electrical problem

[remi]

Hey guys, I need some help. Once my bike gets warmed up a bit I lose #1 cylinder. Determined it was an electrical problem by switching #1 and 4 wires. Problem moved. put a new wire to plug end on and the problem continues. checked the wires to the ignition coil and they seem fine. The bike is an 81 sh with almos 19000 miles on it.

What else can I check? Could the coil be dropping only 1 cylinder?

Thanks for any help or suggestions in advance.

Bill

[natemoen]

What else can I check? Could the coil be dropping only 1 cylinder?

Absolutely. what is your ohm reading across the plug wires?

[remi]

Not sure, I have a voltmeter, but am not quite sure how to check. Electricity is my weak area.

[TopCatGr58]

Hey there Remi,

There is a new tech tip about electrical diagnostics you will want to check out.

As for your gauge, if it's ONLY a voltmeter, then you'll want to get a multimeter, can get one from Harbor Freight for under $10.00. IF your gauge has a few switches, then you may be able to switch it to OHMS....may look like the greek symbol for Omega....an opening at the bottom of the "O".

Anyways, you said you replaced the wire...which is a trick with the OEM coils. The more likely culprit can be the plug CAP...they are usually resistor and they can corrode and go bad. You can take the cap apart, but test it with the OHMMETER by putting the test leads on both ends of the cap once it's removed from the wire. Should read 5-8 k ohms. If much higher, then you will need to replace the cap. The cap can be taken apart to inspect the internal resistor and recheck it's ohm reading once you clean off the ends to remove any corrosion. Also check for corrosion on the screw end of the cap.

Just reread your statement....new wire to plug...did you mean the low power side where it plugs into the harness...that plug?? Use the Ohmmeter and check the resistance thru the low 12 wires for the coil, should see ~2.5 -3.0 ohms...if a lot higher or lower, then the coil could be damaged. Also, use the VOLTmeter and check how many volts you are getting from the red or red/white wire at the low power plug...should be 12 volts, but again due to corrosion, can drop...if gets several volts low....can cause the coil to generate less spark power...it has to travel thru 1 plug wire, thru plug, engine, then 2nd plug, and back to coil. If the spark power drops due to low input voltage, it can loose the power needed to go thru both plugs...so you can loose 1 plug!

T.C.

[remi]

Thanks T.C. I meant the plug cap is what I replaced. And I have a multimeter, not a voltmeter, was tired and could not remember the proper names for either. I will check all the spots you mentioned this afternoon when I get home from work and post the findings. Also, I failed to mention that When I connect the wire to a grounded plug it does produce spark. But when hooked to the plug in the cylinder does not change how it runs.

Bill

[crazy steve]

For help with your multimeter, look here:

http://www.xs11.com/forum/showthread.php?t=35338

http://www.xs11.com/forum/showthread.php?t=35339

[CaptonZap]

Here's a little "one size fit's all" check for coil output. This works for MOST high tension ignition systems. Magnetos, Kettering, etc.
Rig some method to place the end of the high tension wire 1/4 of an inch from the engine metal. Try cranking the engine. If the spark jumps, the coil is good. If it doesn't, shorten the gap. If it doesn't jump 3/16 in, consider it, or it's power supply, defective. This test assumes that the input voltage to the coil is high enough.
Scientific explanation. Electrons will flow in a vacuum at a low voltage potential. As the number of gas atoms in the atmosphere increases, the electrons have a harder time finding a way from one terminal to the other, so it takes a higher voltage to make them jump. Atmospheric pressure is about 15 psi. Cylinder pressure is 140 +/-, meaning there are a lot more gas atoms in a cubic inch in the cylinder than there are out in the open. Which means that it is harder for the electrons to jump the spark plug gap, the higher the cylinder pressure.
Generally, a coil that will produce a 1/4 in spark in normal atmosphere will be strong enough to produce a spark in a 12:1 compression situation.
That size gap will also relieve the voltage buildup in the secondary windings before there is internal arcing between the individual wire coils, leading to coil burnout. Newer coils, with better wire insulation, and more windings, can produce longer sparks without internal harm. But we're dealing with 30 year old technology.
Some old time magnetos had a spark gap built into the system, so that if a spark plug wire came off in operation, it would not harm the mag coils.
But that was in the days before planned obsolescence.
If you are getting a spark at the wire, but none in the cylinder, check the plug. Electrons flow on the path of least resistence. A layer of soot on the center electrode provides a convienient path to ground, no spark required.
A cracked insulator, with some moisture, will also cause a missfire. Which is why sometimes the missfire will go away after the engine warms up, and the moisture evaporates. CZ

[GLoweVA]

Nice write up CZ, I like that explaination.

