carbs backfire

[81midnightspecl]

Just bought an 81 Midnight special (xs 1100). It seems to be running a little rough. Carbs backfiring.
The intake assy has been removed and replaced with 4 individual air filters. The fuel lines from the petcocks have been modified. The two front nipples on the petcocks are connected. The two rear nipples go to the carbs (left petcock to the two left carbs, right petcock to the right carbs). I can get it started and seems ok at idle. But when I go to rev it up, I get some backfire out of maybe two of the carbs. Not sure what the problem is. From previous forum discussions, I see that there could have been an "octopus or spider" diaphram. I don't see any sign of that. So that is why I am guessing why the two front nipples of the petcocks are tied to each other. The other two lines did have filters on them, but I removed because I thought they might be restricting some fuel. So now I have a direct line from the petcock to the carb nipple. When I did this and turned on the petcocks, I had fuel running out of the carbs. I ended up turning off the petcocks and starting it up and letting run briefly, then turn on the petcocks. It seemed to be ok after that.
Anyway, the way it stands is that I continue to get this backfire when I am just running at lower rpm or idle. I have run it up the road a bit and it seems ok when it is wide open....But I am not satisfied with that. Any suggestions?
thanks
bk

[TopCatGr58]

Re: carbs backfire

Originally posted by 81midnightspecl
Just bought an 81 Midnight special (xs 1100). It seems to be running a little ruff. Carbs backfiring.
-snip- Not sure what the problem is. -snip-When I did this and turned on the petcocks, I had fuel running out of the carbs. I ended up turning off the petcocks and starting it up and letting run briefly, then turn on the petcocks. It seemed to be ok after that.
Anyway, the way it stands is that I continue to get this backfire when I am just running at lower rpm or idle. I have run it up the road a bit and it seems ok when it is wide open....But I am not satisfied with that. Any suggestions?
thanks
bk

Hey there 81MNS,

You need to pull your carbs, replace your float needle valves and seats, and also probably the O-rings around the valve seats! It sounds like it's flooding, see your underlined statement above. Fuel should NOT BE FLOWING OUT OF THE CARBS!!

Also, check your oil for the presence of gas, with this leaking situation, you could have gotten some gas in there, and that will destroy the bottom end bearings and such very quickly!!

Once you fix the flooding, then it will behave much better in the lower rpm range!
T.C.

[81midnightspecl]

Thanks for the feedback TC.
I understand the flooding issue with a possible float problem. Are you saying that the flooding is also causing the carbs to backfire? Or is it another issue?

I don't believe the carbs had any fuel running out of them until I switched up the lines. Thought that might have been a one time thing.

I do know that the previous owner did leave the petcocks on and did have fuel in with the oil. He drained the crankcase and let it air out for a while. I did open the oil cap an sniffed for gas. Did not smell any. I also looked at the oil site glass, I did not appear to have two different liquids. I hope I am ok in this area.

thanks

[John]

You should use the rear set of ports on the petcocks. The front set are for the 'Prime' function, and you loose reserve function by doing this. If you use the rear set, and plug the front ones, you will get reserve back. I have run my bike for years without the octopus, only I have both petcocks joined together, and only need to turn on one petcock for my fuel supply.

[81midnightspecl]

Any feedback on the carbs backfiring?
I bought this bike from my uncle. I asked him about the carbs backfiring (I know start at the source). Anyway, he said that the carbs do that until it warms up. Also said that it does not have an accelorator pump. Now my first thought is that this still should not do it.
thanks

[Firehawk]

Last time I had my bike running, it was doing that too. And it's definitely not running right...

[TopCatGr58]

Originally posted by 81midnightspecl
Any feedback on the carbs backfiring?
I bought this bike from my uncle. I asked him about the carbs backfiring (I know start at the source). Anyway, he said that the carbs do that until it warms up. Also said that it does not have an accelorator pump. Now my first thought is that this still should not do it.
thanks

When I had my #2 float sticking, mine would also bark out the carbs when warming up IF I tried to give it too much throttle too soon. Make sure your carbs are right first.

Secondly I remember reading a post about this, and several folks solved a lot of this by resetting the Timing Chain slack tensioner!
T.C.