Help - 05 Bandit 1200 backfiring through carbs.

[captainbeaky]

Please help - this thing is doing my head in!

OK, here's the story so far. Mate brought in completely stock 05 Bandit 1200 with 20,000km, with a bad misfire after being transported and stored for a long time.

Traced the problem to a failed fuel petcock valve - this had remained on, and slowly drained the fuel into the LH carbs/cylinder/crankcase over a period of months.

New petcock seals, changed plugs, oil, oil filter and oem "standard" air filter. (Crankcase was full of oil/fuel mix that had passed the rings.)

Bike ran like poo - misfiring and generally awful, so I checked carbs - full of junk, so gave carbs the ultrasound treatment - cleaned every little part religiously.

Got it all back together - now runs on all 4 cylinders, generally good power it seems (I dont want to stress it when it's apparently running lean, but she pulled very nicely) but it's backfiring like a bugger at idle! So, checked valve clearances - a few were out a little - but nothing to worry about.

Back together It's still backfiring!

I've persevered to get the carbs balanced and played with the pilots - tried setting the pilots at 2 turns out, 3 turns out - 3 1/2 turns out - bike runs a bit happier, but still backfiring so strongly that it keeps popping off the balancer pipes!

I've inspected every hose, pipe and seal for air leaks - nothing. Bike is completely stock and really low miles, Im genuinely baffled now. I did pull the carbs back out and went through them again, but not a spec of dirt to be seen. 

Bike runs the same wether the tank feeds the fuel or my dummy tank. 

Bike has PAIR system - but backfires even if I blank it off at the airbox. 

 

 

 

 

 

[Pegleg]

Possible failing pick up? Sounds like an ignition timing issue. 

[imago]

I wonder if your mate, or the previous owner tried to spin it over before it was cleared out and it hydraulic locked on fuel in the cylinder? Have you done a compression test on it?

[captainbeaky]

Ignition pickup failing? could be. Bike is truly Mint, and low mileage - is pickup failure common on these? I can check the output as per the manual - would this show such a failure (at £300 for a new pickup, I dont want to buy one to try). I can drop a scope on the signal and see if it's got any jitter... I would think that such a failure would become more pronounced at higher load/speed (bike goes very well, and isnt running lean on the go/under load - it just backfires at idle/ fast idle)

It may have been cranked over and hydrolocked - but only one cylinder was flooded with fuel (it was shipped on the sidestand) looking at the plugs. I havent done a compression test, but when cranking, the compressions sound very even - there's no feeling of lack of compression. On test ride, I gingerly gave it more throttle, listening out for lean running or other issues, and she went like a Bandit 1200 should -  like a stabbed rat! There is some hesitation at low engine speeds/small throttle opening. Exhaust colour is fine too - light straw, so she's not leaning out at revs.  

One thing - the little rubber tee-pieces that join the carb float overflows have both got cracks in them (parts on order) WOuld this cause such a problem? Only other thought - it has an OEM "Hiflo" standard type filter.

I'm starting to think I've left a tiny bit of gunk in the carbs somewhere. I was very careful, but it's quite possible I missed something..

 

[TonyGee]

first thing is completely remove the PAIRs system as they dont need it,  some bandits really prefer a Genuine Suzuki air filter not a hiflo.  

[Pegleg]

I think the backfiring is fuel being ignited at the wrong time. 

[Pegleg]

Do you know which cylinder is backfiring?

[TonyGee]

has it got the OEM exhaust can on it still ? 

[captainbeaky]

13 hours ago, Pegleg said:

Do you know which cylinder is backfiring?

All of them! It seems to affect all cylinders - it's randomly popping off the balancer pipes. No discernable pattern / no single carb or cylinder issue.

Infuriating

13 hours ago, TonyGee said:

has it got the OEM exhaust can on it still ? 

Bike is completely stock.

 

13 hours ago, Pegleg said:

I think the backfiring is fuel being ignited at the wrong time. 

Possible - but how? The timing is set by electronics, and the engine develops power fine higher up the rev range (Where I would expect ignition problems to be more obvious.)

 

13 hours ago, TonyGee said:

first thing is completely remove the PAIRs system as they dont need it,  some bandits really prefer a Genuine Suzuki air filter not a hiflo.  

I'll clamped off the pipe from the airbox to the PAIRs, and makes no difference. I can see if I can get a genuine filter - what's the difference? (More/less restrictive?)

