backfiring in my experience is a lean condition thing..Id check for a vacuum leak around the carb manifold while its idling..spray carb cleaner on the outside of the carb/manifold and if the idle goes up or it dies youve got a leak.. Might check the valve clearances too..

My KTM400 will backfire on deceleration if there is a leak at the exhaust manifold.. (where the head pipe meets the head)..

 

Correct me if I'm wrong but your KTM would be backfiring out the exhaust though right, like back pressure?

I've got the 232 page service manual for the Baja so I'll take a look at the valve clearances also. I wasn't able to work on it tonight cause I was at work until 9...

 

Yes your correct..

Youve got a 232 page service manual? Thats cool.. Where did you get it?

Id look at the valve timing and ignition timing also..

 

I watched the video again.. sounds real lean... all mine had what I called a cough and die syndrome when I got them.. try turning the fuel screw out 3.5 turns from seated.. also what is it set at now?

 

I found it doing a Google search, it was in a pdf and free which is always nice! I think I searched something like Baja Wilderness 250 Service Manual or something along those lines..

I'll try to this first when I get home later today, I honestly don't know what it's current setting is because I haven't touched it yet.

When I picked the quad up from my inlaws this hose was not connected to anything and I can find where it belongs for the life of me! It looks like it does belong somewhere also and I have a feeling may be one of the reasons why it's running lean. I also noticed that this black box/breather/maybe emissions related thing (I have no idea what it is!) has two hose nipples on it but there was nothing hooked to it...? There might have been one time before and might be why it's running like crap now, does anyone know what they are or if they're important??

1st picture is the hose I talked about
2nd picture is the black box thing missing connections
3rd picture is what the hose I referenced in the 1st picture is connected to

 

Free is my favorite way to get stuff..

The hose in the first pic...since its got a brass fitting on it..it has to have come out of the engine or carb some where..

2nd pic is smog crap.. Id get rid of it unless you got vehicle inspections..

3rd pic is more smog nonsense.. same

the rubber manifold looks cracked in the pic... does it leak air?

 

I can not find ANYWHERE on the carb or engine where the hose with the brass fitting belongs and it's driving me nuts! It's good to know those other parts are just smog crap.

I noticed the weathering of the manifold and I don't think it's cracked through but I haven't been able to spray carb cleaner on it while it's running yet. I'm heading home soon though and will be working on this thing for a few hours..

 

Maybe on the valve cover? (top of the engine)

Another thing I noticed was its a OHC engine.. most Chinese 250's are push rod style..more likely to have jumped timing with a OHC engine..

 

I gotta say thank you for helping me out on fixing this! I tore down the carb, douched it with carb cleaner, put it back together, installed it, the air/fuel screw was 2.5 turns out from seat so I added 1 more turn to richen it up (3.5 total), and when I was inspecting the rubber manifold I FINALLY found where that hose with the brass fitting belonged... There is a small hole on the topside of the manifold that was covered in oil and dirt, I cleaned it off and used a paper clip to see if it went all the way through, which it did so I knew I had found it's home. When I fired the quad up, it ran better than when it was brand new! No more popping or having to run it with the choke on at all.

So now that it's running great and I can move on to the brakes... Might start a new thread about that since I can't find anything with searching and hopefully (like this one) it can help someone out someday!

 

Your Welcome..