carburation issues with my bandit

[Del]

Looking for some input from you good folk as you are all knowledgeable and give realistic responses compared to other forums

Ive an issue with my GSF1200 Bandit – it's a 1999 Mk1 and it's got 16K on the clock

The issue I have is that number 4 cylinder is very very lean so much, so it is off the top of the scale on the Carbtune balancer
12& 3 are all running at even temperatures and they all look to be balanced well – N# 4 is  barely warming up

Ive stripped the carbs cleaned as much as I can – replaced all the gaskets I can – the float levels are all set – changed plugs over between cylinders – removed the carb to block rubbers and no issued there – also diaphragm is not perished or worn

The bike was lying up, but I had the carbs ultrasonically cleaned last year

It is doing my head in bit on the plus side I can remove a set of carbs on in under 15 minutes

Your thoughts are appreciated

[Speedy1959]

The only thing I can think of is maybe a subtle split in the carburetor mounting rubber thingy..
I know the splits can be quite difficult to spot sometimes when in situ..
Many years ago I owned a Honda CB750 Four (1969 model) and the only way I found the split was the flex the rubber when it was removed..

[seth]

Hiya @Del from what your describing it sounds deffinatly on the carb side somewhere as only affecting 1 (number 4) cylinder.
So my thoughts are simular to @Speedy1959's .
You can check the inlet rubbers and manifold by spraying easystart onto them while the bikes at tick-over and listen to hear if the revs change as the fluid gets into any tiny splits (it's not totally conclusive) and can show up a problem there.
Good luck buddy

[Horse]

Hi , is it lean all the way through the rev range or only at the lower speeds , after a run are the plug colours consistent ? failing a vacuum leak it would have to be in the carb, are the emulsion tube holes clear? I have had them block and cause a lean condition but usually all the carbs have a similar problem and its a associated with the bike sitting for a time and with the current fuel tends to cause a white solid that blocks small holes. If you have ruled out a vacuum leak it would appear you need to go deeper into the carburettor.

Good Luck.
Horse 

[grog]

Del, is number 4 slide moving up with others? Does a splash of carby cleaner in that carb liven it up? Carby cleaner will prove its a fuel issue in that cylinder. Otherwise need to look at other reasons. 

[Del]

oh this thing is just taking the piss

had the carb rubbers off to check clean and renew the O-rings - no issues here the rubbers are all in good order no brittleness of cracks and all supple - Good I hear you cry

so while I'm here Ill try the compression - number 4 is 220 good I says - just to be sure try number 1 crank over and yip 220 so all good . . . . . . . . . . . . .hang on whats that oil doing all over the garage floor - ERSE I had removed the cam cover oil feed pipe to take off the rubbers - and now I have oil all over the floor the door and engine

checked the coil and I think number 4 &  coil is breaking down - Fingers crossed gents

[Andre]

Sometimes it's a slippery slope to success

[seth]

It's a pain but the more you go through it the more things you can eliminate .
If you think it's coils swap 1-4 the problem should swop cylinders .
Then it must only be a plug lead rather than the coil but I'm not sure you can change just a lead .
Good luck buddy.

[Bob]

My pals bandit had running problems due to worn emulsion tubes / needles

[Del]

@seth got a set of after market coils here and a stick coil conversion loom so one way or the other I'm sorted

@Bob  had them all out and checked over and bikes only done 16K so don't think it'll be them but if the coil issue doesn't work Ill look at them mate cheers


Also Ive swapped all the components from carb 4 to carb 3 so if the issue moves its the components

cheers for the help chaps appreciated

[Hooli]

It's a pain but the more you go through it the more things you can eliminate .
If you think it's coils swap 1-4 the problem should swop cylinders .
Then it must only be a plug lead rather than the coil but I'm not sure you can change just a lead .
Good luck buddy.

I assume they are like 14 coils, in that you could swap the coils & see if the fault follows the coil/plug lead.

[Horse]

Are we still talking about a lean condition? I will be very interested to learn how a coil creates a lean burn issue, I would believe that a weak coil will give a cylinder non firing condition under maximum load and maybe slight uneven running but I can not understand how it ends up lean. Maybe slight incomplete combustion ( a stretch )  but not lean , Have been wrong thousands of times before and stranger things have probably happened,

Hope you find the fault soon,

Horse

[Del]

Hi @horse - the issue of the bike being lean was due to the carb balancer on N#4 being off the scale when I tried to balance carbs after refitting (I hate carbs as much as I hate electric string)  - now Ive had the carbs on and off several times stripped and cleaned everything I could get too and decided to check other things as I wait for more parts to arrive -  such as compression and then spark basically checking everything - compression isn't an issue so while in the vicinity thought check spark and that is how I found out 1&4 were not sparking as half as well as 2&3 - I am hoping I get this effin bike sorted as its starting to really fuk me off

hope this explains my thought process a bit

[Horse]

Great Del , I was just a little confused (not hard for the elderly) when the lean issue turned to a spark problem, generally weak spark will usually manifest itself with peak combustion pressure and if its alright there ( WO throttle at low and above speeds) the spark quality should not be a problem elsewhere anyway sounds like after all the work you have been forced to do it will run sweet as for some time to come,

Have a good weekend

Horse

[Del]

Well I think I may have sorted the bastardin thing out - new coils (clutching at straws now) and emulsion tubes (again trying everything) and still No4 not running - so carbs back off and stripped again (this is at least the 6th time) - so as Im checking everything over I notice No4 butterfly not lever as the rest - after investigation I discover a very small spring missing from the linkage - onto Fowlers and identifying the part number I fell over at the price (nearly £12.00 delivered) - fitted carbs balanced and ticking over - a few other things to sort and think that will be it

thanks for all the input fellas

Del