Somethings amiss with my 1984 R65

[Hunsta]

OK lets just get some background for you so you dont have to grasp at straws.
I have a 1984 R65. In the last year I have replaced the coil with a Dyna coil and about 3 months ago I had the heads reconned(new valves for unleaded and such). All went back together nice and valves adjusted several times accordingly. Everything ran smooth and nice.
Now for the problem. For some reason out of nowhere it will start to break down and backfire badly. It did this so badly today that it completely cut out. The last time it did this it was very slight and I fiddled with it and put new plugs in (just incase there was a small crack in one) and it went fine and I thought Id found the problem. Today after having to leave the bike on the side of the road and go home to get my ute, I got the bike off, put the key in and she fired up and purred like a kitten.  
It sounds and feels to me like an electrical problem. Timing or coil. But it can purr all day without a hitch, so its got to be something that is loose and gets fatigued when hot, as I did manage to get it started again on the side of the road but it wouldnt get over idle before it would again start to backfire.
One thing is that with my R100 tank on the bike the Dyna coil sits in an awkward position and rests against the inside of the tank. No connections touch or come anywhere near the tank as Ive put a peice of rubber to insulate this from happening and the rubber is still in place with no wear marks in it..
As Ive said it can run fine all day, then bang she just gives up.
So anyone got any suggestions on what it might be?
 Cheers
Craig

[Bob_Roller]

I had a similar problem with my '81, never really found the problem .

It was suggested to go through the entire electrical system and check for loose connections at all connectors, parts ,etc. .

Did that in 1997, never have had a repeat of the problem since .

[Hunsta]

That will be on my list of things to do.
Cheers
Craig

[raymr]

Make sure there's no gunk in the tank or fuel lines and the fuel is flowing freely. Check for a clogged air cleaner. Check the plug wires for solid connections at both ends. Run it at night and look for stray sparks from coil to head.

It sounds like it *might* be a temperature dependent problem, but not necessarily so.  

[tvrla]

Intermittent problems like this are the most difficult to track down.

As already mentioned, it could be a connection in the ignition system somewhere. Check them all out. And don't forget the kill switch, it's been known to cause trouble like this.

Next time it dies on you, check to see if there's a spark by pulling a spark plug and laying it on the fins with the lead attached. Make sure the plug is grounded to the head! Crank the engine and watch for spark.

This doesn't necessarily mean you've crossed ignition off the list if you get spark because it could be at the wrong time. There are times when the hall sensor fails that a spark will be generated, but not at the right time.

Another thing to check is the heat sink paste under the ignition control unit. It's under the tank and fastened to a finned heat sink and has a very wide plug attached from the wiring harness. If the past is dried out and hard, heat won't transfer from the unit to the heat sink and overheat causing the trouble you describe.

I'm curious what you discover so stay in touch!

[Hunsta]

Make sure there's no gunk in the tank or fuel lines and the fuel is flowing freely. Check for a clogged air cleaner. Check the plug wires for solid connections at both ends. Run it at night and look for stray sparks from coil to head.

It sounds like it *might* be a temperature dependent problem, but not necessarily so.  

Fuel can be seen flowing freely through the fuel filters attached to the outside of the tank, and I really dont think its a starvation problem. But I wont rule it out. Also I replaced the plug leads with new ones when I purchased the coil. I will do a night run to look for leaking spark.

Intermittent problems like this are the most difficult to track down.

As already mentioned, it could be a connection in the ignition system somewhere. Check them all out. And don't forget the kill switch, it's been known to cause trouble like this.

Next time it dies on you, check to see if there's a spark by pulling a spark plug and laying it on the fins with the lead attached. Make sure the plug is grounded to the head! Crank the engine and watch for spark.

This doesn't necessarily mean you've crossed ignition off the list if you get spark because it could be at the wrong time. There are times when the hall sensor fails that a spark will be generated, but not at the right time.

Another thing to check is the heat sink paste under the ignition control unit. It's under the tank and fastened to a finned heat sink and has a very wide plug attached from the wiring harness. If the past is dried out and hard, heat won't transfer from the unit to the heat sink and overheat causing the trouble you describe.

I'm curious what you discover so stay in touch!

