R65 LS missing, backfiring.

[Jmo]

my 82 LS is in good shape, bit less than 50k miles.  Carbs recently rebuilt, Dynacoil installed, fresh fluids.

A few weeks ago it started acting strangely:  at freeway speeds the engine would cut off for a second, then pick back up.  Then it started backfiring and missing, sometimes badly.

I kept riding it to work and back and if I don't get it hot and don't push it past 5k rpm it runs fine, plenty of power and steady idle at 1100 r pm, just enough to keep the alt light off.

The backfires are coming from the mufflers, I think both of them but not 100 % sure.  The plugs and cables are fairly new, less than 4k.

From Clymer's reading I think it's either the ignition trigger unit or the ignition control unit.  Clymer's also mentions valve failure but I really hope that's not it; the bike has never really been pushed or overheated.  I've had it since new and no one else has ridden it.

This may be one of the "soft seats" for the valves engines.  I've never done this update.

Thoughts?  Advice?

I can keep riding it gently (it's better than my K bike in traffic here in L.A.), but I know I will have to fix it eventually.

Thinking of installing the Alpha ignition system from Motorrad Elektrik.  Good or bad idea?

Comments much appreciated.

[Bob_Roller]

Frist off, you need to do some troubleshooting before you start 'throwing' parts at a problem, especially an intermittent electrical problem .

This is a not an uncommon occurance with these bikes .

The 'fixes' for this problem are varied, they range from faulty ignition switches, faulty 'KILL' switch, bad ignition trigger components, loose wires, etc .

You may fix the problem without replacing the parts and never really know what caused the problem .

That was my case about 16 years ago, in my case I think it was a loose wire in a connector, again never positivly identified the problem, but it hasn't happened in 16 years .

I would start with removing the fuel tank and go over all of the connectors for security and that the wires cannot be pulled out of the connector, check for corrosion as well, if that is a problem in your location on planet earth .

When the engine cuts out, does the tachometer go to '0' ??

If you are in dark or night conditions, does the entire electrical system fail also

[nhmaf]

It is likely an ignition system issue, especially if you are getting both exhausts acting up.   It is caused by ignition cutting out briefly-> engine pumps some cylinders' worth of air and gas into the exhaust system without igniting, then ignition kicks back on and exhaust heat ignites the air/gas in the exhaust system again.

Like Bob said, one has to be methodical about these things are you can continue to chase your tail round and round.   There is another thread in teh tech section with Bill Conquest that we are trying to decipher - some of those suggestions could also apply here for things to look into.  Check into these and report back and we'll try to steer you in the right direction as more info comes to light.

[Bob_Roller]

Two other things that I thought of, most likely not the probelm, but while you're working in the area, the metal heat sink on the ignition control unit thats bolted to the frame around the voltage regulator should have a a heat sink or transfer paste between the two parts .

You can get some at Radio Shack, if you have one in your area .

The other is the lousy fuses that this bike came with, it would be a good idea at some point to replace the OEM fuse installation with blade type fuses, again most likely not your current issue, but it is a know trouble spot with these bikes .

[Tony Smith]

In addition to what others have said, for peace of mind I would check valve clearances and do a compression check to eliminate a valve problem.

[georgesgiralt]

I had the same behaviour on mine. As I own a volt meter on the bike, I put the voltmeter's hot wire to the +12V point on the coil. Just to check if the cut was from power to the ignition system or from the ignition system itself.
See "I have an intermittent" post

[Jmo]

Thanks all for your replies.  It sure feels good to have this forum to rely on for these issues.

My gut tells me it's an ignition problem, but the heat sink is an easy fix so I hope it's that.

A compression check is a good idea (must budget for a compression tester).

Thanks again.

[davidpdx]

When you do your compression test don't forget to take the carbs off or you will get depressingly low numbers.

[montmil]

Harbor Freight -bound to be one near you- has a decent compression tester. Use one of those easy-to-find 20-25%-off coupons and you're golden.

There's an old BMW saying: If you think it's electrical, it's probably carburetion. if you think it the carburetors, it's probably electrical.

Do confirm valve lash first.

Check the simple stuff and report back.