Backfire at idle

[mmaddix]

Alright everybody my bike backfires when idling and at low RPMs. Also I hear a pop coming from the carbs every so often. I know the popping is from the carbs because it blew a cap off of one of the carb boots. What is the first thing I should do to try to find the cause. The carbs are synced, at least they where about 1000 miles ago.

[XS1100_OEM4ME]

Carbs

1st, I just went through the same thing, It is most likely, carbs. The jets and ports on these are so small that any thing can cause a problem. Make sure that you remove the emulsion tubes (missed one on mine and POP POP POP Next, the wasted spark system can blow an air filter off, if all is not running right with the carbs, so start with the carbs, they can be a PITA on these bikes, and thanks for your service Marine

Alright everybody my bike backfires when idling and at low RPMs. Also I hear a pop coming from the carbs every so often. I know the popping is from the carbs because it blew a cap off of one of the carb boots. What is the first thing I should do to try to find the cause. The carbs are synced, at least they where about 1000 miles ago.

[crazy steve]

Check your valves, a too-tight valve can cause backfiring issues. Look at your cam timing while you're in there. But OEM is probably right, you'll need to pull the carbs and go through them, these things can plug up at the drop of a hat...

[mmaddix]

and thanks for your service Marine

I guess I will pull the carbs and clean them and see how everything goes after that. And thank you for your support, it is well appreciated.

Check your valves, a too-tight valve can cause backfiring issues. Look at your cam timing while you're in there.

I will check the valves and cam timing. I wanted to anyways and now I have a reason.

Thanks again fellow members.

[XS1100_OEM4ME]

This might be helpful

http://www.zrxoa.org/forums/showthread.php?163000-How-to-clean-carbs-(PICS

Not all carbs are the same, but they all need cleaned to the complet degree

[DGXSER]

For help cleaning the carbs, look up the thread titled "Carb Cleaning 101" by Wildkat.

Tuning, meaning a lean condition can also cause the popping your describing as well. So it coul dbe as simple as another 1/4 turn or so on the mixture screws.

[mmaddix]

So when I pull the carbs to clean them I want to make sure I have the correct jets and everything in them. Which main and other jets (I forget the name of them I think they are pilot jets) should I have in there? I am ruining air pods without the airbox and I have 4 into 1 exhaust with a completely gutted muffler, nothing at all on the inside of the muffler. Is there anything else that should be checked to see if the correct size is in there for my setup?

[DGXSER]

Well, now another light is shown on the subject. What you have is commonly referred to as straight or open exhaust, meaning no baffling for back pressure.

When you jet the carbs, you do need to account for changes from factory set up like the POD filters your using, and the non stock exhaust. There is a thread on here, some where I do not recall right off, on how to select the jetting based upon the year of the carbs, and the options you have for intake and exhaust.

I will add that very few folks have ever found success tuning for open exhaust like yours. It definitely causes a lean condition at idle and will tend to pop on decel and pop or backfire at idle.

Depending who made the exhaust your running, you may be able to get some baffling for it, like a Supertrap insert.

[mmaddix]

It was doing the same thing when I had a baffle in there. The whole reason why its Ann open exhaust is because it back fired so hard one time it blew the baffle and the end cap out of the muffler

[mack]

Jetting

I think this is what your looking for.

Jetting guide...

http://www.xs11.com/forum/showthread.php?t=382

[XS1100_OEM4ME]

Exaust

Well, with "0" back presure, you got a challange on your hands, not saying it cant be done, just very hard to get it to run right that way. If you can mod it to have a super trap kinda end on the exaust pip, you can add baffels as needed till you get it running just right IMHO. Like these:

http://www.ebay.com/itm/SUPERTRAPP-4-6-PACK-DISK-SET-/140567714183?hash=item20ba7d1987&item=140567714183&pt=Motorcycles_Parts_Accessories&vxp=mtr

http://www.ebay.com/itm/SUPERTRAPP-4-STAINLESS-STEEL-END-CAP-/140605558693?hash=item20bcbe8fa5&item=140605558693&pt=Motorcycles_Parts_Accessories&vxp=mtr

It was doing the same thing when I had a baffle in there. The whole reason why its Ann open exhaust is because it back fired so hard one time it blew the baffle and the end cap out of the muffler

[skids]

with a completely gutted muffler, nothing at all on the inside of the muffler. Is there anything else that should be checked to see if the correct size is in there for my setup?

A gutted muffler can giv you fits. Sometimes there is nothing that can be done with carb adjustments to compensate. You are fighting an echo pressure wave at certain RPMS that interfere with exhausting from a cylinder. I would suggest that you get a muffler that has a descent baffle in it. THEN adjust the carbs, otherwise you might have to pull the carbs countless times for nothing!

[skids]

PS, backfiring like that is a fire risk and it will turn your affected carb black.