More problems- excessive backfiring/lumpy running

[Lucien Harpress]

(Sigh) If it ain't one thing, it's another. After "solving" my electrical problem (it solved itself), one more thing has to crop up.

The thing is, just the last day or two, my motor has started to run like crap. It starts off okay, but as you ride it it starts running rougher- popping just a little bit.

When you roll off the throttle, it starts backfiring out the exhaust pipes rather vigrously. Now, it's done this before, and from what I read this is somewhat normal. These, however, have graduated from what I would call "popping" into full-blown backfires.

If I ride it long enough, it starts backfiring even during normal operation, quite loud, and quite regularly. It only goes away if I crack open the throttle a bit, but comes right back as soon as I roll off it.

It also doesn't like low RPM operation at all- bogs, stumbles, threatens to die, etc.

Now, I'll admit, I have yet to do a "proper" air-fuel mixture adjustment. I don't own a colortune kit, and my attempt at tuning by ear failed miserably. However, I had it running relatively smoothly a week or two ago, before it started acting up with the electrical, and now this. I've been told to "read the plugs", but unfortunately I don't know what I'm looking for. So I took the liberty of taking a photo.



All four of my plugs pretty much look like this. I started all four mixture screws two turns out, and after adjusting them further, all are at about 2 3/4 turns out.

Who knows? I might have this bike fixed by Christmas.

[TopCatGr58]

Hey Lucien,

That plug looks like it has decent color, with just a thin layer of black around the insulator base, dry, not wet!

A refresher of what you've done to your bike/carbs would be helpful in our attempts to suggest avenues of attack. With my CRS, I don't know/ remember if you've done a carb teardown and cleaning??

Popping/backfiring can be LEAN, can also be ignition??

Your standard has vacuum controlled petcocks. They can stick, or the vac. hoses going to them can crack, leak, etc., restricting fuel flow.

Poor throttle response in low rpms points towards pilot/idle circuit. Stumbling and threatening to die sounds like lean. Bogging is usually reserved for overly rich.

SO....run some seafoam in the gastank, try the PRIME position of the petcocks. Try turning the pilot screws IN CW 1/2 turn each and see how it responds, if better then turn another 1/2 turn in till starts responding poorly again, then back out the last 1/2 turn.

T.C.

[randy]

Lucien,

You don't need a colortune to tune the mixture (here come the shots across the bow from the die-hard colortune fans). You will need a synch gauge setup. I prefer the mercury sticks ( here come the shots across the bow from the needle gauge and DIY fans). The mercury stick just plain WORK ALL THE TIME without any fiddling.

An external tach also helps, they are much more sensitive than the one on the bike, so you can see small changes as you adjust the mixture and the synch. I use a Sun tach.

You haven't told us what you've done to your setup. I'd guess you've got an aftermarket exhaust. Do you have leaks at the head pipe connections? Have you changed any jetting? Your plugs look a bit lean which would explain the backfiring, but leaks at the head and /or holes in the pipes can cause that too.

[DGXSER]

Hmmm.....I am wondering if the two are linked. IF he had a bad connection in his charging system, then perhaps he had low voltage to run the bike as well.

Now my electrical skills are suspect so just tell me if I am way off target here. MY suspician is that he had low voltage and therefor low spark form the coils so he was not burning fuel completely. This would make it bog down, although it should show worse at more throttle. Anyway, the low charging would drain the battery as the bike would pull more juice than it was delivering.

JAT

[Lucien Harpress]

Okay, answering some questions:

-Carbs. I've been through the carbs at least four times, cleaning every inch of them each time. I started out with low RPM issues, so those were addressed first.

-Petcocks. These are hit and miss. My right petcock seems to work fine, but checking the left one today, it seems that one is always open, no matter what setting it's on (prime, on, or reserve). I just put the bike away, and I noticed that I had gas coming out of the airbox. I HAD left both petcocks on PRIME, though, for at least an hour, so this might explain this.

-Spark plugs. I'm still using the same plugs that came with the bike when I bought it. I have no clue how old they are, or what kind of shape they're in.

[XJOK2PLAY]

Hmmm.....I am wondering if the two are linked. IF he had a bad connection in his charging system, then perhaps he had low voltage to run the bike as well.

Now my electrical skills are suspect so just tell me if I am way off target here. MY suspician is that he had low voltage and therefor low spark form the coils so he was not burning fuel completely. This would make it bog down, although it should show worse at more throttle. Anyway, the low charging would drain the battery as the bike would pull more juice than it was delivering.

JAT

Don,
I was thinking the same thing. They don't have to be related, but it's odd all this is going on at the same time.

I do know you have to have over 12 volts for the tci to work...
If that's not working properly, the coils aren't going to work properly.

And most time (not always, but most) loud backfiring is either caused by bad coils or intermittent voltage to the coils, or timing issues, or exhaust valves...

Popping back on decel a lot of times is carb... mixture adjustment.

But backfiring's a different thing...

I'm sure wishing there was an XSive that lived close to Lucien that could give him a hand diagnosing this... Anybody?

[XJOK2PLAY]

Quote: "I just put the bike away, and I noticed that I had gas coming out of the airbox."


If that's the case, you'd better check for gas in the oil right away... it can go that way as well... and ruin your bearings...

Take the filler cap off, smell... if it smells like gas.... better drain the oil, then fix the petcocks and the float valves...

You might also can tell by looking at the sight glass on the right side... bike on the center stand... check the level.

