What causes Backfire

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What causes Backfire

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CBR Forum >> Past CBR Models >> CBR 600F >> What causes Backfire

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What causes Backfire - 8/24/2005 7:29:30 AM

stealthcbr

Posts: 2
Joined: 8/24/2005
Status: offline

I have a 1987 cbr 600f that i recently bought. I took it riding 4 times and it ran good. On the 5th time i was 45 minutes into my ride when i came to a stop and the bike started to die. I gave it full throttle and it would barely idle. I turned it off and when i tried to start it up again i had to give wide open throttle just to get it to idle. Now when i try to start it, the bike just backfires. I checked the fuel pump and lines, they are working. Could this be the timing chain? Stuck float? Thanks for your help.

Post #: 1

RE: What causes Backfire - 9/1/2005 10:48:09 AM

InTheMaking

Posts: 33
Joined: 7/31/2005
Status: offline

backfire is caused by raw unburned fuel exiting through the exhaust and igniting, usally when you are at high RPM's and you dump off the throttle very quikly

(in reply to stealthcbr)

Post #: 2

RE: What causes Backfire - 9/9/2005 8:42:47 AM

khicken lines

Posts: 3
Joined: 9/8/2005
Status: offline

Hi there.
. Not to shore about the cbr but on my thunder cat Yamaha 600r the valve need shimming at 24000 mile about 40000k if it not bun it will cause all sorts of problems.
Like backfiring pore throttle response, pore idle,
Hope this will be some help.

_____________________________

Its faster Than You Think

(in reply to stealthcbr)

Post #: 3

RE: What causes Backfire - 9/12/2005 8:31:39 PM

transamlt1man

Posts: 795
Joined: 9/4/2005
Status: offline

Sounds like you have a fouled spark plug. It probably isnt running on all cylinders. It runs and the one cylinder loads up on gas and it gets into the exhaust. Then it ignites and bang. I had the same problem before. Check your plugs.

(in reply to stealthcbr)

Post #: 4

RE: What causes Backfire - 9/12/2005 10:58:01 PM

slowpoke

Posts: 518
Joined: 8/6/2005
From: Denver, Colorado
Status: offline

quote:

ORIGINAL: stealthcbr

...I gave it full throttle and it would barely idle. I turned it off and when i tried to start it up again i had to give wide open throttle just to get it to idle.

You have to think what's happening when you do this. Wide open throttle opens the throttle plates that admits the air/fuel mixture from the carb into the cylinder. Opening the throttle does not raise the piston/needle. The velocity of air movement through the carb forms pressure that raises the piston needle. So by opening the throttle wide, you are admitting maximum air into the engine, but it's not enough to burn the rich mixture. I believe you have a fuel problem that can only be fixed by cleaning the carbs.

You will have to remove all four spark plugs. One or all of them will be black from running rich. The Haynes manual is very good in describing how to get the carbs off your bike. This site http://users.rcn.com/kochc/moto/carb/carb.html is pretty good at showing how to disassemble and clean your carbs. You seem to have a problem with the floats or float valves, jets, and sticky piston/needles. Good luck.

(in reply to stealthcbr)

Post #: 5

RE: What causes Backfire - 9/12/2005 11:08:54 PM

transamlt1man

Posts: 795
Joined: 9/4/2005
Status: offline

The biggest problems I find with these forums is everyone overlooks the basics. When something runs perfectly fine for days then a split second later it dies and will not idle.... trust me the reason for this isn't because the carbs got clogged up all of a sudden. It could though be a float needle stuck open. But easiest to check are the plugs. If you have backfire you have an ignition problem or valve problem. Start with the ignition... check the plugs for spark. And if a plug is fouled out you will probably need to lean out the carbs to stop it from happening again.

(in reply to stealthcbr)

Post #: 6