Misc: Ignition Need Advice, can't keep an idle (intermittently) approaching or at a stop with New Amal 276's

Mark Stephenson

Well Known and Active Forum User
Non-VOC Member
Actually, this thread has a certain novelty to it, most riders struggle to start their Vincents let alone get them idling. Bill, only take your hands off the bar to raise your glass and the last new bike l rode was clutchless, however it was a mobility aid! Mark, its pretty obvious but as no ones mentioned it, check your valve clearances, tight clearances don't help slow idling, as the old saying goes, a slappy tappet is a happy tappet
Bill...NO ONE has mentioned this....ON IT! (Soon as I learn how to do this:)
 

Andy H

Forum User
VOC Member
I want to join this thread because after 55,000 very reliable miles my Touring Rapide has been `less than nice` at slow speed. It was starting 1st kick ( A good swing with the valve lifters then let go !) Even with a pair of trainers as footwear. Then I embarked on the 2019 International rally. Before I went I fitted new original type Amals and probably had a bit of cable hang up as it was a bit fast running at times.

Unfortunately in a horrendous thunder storm in Dachau my magneto filled with water. After wonderful assistance from fellow VOC Rallyists ( previously reported on) and a borrowed magneto all appeared well and Peter Volkers tuned my carbs. It ran well afterwards.

I have now refitted my professionally overhauled magneto and it is terrible. Cannot tune it at all to tick over. It just won`t settle down yet will easily exceed permitted speeds and zoom uphill under load., but horrible below 30mph. I am happy the timing is correct. It feels like it always did except below 30 !!

It has been suggested I may have a sticking ATD.

Obviously not applicable to this initial thread with a BTH one.
I fitted new return springs but they were no different than the ones I changed and on the bench it seems to flick back OK. It is a heavy duty one that I bought new when I rebuilt the bike at zero mileage. I would have thought age would loosen it not tighten it !

It is not a device I can take apart to check ,if indeed that is the problem.
I have new Champion N5s which I find are perfect. Had two breakdowns with failed NGKs on the 2014 Italian rally. Was given a second hand set of N5s and did another 2000 miles without a misfire.
I did not touch the carb adjustments during mag overhaul and about 3 months of standing only. Because it would not run right I have since stripped and checked them for swarf but they look perfect.

I know from many years of bike riding carb problems are often electrical and vice versa which is the frustration of which to blame first.
I had this problem when the engine first ran on the 1999 rally and did 3000 miles before the problem was diagnosed. The valve timing on one cylinder was way out of sync. Discovered when I fitted a set of K and N filters which washed clean on the rear cylinder. It was blowing through the carb before sucking !
I have ridden over 50,000 miles with K&Ns with no adverse effects.
Now I will need to check to see if a camshaft has slipped I suppose, but again wouldn`t expect it after all this time.
Any ideas?
 

Bill Thomas

Well Known and Active Forum User
VOC Member
Hello Andy , There is a quick way of checking the valve timing,
Take the spark plugs out and the valve caps off, If a valve is open the adjuster can jam the cap from coming off, So turn the engine over a small amount, You probably know this , Sorry,
Turn the engine over via the rear wheel in second gear till what ever cylinder you want to check is at TDC
On NOT the firing stroke, Both valves should be open the same amount, ie Rocking at TDC,
One going down and the other going up,
You should be able to see the top of the piston though the plug hole,
Maybe get a friend to rock the rear wheel back and forth ? a small amount.
Good Luck, Bill.
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
Andy
Basic engineers logic - if you make a change and it gets worst or introduces a problem then reverse the change to see if you end up back where you start. Also only make one change at a time.
So if you still have access to the mag you borrowed then remove the professionals rebuilt mag and refit the borrowed one. Assuming you have made no other changes since fitting the rebuilt mag then this reversal will answer the question- is the rebuilt mag any good or not. If the bike is back to running ok with the borrowed mag then the problem is with the rebuilt mag. If the bike runs badly with the borrowed mag, just the same as the rebuilt mag then the problem is most probably nothing to do with the ignition.

Simon
 

greg brillus

Well Known and Active Forum User
VOC Member
Any magneto should run 0.018"........The newer BTH mags are a CDI type mag not like a conventional mag. Most all magnetos put out relatively low voltage but higher current, verses coil ignitions which are the opposite. There are many issues that could cause bad running even with a rebuilt magneto........From memory some of the available pickup brushes, the carbon is not good.......they cause tracking around the slip ring and this will cause poor running especially at low engine speed........another mysterious one, was the newer points (contact) assemblies that use the reversible earth contact......We found the actual contact was like a rivet, and this had come loose very slightly.......enough to cause a bad misfire that was very hard to find. The original brass contact assemblies are the best and you can still find them.........So don't assume the mag is ok........Even some of the newer type BTH mags fail for one reason or another........There is always something to keep you on your toes.......
 

rapide049

Well Known and Active Forum User
Non-VOC Member
Greg are you saying the BTH with coils run the plugs at 18 thou as well?
I opened up Brads plugs to 26 thou from 16 thou and it starts easier (thought I read some where up to 28thou -
My bike has standard Mag , suppressor caps (Tacho) BP7ES plugs 18 thou , 34 degrees and is a 1st kick starter , even if it has a sat for a few months on stale fuel
 

greg brillus

Well Known and Active Forum User
VOC Member
The BTH instructions say 0.018" to 0.020" max........the coils are very small, and the unit is CDI discharge to the HT coils........No 12 volt supply to boost anything........A standard Lucas or any other original mags don't like any resistance in the HT system.......this includes resistor plugs.......that is not to say a bike wont run ok with them, but it can cause internal damage that could give some grief at some point.
 

rapide049

Well Known and Active Forum User
Non-VOC Member
The BTH instructions say 0.018" to 0.020" max........the coils are very small, and the unit is CDI discharge to the HT coils........No 12 volt supply to boost anything........A standard Lucas or any other original mags don't like any resistance in the HT system.......this includes resistor plugs.......that is not to say a bike wont run ok with them, but it can cause internal damage that could give some grief at some point.
Thanks for that ,I will gap the plugs back
 
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