[petejw]

Those spark plugs look spot on,
when u did your carbs did u set float heights all equally?
if your leaking fuel out of the airbox then your needle and seat
are leaking, this will make the bike run like crap.
And as some of the others stated, the electrical problem could also
be another cause, unfortunately electrical problems dont fix them selves
up, they might go away 4 a little time, but they always come back to haunt you, check your connections behind the fuse box.

[DGXSER]

Hey Lucien,

The leaking carb issue is a familiar one to me, especially after you just cleaned the carbs. Mine never leaked a drop till I tore into the carbs and rebuilt them completely. Then I had all kinds of issues with the bloody things. I also put on new fuel lines as I dumped the Octy on my special. Well, the fuel lines seem to have been the issue. I used auto fuel line and that stuff flaked little pieces off everytime I hooked up the fuel lines and it got into my float valve seats and caused me al kinds of havoc. I replaced it with B&S lawn mower fuel line from Home Depot and do not even use any clamps on the lines, never leaked a drop since.

Yep, best to check if your oil level is on the rise or if the oil is really flammable (stick a stick into the oil and pull it out and try to light the stick if it flames up easy, there is gas in the oil.

[foreda]

Gas in the airbox

Even though you left the petcocks on "Prime", you should never get gas in the airbox. You have a float valve or valves that are leaking. Make sure the floats are not binding, this will cause havoc as well. Hate to say it but looks like you will need to pull the carbs off again. After you get them off, set them up where they are fairly level and rig up some hose to your tank and test. If the valve or valves are leaking, you will be able to tell which one or ones are leaking. Don't get discouraged, I don't think there is anyone on this site that has not had to deal with a carb issue. Good luck!!

[Lucien Harpress]

Okay, I've found one or two things that at most are causing my problems, and at least are something to fix.

First off, I took a look at my battery. Somehow (maybe during the one or two times I accidentally dumped it), one or two of the cells don't have nearly enough acid in them. I can refill these tomorrow.

Second, I pulled the two inner plugs. While the two outer ones looked like the one in the photo (mixture slightly lean), the inner to were OBVIOUSLY set too rich. I've re-adjusted the screws as needed (out for the lean two, in for the rich two), and HOPEFULLY will be able to get a ride or two in so I can re-check them.

[Larrym]

Suck-Squeeze-Bang-Blow

Simple four stroke engine cycle and ignition sequence is : Suck-Squeeze-Bang-Blow. Diagnosing carb mixture and timing/ignition issues is a lot simpler when there is one cylinder, one coil, and one spark plug. But on the XS there are four cylinders, four carbs, and wait for it.....TWO coils.

It took a while for my mind to get around the fact that these bikes have a "wasted spark" method where every time the coil fires to one of the plugs, it also fires to that cylinder's "running mate". What that means is that if there is ANY unburned fuel in the running mate's combustion chamber at the time the "wasted spark" occurs, it will ignite. (Backfiring versus popping is only a matter of how much fuel is present in the cylinder at the time...)

Soooo......not only do you have to ensure that the carb/fuel system/ignition is just right for the individual cylinder but also you have to look at/verify that it's running partner (the one that shares the same coil....) is problem free.

Rich mixture, up to and including globs of fuel from a leaky/maladjusted float or in my case from an iffy plug wire can result in very rough running and backfiring from the "wasted spark". In my case this made the engine run so poorly that the engine seemed to almost "stall" and it felt like the motor was being Kicked backwards.

Looks like you're gonna get more up close and personal face-time with the working components of a classic 30 year old super bike.

You DAWG, you!!

[Lucien Harpress]

The more I think about it, the more I'm wondering if this isn't a fuel/air problem, but a spark problem.

No matter what I've done (clean carbs, mixture screws), I've had the same problems- under 3K, the engine runs like crap. It's not the carbs- I've been though them four times (like I said), and the first time I opened them up they looked surprisingly clean anyway.

Seeing as how the charging system doesn't really "kick in" until 3K RPM anyway, I'm just wondering if UNDER that I'm not getting enough juice to have any spark worth a damn. Bad coils have been mentioned before, and as I said before, I'm still using the spark plugs that came with the bike when I bought it.

I think first off I'm going to get some new spark plugs, and if that doesn't solve the problem, I'm tempted to just bring it in to a repair shop to see if THEY can figure out what the hell is wrong.

[Ivan]

If you haven't changed the plugs, and you don't know how old they are, change them. They are cheap. If they don't cure it, you have a spare set.

[TopCatGr58]

Hey Lucien,

DON'T take it to a shop! The price you would spend for them to run diagnostics and such, you could easily purchase a set of new ignition coils, wires, plug caps from MikesXS or similar.

Have you taken the plug caps OFF the ends of the wires, and checked/looked for corrosion at the wire ends. Then measure with your OHMETER, should only be about 5k ohms, if much higher, then the built in resistor may also be corroded. You can take the cap apart...look inside where the plug goes, a flat head screwdriver will unscrew that part, and the resistor will come out, you can check it, clean the ends/contacts. IF you still get much higher than 5k ohms on the resistor, then it's gone bad, and you will want to get a new cap. If corrosion is found on the plug wire, snip 1/4" of the end to expose clean copper wire. THEN also test the coils with your Ohmeter measuring thru the 2 plug wires for the same coil, ie., 1-4 or 2-3, and it should be about 15K ohms +/- 10%....if much beyond those values, then they may also be dying!?

Several members have posted about their carb tuning woes that were fixed once they got NEW coils/wires/caps! YMMV!

Also, try to find a fellow Xsive in your area that can help you with the repairs, tuning, etc.!! IF you have to travel 50miles or so, small price to pay for some experienced assistance!

T.C.