Backfiring into air filter?

[Anonymous]

My bike is running a little rough at low RPMs and sometimes will backfire/pop into the air filter. It generally only happens at low RPMs when taking off from a stop but it does not happen all the time. It will occassionally pop a little at higher speeds if I have to roll off the throttle quick. I also feel a slight stutter at low RPMs (in any gear). I think the chain needs a slight bit of adjusting so that may be the cause of the stutter, but any ideas on the backfiring? My knee rest on the side of the air filter cover and I can feel when it happens.

 

[daveo]

backfiring through the carbs is indicative of a lean condition, most likely early season grunge/varnish obstructing a passage or jet

 

[earlfor]

Re: Backfiring into air filter?

The first thing I would check would be the sparkplugs to see if they are fouled. After that, I would check the airfilter to see if its dirty.

Earl

My bike is running a little rough at low RPMs and sometimes will backfire/pop into the air filter. It generally only happens at low RPMs when taking off from a stop but it does not happen all the time. It will occassionally pop a little at higher speeds if I have to roll off the throttle quick. I also feel a slight stutter at low RPMs (in any gear). I think the chain needs a slight bit of adjusting so that may be the cause of the stutter, but any ideas on the backfiring? My knee rest on the side of the air filter cover and I can feel when it happens.

 

[Redman]

You will want to do something about this before it blows out your carb boots.

My 850 was backfiring into air box, mostly when letting off the throttle a little, but other times also. I tried my own cleaning of carbs with some improvement but didnt really take care of it. I waited too long, it also damaged my carb boots after a while (but maybe old weak cracked anyway). Eventually I took carbs to a shop that took them apart further than I was doing. Probelm in my case was the little screens above the float valves were crusted over with crud, had to be replaced.

 

[Anonymous]

Thanks for the input. I had a feeling it was a lean condition. I got in there the other day and the screw was only a 1/4 turn out on the carb (this is on my Vulcan which has only 1 carb). I had a post on here before about the pipes which the previous owner removed the baffling from which led me to back the screw out a bit. It's at 2 turns now and that seems to have helped reduce the frequency. I just found (a few miuntes ago) a site describing someone doing exactly the same thing to the exhaust on a Vulcan and they said they had the same problem and 3 turns out did the trick. Guess I'll pull it apart again tomorrow and back it out another turn and see if that works. I know re-jetting would be ideal, but I'm trying to find a stock exhaust so I would end up having to change the jetting back very soon. I'll also check the air filter and plugs as suggested. I was already thinking about replacing both soon anyway since I just got the bike 2 weeks ago, but I haven't had time yet.

Any ideas on the hesitation at lower RPMs as well? Is it probably the chain needing adjusting or does that have to do with the carb as well?

 

[scotty]

check the plugs first before you adjust anything

 

[beby99]

I would also check your intake boot to make sure its
not already cracked and/or leaking.

 

[AOD]

spark plugs...as Earl said. A fouled plug will backfire through the intake randomly. You will also be able to check if you're rich or lean.

~Adam