backfire, 250R

[sunblock]

One of my 85 250R's has started to backfire on occasion when kicking it. Last couple of times I have had it out It would do this mid kick and really really hurt the bottom of my foot. One time it came around and hit my chin .. massive pain .. Now I'm scared to kick it. am I doing something wrong or does my trike have some issues?

[juggaloclownz18]

a couple of weeks ago my buddy had this problem with his blaster and it would not start, it would just backfire mid kick..... ended up being he sheared his woodruff key, i dont know if this could be your prob. or not but might be something to look into, but you might want to wait until someone else chimes in because im just guessing....

[nd4speed]

most likely it is building up unburnt gas then a spark sets off the explosion. Poor timing or weak stator can cause that (exhaust backfire)

I think lean or preignition or over advanced timing does it too and is a carb side backfire

[leviblue]

Watch your reeds, I use to blowout stock reeds all the time when she backfired on the start(unspent fuel in carb). If she don't start up after the BF check the plug and if it not that it's the reeds. As for kneeing yourself in the chin,,,well that does happen now and then and a good way to know you have compression. A few weeks ago I was at a race and stalled on the gate. I ate my knee and the quad riders got a laugh

[nd4speed]

oh bad reeds, forgot about that. I totally agree

[Yamaha_Rules69]

I agree with juggaloclownz18 above ^ Sheared flywheel key. I have had the problem numerous times on 2 stroke dirtbikes/ 3 wheeers. Pull the flywheel, and check out the key that holds it on the end of the crank shaft.

[TeamGeek6]

I agree with juggaloclownz18 above ^ Sheared flywheel key. I have had the problem numerous times on 2 stroke dirtbikes/ 3 wheeers. Pull the flywheel, and check out the key that holds it on the end of the crank shaft.

Only two possibilities:

1.) sheared key, but it probably wouldnt run at all then, depending on where the rotor stopped at. A sheared key probably lets the rotor spin.

2.) bad wiring in the ignition system. The CDi stores charge but wont fire it until it gets a signal from the pulse generator. A loose terminal on the PG or some other flaky connection on the CDI. Thats the only thing that can cause early fire. The only other way is to have an extremely hot ignition system, which it probably doesnt have.

[sunblock]

Thanks for all the replies. I totally forgot about posting this. I may take a look at the reeds and flywheel tomorrow. it is a bit on the rich side too, I bet that the potential for backfire would only be made worse by that, if the reed is broken.

[ridecaity]

I'm having the same problem with my 86 250r,it did run for a bit but now i can't start it.And when it does it only runs a few seconds.I have a Boyesen reed block system.Should that make a difference on my carb settings?Srry for asking this in your thread,just frustrated.Oil seems to be really dirty too from just a ride around the block.This is the first time out since the rebuild.Anyone have any ideas other then whats mentioned here?

[jeffatc250r]

Pull the flywheel, sounds like a sheered key, although i have no input on dirty oil. Is it just dirty or filled with alum? Slipping clutch discs can make some cruddy oil.

[ceaserthethird]

Exhaust leak will cause a backfire, check the woodruff key, check your reeds.

Make SURE your the head pipe is fully seated and sealed on the flange!

Keep us posted

[ridecaity]

thx guys ,will try in 2 weeks when i get home.

[ridecaity]

i tryed everything u guys suggested.The trike still doesn't wanna run.It wants to start but doesn't.Has lots of spark.reeds have been changed to stock.Spark plug is soaked every tome.carb was clogged at main fuel line.Seems to me a fuel prob,any suggestions?