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Can Bad Coil Resistor Be Affected By Heat?

  • touringguy
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9 years 7 months ago #7436 by touringguy
Can Bad Coil Resistor Be Affected By Heat? was created by touringguy
I've been having trouble with my B2 not starting -- cranks but won't start -- when the engine is warm (see my previous topic on this issue). It starts right up when cold, but if I ride it even 1/4 mile and shut it off -- I have to wait 20-30 minutes before it will start again.

I've pretty much eliminated the fuel possibilities of the "fuel or electrical?" question. So I've started investigating the ignition.

Although I thought the chance was slim that all three coils would go bad at once, I tested the primary/secondary resistance on them today. Indeed, all are fine.

However, when I check the resistor, I found 1.9 ohms (high end of acceptable)at one lead, and 3.5 ohms at the other lead -- well outside of tolerances.

My question: Could the coil resistor be the source of my "won't start when hot" problems? Does heat affect a bad resistor? Note: Bike runs fine once it's running.

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  • KZQ
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9 years 7 months ago #7439 by KZQ
Hi TG,
A B2. That's a 1980 KZ. Correct?
I only have the stock resistor from my 81. It has four leads a yellow (common) and three pinks. From the common I get 2 OHMS at each of the pinks. I know that the 81s had an ignition system unto them selves so what I have to offer may not help you at all. I do know that coils often fail once hot and then start working again when they have cooled off. But a 1/4 mile? I can't imagine that being enough to over heat them.
Wish I could offer you more.
Bill

1947 Indian Chief, 1968 BSA Shooting Star, 1970 BSA 650 Lightning, 1974 Kawasaki W3, 1976 KZ900 A4, 1979 KZ750 B4, 1979 KZ750 B4 Trike, 1980 KZ550, 1981 KZ1300, 1982 KZ1100 Spectre, 1985 Kawasaki ZN1300, 1987 Yamaha Trail Way, 2000 Honda Valkyrie Tourer, 1981 GL 1100, 2009 Yamaha RoadLiner S

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9 years 7 months ago #7440 by Kawboy
Replied by Kawboy on topic Can Bad Coil Resistor Be Affected By Heat?
I would think you're on the right track with your diagnoses. the resistor for these bikes is comprised of 3 probably stainless wires which would be wound up like coil springs. The stainlees wire has a higher resistance than copper wire so in essence, what you've got is a power source supplying a heating element and the downstream side of the resistor is a reduction in voltage and current. These three wires are encased in a ceramic housing so to speak because they get cherry hot. Now think of what happens when you heat up a coil of wire. It expands and if it's a coil it will "unwind" Now if there's a break in the wire you could get an open circuit when it gets hot then when it cools it will close the circuit again BUT where it broke there would have been a tiny bit of molten metal that would oxidize, then when it cools off and attempt to close the gap that little bit of oxidation added more resistance which might explain the higher resistance you're measuring.
The old Chrysler Dodges back in the late 1970's had ballast resistors quite similar to the ones on our bikes but only 2 wire resistors. Any customer who had an issue with a no start or no run after start knew that all they had to do was pull out the spare ballast resistor I sold them and told them to put in their glove box, and attach it to the 2 wire connectors and then drive the car back to me to install it properly. I just got used to selling them the extra resistor so they didn't get stuck and have to call a tow truck.

This 15 to 20 minute wait time also brings up the thought of carb vapor lock, where the fuel is literally boiling in the carb bowl. Seems to be a lot of reports about vapor lock. It would be especially prevalent when the fuel in the fuel tank is quite warm to begin with, then the added heat from the engine while it's sitting might be enough to cause the fuel to boil in the carb. waiting the 15-20 minutes would bring the temperature of the carb bowl down enough to eliminate the boiling effect.

Can't think of anything else at this point. Hope these thoughts help.
Kawboy

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  • zed_thirteen
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9 years 7 months ago #7444 by zed_thirteen
Replied by zed_thirteen on topic Can Bad Coil Resistor Be Affected By Heat?
I used to get this issue with my B2 and I don't have the ballast resistor as I have a Dyna ignition system with three ohm coils. When I was younger I would have just taken the opportunity to have a cigarette but I don't smoke any more.

I only say "used to" because my bike is still off the road. As far as I can tell it will probably still suffer this issue when it returns to the road as I never got to the bottom of it.

I'm now wondering if the carb overflow modification documented by Scotch would help with carb boiling issues? I had wondered about pressure build up in the larger B2 fuel tank but I've checked the tank breather is clear - however - I can't vouch that the circuit to it through the fuel cap works effectively.

I guess Momma K found there were heat issues with the B2 tanks as they installed a thermal barrier on the underside of the B2 fuel tank. I don't think this was standard on the smaller A1/A2 tanks.

1980 KZ1300 B2 Touring/A2
1990 ZZ-R1100 C1

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9 years 7 months ago #7445 by Kawboy
Replied by Kawboy on topic Can Bad Coil Resistor Be Affected By Heat?
I have the larger B2 tank and just prepared it for painting. I had to remove the thermal barrier Zed_thirteen is talking about. It's a foam pad about 1/4" thick and formed to the tank. I feel it gets half the job done so I plan on adding an aluminum foil skin to the outside face of it to reflect the radiant heat back down towards the engine. the foam acts like an insulator because of the entrapped air in the cells but it still will absorb heat and if it's glued to the tank (which it is) it will transfer the heat through conduction to the bottom of the tank and heat the gas up. There are thermal barrier products out on the market which have a layer of foam with this skin of aluminum foil that I'm referring to. I have a 1985 Porsche 928 which I've been restoring for the past 5 years and one of the big problems with these cars is the lack of air circulation under the hood and it's so bad that they had to apply this barrier material to the bottom of the hood to prevent the paint on the hood from baking off. After a few years owners see the barrier material laying on top of the engine because the glue broke down so they just removed the foam/aluminum pad and tossed it. Next thing you know the paint on the hood was peeling off with burn marks around the edges and that's what my car looked like when I bought it. Needless to say, I've done some research on this issue for the Porsche and now that I'm aware of a similar issue with the gas tanks on the KZ, I'll be applying a similar product to the Porsche's heat barrier to the KZ.

My 2 cents.
Kawboy

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  • touringguy
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9 years 7 months ago #7446 by touringguy
Replied by touringguy on topic Can Bad Coil Resistor Be Affected By Heat?
Vapor lock was my first thought. But this can happen even in winter, after a 1/4 mile ride to the gas station -- not nearly enough engine heat generated in that scenario to boil carb bowls dry. And my fuel line is short, steep, and clear (tubing) anyhow -- no chance for gas bubbles forming that I can't see. I also considered a gas tank venting issue, but the gas line is always full, and it never starves during high "demand" for gas, like during highway riding.

Maybe all three coils go bad when they get a little warm, but then test OK when they cool off, but that seems a stretch? And as I've mentioned, I can burn an entire tank of gas with no problems -- as long as I don't stop and turn it off, it runs fine.

A previous owner apparently sprayed PlastiDip on the wiring and electrical components under the tank in some misguided attempt to insulate or waterproof them. The rubber is flaking off now, but maybe putting a thin coat of rubber on the ballast resistor shortened its life by retarding its heat-dissipating abilities?

I'm tempted to just change out the resistor to see if that helps, but the only KZ1300 resistor on on EBay is listed for more than $300, so that would be an expensive experiment.

I notice that lot of KZ1300 owners upgrade their coils. Is this mostly a search for better performance, or is there some inherent flaw in the stock set-up? I'd consider changing out the coils if that's what I need to do . . .

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