His problem is the spark is lost after the warm up.
I suspect the wire could be losing it's insulation resistance and as it gets hot, the spark jumps thru the insulation to the engine vice thru the plug.

I have a similar issue with my G. It doesn't like to get soaking wet.
After washing, or a severe downpour, I drop a few cylinders until the thing heats up a lot and drys everything out above the valve cover.

Silly me though, I've got a perfectly good set of coils sitting on my project bike right next to my G and I didn't even think to swap them out a few weeks ago after I replaced my vavle cover gasket. Maybe next time I take the fairing and tank off, I'll remember.

[remi]

Well, I did'nt get to work on her today. Spent the last 3 hours sitting on my mower. But just printed about 20 pages off from here. I will update when I get some more trouble shooting done. Thanks for all the help so far guy's.

Bill

[remi]

update

I started doing tests and the first thing I found is that my battery was'nt holding a good charge. So, I went and bought a new battery and while waiting for it to charge I went through and cleaned all the wire connectors. Once I installed the battery, did all the ignition tests, and everything checked out. Decided while I was rearing everything apart I might as well go ahead and clean the carbs. Took em out cleaned everything up, Did a bench sinc. And put em back on. Seems to be running pretty good now.

Friday I'll be getting a sinc guage and taking her for a nice long ride to make sure everything is good to go.

Thanks for all the help, You guys are great!

Bill

[remi]

So, I decided to take her for a ride today to see how she would do, and the problem is still there. after she gets warmed up she runs like crap at low rpm's. If i get the rpms up to 35-4000 she runs great. but below that she just stumbles. when I came to a stop in the driveway she stalled on me.

So I pulled the plug wire hooked another plug to it and ground it. it had great spark. Then pulled the plug out of the engine and it was wet. Also it looks like a brand new plug, no carbon and not white.

Now I'm confused. If I have spark and fuel it should fire the cylinder. I don't know where to go from here. Help please.

Bill

[TopCatGr58]

Hey again,

Okay, recap, new battery fully charged, cleaned electrical connections, hi tension coils check out ohm within specs. You say you've cleaned the carbs, but don't know if you used KITS, if you've replaced the pilot jets with any others?

As an engine gets warm, it doesn't need as much fuel to run. The rpm range you're experiencing the problems are in the Pilot jet range. Also, a sticking float valve can cause flooding in just 1 carb that can kill the balance, flood that cylinder so it has the WRONG air/fuel ratio, and fuel foul the plug. I had a re-broken float post unbeknownst to me, causing my #2 carb to intermittently flood, I had NO low throttle response, it was either Full WOT or not! Made running the twisties during a rally a real challenge!

As has been posted in recent other threads, old style black rubber fuel lines and degrade, break apart internally and put particles into the carbs that can interfere with the float needle valve and such!

Aside from bench synching, you'll want to do bench leak testing before mounting on the bike. Also float level...and that it isn't getting hung up or sticking from too wide a bowl gasket, or float pin corrosion,etc.!

T.C.

[jimbyjimb]

Remi,

After you're able to determine for sure it's a coil issue I have one I can give you.

I replaced my stock coils with aftermarket units so I have two working stock coils laying on my bench. the wires are a bit ugly but I assure you they are in perfect working condition, or were when I removed them.

Hopefully you're able to fix the problem, if not, please breathe out.

[CaptonZap]

No good kind (NGK) plugs are funny things. They can look new, but if they have been fouled, and blown clean, they can have a layer of hydrocarbons imbedded into the porcelain insulator, and that provides a surface conduction route to ground. i.e. No spark across the gap.
Since you said that switching wires on 1/4 moved the problem, try switching plugs and see what happens.
Are the two plugs gapped correctly? Both the same?
You might try a NEW plug in the offending hole. Not a looks like it's new, but one straight out of the box.
There could also be a problem in the high tension lead. A break in the insulation somewhere close to the metal engine. Wait till it gets dark out, and get a spray bottle of Club soda water. Start it up and spray the plug wires and look for blue sparking from the wire to ground.
Keep after it, it can be fixed. CZ

[remi]

Thanks guys. After I posted yesterday, I went out started it and it ran fine. went down the block and back to warm it up good and the problem came back. Started messing around with the plug wires and noticed that If I held the #1 plug cap and lightly touched metal I would get a light shock. So looks like I need to get to the part store and grab 4 new caps. I have also put in new plugs and fuel lines since the problem began. all are gapped the same. I will check float levels and re-clean the jets as well before next test ride. I have not changed any of the jets, just pulled the top and bottom covers off the carbs, removed, cleeaned jets and replaced. Will post more progress later.