#4 Cylinder Dead Until Warm, Then O.K.

[Dux]

Let me start by saying "Thank You" to everyone who has shared information here... XS11.com has been an invaluable resource for me. I found the site in 2006 when I first borrowed this bike (80 LG) from my brother (original owner), and now that I have the bike back again I have found solutions here to almost all of the issues I have met as I get it back on the road. Thank you all!

The latest, most confounding issue (aside from some intermittent electrical gremlins) is that my #4 cylinder is cold at startup. It will not fire consistently no matter how long I let the bike warm up on the side (or center) stand. However, by the time I make it 1/2 mile down the road (at half to WOT), it comes alive and the bike runs normally. After warming up, it idles normally as well.

I rebuilt the carbs this winter.
I adjusted the idle mixture for max vaccuum using a homemade manometer, and balanced the carbs using a similar device.
I checked the actual fuel level in the #4 bowl using the fluid-tube method and it is identical with #1.
I have swapped plugs with #1 and the problem stays at #4 (plug looks normal, if not a little lean).
I have inspected the idle mixture adjustment screw and it is not broken.
When removed, I get a strong spark between the plug wire(cap) and ground.
Compression (cold) is the same as #1.
The position of the fuel petcock, run or prime, has no effect.

Ideas?

Thanks in advance.
Dux

1980 XS1100LG, Antique Supertrapp 3.5"~ Muffler w 4 discs on 4>1 headers. K&N Air Filter

[IanDMacDonald]

Strong spark even at start-up? If you have consistent spark at start-up as well as when the bike warms, I'd suspect the carbs. However, I'd still check to see if your pickup coil wires are okay? Would a burnt valve cause similar issues?

[natemoen]

Do you still have the original coils or have they been replaced? You say you swapped plugs but did you swap the actual wires connected to the plug? (Wasted spark system, just unplug from the #1plug and put it on #4 plug and vice versa)

[BA80]

JAT......before you go tearing things apart, swap plugs with another cylinder and see if the miss follows that #4 plug or stays there.

Also check the resistor caps and also be sure they are making good wire contact. The wires may need to be trimmed.

[TopCatGr58]

Hey Dux,

Okay, COLD startup problem. I'm going to assume that you are using the Fuel Enrichener for starting. You say you cleaned/rebuilt the carbs and so I want to assume that you have ensured that the PILOT circuit is clear and open? Did you find the tip about the little JET that's down in the float bowl where that brass tube from the carb body fits down into???? That jet can get clogged and will prevent any fuel flow thru the Enrichener circuit! So....the #4 cylinder runs cold/without fuel until you actually ride/run the bike and engine well above idle which then gets the MAINs involved and the cylinder finally gets fuel to burn.

So....my vote is either clogged float bowl jet, or still clogged pilot jet circuit.

T.C.

[motoman]

'Rebuilt the carbs' is a fairly broad term here...............you got a plugged idle circuit........do it again....throughly.

[motoman]

'Rebuilt the carbs' is a fairly broad term here...............you got a plugged idle circuit........do it again....throughly.

BTW, seeing your new here, no offense intended.

[BA80]

Hey Dux,

Okay, COLD startup problem. I'm going to assume that you are using the Fuel Enrichener for starting. You say you cleaned/rebuilt the carbs and so I want to assume that you have ensured that the PILOT circuit is clear and open? Did you find the tip about the little JET that's down in the float bowl where that brass tube from the carb body fits down into???? That jet can get clogged and will prevent any fuel flow thru the Enrichener circuit! So....the #4 cylinder runs cold/without fuel until you actually ride/run the bike and engine well above idle which then gets the MAINs involved and the cylinder finally gets fuel to burn.

So....my vote is either clogged float bowl jet, or still clogged pilot jet circuit.

T.C.

'Rebuilt the carbs' is a fairly broad term here...............you got a plugged idle circuit........do it again....throughly.

'Rebuilt the carbs' is a fairly broad term here...............you got a plugged idle circuit........do it again....throughly.

BTW, seeing your new here, no offense intended.

Just curious why y'all would think that a carb problem would go away after the engine warms up. From my experience the only thing heat will affect is something electrical.

[motoman]

Just curious why y'all would think that a carb problem would go away after the engine warms up. From my experience the only thing heat will affect is something electrical.

Very probable BA80, since its been sitting for an extended time, and not a very dry climate to boot. Likely combination of both elect./fueling. An ANOLOG volt meter and some voltage checks, AND actual unplugging any and all connectors, cleaning and stuffing some dielectic grease in plug-ins BEFORE re-connecting would be a good next step, noting any seen differences of prim./secondary voltages afterwards.
At one time, my Venturer had an internally broken pick-up coil wire(white one) that occassionally caused the same scenario when cold and getting an anemic spark. Heat from resistance would melt a couple strands together allowing it to run fine, til that finially gave out and it would die along with letting out a 12ga. blast from the stock exhaust......wait ten seconds and start up and run fine.....till next time, whenever those couple strands would melt apart again.

[BA80]

Here's a good story for y'all.

When I was helping RockinD do a frame off rebuild on his SG as we were re assembling we checked the pickup coils and found that he had a couple wires that had been repaired and, of course, were intermittent in their ohm readings. I had a good set (I thought) from an SH parts engine I had laying around and they ohmed out with slightly less resistance than most I had seen but were both the same so I attributed that to accuracy of my cheap ass ohm meter.

We put it all together and it started, tuned, and ran great................in September...... In November it wouldn't start unless you cranked and cranked on it and then it would fire on only 2 cylinders until it warmed up then the other 2 would kick in and it would be fine for the rest of the day.

