spark / no spark

[tab1324]

Well, I got the choke holes in the carbs fixed but now it seems that in addition to that problem, there's another..... I got the bike running (cold) and it was still running rough so I pulled the #1 plug wire off while it was running.... No change. So either the #1 is still not getting gas, or spark. How can I accurately diagnose this? I'm tempted, although I don't like the idea, to pull the carbs and completely rebuild them again (4th time). I just don't get it.

I keep thinking it could be the coils but it's #1 and #3 that have always been the problem. Does anyone know the resistance the plug wires and boots should measure. I'm going to get a reading and compare to what they should be. Maybe it's just weak wires, I don't know.

HELP

Tom B.

[thumperjsa]

You should be able to check for spark by pulling the plug and leaving it connected to wire. Let it hang near the clinder head and do it in a darker area. You should see a blue spark when you start the bike. If not, suspect you have a bad wire.

By the way, I can't remeber, did you check if your intake boots are leaking. You can have a large enough leak that it is sucking in air by the intake boot into the cylinder and not pulling through the carb. No fuel, no heat. I had this problem with an outside cylinder being cold. Replaced the intakes and then that resolved the problem. I tried repairing the intake but it was still leaking right by the head.

[TopCatGr58]

Hey there Tom,

Well, first you can swap #1 with #4 and see if #1's pipe gets warm, same for #3 with #2, and if they get warm, then you know the carbs are working, but the spark isn't getting there.

Now, since it's #1 and #3, it's not the pickup coils and most likely not the ignition coils themselves, cause you are loosing spark from each coil, but could be part of the coils, but you figured that already!

Uscrew the plug caps and check for resistance and continuity! Plug caps have around 5Kohms, usually! The manual shows testing thru both plug caps to measure secondary resistance, but the value they give is WITHOUT the caps, you will need to add 10Kohms to the Manual's 15Kohms + 10% values!

Also, inspect where the wires connect to the caps, corrosion can occur there easily. If found, trim back a little of the wire to expose good copper! Retest your resistance values. If good, then put back together and go! IF still bad(out of spec vs. Infinite resistance or none!), possibly could be bad wire up to coil, only way to find out is to follow the Replace Coil Wire tip here:
Coil wire Repair/replace tip

You can get replacement caps from several sources! Good Luck!
T.C.

[tab1324]

a bit embarrassing

Tonight I went out to see if the bike was goign to start up and run and it did - but very rough. So I thought I should stand back and look at things for a moment - maybe I was missing something here.... Turns out that the fuel line to the #1 & 2 carbs was kinked - must have gotten that way when I set the tank down. I unkinked it, and bike started right up and ran. I felt the pipes after a moment and believe it or not, #1 and #3 weren't cold anymore. Hoora! They still don't seem as hot as the others but I solved the problem I was having.

Thanks for the tips TopCat! I think I'll investigate the wires just to be sure. What exactly are the plug caps and are they easily removed? Sorry if that's a stupid question..

Tom B.

[TopCatGr58]

Tom,

The Spark Plug caps are the hard plastic ends that are on the plug wires, they contain a resistor, and clamping wire design which holds onto the unscrewed covers of the plugs.

When you get new spark plugs, they usually have those nice rounded tips on top for auto plug caps, but you can take a plier and unscrew the tip, leaves a screw shaft that fits nice and snugly inside the MC Plug cap, inside the "little" hole just right for that screw shaft!!! You should feel/hear a ratchet sound as you slide the cap down onto the plug.

Congrats on finding the possible source for the miss, although it's odd, 'cause 1 supply should feed carbs #1 and 2 and the other #3 and 4, so again , having problems with #1 and 3 don't completely add up, but what the hey, enjoy!
T.C.