no heat on pipe on number four cyl on my dresser

[yamtom]

Hi All,

I have a got problem with my number four cyl. 79 dresser xs11, I have spark at the plugs on the outside, my spark comparator shows that wire throwing a half inch long spark in it. The original plug was wet with gas so I put a new iridium in it, no difference, pipe still stays under a hundred degrees, while the others get to two fifty in three minutes. I also freshened up the last quarter inch of plug wire on that cyl and de oxed that cyl wires, no difference, the cyl has excellent compression. So I have gas, spark, and compression, why isnt number four pipe getting hot. I dont think Ive overlooked anything, but I did not actually check the compression in the cyl, but it blows compression out when the other cyls are running just like youd think.

[rangerguy302]

Same

Hey...I have the same problem on #1.....does your bike seem to take the hell off at about 32-3700 rpm?

[yamtom]

not riding it,, dont know

I am currently just getting it going after a hiatus of two or three yrs. I dont know , its just been idling and maybe up to 2500 rpm on the work stand. So your exhaust temps are cold on number one,, checked with a laser temp gage? Its funny, but mine sounded ok,, and idled fine, until I went and actually listened to the output of the exhaust where there is a serious burble on the right side. I would check your pilot jet/circuit on that cylinder if it were me. My number four obviously has gas at the plug, and the new plug made no difference at all.

[yamtom]

pilot circuit etc

If you havnt cleaned that pilot jet circuit thoroughly lately, I would definitely suspect that first. If you dont have a dedicated gas filter for that side of fuel line, put one in.

You could also unscrew the plug cap and trim back the plug wire, which you will find is probably blackened,, cut it back a quarter inch, cut the rubber a bit further,,,,expose fresh copper,,just bend the fresh copper back,,, clean all with contact cleaner and de oxit, and you may want to check the cap for resistance, I dont know what the figure is sposed to be.

Then screw the cap back on, and install back on with a new plug and see whatcha got.

[yamtom]

anyone have any ideas?

Is it possible for the spark to be blowing out under compression, perhaps due to a flaw in the coil,, keep in mind, number one is running fine, and number four is showing excellent spark on the outside of the engine. The spark showing on the spark comparator, is literally a half inch long, as long as any I have ever checked, but still, this is under no compression. Could a cracked coil or some other mishap be affecting this thing, only under compression.? I do have another xs11 I could pull the coil off and check it out if you think this could be a hidden factor.

[CaptonZap]

Is it possible for the spark to be blowing out under compression, perhaps due to a flaw in the coil,, keep in mind, number one is running fine, and number four is showing excellent spark on the outside of the engine. The spark showing on the spark comparator, is literally a half inch long, as long as any I have ever checked, but still, this is under no compression. Could a cracked coil or some other mishap be affecting this thing, only under compression.? I do have another xs11 I could pull the coil off and check it out if you think this could be a hidden factor.

Yes indeed, a bad coil could be the culprit. A spark has to travel through a bunch of air molecules to complete the circuit, and the more molecules there are, think compressed air, the harder it is for it to get through.
However, if you are getting a half inch spark in ambient air, you have a good coil. (A quarter inch gap is about 8000 Volts, +/-)
But since you haven't checked the compression with a gauge, per your previous post, how do you know you have "good compression"? Check that.
If it is good, "BING"
" stoichiometric mixture "
and consider Motoman's maxim, that 50% of electrical problems are carburetion problems.

CZ

[DiverRay]

I would also check the floats, and settings again. I had a close problem due to a pinhole in a float. The fuel gets too high, and the pipe is cold. The gas on the plug is a clue.

[TopCatGr58]

Hi All,

I have a got problem with my number four cyl. 79 dresser xs11, I have spark at the plugs on the outside, my spark comparator shows that wire throwing a half inch long spark in it.

Hey Tom,

I'm not familiar with that particular device: spark comparator, but you say that "Wire". Did you take the cap off to check the wire, or were you using it with the plug cap on? The reason why I ask is that the plug caps are resistor type, and can develop corrosion INSIDE The cap despite the screw end and plug end looking clean. You can unscrew the insides from the plug end to get the inner spring/resistor out to check. JAT!?

A quicker easier check would be to just swap the #1 and #4 plug wire since they fire at the same time....if the same cylinder still doesn't fire/fouls with fuel, then it's probably the carb. IF the fouling moves to #1, then you've found spark problem.

Like has been said, you've got brass floats...ensured that it doesn't have pinholes and sinking???

T.C.

