XJ650 Air Box Pop when trying to start.

Hey all,

I have just finishing rebuilding my carbs and got everything back together today. I was trying to get the bike to run for the first time and having all kinds of issues. First I left the petcock in prime by accident and think I flooded the engine. I took the spark plugs out and checked all four for spark and then were good. I put them back in and tried starting with the choke off and the throttle wide open. I got the bike to start for 2-3 seconds but then it shut off.

I kept trying different things and one of the times I heard a really loud backfire (or what I thought). I started filming the bike starting and only notice this after I watched the footage. After the first backfire there were only a couple that were as loud. The rest were just little pops. I noticed in the video that with the little pops I could see a small burst of flame around the airbox. I went out to look at the bike and it turns out those flames where in the air box. There is a sizeable crack in the airbox on the right side towards the front of the air box right where the seam is in the plastic. My only guess is that the first big bang some how "exploded" my airbox and cracked it. Has anyone ever run into this? Anyone know where I can get a new airbox?

Thanks,
Ben

 

Running for 2 or so seconds sounds like a flooded engine, but no enrichner to keep it going, hence the popping back into the carb. That's assuming your ignition leads are correct as well as valve clearances....

 

Mind if I merge this into your existing thread for this bike?

 

you should not touch the thtottle when starting the bike choke only and only if needed.

if your carbs were flodding because of petcock being left on prime fuel would have flowed into the air box.
it also says you have float needle valve issues

you can glue the airbox back together with black pvc/abs pipe cement

 

Yes but float valve issues can often be caused by debris getting into them from a rusty tank. Btdt, last week in fact.

 

does not matter what the issue is ,it needs to be corrected.
if it is debris he needs to add a filter untill he flushed and cleans his tank, if he still has the little filter caps on the float valve bodies those will/would get plugged up.
so he needs to revisit his rebuild(other thread speaks of a kit with canadain size jets)
flooding could be
could be wet set level
debris keeping needles open
or bad dirty seats/needles
he did not state if he replaced needles and or bodies and o rings..
what ever it is causing the flooding it should not be a hard fix
.
I would also suggest not connecting carbs to air box on your next removal reinstall cycle it wil be easier to see the fuel flooding.
bike wil start and run with out air box. you will be able to get rough tuning and idle set then connect the air box for the fine tuning

also check the wells in the bowls to make sure they are clean as well as the enrichment circuit tubes.