• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

Ignition kill while shifting mod cause backfire?

  • Thread starter Thread starter ashdricky
  • Start date Start date
A

ashdricky

Guest
So I recently heard a highly tuned sport-bike of unknown make. racing down a road near my home. Listening closely as I always do in the presence of "internal-combustion-speed-metal" I noticed that each shift was followed by a backfire. I am trying to understand how a bike must be tuned to cause this? here is the only idea i could come up with; the engine is revving at speed and as the rider shifts up the ignition is momentarily killed, filling the header/exhaust with unspent fuel/air. then as the gear is engaged the ignition returns burning up the unspent fuel in the header causing the backfire?
 
If it was a fuel injected bike, it was probably the fuel Cut function. Basically what you explained, but with fuel. If he is running an air or electric shifter, those do momentarily cut the ignition.
 
what if the bike used carbs instead of injected? would an ignition cut cause the same shifting backfire?
 
running too lean (too small a main jet? Too "Breathy" an exhaust?
Hole in exhaust/ manifold?
A Triumph???
only joking!
:D
xxx
 
Pretty common. Even the GP bikes do it. SBK. The lot. It's a simple spark cut when the lever is toed. Allows for wide open throttle shifts. Doesn't (or didn't last I read, theyre changing the rules all the time..) cut fuel delivery as they want that wide open to get from one gear to the next as quick as possible. (that new Honda tranny theyre usin in the GP is even faster. Slick stuff) So, you have a momentary spark cut but fuel is still being delivered. Shift. Spark comes back, and BOOM. Backfire out the tail pipe. You can replicate this with your GS to a degree. Cruise down the road, pull the clutch in, hit the kill switch, coast, at te same time let the clutch out and hit the killswitch back to "on". BOOM.

Same difference roughly. Motor us still spinning, still sucking fuel but has no spark to ignite it. It builds up, then ignites.
 
thank you cafekid this is the information i needed, I am building a very special GS and want to replicate this, My ignition module has an input for a shift ignition kill switch, now I just need to figure out how to rig a switch to my shift lever.
 
TheCafeKid said:
Pretty common. Even the GP bikes do it. SBK. The lot. It's a simple spark cut when the lever is toed. Allows for wide open throttle shifts. Doesn't (or didn't last I read, theyre changing the rules all the time..) cut fuel delivery as they want that wide open to get from one gear to the next as quick as possible. (that new Honda tranny theyre usin in the GP is even faster. Slick stuff) So, you have a momentary spark cut but fuel is still being delivered. Shift. Spark comes back, and BOOM. Backfire out the tail pipe. You can replicate this with your GS to a degree. Cruise down the road, pull the clutch in, hit the kill switch, coast, at te same time let the clutch out and hit the killswitch back to "on". BOOM.

Same difference roughly. Motor us still spinning, still sucking fuel but has no spark to ignite it. It builds up, then ignites.
Click to expand...

I bet muffler life is pretty short due to ignition cut/overpressure cycles. Not a problem on a race bike that you can put a new exhaust on for every race, but a bit expensive for a daily rider.
 
ashdricky said:
thank you cafekid this is the information i needed, I am building a very special GS and want to replicate this, My ignition module has an input for a shift ignition kill switch, now I just need to figure out how to rig a switch to my shift lever.
Click to expand...

Ask the drag guys. They use air shifters and spark cutout a lot. Of course all you're really replicating is a "hot shift". Toe the shift lever as ready to shift, unload the trans with a quick flick of the throttle toward closed, while at nearly the same time shifting.
Not easy on the one-two shift as the gap between gears is pretty steep, bu cake from 2 on up. Down shifting takes more practice and some say it's not really good on the dogs. But if you've built the engine for racing, you've built it for racing and have spares on the shelf ;)
 
earlfor said:
I bet muffler life is pretty short due to ignition cut/overpressure cycles. Not a problem on a race bike that you can put a new exhaust on for every race, but a bit expensive for a daily rider.
Click to expand...

To those street guys that can afford those tricks, baffle packing is cheap.
And on a race bike...what mufflers?
 
so it is not the actual metal of the muffler/header that is damaged by this but the packing in the silencer of the exhaust? so in theory if a baffle-less or "straight-pipe" design was used damaging the exhaust would not be an issue?
 
ashdricky said:
so it is not the actual metal of the muffler/header that is damaged by this but the packing in the silencer of the exhaust? so in theory if a baffle-less or "straight-pipe" design was used damaging the exhaust would not be an issue?
Click to expand...

I don't see how the metal could be damaged unless it was made out of Alu foil.

The Aprillia RSV4R and Factory, and the BMW S1000RR both have quick shifters from either the factory or an aftermarket company designed for plug and play. Granted they're both on the extreme end of "sport" bike but one would assume they'd done some homework. Then again, if you can afford one of those...changing a baffle is pocket change...
 
You must log in or register to reply here.
Back
Top