[shadow_wolf]

1983 Shadow 500

Bike starts fine when cold, but after warming up gradually loses low-end power to the point I have to baby the clutch and throttle much more than normal in first from a dead stop. Eventually, it will start cutting out in overdrive if I ride it long enough. If I do several short runs, it starts cutting out even quicker. When hot, it is a bit stubborn to start.

At first I thought it was overheating. I can't tell by the gauge, since it doesn't work. But the fan doesn't seem to be running more than normal, coolant isn't boiling out and there's no coolant in the oil. Then I thought it was the carbs, possibly the enrichment circuit or low speed jets, but that really wouldn't be temperature related that I could see.

Finally I decided to test the ignition system. The coils tested fine, 2.6 resistance on both which is a sign they're getting old from what I've read here and on other sites. All other ignition tests passed within specs listed in the manual. Since it only acted up when hot, I took it for a fairly long run. By the time I got back, it had reached the sputtering stage, so before it could cool down I tested the primary resistance. This time the front coil tested 9.5 ohms and the rear tested 8.2.

This seems to tell me that the coils are bad, cutting out after heating up, but since there is no mention anywhere I can find of the coil resistance being different after heating up I wanted to make sure before I handed over the money for new coils. On a side note, sometimes when it's hard to start hot I smell gas, like I've flooded it a bit. I just figured that was unburned gas from the spark not being hot enough.

So are my coils definitely bad or are there other tests I need to do before I spend the money?

 

[cl65ame]

Coil resistance does change with heat. Its physics and you can't change that. if they are reading out of spec hot or cold then I would replace them. the specs in the manual take any thermal changes into account, thats why there is a range given.

 

[GadgetDad]

Stlouisaaron and i have been going through something similar. You can follow it here http://www.hondashadow.net/forum/72-technical-discussion/109662-sudden-loss-all-power-rpms-help.html
He's tried replacing the coils and it hasn't helped. He replaced the pulse generators, but has yet to get it running (waiting on a gasket). Mine is at the mechanic and I'm hoping to hear back from them today.

 

[93gc40]

Before you go any further on the ignition parts replacing. Check and test the connections of the charging system. The wires and connection from the stator to Rectifier are KNOWN to be weak and prone to overheating. This is the #1 cause of issues your are having. Weak electrical supply can cause down stream components to overheat and fail. Coils or other ignition item, Might be the issue, but check charging circuit first. This includes the battery.

 

[shadow_wolf]

The notorious stator connector has already been cut out and soldered. I do that with all older bikes now. I've heard the newer stator/regulator setups have better connectors and technology, plus they're not 30 years old. The battery is a little over a year old according to the markings, but it is a walmart wet cell so it might be going bad. All of the other cables and wiring looks good.

Gadgetdad, I'll read up on that thread, might show me something I've missed. I'm still thinking that the resistance shouldn't quadruple on the coils when hot. And on the ranges given, I did note that there were ranges given on the other readings, including the pulse generator, but the manual only stated a flat 2.0 for the primary connector-to-connector resistance with no variables.

I've also read up on the coil relay modification, and will probably do that sometime in the near future. If nothing else, the coils should be happier at getting a full 12v.

 

[93gc40]

I've also read up on the coil relay modification, and will probably do that sometime in the near future. If nothing else, the coils should be happier at getting a full 12v.

Whats this? Got a link?

Stator wire are issue at least into the 90's. At least to 93.
But then your bike is about that age when the coils start going bad on ALL the Hondas I've had.

 

[shadow_wolf]

The relay mod is like this setup, I know I saw it mentioned here but can't find the link:

wiredgeorge motorcycle carburetors - Vintage Japanese Motorcycle Carburetor Sales, Rebuilding and Restoration - Repowering Ignition Coils To Get Full POWER!

Basically hooking the coils up directly to the battery via a cheap relay that's turned on by the old power wires.

 

[93gc40]

Cool, I know what I'm doing, next time I have the tank, off.

 

[Custom85VT]

^^ Thank you, that looks like some useful info!

FYI there is a small link at the top of that page so you can D/L all that as a PDF file to save for future use.

 

[cl65ame]

I am not seeing the advantage? The test indicated in the article is bogus too. If you take the measurement while cranking the bike, of course you will see less than 12 volts, the Starter is pulling a ton of current and drawing the battery down. this is normal. What are you seeing with the bike RUNNING is whats important.
All the relay does is switch battery power direct from the battery through the relay. A switch is a switch whether it be the switch on the handle bars or the relay. Cleaning or replacing the switches on the handlebars works too.
Not worth the time in my opinion.

 

[still_bluenoser]

All the relay does is switch battery power direct from the battery through the relay. A switch is a switch whether it be the switch on the handle bars or the relay. Cleaning or replacing the switches on the handlebars works too.
Not worth the time in my opinion.

Yet if there are less switches there are less losses. The wire gauge is small on stock bikes too.

Real world test: I tested my coil voltage at stabilized idle on my 81 cb750c. 12.3 volts at coils, battery voltage was about 12.8 volts. 0.5 volt drop over the switches and wiring. Performed the coil relay in about 2 hours, started the bike and let stabilize. idle. 12.7 at coils, battery 12.8. 0.1 voltage drop.

Big improvement. I also keep clean electrical connections on my bikes, this change could not be accomplished with a simple cleaning.

I assure you that this mod is worthwhile. It was a noticeable change in my tired old bike.

 

[shadow_wolf]

I've seen this mod on a lot of older and some newer bikes. The wire gauge is a definite improvement. The way I look at it, more voltage=happier coil=hotter, more reliable spark=less fouling and more efficient burn=little more power and fuel economy=happy bike and more money in my pocket. Not bad for a mod that looks like it will cost about $10 and an hour, tops, of my time. Plus, if I do have to fork out for new coils, I want them to be very, very happy considering what they cost.

 

[shadow_wolf]

Okay, I'm going to drag this back into the mix.

Still haven't had the money for new coils, been a bad time financially lately. Haven't even seen a decent set of used on ebay that I could afford at the time.

However, I recently noticed a couple of things. The bike is definitely getting harder to start when it's warmed up. I think if it is the coils like I think, they're on their last leg.

The main thing I discovered was that my headlight DIMS as rpms INCREASE. Now, normally if the battery is a little low or the charging system isn't quite up to par, the headlight will get brighter with more revs. I've never had a vehicle that did the opposite. My thoughts on this is maybe since the coils are increasing in resistance, they're drawing more current to fire faster in higher rpms. Anybody else experienced this issue?

The battery is a regular wet cell, around a year old. Regulator/stator connector has been soldered.

 

[verdeva]

Clasic symptom of a charging system issue. Coils cannot cause this, nor can the battery. What is the voltage across the battery?

Too bad you soldered your stator wires already (hint Posi-Loc connectors). The single best test is to measure AC voltage between each yellow wire. Exact voltage is not important as long as the voltage is about the same on each pair of wires. Run the bike with open stator wires, and check voltage at idle and rev'ed, and expect ~20 and ~60 volts respectively for each yellow wire pair. If this passes, the stator is ok and the RR is probably failed.