

If you spray a bit of carb cleaner or easy start etc at the inlet rubbers if the revs rise a little you have got your leak, replace all the inlet rubbers if this is the case as they are probably on the way out and if fix one another will go soon after ;-)

Good luck
Mot

Ok will do, its scheduled in for this weekend, will try that, thanks all

Over 3k rpm the diaphragms aren't doing much so definitely check the diaphragms. Also check the carb rubber mountings onto the inlet manifold as they can become split or actually detach!

OK had the carbs off and gave them a thorough clean, re-attached and 1 carb isn't creating any suck, so I am replacing the diaphragm as there may be a tiny hole, also replacing another diaphragm as one looks pretty tired. Checked both sets of rubber inlets and they are in good condition, made sure they were on properly and done up tight (but not gapping with the clips)

Got 3 carbs balanced now, running 10x better, just going to replace these two diaphragms and balance, and it should be cool.

thanks for your input everyone, much appreciated.

Hi, I have just used this

http://www.plastidip.co.uk/eStore/index.cf...dip&stage=1

on the diaphragms on the FJ1200, it has worked at the moment, but at less than a tenner its got to be worth a try.

Will be using these guys

http://www.nrp-carbs.co.uk/index.htm

when I need to replace them all (I think you should replace the set, not just the two, as they have all done the same amount of work).