spark plug leads

[buzza]

Hi  All,
Do spark plug leads deteriorate with age? My 81 r65ls has done 20,000 km, has a new coil and plugs but the original leads. Sometimes when I start the bike from cold it appears to run on one cylinder for a few seconds. Runs well otherwise.
Steve

[Barry]

They can but did you try swapping the leads over to the other cylinder to see if the none firing cylinder follows the change. It doesn't matter which coil fires which cylinder so you can do this.

If replacing the leads go for sold copper cored HT lead and most people use NGK LB05 caps.

[montmil]

... Sometimes when I start the bike from cold it appears to run on one cylinder for a few seconds. Runs well otherwise. Steve

An old Airhead axiom:

 Â   If you think it's electrical, it's probably carburetion.
 Â   If you think it's carburetion, it's probably electrical.

Now that we've gotten that outta the way, and before you begin throwing money around, do this absolutely free and easy check.

Drop the float bowl off the "quiet" cylinder. On the carb's body, notice the long, brass tube that projects downward into the float bowl. This tube feeds fuel to the enrichener circuit that is activated when the chock lever is in the 'on' position.

Now look into the float bowl. That brass tube extends into a small "well" that feeds the enrichener circuit. At the bottom of the well is a small opening whereby fuel from the main chamber can pass. Should that small opening become clogged, no fuel will pass and the problem cylinder will not fire until the engine develops enough temperature and revs to support combustion on that evil side. Strip a thin strand of copper wire from some scrap and probe the opening to clean any obstruction. And check both bowls for any silty debris in the bottom.

This was quite evident when I went to inspect my 1981 R65 just prior to talking the seller into a lower price.

[URon]

Yes, like all rubber, plug leads deteriorate with time.
Quick check: try dielectric silicone lube or spray on the leads.
Wipe off excess.
This should tell you if it's the lead or not. Then you can go from there.

Ron  

[buzza]

Thanks for the response guy's. I swapped the leads over and sure enough the other cylinder was slow to fire. I had a close look at the lead and found what appear to be small cracks in the insulation down near the caps. I will get new leads and hopefully the problem will go away. I did check the float bowl, OK.
Steve.

[buzza]

Hi guy's
New leads did'nt make any difference so have begun to pull down carbs and clean them. Diaphram was stuffed in the first carby ( doing one at a time) and the washer (o-ring) between the needle jet and the jet stock , according to Clymer manual, is not there. Carbys are 64/32/307 & 308.
What does this washer do? With only 20000 km on bike I would'nt have thought the carbys had been pulled apart previously, certainly no evidence of this.
Steve

[Barry]

The washer between the main jet and the main jet holder will not be related to your problem but it should be there. Notice the main jet sits in a well. The washer acts as an anti-surge device to help stop fuel flowing out of that well under braking/acceleration.

I'm wondering now if we are talking about the same washer. There is no washer or O ring close to the needle jet but there is a large O ring on the main jet holder - the big lump of brass that the main jet screws into. It's purpose is to prevent fuel leaking past the threads and therefore bypassing the main jet and needle jet. Again I can't see how it would cause your symptoms and early Bings on older airheads didn't even have this O ring.  All R65 carbs should have it though.

[montmil]

Interesting that the 'slow" cylinder followed the plug wire. Makes me suspect the ignition coil and/or its plug wire terminals.

Just a thought: Do you still have the original black and gray, Bosch ignition coil? Notorious little buggers prone to cracking and causing misfires. Popular nickname for the Bosch is the Crack-O-Matic.

You might check the coil/plug wire connection. Understand you installed new wires, but check for corrosion inside the coil's terminals. Also clean off the coil and look for tiny cracks on the exterior; usually on the end opposite the plug leads.

[buzza]

Thanks Barry, the moment I saw your photo of components I realised that I had made the  mistake in reading an exploded diagram and saw the o-ring on the main jet holder in the wrong place.....makes me feel very stupid.
Montmil I have replaced my cracked coil. I am now going through all maintenance items, carb, valve clearences etc so I can set everything as it should be.
Steve

[buzza]

I am ordering carby kits and noticed a large price difference for the diaphrams in the kits and the genuine bmw parts . I have read that the cheaper diaphrams have issues with thickness and general reliability,so are they worth considering?
Steve.

[Mike V]

Steve,

I would recommend ordering genuine Bing kits, or individual pieces.  There are many reputable sources to consider other than Bing International if you choose such as Tom Cutter's Rubber Chicken Racing Garage, Ted Porter's Beemershop, Hucky's, etc., to name just a few.  These are items I normally don't try to cut corners on regarding cost. For me; it doesn't pay in the long run.  A carb rebuild should last you many years of reliable service. The genuine correct Bing parts are a bit pricey, regardless where you find them.

It's your decision in the end.  

[Bob_Roller]

From what I have read, this is a fault of the ignition control module .

The first version of the ignition control modules have this characteristic .

My bike has pretty much done this since I first got it 34 years ago .

http://bmwmotorcycletech.info/Ignition.htm

The above link does have a little one line explanation, of it .

Yes, it's ' wordy ', but there is a wealth of info in this site  .

The later versions of the control module, have cured this problem .

[mrclubike]

Quote from Snowbum's site
"Another thing about the earliest modules was that the module could misfire between the two cylinders.  Weird, but, yes, could happen.   BMW eventually cured this problem in later modules.  BMW also fixed the modules so that there was NO SPARK unless the engine was being rotated. One could obtain a spark by turning the KILL switch on and off, however....which is handy for certain tests."

[buzza]

Hi Guys,
Been away for a few days and got back to find the carby rebuild kit had arrived. Have rebuilt first carby and have begun to dismantle the next.Both of them seem in good condition. Apart from o-rings that were hard and brittle and the diaphrams that soft,slimy and torn,there was no build up of gunk or blocked jets etc. Not even sure if the diaphrams were torn before I pulled the cover off as they were stuck to the grooves so were certainly torn by the time I separated the cover from the carby body.
Thanks Bob and Mrclubike for the reference to Snowbums site and the interesting info. re. starting on one cylinder. Look forward to trying the trick with the kill switch. Seems to be a reasonably common problem. I have looked at Snowbums site often but end up with info. overload and imagine more problems than solutions.

Thanks
Steve.