Starting Problems lots of backfiring

T

tlued047

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Dec 27, 2012
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Location
wisconsin
Hello, i have a 1999 Yamaha Vmax 600 sx triple. went to start it up this past weekend and it wouldnt go. so i cleaned the airbox, the carbs jets and bowls, and it still wouldnt go. so i put the spare set of plugs in from when i bought the sled, and it started up, idled for bout ten minutes before it stalled. i wanted to let it warm up because it was the first start up of the season. after that wouldnt start again. lots of huge backfires enough to knock the exhaust off. so i replaced the plugs with brand new plugs. checked the spark, compression, thought it seemed like it wasnt getting enough fuel so i checked the fuel pump and cleaned the diaphrams, cleaned the reeds and even recleaned out the carbs again. i still get nothing except big backfires every couple pulls. ive even gone as far as spraying some either in it. the sled appears to start up with either but as soon as it burns off it shuts back down. which is about three seconds. Help me someone Please Ive tried everything i can think of ive got spark and compression
 
When you cleaned the carbs did you A pay special attention to the pilots, they need to be 100% clean B pull the float needles and seats? With todays ethanol fuel pilots,seats and top hats (screens on top of seat) get plugged very easily and cause 100% of the symptoms you describe. You can test this theory by pouring a snort of gas into each cylinder. If she fires right up for a few seconds and dies your problem definately in fuel delivery.
 
Devilin AblueDress! said:
When you cleaned the carbs did you A pay special attention to the pilots, they need to be 100% clean B pull the float needles and seats? With todays ethanol fuel pilots,seats and top hats (screens on top of seat) get plugged very easily and cause 100% of the symptoms you describe. You can test this theory by pouring a snort of gas into each cylinder. If she fires right up for a few seconds and dies your problem definately in fuel delivery.
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I pulled everything cleaned it out with carb cleaner including the hoses took the carbs apart top to bottom. cleaned the insides of the carbs out with a Qtip to avoid missing anything. and yes i pulled the float needles and seats.
 
Old fuel or new? Old fuel prolly sucked more ethanol jelly balls into carbs. New fuel......Got nothing. You said you pulled lines of from carbs and had fuel. You said spraying ether into cylinder she fires. I would have to say logic points at problem being in carbs. For giggles pull carbs off and pull pilots out. Willing to bet you find them plugged.
 
When you pulled lines off nipple at carbs was the a bunch of fuel or was it just there? With lines off you pulled it over and verified fuel pump is pumping?
 
yes i have. i think i have narrowed it down to being something electrical. hopefully its just something shorting out. time to take out the multimeter :o|
 
tlued047 said:
yes i have. i think i have narrowed it down to being something electrical. hopefully its just something shorting out. time to take out the multimeter :o|
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You lost me there.......Putting ether down plug hole it runs, you have gas going into carbs.....but you have narrowed it down to electrical.....
 
well i think its got spark but not continuous spark. i checked them top hats and they were completely clean. so idk what else it could be. for all i know it could be that the cdi box is goin out causing the firing order to be screwed up which is why it could be backfiring, and yet have spark. and the ether could just be giving it enough bang to get running even with the timing being off. ya know its a shot in he dark but its about the only thing left so ima giver a go. you know where i can find a wiring harness diagram for this sled?
 
tlued047 said:
well i think its got spark but not continuous spark. i checked them top hats and they were completely clean. so idk what else it could be. for all i know it could be that the cdi box is goin out causing the firing order to be screwed up which is why it could be backfiring, and yet have spark. and the ether could just be giving it enough bang to get running even with the timing being off. ya know its a shot in he dark but its about the only thing left so ima giver a go. you know where i can find a wiring harness diagram for this sled?
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I THINK the 99 redhead doesnt have a firing order, pretty sure all 3 coils fire at the same time. Crank could be out of phase but thats a whole nother can of worms. Is exhaust clear? Mouse nest in can might have ben compacted while it idled for the ten minutes that it did and no not letting exhaust out of the motor. Will only take a minute to pop the pipe off and see if it will run open header. Not the best thing for the engine, wouldnt recomend revving it up up it does fire.
 
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made sure there were no mouse nests in the airbox or the carbs before i started it up are you talking about a mouse nest possibly being in the exhaust
 
tlued047 said:
made sure there were no mouse nests in the airbox or the carbs before i started it up are you talking about a mouse nest possibly being in the exhaust
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Yes, if exhaust is blocked off sled wont run right or at all. Has to be able to exhale.
 
checked the exhaust it was clean got the new cdi box, and it started right up. but now it seems like i have a cyclinder that is not firing properly. any ideas
 
pilot jet circuit isnt clean, you need to take the carb cleaner hose and stick it in the threaded hole where you removed the pilot jet, spray the cleaner and it will come out the fuel screw orfice hole in the FRONT side of the carb if the curcuit is open if it doesnt, its clogged up in the carb and needs to be opened.
I know you cleaned the carbs... but if your spraying starting fluid in it and it fires till it burns it out, then your not getting fuel in the idle circuit. if you remove the plugs and pour just a tad of mixed gas in each cylinder does it fire up and idle for a 5-10 seconds?
I would also look at the choke plungers and make sure they are clean and opening up, it should start on the choke, if it doesnt then its also very possible you have a bunch of gas puddeled up in the case and pipe. if the plugs are wet when you take them out after trying to start it then likely this has happened.

You said you checked the pump and its working so it only leaves 1 thing in between the fuel pump and the engine, the carbs. I would also drain all the old gas and replace with new.

as mentioned there is no firing order, all 3 plugs are fired at once, so if you have spark its not electrical.
 
one other thing its a dumb one but it happens, does it have more then a 1/4 tank of gas in it? even though you can look in there and it seems like a couple inches deep, lots of times the pick up hose is getting air from the sled being up on a jack stand or whatever and it doesnt get enough gas to fuel the carbs............ :dunno:
 
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