VB600 update

[MarkO]

An update on the VB. Previously although running pretty well, it was a pig to start hot and cold. I swapped out the compatible NGK for a brand new one, tried a Champion, but no appreciable difference. Couple of weeks ago, I decided to try a Lodge 3 pronged plug - I forget exactly what but it was whatever the book said it should be. I (carefully) gapped it to 16 thou - I think spec said 18 - and gave it a try. Basically it now starts 2nd or 3rd kick from cold - full advance, bit of tickle, half choke, and so far, first kick from hot - full advance, no tickle no choke.

I also replaced the needle, needle jet and main jet. Bike is more responsive, cruising speed is a wee bit faster - 55 or so - hard to say from the erratic speedo!, and it "feels" smoother at all revs.

I am fairly convinced the plug has helped with the starting issue. My belief is modern plugs are built for high voltages, larger gaps and coils rather than our more feeble mags, so the idea that compatible modern plugs may be used in lieu may not hold water for some bikes. Obvious perhaps, but than again, my 56 Velo seems happy running with an NGK.

Replacing the jets etc is another thing I should have done long ago. For a few quid it represents a good return.

[nevhunter]

Magneto's are weakest at starting. (1/2 engine speed). Don't use 'R' Plugs or suppression leads and keep the Magnetism high. IF the Points burn the Condenser is suspect. THAT will also affect starting. There's also a "Proper" way of kicking. use the 'flywheel" effect and don't have throttle too wide open. Nev

[MarkO]

Nev - all true, but in my case, mag, points and leads were fine as was pick up, carb pilot setting, tappets and timing. I cannot be 100% sure it was the plug, but as I checked everything else beforehand with no appreciable improvement, I cannot think what else it was.

[nevhunter]

Some anti scuffing oil additives short out Plugs on the insulator internal surface. It Gets onto/into the insulator and shorts it out. That will show under load. Multi gap plugs have been found to make No difference. Electricity will always take the Path of least resistance and jump ONE of the gaps. The smaller the Plug Gap the less likelihood of it going somewhere else. I'd use about .020". Small plug gaps make engines on float (Low Load) run less evenly. Cars etc on CDI etc run about .032" and run better on Lean Mixtures. Having more adequate ceramics can't cause any Problem (In My opinion). I've worked om Magnetos all my life and do all my own except for the Coil winding, which is a specialist Job.. I prefer them to COIL. Some of them run a bit hot, where they are situated near and at the rear of the Motor, and many of US ride them Harder than the roads of the day permitted when they were New.. Nev

[MarkO]

My experience is when a poor mag is hot - especially after filling up with fuel when it absorbs more of the heat from the engine and base frame etc - it behaves badly. More so than when cold. Indeed such behaviour can be symptomatic of a mag on the way out. The mag was therefore bench tested with bare HT end and with scope attached to monitor the pulse. All was well so I ruled it out as being the root cause of the problems, so attention turned elsewhere.

I had very similar issues with the Sunbeam. That was definitely the plug. The NGK was dumped in favour of a KLG and the difference was huge. My mantra from now on is use an appropriately aged plug for the bike in question. No more modern plugs for me on older bikes.

[chris.shearwood]

Where are you buying your plugs? There are counterfeit NGK spark plugs on the market.

[MarkO]

Chris

Yes indeed. I am aware. I think the brand new ones were from a decent eBay supplier, and I also fitted a couple of compatible used low milage NGKs before resorting to the Lodge/KLG on the VB and the Sunbeam respectively. I may have been extremely unlucky that all my NGKs were fakes, but it seems unlikely.

[TonyBaxter]

Some of the guys on other forums have had good results on various bikes using BRISK plugs. I haven't tried them myself, but wonder if some on here may have done?

[nevhunter]

A "Crook" mag Coil will run the "shellac" out of it and may seize up as a result when you next attempt to start the Motor from cold. That Heat is caused by leakage of current and may not show till Hours of testing. IF the Coil feels soft It's had it.. There should also be a safety Gap somewhere in the HT side for Protection. You CAN test Plugs AND clean the Insulators with a sharpened Chisel Pointed Hairpin. "Colder" Plugs will soot and short out easier. Nev