 

It's very hard to balance the carbs, and when I partially obstruct the air intake with my hand (Thus richening the mixture), the revs rise considerably. Am I dealing with ludicrously lean mixture?? 

 

I've got to go into town for a Hospital appointment, so I'll pop into the bike shop to see if they have a rebuild kit for the carbs, and some rubber tube and caps for the balancing nipples (The pipe I have isnt a fabulously tight fit).

 

 

[imago]

3 hours ago, captainbeaky said:

All of them! It seems to affect all cylinders - it's randomly popping off the balancer pipes. No discernable pattern / no single carb or cylinder issue.

Infuriating

Bike is completely stock.

 

Possible - but how? The timing is set by electronics, and the engine develops power fine higher up the rev range (Where I would expect ignition problems to be more obvious.)

 

I'll clamped off the pipe from the airbox to the PAIRs, and makes no difference. I can see if I can get a genuine filter - what's the difference? (More/less restrictive?)

 

It's very hard to balance the carbs, and when I partially obstruct the air intake with my hand (Thus richening the mixture), the revs rise considerably. Am I dealing with ludicrously lean mixture?? 

 

I've got to go into town for a Hospital appointment, so I'll pop into the bike shop to see if they have a rebuild kit for the carbs, and some rubber tube and caps for the balancing nipples (The pipe I have isnt a fabulously tight fit).

 

 

Ruling the stuff you have out, what you describe there sounds like low rpm intermittent misfire. Every now and again at low rpm one or more cylinders doesn't fire. Not mis timed, it just doesn't happen. So you get fuel in it doesn't fire, it goes out into the exhaust, then when one of the other cylinders fires it goes bang. Once the rpm is up then things smooth out to a degree.

Crank sensor, wiring from it to the box, coil wiring and the coils themselves are to most likely culprits IMHO.

[TonyGee]

imago might be on to something their, worth checking all the ignition system wiring and the connector plugs for a good connection. 

[captainbeaky]

2 hours ago, imago said:

Ruling the stuff you have out, what you describe there sounds like low rpm intermittent misfire. Every now and again at low rpm one or more cylinders doesn't fire. Not mis timed, it just doesn't happen. So you get fuel in it doesn't fire, it goes out into the exhaust, then when one of the other cylinders fires it goes bang. Once the rpm is up then things smooth out to a degree.

Crank sensor, wiring from it to the box, coil wiring and the coils themselves are to most likely culprits IMHO.

I'll check for signs of trauma to wiring etc,. but I'm not 100 percent convinced - this is a "showroom example" - mint condition, and 22000km on the clock. Not a spec of corrosion on any of the connectors or bolts. Also, usually, ignition components show the faults under low RPM load, and while the idle is terrible, low RPM performance is good - pulls nicely and is smooth. Weirdly, no2 isnt misfiring at all. Mmmm. 

 

[TonyGee]

I'd still completely remove the PAIR's though. you can make blanking plates for the cylinders or buy a set of stainless ones of the bay of E.  

[imago]

19 minutes ago, captainbeaky said:

I'll check for signs of trauma to wiring etc,. but I'm not 100 percent convinced - this is a "showroom example" - mint condition, and 22000km on the clock. Not a spec of corrosion on any of the connectors or bolts. Also, usually, ignition components show the faults under low RPM load, and while the idle is terrible, low RPM performance is good - pulls nicely and is smooth. Weirdly, no2 isnt misfiring at all. Mmmm. 

 

Showroom or not, it's nearly 20 years old and the wiring is just as susceptible to time as the fuel system was.

A poor connection on the LT side or weak signal from the crank sensor will show up under light conditions rather than load. Whereas something like a high resistance in a HT lead or a coil breaking down will happen under load as it'll give a weak spark. So the fault you have fits the bill for an issue on the LT side of things. A connector 'varnished', loose spade, multiplug pin, some shite on the face of the crank sensor.

 

[Rijko]

1 hour ago, TonyGee said:

I'd still completely remove the PAIR's though. you can make blanking plates for the cylinders or buy a set of stainless ones of the bay of E.  

Disagreed, but that's just preference.

Had a set of blanking plates but I love the sound it makes with PAIR

[Rijko]

May want to check the TPS ..

[TonyGee]

21 minutes ago, Rijko said:

May want to check the TPS ..

