92 vfr exploding sound when starting

alright question from a noob......im swaping the tail section of my bike and its been sitting in the garage for about 2 to 3 weeks now....so i went to run the bike cause i didnt want the gas to stagnate in the carbs and clog it....of course i got everything on and pluged right but when i started the bike it seems like it wasnt getting any gas....then i keep starting it then suddenly it when "KABOOM" on the exhaust end....got a little startled a bit so i stop and waited the next day.....the next day i started it again and still making the sound and having a spark now.....HELP PLEASE!!!!!!!

 

Sounds like leaking float valve allowing fuel into inlet, then exhaust & then detonating once its dry enough to fire.

DO THIS First - Check your oil to make sure its NOT contaminated with fuel.

If the oil is OK then Turn the fuel tap to OFF & crank the engine over a few times with the kill switch in the OFF position. Then turn the kill switch to RUN & crank again, if it goes BOOM, but then settles to a normal idle, leave it to run out the gas in the carbs. If its a small piece of dirt on the valve seat, this may flush it.
Now turn on the fuel & crank it over again, it should fire up as the fuel is drawn down to the carbs. If it does NOT go BOOM, then you have a fuel leak from the carbs into the intake !

Now you need to wait a day & do a normal start. If it goes BOOM, then it was not dirt on the valve seat, but probably the valve seat or a sticking carb float, either way its time for a carb strip. You could try some carb cleaner through the carbs first, if that does not clear it, then its a definate carb strip.

Hope you sort it easily.

 

how do i know if the oil is ok...would it rely b obvious if its contaminated wit gas....n by contaminated u mean gas ryt?.....ill surely check that out thanks for da reply!

 

Mohawk's comments are great for his theory of this not-that-unusual case; but, backfires are most often a sign of leanness, not flooding.

It's helpful to crank the engine for a few seconds--battery permitting--with the running switch OFF, time to allow fuel to refill carbs and start flowing. Not so often a problem on bikes that get ridden often.

Carb clean with special attention to clearing out the long brass tubes that feed the "choke" system only if you must.

But you could try doing a bit more cranking with the RUN switch OFF
to allow more fuel into the cylinders before you switch ON, and you might not need to grapple with carbs. My Hawk does the bigbang often, but only when i switch ON too early. Doesn't harm anything, but a local SWAT team might get deployed, ya nevva know ! And it annoys the neighbors too.

 

Just use a syringe or a thin tube to suck some oil out of the oil filler point on the clutch housing. Take it out side & put it in a small dish. Smell it ! Does it smell of petrol ? Compare it to some new oil is it thinner ? If you can't tell then as a last resort, put a few drops of fresh & old oil on something metal like a spade & try to set them on fire with a match or lighter. Oil does not catch fire very easily, if its contaminated with fuel it will !

 

since we have dip-sticks for our oil, you can just do the dip method and kinda run it between your fingers. It should still have some resistance and not smell of petrol. Fire route mentioned above sounds good for the fourth of July though. If you were local to south FL, I would help you oot.

 

While you were working on your bike could you have mistakenly got some coil wires mixed up? This is something new right? It sounds to me like one of your spark plugs are firing at the wrong time. My memory sure isnt what it use to be but i think i remember doing that on a 600 ninja i was putting back together once. The owner had taken everything apart for no good reason and when i got to wiring the coils back on i had two of them backwards and i got that same ka-boom. And no its not good for the bike at all. Thats where i would look is to double check all your wiring again. It can happen to anyone.