backfire

[Buddy]

Hey guys, I really need some help on this one.
I have a 80 xs11 that I have owned for a couple of years. I bought it from the original owner with about 16000 miles on the odometer. He had taken very good care of the bike and it has run well until recently. It developed a problem with the pick up wires so I did that repair and it ran fine again but now it has started backfiring out the right hand exhaust and the engine misses badly. It's weird because it runs like a rocket for about ten miles then this problem begins to manifest. At first, you notice a slight miss on light throttle but it clears up as you roll on more throttle. But it progresses to the point where anything above an idle produces loud backfire from the right hand muffler. I'm guessing it is heat related.
I've checked the pick up wires and they look OK. Also, I've inspected the carbs, looked for vacuum leaks, put in new plugs cut a quarter inch off the end of the coil wires. I've drained fuel out of the float bowls looking for dirt. Nothing I have tried has solved the problem.
I would really appreciate any ideas on this one. Thanks.

[Toolmaker Tim]

Are the pipes stock or aftermarket? Since you said right hand exhaust, I am assuming it is a 4in2 set. It sounds like your right side is running out of fuel. Are you running inline filters? You might check for a pinched fuel line. That might keep the carbs fed for the ten miles you ride then not be able to catch up.Running some Seafoam might help. If you stop and sit for a few minutes with the bike off,but the fuel valves on, will you still have the problem when you restart, or will it go away for the next ten miles and do it over again. The back firing sounds like it is running out of gas on that side. You could also put the petcocks on prime and see if that helps.

[DGXSER]

Yep, sound slike your bowls are getting filled slooowwly when you first fire it up, but then it can not keep up and your starving for fuel on that side.

So, of course, check you have fuel in the tank, and that the petcock is turned on. I know your not an idiot, but I also know a person I consider to be fairly intelligent that pushed their bike for a mile before recalling the petcocks were not on And these beast are heavy!!

Next as Tim suggested, check for kinked fuel line, or could even be a plugged petcock.

[natemoen]

Along the same lines as the others. If you are not running inline fuel filters there is a small screen on the float valve in the carbs. Could be that it had just got come crap on it that is slowing the fuel flow into the carbs. Nothing would fix that problem except taking the carbs out and looking.

[Rstyduck]

I was thinking a bad coil. Starts to get hot after 10 miles and then acts up.
Park it overnight and it runs good again for 10 miles.
Just a thought.

[CatatonicBug]

Have you cleaned the carbs lately? If the pipes are stock, as is the jetting and coils, I would look toward the carbs being out of tune. If it were me, I would take the carbs out and clean them completely (checking the float needle screens) and double check the float height. Upon reassembly, be sure to sync and colortune (or tune by ear) to be sure of the correct fuel/air mixture.

You could also check the coil idea by swapping them, and see if the problem follows the coils. Remember to switch the plug wires AND the connectors at the Reg/Rect.

[Buddy]

Backfire

Thanks for the advise guys. It sound like I really need to remove the carbs and go through them. Didn't want to do that but it looks like there aren't any short cuts to doing the job right. I'm thinking it probably isn't the coil because if either coil was bad it would affect both exhaust pipes, wouldn't it? One coil fires 1 and 4, the other 2 and 3. By the way, it is a four into two exhaust and it is stock except that the PO put Harley mufflers on it, and it has run well for three years with that configuration. I have checked the petcocks for function and flow and they are working fine. But, I checked them when they were cold although I tried turning the prime and it didn't solve the problem. You can stop and wait awhile and it will improve but you have to wait quite awhile like about a half hour until it cools down a bit.
Sorry about the rambling. All ideas are welcome. Thanks so much.

[DGXSER]

One other item to check is the vent in the gas cap. If air can not get into the tank, gas can not get out.

Cleaning the carbs if you do not know they are clean is never a bad idea. But it seems less likely to be the cause of your issue here. Carbs rarely run good for ten miles then turn to complete crap. But stranger things have happened in life to be sure.

[TopCatGr58]

Hey Buddy,

You said 80 XS, but you didn't clarify which model...standard or special? Would advise editting your profile, or signature to include the style as well as the year, and any other mods that have been done to the bike!

The petcocks on the standard, along with the Octy on the special have vacuum controlled valves, and if the hoses are damaged, leaking, then the valves won't open fully, restricting fuel flow thru either, so another thing to check! The valves can also get corroded and don't always work as they should in this condition.

Also, fuel lines can go bad, break down, and small particles can flow down and clog up the small screens under the float valve needle seat.
T.C.

[Buddy]

Well... I cleaned the vent in the gas cap and made sure it is clear and took her for a ride. Now the symptoms begin to appear sooner and get worse faster, after about five miles so I'm thinking it's probably electrical. I think I'm going to replace the coils with the Mikes upgrade and also check the resistance in the pickups both cold and after warming them up. Maybe that will give me a clue. I'll post the results. Thanks everyone for your thoughts. Much appreciated.

[CaptonZap]

Check your exhaust valve clearances. CZ

[WMarshy]

Maybe when you cleaned the vent on the cap it clogged it up more..possible i guess... To make sure its not the vent cap you should run the bike untill it starts acting up then open the tank cap to see if it straightens up. If you have two keys then you can just go for a short ride with the cap closed and leave one key in the cap, once it starts acting up just pop that lid open and see if it helps. Other wise just leave it open and go for a ride. If it acts up with it open then its time to look else where. GL

[TopCatGr58]

Another thought!?

When it starts acting up, shut it down and quickly check the ballast resistor resistance with an ohmeter! It heats up considerably when it's working, and has been known to crack. Most of the time it completely separates and totally cuts off power to the coils, so the bike just stops running. But I could see where it could partially crack enough to cause increased resistance so it would allow even LESS voltage than the ~9 that it normally sends to the coils, causing weaker sparking....and even possibly poor sparking on cylinders that would otherwise be paired for fuel problems....ie 1-2, or 3-4. However depending on which cylinder you have the main coil/plug wire going to....with the wasted spark system, it flows thru the "main' coil wire, to plug, thru engine, back thru the subordinate plug, and back to the coil. And with low voltage for the ig. coil, it can have lower Kvolt power, so that it would have enough to fire 1 plug, but not the subordinate one, and so if the "main" plug wire for each ig coil is on both 1-2 or 3-4, then the subordinate plugs could not be firing....but being on the same side...3-4 or 1-2, would lead most of us to think it's a carb issue, not an electrical one!? JAT!

T.C.

[Buddy]

Well.... Finally got this one sorted out. I put Mike's coils in thereby eliminating the ballast resistor but the problem didn't got away. I did lots of other stuff but to no avail. After much thought I decided it was most likely electrical because the bike ran so well for a short period of time. About the only things left were the pick up coils so I found a pair on ebay. The wiring was a mess and had to be rebuilt but they came complete with the pig tail. When I was installing them and disconnected the plug on the old set that connects the pig tail to the wiring harness (the one behind the fuse block) I found the connectors to be corroded with a blue/green substance. Anyway, I cleaned up the female side of the plug and installed the new set and the bike runs fine now. I don't know for sure but I'll bet the problem all along was the corrosion in the plug. I think the old pick up coils were OK. One of these days I'm going to put them back in just to find out for sure. Thanks again for everybody's help.