one exhaust pipe cooler/coil problem?

kz 650 '78 with dyna coils/v&h 4X1 exhaust, K&n air filters.
the second pipe from the left sometimes feels cooler and sometimes cool all the way compared with the other three. I checked the dyna coils and found that the spark plug wire that goes to the second spark plug in the dyna coil had a bit of rust. I cleaned it up put it all back and the bike did the same thing, the exhaust was cool, another time a bit later just a bit cooler.

should I get new dyna coils with the wires? can I get new wires only? is there something to put in the connection wire/coil to get better juice flowing to the spark plug? should I change to accel coils and if I do that do I have to tune up the carbs,etc. again? thank you very much

pato wrote:

kz 650 '78 with dyna coils/v&h 4X1 exhaust, K&n air filters.
the second pipe from the left sometimes feels cooler and sometimes cool all the way compared with the other three. I checked the dyna coils and found that the spark plug wire that goes to the second spark plug in the dyna coil had a bit of rust. I cleaned it up put it all back and the bike did the same thing, the exhaust was cool, another time a bit later just a bit cooler.

should I get new dyna coils with the wires? can I get new wires only? is there something to put in the connection wire/coil to get better juice flowing to the spark plug? should I change to accel coils and if I do that do I have to tune up the carbs,etc. again? thank you very much

Would first experiment by switching plug wires running to #2 and #3 plugs. Then start the engine to determine whether the cold exhaust issue moves from #2 to #3 cylinder. What happens then?

Btw, it's better to determine hot pipes by spraying with water mist (easier on the fingers and hands)

FWIW I like to start with the least expensive first. I'd put a new plug in it and see if that cures it. If it's only one cylinder not firing I think the odds of it being a bad coil are slim. I'd be looking more at plugs, wires, caps, etc. All this assumes you know you are getting fuel and have good compression in that cylinder.

Post edited by: Vter Bob, at: 2007/11/11 16:24

thanks. I changed plugs, put black tape on spark plug wires and nothing changed. I checked that there was gas in the bowl on carb 2 where the exhaust is cool. I also checked for spark and there is a spark, a redish one, a bit different than the bluish in 1. what's strange is that the bike runs fine, I mean it can be a bit better but it's a 78 with 30,000 miles. I will like to find out why the cylinder is not firing or why the pipe is cooler, that's why I keep asking. maybe you have any other hint... thanks in any case

I switched wires 2 and 3, and after some backfiring I checked and the same thing, exhaust pipe 2 cool. otherwise the bike runs good but I will like to fix this. any other hints? thanks

Thanks for the progress report.

With new plugs and with #3 plug wire not curing #2 cylinder issue, the ignition components (coil/wire/cap/plug) may be okay, although quality of #2 spark may remain a concern.

Insufficient compression on #2 cylinder could be causing the problem, perhaps from too tight valve clearance in #2 cylinder on either or both valves.

So would first check compression and valve clearances before addressing carbs.

Pato, You may think your bike is running good, but it is only running on three cylinders. A four cylinder bike with 75 percent power doesn't feel bad but once you get this licked, you will be surprised at how well your bike seems to run compared to now.

OK... you did switch plug wires... #2 for #3? No change... right? You tried a new spark plug in #2? No change...

When a cylinder doesn't fire, can only be three things:
NO gas, NO spark, NO compression

You claim to have gas and spark. Well, the spark can be delivered at the wrong time and not fire the mixture well... this is a ignition timing issue but since you only have the problem on one of the two cylinders fired by the same coil, I suspect I would find a compression gauge and start checking...

To check, you might warm the bike some. Then remove the plugs. Check compression in all the cylinders. Screw or press fit the gauge tip in #1 cylinder (they are counted 1 to 4 from left to right as if you are sitting on the bike). Turn the engine over with the starter a few times so the gauge pumps up as far as it will go while keeping the throttle all the way open. Write down the measurement... should be about 150 PSI or so for a 650. Do this for each of the cylinders.

If you find a low compression cylinder relative to the others... say you find a 130, 80, 135, 145 pattern, the 80 would be low... now repeat your compression test but this time, add one TEASPOON of oil down the plug hole for each cylinder... don't all the oil all at once or it will splatter when you check. Do Cylinder #1 then repeat for the others and record your findings.

If you have 160, 180, 165, 175, could be that you have piston ring issues in the cylinder with low compression. If you have 160, 100, 165, 175, could be valve issues. Time to check valve clearances with an eye on the #2 cylinder. Don't skip compression testing.... OK if you find compression OK; say somewhere between 130-160 for all four cylinders, then next step is to rethink what you think you already have checked.

GAS!!! Does the cylinder never fire or just sometimes not fire? If the bowl has gas but a pilot jet is plugged or the internal passageway that carries gas, then you won't fire till you get into mid-range or main jet. If you find that the bike fires at higher rpms (cylinder kicks in), clean the carb internal passageways and replace all four pilot jets.

I really don't think you have electrical issues at this point and would work through this problem in the order I suggested because if you do it by the numbers, you will eliminate a lot of frustration. Good luck!

last summer compression was 160 160 160 160 but I will check again. the cylinder fires sometimes. today it fired when the bike was cold and I just rode a couple of blocks away to get gas. then it did not fire any longer. I will get a compression gauge tomorrow. thank you very much wirdegeorge:cheer:

hi. I cut the tip of both ends of the spark plug wire in #2, the bike started up fine, running on four cylinders, then it was running on 3, #2 out again

also, I do not know how this is related but the bike began leaking gas off the overflow tube, I believe from #2, as it did last year (something that had not happened for a year)...

thank you

Compression reading may be okay, but drop quickly after a short run. May be caused by insufficient valve clearance (gap). As engine warms, valve clearance reduces. And may reduce to the point where the valves are unable to completely close. Then it becomes a "leaking" valve (which drops compression).

So even where compression testing figures read okay, proper valve clearances are also necessary to maintain the compression at normal operating temperature.

Even perfect carbs won't compensate for inadequate compression due to a leaking valve.

Yes, there may be carb problems, but they should be addressed after assuring proper valve clearances.

Btw, a leaking valve due to improper clearance may result in a burnt valve and damage to the valve seat. $$$$$

Post edited by: Patton, at: 2007/11/17 05:06

I hear you nice and clear Patton and I will take the bike to Little Al for valve adjustment right now. Thank you very much.