[rangerguy302]

Nos

I got lucky and found a pair of NOS coils, same problem, and still if I hold the plug wire away from the plug it pops about half of when it should and the pipe does heat up.

[yamtom]

yes TopCat, yes

That would help diagnose it, to swap wires. It has been a year since I checked out the float for that carb, so I will redo it if the wires prove to be good.

Re the ,,,,,,,,,comparator,,, what it is,, is something recommended off the venture list. You put it between the plug wire and a ground, and its adjustable, you just unscrew it to the length that you think the spark should jump. Your sposed to test all the plug ends, and compare them to see if there is a wire that doesnt want to fire as much or I should say as far as the other ones. I bought it on ebay for ten or so dollars, and it sure seems to work so far. On a good running cylinder/wire, with the modern electronics , it will tend to throw a half inch spark. I havnt found a comparatively short spark with it yet, but prolly will sometime soon. I think it was twelve bux shipped, I figured something like that would go for thirty bux, but not so. It looks cheap, but it sure seems to work, now I have to find a cyl with a dying or dead wire, and see if it works or shows a problem that points to a dead wire or whatever.

[yamtom]

again top cat,

Yes I did pull the plug cap off, cleaned it out with de oxit, checked the resistance at about 10k ohms which is a bit high I think. I freshened the the wire end up and de oxed that too.

The comparator, could be used by grounding it thru the spark plug itself, but I just hook it to a cyl fin.

It will be tomorrow night before I can get back to it, if any more want to weigh in, lets hear it. At least Ive got some new stuff to look for/at. Thanks

[yamtom]

news

Well I got back to it today. I swapped wires with number one to four, same problem, I also torched the plug, burned the black off of it with propane till the insulator went white, as was told by a cert mechanic. I checked the compression in number four, cold, its a hundred pounds, so thats ok. I checked it a few hundred miles ago hot and it was fine too. I pulled the carbs, pulled number three and four float bowls off, exactly the same height for both, and pulled the three and four floats off and weighed them within fifteen mins of taking them out of gas, both weighed ten grams. I heated up water, and put it in,, #4 float, no bubbles are escaping from it, after ten minutes of immersion , there is no weight gain in number four float. AArrgggh, anyone else have anything in line of ideas on this. Is it possible that bad pickup wires can cause this sort of thing? I know , some time ago it was demonstrating symptoms that some here thought could be pick up wires . I never have worked on them yet.

[TopCatGr58]

Hey again,

Okay, floats check out okay. Still can be flooding due to leaky float needles, will want/need to do a bench test with fuel to see if it leaks.

I assume they are OEM coils. 30+ years old. Have you checked the primary voltage to the coils? Has been demonstrated that when too low voltage to the coils causes weak spark so that 1 will fire, but not the other on the pair. However, you say you just swapped the wires. Albeit you used a "cleaned" plug and not an actual new plug. But problem stayed with the cylinder, and the other suspect plug wire fired properly. The weak voltage spark theory would stay with the plug wire since the stronger spark will be with the primary out going wire, the weaker spark will be in the incoming plug wire.

SO...this makes me think it's carb. Just a thought, it's the 79 carbs, it uses the upper T's for venting. They can get clogged, and can cause flooding. You should be able to test air flow with either compressed air, or carb cleaner blowing into the Vent "T" fitting.

That's about all I can think of for now! T.C.

[yamtom]

thanks tc, will check all this pronto

I am gonna be sure the pilot circuit is clear on four, will check the vents,, I think I will swap the needle and seat with cylinder three , see if the problem transfers, or do you think I should retest first with the original parts,,,,,regarding the amount of fuel in the bowls,, four seemed to be somewhat smaller amount when I drained the float bowls, but I did not measure precisely,,

Tell me how to do the bench test for fuel leaks,, if its just fill em up,, and see if fuel comes out of the air bleeds,, I can say for sure,, it does not come out the air bleeds,, like Ive seen on some carbs if they overfill,, at least as far as I have seen so far,,,

I am also gonna run it and hold it at 3500 steady for a min or two,, to see if the pipe is hot after that,, heretofore,, I have only revved it to the mains,, for about fifteen or so seconds,,I think someone said that might indicate pickup wires if the pipe then gets hot,,,

Regarding new versus used plug,, I did try a brand new iridium plug in it,,, four days ago,,,in number four,,, and it made no difference at all,,,

[BowlingSS]

I had the same problem. I replaced the idle adjustor screw and blew out the carb. It works now. So mine was the carb causing the problem.

Good luck.

Bill