Backfiring

[marcopol]

02 GS1150 , backfiring when throttling off from high speed mostly.
Bike has had the cat removed and a Sebring exhaust fitted. Cat code plug changed as per Steptoes instructions and exhaust resealed at both ends of the manifold downpipes but still backfiring, any ideas.

 

[Stewart H]

they all do that sir, I found I was holding the throttle slightly open on the overrun, if you have eliminated any airleaks on the exhaust then the odd pop and bang is pretty normal.

Stewart

 

[kez097]

Check the coils on the spark plugs. I had this and the coil on the left hand pot had started to burn out causing an intermittent misfire.

 

[DaveGSCymro]

they all do that sir, I found I was holding the throttle slightly open on the overrun, if you have eliminated any airleaks on the exhaust then the odd pop and bang is pretty normal.

Stewart

+1

 

[Hong Kong Nick]

+1

+2 ... with the REMUS fitted ... heee heee ... great at night!

Nick

 

[Littledumptruck]

+3

Although i did feel the Dealer used it as an excuse not to service the bike before delivery, and I got the 'Thats character sir' comment.
From personal experience, if the valves are spot on, and the throttle cables are in perfect synch 'they don't do that sir'

But it seems most owners are happy to have the odd pop and backfire going on, children.......

 

[Decster]

Backfiring....

 

[argos]

check stick coils and spray something volatile like carb cleaner to check for air leaks on inlet stubs ,make sure its balanced on the cable adjusters at around 3-4k rpm

 

[Steptoe]

Check the coils on the spark plugs. I had this and the coil on the left hand pot had started to burn out causing an intermittent misfire.

check stick coils

Your info is only relevant to twin spark bikes - It's an 02 bike, so could well be a single spark.

Your cause for backfiring is the combination of sebring can and Y peice.

 

[argos]

obviously the mans right..however check for airleaks,check for balance at 3-4k

 

[ciderman gs]

by removing the cat and also having a straight through exhaust you have removed the back pressure from the system which keeps the fuel air mix escaping, this then meets the hot exhaust pipes and bang popping on the over run, if you are really worried then check your valves and your balance and if these are ok then do a cylinder leak down test to see which cylinder is leaking then take off your heads and regrind the valves and check to make sure these do not leak using masking tape and commpressed air.


or just go with they all do that sir

see ya at gotc

 

[argos]

well there you go i was completely wrong...surely the objective of a forum is to help people who are not quite mechanicaly together?do you think he should check for air leaks and make sure that his injectors are balanced...i do

 

[argos]

sorry ciderman its FI,backpressure?

 

[ciderman gs]

the exhaust is a tuned length to some degree so that sound waves and exhaust gas pressure act like a valve to stop the petrol air mixture escaping from the cylinder on the intake stroke (even more so on a two stroke ) if you remove, change this you then effect the exhaust pressure wave this then lets the fuel air mixture into the hot exhaust which then ignites through the heat causing the pop noise. thats why you see flames coming out of some race bike exhausts (classic was foggy petronas team ) also extreme valve timing overlap allows fuel into the exhaust theseare some of the reasons for exhaust popping if you want to stop it then just put the standard exhaust and the cat back on.

just trying to be helpful it does not matter about balance this just makes the engine vibrate

to lessen the pop check the valves for correct clearance other than that

they all do that

 

[Steptoe]

check stick coils and spray something volatile like carb cleaner to check for air leaks on inlet stubs ,make sure its balanced on the cable adjusters at around 3-4k rpm

Airleaks on inlet stubs don't produce back fires.

Airleaks on exhaust joins can produce backfires.

Fuel injection backfires are mostly caused by the system shutting off fuel supply when the throttle is shut until the revs drop to a certain level ( 2000rpm in BMW's case), when the fuel comes in again you can get backfires.

I can make my bike backfire on demand great for scaring old ladies crossing the road or waking up dozy car drivers

 

[Steptoe]

sorry ciderman its FI,backpressure?

Are you suggesting that FI doesn't need back pressure

 

[MattW]

My 1100 (completely standard) makes little wuffly pops every now and again (not proper backfires, more like sneezes). I just treat is as part of the character

 

[King Rat]

Where can I buy a set of backfires please?

You stock them Steptoe?

 

[hank]

King Rat.

No need to purchase backfires. You get a lifetimes supply free with every Y pipe.


Hank.

 

[Comfy Old Boots]

King Rat.

No need to purchase backfires. You get a lifetimes supply free with every Y pipe.


Hank.

yeah and the bike does it when IT want's