XS650 Suddenly Sputtering.. Won't Idle.

[dontarantini]

Hey Guys,

I've suddenly got a problem with the bike out of nowhere.. I was hitting 70, cruising strong.. suddenly the engine starts making some strange noises (metallic possibly) and then can't keep up the speed.. the engine is sputtering and running very unevenly.

I stop at a gas station, shut it off for a minute or two and decide to try to keep going. Figure this out.. it went back to normal.. it got me back home that night just fine. It even got me to work the next day, unfortunately on the way home from work it failed and it wouldn't run right again. It just won't go above 2-3k rpms or stay idling.

I just recently did rings to the engine a couple weeks ago, so I decided to check compression, both have 90 lbs (kinda low?). So I put a capful of oil down the sparkplug hole of each cylinder and tried running it again, it ran exactly the same as before.. can't be the rings. I've taken the carbs apart twice and cleaned them, put a gas-soaked rag in the air filter's place, nothing changed.

Then I tried removing a carbon brush from the alternator.. bingo! Now the bike starts up and cranks right through the 2-3k barrier to any rpm I want, and it sounds pretty decent while doing it, but it still won't idle and that isn't exactly a way of fixing the problem.

Anyone have any clue whats going on? It seems electrical but where could the problem be? Also, could a valve/valves be causing the low compression? How do I check to see if theres something wrong with the valves?

ANY help would be appreciated, can't wait to start riding again.

 

[shotgunjoe]

have you re-torqued the head yet?

 

[sgallaty]

First, whenever you hear any unusual noise you need to stop the bike or risk doing compound damage from failure. Strange metallic noises are rarely a good thing.

Your compression is very low, and the oil test only works for some ring issues. It won't work for improperly installed rings, upside down oil scrapers, stuck rings etc.

 

[dontarantini]

I have re-torqued the head once, I may need to again, but would that be causing this problem?

Yeah.. I thought about stopping immediately but was crossing a bridge in the middle of the night.
Thanks for disproving what I've done.. it is useful in a way to know that the oil test doesn't necessarily mean the rings are okay.

Anyway, so you're pretty good at showing I'm a bit of an idiot mechanic. How about proving you're not by giving me some ideas on how to fix this?

 

[XSLeo]

What year, model and any mods have you done to the bike?
Different years used different ignitions. Low voltage causes some of them to not work so well.
The alternator uses battery voltage to generate electricity. If the battery is low, unhooking one of the brushes lets more of the batteries power go to the ignition.
It could be the alternator isn't charging well enough to charge the battery fully. This will slowly draw the battery to low to run the ignition.
Leo

 

[shotgunjoe]

Head needing retorque CAN cause the issue you are having, but its not definite. The low compression is a symptom of something... thats for sure.

Check your oil. If its low, and I have feeling it is, you overheated your bike, and it started pinging. Causing exactly what you are describing.

Look here.

 

[sgallaty]

I agree with what's been said, the funny metal noise sounds like overheating which causes pinging, sticking valves, lifter rattle...

that might not have done much damage, it'll probably do SOME wear, but change your oil and check to make sure you've got the right amount.

Maybe you're burning oil - that low compression is suspicious. I would do a leak down test.

You've got the SAME low compression on both cylinders which sort of makes a lot of things unlikely..


EDIT:

You have to check compression with the throttle wide open, did you do that? 90 with throttles closed is like 120+ with them open.

That being said, I've never claimed to not be an idiot.

 

[dontarantini]

Hey Leo, sorry about that, should've included more information about the bike.
Its a 1980 Special so its electronic ignition, and I've kept it completely stock except for a Chrysler regulator.
I've changed out the Rotor and voltage regulator, the Stator is old so that might be the problem.

Thing is I've been trying fully charged batteries in the bike because I've learned the hard way how a low battery can make a bike do strange things.
Would a bad alternator be affecting the bike in this way even with a fully charged battery?

Checked the oil, its 1/4 of the way up from the bottom line, so its still inbetween the two lines and thats with cold oil.. cant see low oil having caused this unless my oil pump isn't working anymore. I will re-torque the head tomorrow though, its definitely worth a shot, I'm out of ideas at the moment.

Crap- I didn't check the compression with the throttle open! Good call man, I completely forgot about that.. I'll recheck in the morning and if they're still low I'll try a leak down test.

 

[shotgunjoe]

Too advanced timing can cause overheating as well. Maybe a bad ignition module?

Either way, sounds to me like your only having problems when the bike is hot, yeah?

If so, you are overheating somehow... letting it cool will make the symptoms go away temporarily, and overheating it again and again can cause permanent damage.

 

[dontarantini]

I don't believe the way the bike runs changes as it warms up, I was running it this morning and didn't notice anything different from cold to hot. I will still re-torque the head though soon, it needs to be done either way.

Re-did the compression test with the throttle open this time, gave me 130ish on each cylinder, so I'm assuming that means both rings and valves are sealing fine. Both spark plugs were soaked with gasoline when I took them out, so I know gas is getting there, its just not being burnt.

I also checked the alternator with the carbon brushes in, it went up to 13v easily, and with the throttle wide open and the bike unable to get passed 2.5k rpms the voltage slowly built up to 14v.

Does this mean the alternator is fine? If so.. why does the bike no longer have the 2.5k rpm limit with the carbon brush out?

Also, the ignition coil is new so that shouldn't be the problem.. Should I just invest in a Pamco Ignition and get it over with? Is this seeming more and more like an electronic timing issue?

 

[XSLeo]

On my 75 I have the Chrysler reg and Radio Shack rec. At idle I get 12.5 to 13 volts with the lights on. Anything over about 1800-2000 rpms it comes up to 14.5 almost instantly. Never goes over 14.5 at any rpms.
The book calls for 1/4 inch minimum length on the brushes. Most find anything under 3/8 inch can give weak charging. Thats the first thing to check, not much cost to replace.
You have a new rotor and reg. Did you do the Radio Shack rectifier mod as well?
The TCI is very voltage sensitive. The slow increase in voltage maybe enough to give you some trouble.
On my 81 it needs a charging rotor. So it don't charge the bettery. Keeping the battery charged kept it running well for short rides. After a few monthes it started popping a running just on one cylinder even with a fully charged battery.
I pulled off the TCI box and did a few tests to see if parts needed replacing, found none. I resoldered all the solder joints on the circuit board. It now runs great again. Still needs a rotor but it runs well.
I might suggest resoldering your circuit board. This may not fix your trouble but it might.
If you have a repair manual it explains how to test the stator. If it tests ok then the age won't matter.
There are several threads on peolple replacing some of the diodes and transisters. Look in the tech section or do a search.
Leo

 

[Kev1]

I have the same problem. It first started i was accelerating to 50 mph at about 3.2k rpms and it started to sputter and the bike sufficiently lost power. Then like
dontarantini said you cant get he rpms over the 3k range. After shutting off for a five to ten minutes the bike returns to normal. Problem also happened when i accelerated too hard...recently put in new spark plugs (they are the correct ones)

 

[XSLeo]

Check your battery voltage at idle and 2500 rpms. What are your readings? 12-13.5 at idle is ok, 14.5 volts at 2500 rpms is right. Much less at either then your charging system needs attention.
Leo