I disagree as they do feck all, but thats my view  

[Rijko]

1 minute ago, TonyGee said:

I disagree as they do feck all, but thats my view  

haha you just had to disagree eh ?

Well, agreed as far as bad set TPS usually causes low rpm rumbling, no backfires.
Not checking .. well ... they do something.
I like my bikes set up optimal, so i do check them.

[TonyGee]

2 minutes ago, Rijko said:

haha you just had to disagree eh ?

Well, agreed as far as bad set TPS usually causes low rpm rumbling, no backfires.
Not checking .. well ... they do something.
I like my bikes set up optimal, so i do check them.

 yep    

in my experience ive disconnected the TPS on a few bikes as well as my own and  cant tell any difference what so ever !!!!!!!  others will tell you the same thing that they don't do feck all.  can't see the reason why suzuki fitted them to the bandit   it doesn't even show up on a dyno.  

[Rijko]

TPS relates to ignition advance.
I noticed a difference on several bikes that would not idle nicely before adjustment.
Better idling and a bit smoother acceleration without hesitation.

Some may not notice it especially on a Bandit or XJR because of the massive torque they have at low rpm.
Many use ignition advancers that disguise a badly set TPS so will not notice it.
 

[TonyGee]

1 minute ago, Rijko said:

TPS relates to ignition advance.
I noticed a difference on several bikes that would not idle nicely before adjustment.
Better idling and a bit smoother acceleration without hesitation.

Some may not notice it especially on a Bandit or XJR because of the massive torque they have at low rpm.
Many use ignition advancers that disguise a badly set TPS so will not notice it.
 

yes on bikes like a GSXR1000 and others will make a difference, but not with a bandit. ive yet to come across one that adjusting it makes and change !!!!!  

[Rijko]

TPS operates low rpm ... which is not the range the Dyno looks at so no, won't show up on the chart

[captainbeaky]

15 hours ago, Rijko said:

TPS relates to ignition advance.
I noticed a difference on several bikes that would not idle nicely before adjustment.
Better idling and a bit smoother acceleration without hesitation.

Some may not notice it especially on a Bandit or XJR because of the massive torque they have at low rpm.
Many use ignition advancers that disguise a badly set TPS so will not notice it.
 

Will check.

18 hours ago, imago said:

Showroom or not, it's nearly 20 years old and the wiring is just as susceptible to time as the fuel system was.

A poor connection on the LT side or weak signal from the crank sensor will show up under light conditions rather than load. Whereas something like a high resistance in a HT lead or a coil breaking down will happen under load as it'll give a weak spark. So the fault you have fits the bill for an issue on the LT side of things. A connector 'varnished', loose spade, multiplug pin, some shite on the face of the crank sensor.

 

I've gone through all the connections I can see/find - all look amazing - this thing is really corrosion free.

I've put it back together for now - other stuff has priority. Have filled the tank with nice fresh fuel and some carb cleaner. once it's cooled down I'll check the crank sensor and do a short test ride tonight - lets get some fuel run through the carbs, a few miles and lets see what the plugs tell us...

 

[captainbeaky]

OK - latest...

You can do all the tuning and fettling you want in the workshop, but sometimes you just need to put some miles on it - push some fuel through it, and let it settle in.

Was initially running like a dog, misfiring, pops and bangs, I was wondering if a test ride was a good idea, but it cleared up, smoothed out, and I gingerly eased in the power bit by bit as she cleared up. And clear up she did.

My bikes not slow ( KTM 950 SM), but I didn't realise what a weapon these bandit 1200's are, and how tractable that 1200 is. With large to wide open throttle, power is now utterly smooth from idle to redline, and boy do these bikes shift. Exhaust colour is straw (not blue), so she's running nicely - not lean.

Idle is better, but rough and backfiring still. When I'm doing a power pull from idle, it's hiccuping/rough with the throttle closed, but this disappears immediately when I seriously open the throttle, and it's pulling 100 percent smoothly and with no backfires at all - even when I snap the throttle open at 1200rpm in 4th.

This has to be carburettors?

[TonyGee]

sounds like one of the float valves is slightly leaking,  they will over fuel giving a rich mixture and fowl the plug, but when you wind it on the extra fuel gets used and runs good. run it round at low revs for a while so its popping again then check all the plugs, if one is black and sooty theirs your problem.