Points Set-up

[gregwils]

Something inside the points/advance mechanism seems to be grounding.

I started today by cleaning out the vent cap - stuck a thin wire through the hole then blew compressed air into it. I have no idea where the air comes out on the inside of the cap, but hoping 50 lbs of pressure did the trick.

Next, I thought I would reset the timing, which I did and thought everything was good. I tried testing the spark by flicking the points arm with my finger, no spark through the tester. I hooked the timing light back up to see what was going on. Moments ago, my timing light was going on and off very clearly, but now, the light would only go from bright to dim - not off. After, screwing around a bit and thinking I needed to remove everything and start over, I loosened the top advance plate screw and the dim light went off entirely. Hmmm. I loosened the bottom one, then tightened both a little more gently, the light was still off. It would spark with the finger trick. I put the cover on wheeled the bike outside and tried restarting the bike, but it wasn't sparking. I hooked up the timing light and it was bright to dim, not off.

The difference between grounding and not grounding seemed fragile, and the slightest change causes it to ground. I am basing this on whether the timing light goes off entirely or not. If it doesn't go off entirely, no spark. If it does go off, then it sparks.

I feel like I should remove everything, clean it and try again. I just can quite figure out the cause of the grounding other than it seems associated with the tightness of the advance plate. Any thoughts are welcome. PS - I am not cranking down on the plate, just a reasonable degree of firmness with a small screwdriver. Thanks.

[Bevel bob]

Hi Greg, It seems clear to me that your problem is poor ignition, if your plug is sooty it wont spark well, so when testing I would use a new plug and Not use it for running . Its also possible that you have an intermitent short to earth at the points or even a bad earth ,I would run an engine earth wire from the crankcase to the earthing point on the frame where the battery and regulator earth.If the frame has been powdercoated clear that away. If you are using battery ignition then make sure you have the normal bike coil, the magneto type coil won't do.I recently had a lot of trouble with a HT lead that looked and tested fine ,but when replaced made a huge difference to the plug condition , go figure!!. HT plug caps can go high resistance from the correct 5 to 10k up to infinity and still somehow work badly. An oily residue on the points will mess things up.Once you have a regular strong and reliable spark if the plug soots up and missfires then its time to look at mixture and oil, but not before. A bike with a strong spark will get you out of trouble ,but a weak one will always be a pain and waste your time over and over.

[Nick]

Funny you should mention fuel tank breathers..... Just two days ago I was bombing down the freeway on my Sebring WFO in top gear when it died cold (I always ride in the No. 1 lane for just such eventualities). Anyway I barely made it work with the engine running, quitting, etc. Cause? Plugged breather.

If you look under the forward part of the fuel cap lever you'll see a small hole. 180° away from it on the underside of the fuel cap is another hole in the inner cap. That's how the tank breathes. The inside hole on mine was rusted closed. I had to dig the rust out with a tiny screwdriver--compressed air would never have cleared it.

Probably not your problem, but something to check at your leisure.

No need to obsess about timing lights. Cellophane will tell you when the points open. I just use a screwdriver to open and close the points to check for spark.
As mentioned above, points must be clean! If the bike has sat for any length of time, the point's contact surfaces are probably oxidized. Use a points file or wet/dry sandpaper to clean them. Then spray clean with points cleaner or lacquer thinner, then run a piece of absorbent paper through the points to clean any residue (I use the spark plug box). Sometimes you even have to snap the points closed a few times.

Set the gap first, then the timing.

When I bought my MKIII Diana for $100 in non-running condition many years ago it had a bad connector on one of the coil's low-tension wires. Fixed the connector and it fired right up and ran fine. Never even checked the timing or messed with the points.

Did you check the valve clearance?

[Bevel bob]

A bad connector just above the points caused my only stoppage in the IOM this year and occurred at the top of the mountain ,took about 30 mins to find it. The clue was a very intermittent spark when flicking the points. I was encouraged in my efforts by a Scotsman in a campervan who said very uncomplimentry things about Ducati electrics, I berated him for not having some whisky and haggis to hand!! as a proper Scot should have.

[gregwils]

Bob - Thanks for the thoughts on the ground. I will consider running an additional ground if the ignition continues to be intermittent. I removed the points plate (arm and base) without even disconnecting the condenser or coil lead, sprayed it with brake cleaner to remove any oil residue, then reinstalled and gapped the points. I put the key in the ignition and as fast as I could flick the points arm, I would get a nice blue spark jumping across the spark plug. Go figure. I am not sure if the electrics or the mechanic is unreliable at the moment. I know it's all about the quality of the connections.

I had to look up the word haggis, then remembered reading about it in the past. I would have just berated him for not having whiskey :- )

Nick - Thanks for the fuel cap vent info. The outer surface of my cap is rust free, no issue identifying the hole. Inside of the cap is a different story, there is definitely no hole on the inside at 180 degrees from the outside. I am not even sure I can identify where to start digging, but I will re-examine the thing. I have another cap, will check to see if it has an interior hole.

[gregwils]

Okay, some progress today. The bike started and I have had it running for about 15 minutes or so. It seems to run rich, really rich. I pulled the plug after it was running it is black and sooty. I am not entire sure if this is oil, because the bone head former owner didn't seat the rings properly or if they are still in the process of seating themselves, or if the carb is not jetted correctly. However, rather than continue with this thread, I am going to search the forum a bit and if I don't find the correct answer, I will start a new thread about carb/mikuni tuning. Thanks.

[gregwils]

Okay, I lied, one more post. I found a Youtube video which suggested that moving the needle up one notch had a "massive" effect on richness, so I decided to go for it knowing mine was on slot 3 of 5, the middle. It only took about 15 minutes to make the change, put it all back together and Oh My!!! I now have a smooth running motorcycle that isn't blowing black sooty smoke, revs freely and seems to be making power. What a concept, a motorcycle that I can ride! If it hadn't started raining here, I would be riding at this moment, not posting.

I will need to experiment more on tuning the Mikuni and am sure I will have other questions and challenges, but I feel really good about my current status. I am going to head over to the parts store to buy and hand full of new spark plugs so I can get this perfected, but at this point it will be fun going from good to great. Thanks again to all.

[BDang]

"If you look under the forward part of the fuel cap lever you'll see a small hole. 180° away from it on the underside of the fuel cap is another hole in the inner cap. That's how the tank breathes."

Sorry if I looks like i'm hi-jacking this thread, but since it's a simple question of the fuel cap, I will ask it here:

I didn't see a gasket between my cap and the tank's neck as most other caps had, and so I thought a little gap between the cap's spring plate and the tank was for breathing. Should it have a gasket?

Regards,
Brian

[Nick]

If the cap leaks you need a gasket. If not, no worries.