1986 Yamaha 225dx

[Ahatchett]

I got a 225dx a few days ago, looks to have been restored or just a really nice original.
Has one issue though, it backfires when I let off the throttle. I cleaned the carb and moved the needle down one clip because the plug was black but it still does it.

[Ahatchett]

[350for350]

Usually (but not always) when it backfires while letting off of the throttle, it means that it's running lean. The black plug could be 20 years old and barely firing. I'd try a new plug, put the clip back in the middle groove and see what it does. You should check the air filter too. They weren't great to say the least. If it has fallen out of place or has rotted apart, that would cause a lean condition since you no longer have the restriction of the air filter. This is assuming that it's all stock.

[Ahatchett]

It looks to be all stock, someone may have restored it though. I'll do the needle and air filter tonight and get back to you.

[Ahatchett]

Update; Set the needle back in the middle and put a new air filter on it. Backfire was better but still there.
Worked through most of the jet settings but it didn't get any better. So I'm just gonna leave it I guess since it doesn't seem to be running lean by the plug.

[Ahatchett]

[350for350]

It looks pretty clean.

[3Z with Fangs!]

Backfire letting out of the throttle typically is lean on the pilot. You can try to richen it up by adjusting the air screw (research your carb to know which way to turn the screw) it's different depending on placement of the screw, whether it's closer to the air intake or closer to the head. If adjustment of the screw don't help and it's all stock check for a vacuum leak. If you don't have one order a couple of new pilot Jets in the next couple of sizes up.