What causes Backfire
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08-24-2005, 09:28 AM
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What causes Backfire
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.
#2
08-24-2005, 03:02 PM
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08-24-2005, 04:18 PM
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RE: What causes Backfire
ORIGINAL: stealthcbr
...Now when i try to start it, the bike just backfires...
...Now when i try to start it, the bike just backfires...
Except for spark plugs, I believe the pulse generator goes bad more often than any other ignition part. It controls the ignition timing. A simple timing light can check that the pulse generator is advancing correctly. Then I would change the spark plugs and see if they have a nice good spark. The coils can go bad, or the resistors in the plug wires can go bad. After you have a good spark occuring at the right time, move on to fuel. It has to get to the carb, and from the carbs it has to get to the cylinders. Sometimes, the pistons in the carbs stick open or closed. If you can pull back the airbox, you can stick your finger (engine off) in the carb opening and lift the piston. It should move freely, but with a little resistance like pushing air.
#4
08-27-2005, 04:55 AM
RE: What causes Backfire
ORIGINAL: slowpoke
Backfires occur when a spark or ignition occurs at the wrong time, usually with a valve open. With the intake valve open, the backfire occurs out the carb. With the exhaust valve open, the backfire occurs out the exhaust. This usually occurs when the spark plug wires are on the wrong plugs. Check them first.
Except for spark plugs, I believe the pulse generator goes bad more often than any other ignition part. It controls the ignition timing. A simple timing light can check that the pulse generator is advancing correctly. Then I would change the spark plugs and see if they have a nice good spark. The coils can go bad, or the resistors in the plug wires can go bad. After you have a good spark occuring at the right time, move on to fuel. It has to get to the carb, and from the carbs it has to get to the cylinders. Sometimes, the pistons in the carbs stick open or closed. If you can pull back the airbox, you can stick your finger (engine off) in the carb opening and lift the piston. It should move freely, but with a little resistance like pushing air.
ORIGINAL: stealthcbr
...Now when i try to start it, the bike just backfires...
...Now when i try to start it, the bike just backfires...
Except for spark plugs, I believe the pulse generator goes bad more often than any other ignition part. It controls the ignition timing. A simple timing light can check that the pulse generator is advancing correctly. Then I would change the spark plugs and see if they have a nice good spark. The coils can go bad, or the resistors in the plug wires can go bad. After you have a good spark occuring at the right time, move on to fuel. It has to get to the carb, and from the carbs it has to get to the cylinders. Sometimes, the pistons in the carbs stick open or closed. If you can pull back the airbox, you can stick your finger (engine off) in the carb opening and lift the piston. It should move freely, but with a little resistance like pushing air.
Backfires are a flame/fuel/air imbalance situation, with the symptoms you describe it sounds like the fuel is squelching the flame, so I agree with checking the wires first (sometimes if you observe them in the dark you can detect the faulty wire by visibly seeing the arc). Follow through with tracing the rest of the electrical before moving on. Then check the air intakes/air filter, etc making sure there's no blockage. If no avail, proceed to the fuel filter; drain tank - inspect contents; try completely new gas if old is suspect.
Cheers
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08-27-2005, 01:15 PM
#6
08-27-2005, 02:35 PM
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RE: What causes Backfire
ORIGINAL: Power2weight
so is it bad if my bike backfires but runs fine?
like if I rev it up high at a light it will backfire on the way down and sometimes throw a flame, I think its pretty cool, but is it bad?
so is it bad if my bike backfires but runs fine?
like if I rev it up high at a light it will backfire on the way down and sometimes throw a flame, I think its pretty cool, but is it bad?
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08-28-2005, 05:08 PM
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08-28-2005, 05:49 PM
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09-08-2005, 08:46 AM
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#10
09-08-2005, 01:26 PM
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