I just got a crf 450r and every time i go to start the bike it always back fires for ages then it mite go or not is it stale gas or is av gas the bike shop ffilled it up when i got it what would be a good gas to run plz
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Re: bike keeps back fireing when first starting
Hi and welcome to FixYa,
Initially, backfiring is a spark/timing issue or contaminated fuel (water) or as you stated stale fuel. AVGas would not result to backfiring but rather a stronger pull though would heat up easily.
Good luck and Thank you for using FixYa. Happy Holidays.
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Hi nice ATV, Usually a single cylinder motor that back fires is either the timing Or a dirty spark plug. Check out this youtube video, This guy shows the right colour spark and I didn't know this but it should spark over the top of the centre electrode, Hope the is helpful.. CHEERS... https://www.youtube.com/watch?v=mUOmsGiirTU
Back fire is an indication that the bike is firing incorrectly.
Your timing chain is probably stretched, due to the year.
inproper valve timing due to stretched timing chain will make the bike backfire.
I have other thoughts like stuck valves or inproper sparkplug wires on wrong plug,
i always start with easier and less expensive method.
1st check your sparkplug wires to make sure they are on the right plug.
2nd pull sparkplugs and do compression and leakdown test.
3rd pull componets to see if valves are opening and closing, (valve clearance check)
4th if valves are good, then timing chain is probably stretched.
5th if timing chain and timing marks are good, and valves are good, then proceed to
testing the signal generator to make sure your getting a signal to the cdi,
6th if you have a signal to cdi, the cdi tells which coil to fire. either # 1&4 or # 2&3.
if signal generator is working, but coils aren't firing right then its the cdi.
obviously your coils work because its firing, just back firing.
Thats all it could be from easiest to hardest.
Good luck and have a great weekend.
Try a small shot (about a 2 second spray) of starting fluid in the air intake then cranking....
WARNING- DO NOT TRY AND KEEP IT RUNNING BY USING THE STARTING FLUID! It can damage your engine.
If your bike fires and runs for a bit, the most likely problem is your gas has gone "sour". You need to drain all the old gas out and properly dispose of it.
Over time, gas will cause a varnish buildup in your carb if it sits too long. You can try adding some carb cleaner to fresh gas, but the results will not be immediate. You may have to have the carb rebuilt.
When you store anything gas powered, there is an additive called Sta-bil that will act as a gasoline preservative for about a year.
It may still have some water in the tank/system or the spark plug is no good.With a full tank of fuel,add 200ml of methilated spirits.It breaks up any moisture and lets it burn away.Also,with the motor out of gear,run the bike at higher revs and close the choke fully on and give full throttle at the same time.When the motor starts to die,flick the choke off.This can sometimes unclog a carby jet that may be slightly blocked because with the air choked,it gives a sudden **** off fuel.This may/maynot fix the bike but it the 1st thing to try before paying a dealer and it can't hurt anything.Hope this helps you
hi,without seeing the bike i would guess that the head gasket has failed,when this happens the compressed gasses inside the combustion chamber escape into the coolant system and presurize the coolant,the end result being coolant escaping out through the overflow as the pressure increases,i would recommend getting it looked at fairly promptly as the engine will start running poorly and possibly fail...cheers
sounds more like a slipped timing chain to me, big problem area on the big power 4-strokes, tokyo mods makes a manual timing adjuster, will make a big difference in longevity of your next timing chain, i wound also check the vaves to make sure the piston hasn't shaken hands with the valves