[jonathan180iq]

Originally Posted by Jaime

Are backfire and afterfire different things? Also, which claim do you think is wrong? Just to know, I'm not angry.
In my experience recarbureting the GZ250, a lean mixture causes popping in the muffler, but sure that some gasoline must reach there. That happens when you give no throttle but fuel is still sucked in, for example, going down a hill using the engine brake. The thing is that fuel and fresh air would only need high temperatures to explode.
When the mixture is rich, there's a little or no fresh air remaining in the exhaust fumes (enough fuel to burn everything), so there's not enough O2 for the combustion to take place in the pipes/muffler.

Sorry, I can't explain this better, in English.

Anyway, there are many wrong thoughts about backfire, so maybe I missed something.

Regards.

Jaime,

Your english is fine and I'm really glad you are a part of this forum. You took over carb tuning where I gave up. Also, I wouldn't fare so well en espanol. That's why I don't hang out much on marauderos.org.

Backfire is an explosion that occurs in the reverse direction from the carb back into the air filter housing. It's completely different from afterfire in that it occurs in a very lean carb mixture, in my experience and research. This is the rarest type of "funny" explosion that people deal with.

Afterfire, as I said earlier, is caused by a rich fuel/air mixture and occurs in the muffler. It is also the most common hiccup commonly mistaken as "BACKFIRING". You were right when you said that there is always a trace amount of fuel vapor in the exhaust. The problem, however, in an afterfire situation, is that the amount of unburned fuel is more than trace. When the rich mixture allows enough fuel to enter the exhaust system, the ambient air, which is always in the muffler since it is not a closed system, combined with the heat of the muffler, causes a secondary explosion which may even result in flames coming out of the exhuast. This is called an afterfire.

Looking up the two words in google may give a better explanation than I did.

Sinceremente,
Jonathan