This interests me. If this is the problem, what is the fix? Do I have to replace the whole heat sink or can I apply new paste? Im kinda auto electrically retarded  :-? hence the question.
As for the Hall sensor. I was under the impression that if it fails, it fails. Can they fail intermittently?
 If it has failed, would anyone recommend the Alpha Ignition system from Motorad Electrik ?
 Cheers
Craig

[Hunsta]

OK small update. Checked Control unit and heat sink. Firstly there was only one bolt holding the heat sink to the control unit. Instead of two. Secondly there was little if any form of paste between the sink and the unit. There was some residue of something there, but it looked more like a small smear of glue than paste. Im would assume that if this is the problem, that the control unit is working but overheating. However if its been overheating for some time, I would assume that its life may have been shortened. I`ll clean both surfaces and apply heat sink paste(which I found you can get ) and go from there. I will still run a disconnect and reconnect run through the ignition system.
Unfortunately I go interstate in 2 days so you guys may not get an update til after Christmas.
 Cheers
Craig

[Barry]

This will sound like a bodge but if you don't have any proper heat sink paste to hand and want to do a quick fix while you get some then you can use copper grease as a temporary heat transfer medium. I promise you it will work.

Whatever you do use the secret is to start with both surfaces as clean and smooth as possible and then use the minimum amount of paste that will fully coat the surfaces. Reason for this is that you are only trying to fill in the microscopic imperfections in the surfaces rather than separating the surfaces with a thick layer of paste. A thick layer is bad because in spite of it's name heat transfer paste is a lousy conductor of heat when compared to the metal itself.

[tvrla]

I'll second what Barry just said. Also, these control units are pretty rugged so there's a good possibility it's fine, but you may have just located the source of your trouble. Some guys have recommended polishing the two mating surfaces by laying out a sheet of very fine sandpaper on plate glass then dressing each piece to remove any imperfections.

[Bob_Roller]

I'm not so convinced that heat sink compound is really as important as it's made out to be .

I had by bike 19 years before I found out about it, that includes 7 years of riding all year round in a (did I mention a hot) desert .  

Some newer replacement ICU's and newer bikes from the factory (monoshock), are bonded to the heatsink and they cannot be separated without destroying them .

A neighbor one street south of me has an '82 LS, not mechanically inclined at all,  I looked the bike over when he had the fuel tank off, he lost the heatsink and had the ICU cable tied to the mounting area, rode it like that for two years without any problems .

 Unfortunately, I don't think applying the compound is going to solve your issue .

By chance, do you do any night condition riding, that's when I found out, that I had a complete electrical system failure, all of the lights went out and the engine quit with a few loud bangs out of the exhaust .

[montmil]

...As for the Hall sensor. I was under the impression that if it fails, it fails. Can they fail intermittently? If it has failed, would anyone recommend the Alpha Ignition system from Motorad Electrik? Cheers Craig

Craig, I have had experiences with two different vehicles where a Hall sensor had intermittent and random failures then later restarted just fine. Both sensors were the same as in the BMW's bean can. I don't believe either were heat related issues.

I also once pinched the Hall sensor lead as I was replacing the front engine cover on one of my R65s. Eventually, this lead to a shorted ignition, but it wasn't the fault of the Hall unit.

I would suggest revisiting the last electrical and/or ignition service you performed on the scooter. Confirm all connections are secure and tight.

Also, have you replaced spark plug wires and caps. I didn't notice in your post but there may be a plug wire breaking down as it "jiggles" during bike ops.

It's likely going to be something quite simple to fix yet challenging to locate. Luck to you, mate.

Monte

[DgM]

Check gas tank cap venting.  Clogged / partially clogged vent will produce problems as described.

[suecanada]

This will be interesting to watch and find out what the gremlin really is! Gotta say that Hunsta explained his problem with details very well and is a grand example of how to ask a question for help on this forum. Intermittent problems are really trying but he did do well to describe the circumstances as best he could and Hunsta, I think you underestimate your abilities. A pleasure to read!

[Bill Conquest]

Hey Husta - I'm going through the same thing with my '79 r65 & will be watching to see what you find out & hope to learn from it!
Bill

[Hunsta]

Also, have you replaced spark plug wires and caps. I didn't notice in your post but there may be a plug wire breaking down as it "jiggles" during bike ops.

new plugs went in first time this happened. New lead went on with the new Dyna Coil

Check gas tank cap venting.  Clogged / partially clogged vent will produce problems as described.

Doesnt seem to me to be clogged. However I would assume that the problem would manifest itself far quicker than it does. Yesterday I had been out for a 150km round trip and was halfway on the return leg when it happened.

Im kinda going with a heat related problem as I was giving "Lotti" a hard time.