Suzuki bandit Problem - totaly stuck, any help appreciated

[Greg2457]

Hi

Ive owned my Suzuki bantit gsf600sy x reg (30,000 miles on clock) for a couple of years with no issues, although for 2 months now its been almost un-ridable. between 6-8k rmp the bike stutters and jumps for about 4 seconds then it will pull away. at the same time it will be backfiring. when you give it full throttle the same problem occurs, it feels as if your running out of fuel for a split second then getting it back again, Ive been to 3 different garages and had the following work done/or done myself:

New carbs (balanced, floats adjusted etc)
new fuel tap
new pulse generator coil
new ignition coils
new inline fuel tap
new spark plugs
air box and filter checked
battery checked - all OK

The last garage i went to said it was running rich, but why? can anyone give me any advice as to what else i could check or change? i look after the bike well and its in good condition, also it has a data tool Veto Evo alarm (could this have any effect?)

Any help would be much appreciated,

Cheers, Greg

[Kickstart]

Hi

Main guess to me would be the carb diaphragms. However I would expect that to have been checked.

All the best

Keith
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[defblade]

Petrol filter?

Carb icing?


Although it sounds like it's flooding when you open the throttle in mid-range. I'm not really up on the specifics of bandit carbs (yet!) but my general feeling would be either whichever jet kicks in around then is wrongly sized or needles are worn, or maybe if there's an accelerator pump, that is over-fuelling.
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Honda Varadero 125cc => Suzuki Bandit 650 33bhp => 77bhp =>
BMW K1200R Sport 163bhp => Aprilia Shiver GT 750 95bhp

[Greg2457]

Ive just checked with the garage who fitted them and they say they checked the diaphragms when they fitted them, but thanks for the suggestion.

Also - I don't think its to do with icing because its been happening over the last 2 months when the weathers been fairly warm. the filter is 6 months old.

Yes, when Its mid to high range when its flooding. The Carbs i got fitted where not new, since they cost about half the value of the bike! but came of a working bandit which had done 20k miles. would you expect that both my original carbs and the replacement ones had the same problem? - I suppose they could have potentially. I'm fairly sure it doesn't have a fuel pump either. Thanks for the ideas!

[MickC]

Just as a thought have you checked the charging system?. When i first got my current Honda it would cut out around 5000rpm and under heavy acceleration. Like you i got replacement carbs (a lot cheaper though) and still had the same problem. It was only when i checked the reg/rec against manual specs that i found the problem (easiest check is put a meter across the battery and rev the engine to 3000rpm, you should get 14.4v, if its over or under you have a problem).
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Previous: CG125,XS250 (converted to 400),Z250A, GPZ550, Norton Commando, XS500, 78 Laverda Jota, GPZ1100,Harris bonneville, XV750 (mono shock),TR1

[Bezzer]

I'd have said diaphragms like Keith or worn emulsion tubes, when they go oval where the needle has battered them you get all kinds of problems similar to yours, but if it's been the same for both sets of carbs seems unlikely.
A lot of the time when you thinks it's a fuel problem it's electrics and vice versa. Worth checking the alternator output as suggested, a Bandit hasn't got an external reg/rec it's built into the alternator so just check the DC output at the battery.
Just a thought on the carbs, it has got OE needles and jets hasn't it?, if they were from another bike it might have had a Dynojet fitted if the bike was modded, as 90% of Bandits are, and possibly wouldn't suit your setup, might be if they are saying it's running rich.
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I used to be indecisive but now I'm not quite so sure.

[Kickstart]

Hi

Unlikely a 2nd set of carbs would give the same problem. With CV carbs the needle valve controls the fueling through most of the range. The needles can wear the atomiser tubes, but normally only a common issue with aftermarket jet kits.

The charging system alone I would doubt would cause this kind of problem (low charging would likely be noticeable in other way, such as the starter landing up very slow). However it is possible for the failed regulator to result in a high voltage which can fry delicate electronics (like the cdi unit).

I have had a similar problem many years ago with a dodgy ignition switch which shorted out as revs increased. However that was on a 125 with a cruder ignition system, and not certain with the Bandit off the top of my head how the kill switch / ignition switch off works. If it works by shorting the ignition to earth (unlikely) then it would be worth bypassing the ignition and kill switch to see if this fixes it.

On a similar point, check the side stand switch.

All the best

Keith
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[Greg2457]

OK - I will check the Voltage at high revs tomorrow as i need to buy a new multimeter. although as Kieth said Wouldn't you expect other symptoms like poor battery strength on starting? the bike starts first time very quickly, lights, horn etc seem normal. But for what its worth i will check it.

I understand the points about the diaphrams but I'm fairly sure considering its the second pair, and they where checked its not that. I will find out if they where modified.

I had wandered about the CDI unit, i don't know much about it and a second hand one is £90, but might be worth it? Sorry i forgot to mention i had an issue with the kill switch which the garage sorted, also kill switch has been checked, and the starter relay is new. I will do all the electrical checks you guys have mentioned and get back to you with the results.

I really appreciate all the suggestions - hopefully some electrical tests will shed some light on the problem, is there any way in testing the CDI?

Thanks, Greg

[Kickstart]

Hi

Easiest way to test the cdi is to swap it onto another bike that runs well and try it that way.

And check the side stand switch

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Greg2457]

Ah, good idea. also if i check the DC voltage across the battery and realize its to high it might mean the regulator within the alternator is faulty - causing the CDI unit to malfunction as you said it could. Ive checked the side stand switch and all seems as it should be.

Cheers,

Greg

[Pete.]

Is the bike fitted with an alarm/immobilizer? If it is, find it, wrap it in foam or cloth for padding and go for a ride.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Greg2457]

I presume your suggesting that there is a loose connection in the alarm box? Its a data tool veto evo alarm which seems to be working normally - are you suggesting that from the vibrations of high revving the alarm shakes enough to make the connection flicker on and off. I had considered that the alarm was faulty and wanted to remove it, but having read the data tool web site I decided against that idea!

Cheers,

Greg

[Kickstart]

Hi

We had a Datatool alarm that caused rough running at medium revs.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Greg2457]

Thanks for all the advice guys, Ive just checked the regulated voltage output across the battery - at 5000rpm Haynes sais it should be between 13.6-14.4V I was reading 14.5/14.6V. I know this is outside the tolerance band but can 0.2V make that much difference? I am concerned about the alarm but am reluctant to totally remove it until its the last resort - also Id have to get a garage to do it!, I might open the alarm box and check all the connections and terminals are ok.

[Bezzer]

0.2 volts isn't anything to worry about and won't be related to your problem, the Mk2 1200 Bandits are rated up to 15 volt output with the same 550w output alternator as yours. Looks like you've got to carry on checking the other bits again
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I used to be indecisive but now I'm not quite so sure.