1100 Slabby low speed running rough - not carbs!

[GixxerDale]

Hi there, I have an odd problem on my GSXR1100 Slabside which is defeating me, basically between tickover and just open throttle the bike runs erratically, after some investigation I noted that at tickover it was randomly dropping out on different cylinders, with a carb balancer on it the tickover was hunting a bit and every now and again one of the cylinders would 'drop out' for a fraction of a second. Rev it and it would settle for a while and then do it again.  the problem does not occur when warming up but once up to temperature starts doing it. when riding at low speed say coming into a roundabout . throttle off and get slight erratic surging, then when throttle is opened slightly bike stutters before picking up suddenly, which can make taking roundabouts interesting as never sure if the bike is going to low side or run wide.  Any ideas, much appreciated !!!, some background of bike , and what I have tried so far, including running a spare set of carbs:

1100 slabby with 1200 bandit engine , GSXR pickups & CDI, standard 34mm carbs, Dynacoils, Taylor leads, standard air box with K & N, crankcase breather to K &N rather than to airbox.

Swapped out pickups, CDI, carbs, new taylor leads but made no difference

replaced rubbers on inlet stubs, played with timing on pickups (have slotted holes on back plate , returned to standard setting), checked all the connections on the LT side of the coils , checked the taylor lead connections , changed the plugs.

also monitored the voltage on the system during the rough running , sits at 14.6V with lights off and 13.4V with the lights on, no real fluctuation in voltage.  bike is reliable and is charging , took it up to the isle of Man in august, ran fine apart from this problem, and certainly did not lack power at the top end etc.

ran the bike on gravity feed from auxiliary fuel tank, that made no difference either.

when it drops out almost sounds like it is back firing through the carbs , but not sure?

[fatblokeonbandit]

If you let it tick over dose it sound like a cough then tick over ok again???

But the first thing id do is get some standard bandit or gsxr coils ant try them as when dynas are old they can break down when hot and misfire..

[GixxerDale]

thanks that's was what I was thinking, as it is the only component in the ignition system that I have not changed, the Dynacoils are at least 15 years old, and yes it does sound like a cough, I was initially discounting coils on the randomness of the cylinder that dropping out, but I will give it a try .

[banoffee]

My 750 slabby did something similar only when hot on the original coils. Turned out to be tiny cracks around where the leads fitted.

[spiderpig]

+1 on the coils 

[Fula28]

Dale, if you want quality replacements 3ohm-5ohm call my man Marcus at Rex's speed shop, he does really good coils which work with Dyna ignitions Dsc if needed, and there fair priced too. 

Hes a genuine biker and oldskool guy.

http://www.rexs-speedshop.com/epages/es143131.sf/en_GB/?ObjectPath=/Shops/es143131/Categories/Imprint

[GixxerDale]

Well after a bit of wait a set of used bandit coils and leads arrived off Eblag, and have been fitted , so far so good, seems to have fixed the problem. Thanks for all the advice