The next time I checked when it wouldn't start and it was only getting intermittent fire (one then none, then 2, then none) to the plugs. We swapped TCIs, coils, even wiring harnesses with no improvement. Then my brain kicked in. When it was warm out it would start right up with no problem so, out came the space heater. TCI no help, coils no help, but when I put it on that ignition cover on the left side and let it warm up it started RIGHT UP!!!!!!

Changed out the pick ups with a set that OHMED OUT RIGHT and it hasn't had a problem since.

I have no morals so there is no moral to this story. Just some factual experience.

[TopCatGr58]

Just curious why y'all would think that a carb problem would go away after the engine warms up. From my experience the only thing heat will affect is something electrical.

Hey Greg,

I had a set of carbs that had a bunged up pilot jet that back in 1999 I couldn't get out, and so that cylinder was a bit weak. The bike would start up, pop and such, but once it warmed up, I could ride the bike just fine, throttle response was okay, plenty of power to redline, and would idle just fine. Mine is the 81SH and I have yet to have to do the pickup coil fix, and my OEM 3 ohm coils were working just fine.

His problem is with only 1 cylinder, not a PAIR, and that's a big part of why I'm not suspecting the PU coil wires because when they fail they drop out 2 cylinders. Now, a weak coil can cause 1 cylinder loss, as well as corrosion in the plug cap, or weak/low voltage can also cause the 1 cylinder drop.

But usually when 1 cylinder is faulty, it's usually carbs or mechanical related.

Hopefully he'll test it all, and find the problem.

T.C.

[BA80]

I understand what your saying TC. It seems that the enricher would over ride the pilots on startup though. But it could be a problem in both circuits, I've seen stranger things.

I wasn't pointing directly at the pickups with my story, just the effect heat can have on electrical components.

[Dux]

Thanks for all the great feedback and suggestions...

The spark on #4 (even when the engine is cold) is strong enough to arc 1/4" from the plug cap to ground when removed from the spark plug (strong enough to make me wish like the dickens I hadn't tried to remove it without a better insulated tool )

Original Coils; I haven't tried swapping the wire and cap with #1, but I will

After reading all about "Triple Cleaning", and having been my second attempt, I took great care when cleaning / rebuilding the carbs. They did in fact have clogged pilot jets before (which was the reason for the rebuild), but as it idles nicely (and runs well with the throttle barely cracked open and enrichment lever off) after going around the block, I believe I got them clean. I didn't do a very close inspection of the slider boots for pinholes, etc. Could a small pinhole make difference cold, but not warm?

I saw the tip about the enrichment circuit in the bowl and did clean that passage. It's possible I missed one and I will re-clean that one.

Using the enrichment lever (in any position) has no affect on #4.

I did go through all the electrical connections with deoxit chasing an electrical problem but did not think to add dielectric... I suppose that will go on the list. I'm still having an issue with an occasional voltage drop (lights run great, voltage at charging levels (don't remember exact voltage) but then, usually at very low RPM combined with a gear change or rear brake activation, the charging drops off and the head light goes very dim. this usually resolves with a few high revs combined with a gear change or rear brake activation... i think it may be a bad ground somewhere... Very odd though, it is either good or bad (on/off) and nothing in between. This symptom does not happen at the same time as the #4 cyl cold runability issue (or any change in engine performance); when it is happening, i'm still getting magnetic attraction to the generator cover and the tach functions normally.

[IanDMacDonald]

I'd say that voltage drop is definitely something to be concerned with, especially if you do not have source voltage at the coils.

[motoman]

Thanks for all the great feedback and suggestions...

The spark on #4 (even when the engine is cold) is strong enough to arc 1/4" from the plug cap to ground when removed from the spark plug (strong enough to make me wish like the dickens I hadn't tried to remove it without a better insulated tool )

Original Coils; I haven't tried swapping the wire and cap with #1, but I will

After reading all about "Triple Cleaning", and having been my second attempt, I took great care when cleaning / rebuilding the carbs. They did in fact have clogged pilot jets before (which was the reason for the rebuild), but as it idles nicely (and runs well with the throttle barely cracked open and enrichment lever off) after going around the block, I believe I got them clean. I didn't do a very close inspection of the slider boots for pinholes, etc. Could a small pinhole make difference cold, but not warm?

I saw the tip about the enrichment circuit in the bowl and did clean that passage. It's possible I missed one and I will re-clean that one.

Using the enrichment lever (in any position) has no affect on #4.

I did go through all the electrical connections with deoxit chasing an electrical problem but did not think to add dielectric... I suppose that will go on the list. I'm still having an issue with an occasional voltage drop (lights run great, voltage at charging levels (don't remember exact voltage) but then, usually at very low RPM combined with a gear change or rear brake activation, the charging drops off and the head light goes very dim. this usually resolves with a few high revs combined with a gear change or rear brake activation... i think it may be a bad ground somewhere... Very odd though, it is either good or bad (on/off) and nothing in between. This symptom does not happen at the same time as the #4 cyl cold runability issue (or any change in engine performance); when it is happening, i'm still getting magnetic attraction to the generator cover and the tach functions normally.

Sounds like you got SOME of the suggestions done! I'll add a few more to the more, and more sounding electrical issue. If you have not ACTUALLY checked voltages TO the coils(key on, INPUT volts at each coil and its assocciated plug-in), need to do that.
With more feedback from you now, I suspect a loss of the all important smoke is eluding you(what BA80 stated). The first two most notorious places are the ignition switch AND.....wait for it.......kill switch, AND if the stock coils don't ohm out correctly, that just adds another issue, which is secondary igition.
With you adding the fact of the seriously dimming headlight, I seriously doubt your coils are getting enough voltage(primary ignition).

At this point, your carbs are having electrical issues...........fix that....FIRST!

BTW....just recently BTDT with ALL three of the above mentioned.........and ALL three, including the stock coils themselves were bogarting the all important smoke.