Won't start and backfires when trying - Sportbikes.net
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post #1 of 13 (permalink) Old 04-04-2007, 02:36 PM Thread Starter
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Won't start and backfires when trying

I have a '94 CBR600F2 with stage 2 jetting. I had a full tune up, including replacing 1 carb, valve adjustment, new plugs, and carb sync last June.

Ok here it is, last Wednesday I pulled my bike out after it had been sitting for about 2 months. I forgot to put fuel stabilizer in it, I know stupid, but it started right up. When I opened the throttle at all it died so I figured it was just cold and needed to warm up, I went upstairs to get my gear and when I came back down the darn thing ran out of gas. I put 2 gallons in it on Saturday and tried to start it again. It won't start. It acts like it wants to, ala sounds like it fires a couple cylinders, then just backfires REALLY hard and nothing.

I have spark tested all 4 cylinders and they get spark, I have tested the coils, the ICM, and the IPC. They all test out fine. I do not have a peak voltage adapter for my multimeter so I can't test the firing voltage but all other parameters are fine. When the petcock is disconnected from the carbs it flows fuel just fine, not sure if it does when connected.

I have been having a small leak from the tank vent tube and found out that it is due to a crack in the tube where the tube passes through the tank. I have the tank drained and plan on repairing it this weekend. I think the lack of proper tank ventilation may have been restricting fuel flow into the carbs but I can't explain why it just started happening.


Sorry for the novel but I wanted to give everyone the full story... So... Any ideas why this beast won't start?

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post #2 of 13 (permalink) Old 04-04-2007, 05:48 PM
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Id suspect two things...............

You turned the petcock to OFF

or the vacuum line from the petcock to the intake is off.

You didnt specify if the bike was getting fuel.

cause rascus said I had to.........
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post #3 of 13 (permalink) Old 04-05-2007, 10:11 AM Thread Starter
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First let me say, Sup Hybrid, long time no talk...

Second... The vacuum line and fuel lines were connected and the petcock has been moved from on to reserve and back again with no change. I don't know if the bike is getting fuel. I know that when the tank is disconnected from the bike and I turn the petcock to on fuel flows from it quite nicely.

I am going to put a small amount of fuel down each carb intake tonight and see if it fires, that should tell me if it is a carb or spark issue.

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Last edited by ryu954rr; 04-05-2007 at 10:45 AM.
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post #4 of 13 (permalink) Old 04-07-2007, 11:26 PM
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If all fails check timing, a guy on another forum did the exact same thing, pulled the bike after winter, he let the bike run for 10 min and it died and backfired like crazy, he was getting 3-4 spark for each events, the pulse gen was ok he found that the ignition computer was toast. Bike was a superhawk. Good luck
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post #5 of 13 (permalink) Old 04-07-2007, 11:53 PM
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Quote:
Originally Posted by hybrid
You didnt specify if the bike was getting fuel.
If you don't want to hear that backfire...try and start it, pulling one plug
wire at a time..leaving three connected when trying to start it.

If you find the one causing the backfire...leave it disconnected...and try and
start the bike.....hard. (Don't run down the battery.)

Pull that plug and see if it's wet...as in gasoline.

My guess is you are not getting any fuel...or not enough.

Floats are probably stuck...jets clogged...

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post #6 of 13 (permalink) Old 04-23-2007, 03:23 PM Thread Starter
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I poored some gas down the intakes of the carbs and it still wouldn't start. This tells me that the problem is not a lack of fuel. I am getting spark on all four cylinders so I think the timing may be way off. Without being able to get the bike running to check the timing how can I set it to a good starting position?

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post #7 of 13 (permalink) Old 04-23-2007, 04:05 PM
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You have electronic ignition. The timing does not go off by itself. Plugs may be fouled and when fouled do not fire under compression. The engine may also have too much fuel inside the cylinders. Try new plugs first before spending additional money on ignition parts. Sometimes the plugs tips can be cleaned by heating with a propane torch.
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post #8 of 13 (permalink) Old 05-05-2007, 08:36 AM
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i'm having this same issue with my fzr600 - well, close enough, maybe a little worse...

was there a resolution? did plugs work? (i'm planning to change mine anyway, i just wanted some reassurance that i was going in the right direction)
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post #9 of 13 (permalink) Old 05-06-2007, 09:55 AM
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fyi, in case anyone comes across this while searching the archives:

my bike was doing as described above, but my backfires were most of the time about 5 seconds after i stopped trying to crank it. i was getting fire on all 4 plugs and i was getting gas.

the gas was anywhere between 2 to 7 years old, so i made sure to drain the tank and put nice clean gas in it, and made sure the fuel pump as purged of all the old rank gas.

i replaced all 4 plugs (which showed plug #2 was cross threaded by a previous owner ) after that, it would hit and try to idle, but would die off (as if it was trying to idle at 200 rpm's)

i put my hands (and eventually a rag) over all 4 carbs to suck in good clean gas into the carbs - i got it idling and after a min or 2, i was able to rev it up!

a quick spin around the block proved promising but it did have some studdering. a few hours later i took it for another quick spin and it keeps getting smoother - i believe the old gas is working it's way out...

moral of the story? old gas and slightly fouled plugs both in combination were causing my delayed backfire and non-running state.

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post #10 of 13 (permalink) Old 05-06-2007, 10:57 AM
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Quote:
Originally Posted by cokeacolasucks
...a quick spin around the block proved promising but it did have some studdering. a few hours later i took it for another quick spin and it keeps getting smoother - i believe the old gas is working it's way out...

moral of the story? old gas and slightly fouled plugs both in combination were causing my delayed backfire and non-running state.
If that old gas was sitting in the bike, you should clean the carbs really well. At a minimum, run some SeaFoam or Berrymans cleaner through the tank.

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post #11 of 13 (permalink) Old 05-06-2007, 06:24 PM
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i may look into the seafoam or berrymans, but i'm hesitant to take the carbs off and clean them. i cleaned my 88 fz's once and made them work like new - but i think this bike is running too good now to mess with. i'm also hesitant to use any fuel system cleaners - while searching through the threads, the cleaners seemed to cause more problems then they did good...

sadly i don't know how long the gas had been sitting - the bike was bought at least 3rd hand :-\ but i took it for another spin after i had flushed the cooling system and installed the new radiator - it really is running good - if not better than my '88

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post #12 of 13 (permalink) Old 11-04-2012, 10:41 AM
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FZR 1000 and its been sitting for a while and I've been trying to start it and it turns over and sounds like it is going to START then violent backfire like a cannon and then just keep TurnING OVER ITS LIKE ITS out of timing but it's not I'm trying to figure out what is GOING ON if anybody has any input please let me know thank youstart
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post #13 of 13 (permalink) Old 11-04-2012, 10:50 AM
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87 FZR 1000 and its been sitting for a while and I've been trying to start it and it turns over and sounds like it is going to START then violent backfire like a cannon and then just keep TURNING IT OVER ITS LIKE ITS out of timing but it's not I'm trying to figure out what is GOING ON if anybody has any input please let me know thank you I JUST bought IT FOR $650
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