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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 Website User
VOC Member
Hello VOC Experts--need some advice

Problem:
Warm or cold idle is not reliable as I come to a stop. On a fast stop even I can experience bike just going dead-but easily re-started thereater. Sitting, the bike will idle generally fine. Trying to set up a reliable idle with New Amal 276's from Coventry

Background:
Series B (2501) with Alton 12V, BTH Mag both <3rs; new replacement 276's with new dual throttle set up and cables. I do notice that my BTH lead cases have become somewhat melted on exhaust fin (cables were to close)...I put electrical tape around the casing damage--could this be the issue as has happened around the time of my new carb install?

What I have tried:
1. Adjust mixture, 2. set throttle stops 3. new spark plugs. (B6's w .16 gap)

What should I try?

Thx so much

Mark
 

greg brillus

Well Known and Active Website User
VOC Member
Brian, yes you are correct when looking at Mk 1 concentric's, but the original side bowl carb's only blowing compressed air through might get a result, as using fine wire will do nothing. To get to the actual fuel pilot jet you need to remove the jet block itself from the main body of the carb........It may come to that if nothing else works.......This is very common on the 229/289 carbs.......either the pilot jet passageway is too small or there can be swarf restricting the same passage.........I have removed the actual fuel pilot jets from newish 36 mm round slide Mikuni's........You could see light passing through the jet, but it had a tiny membrane of dried out fuel across it.......It would not shift with compressed air, and required my using my tapered jet drills to clear the buggers.........These were off a late model Goddet Egli 1330.
 

Chris Launders

Well Known and Active Website User
VOC Member
One problem getting a nice tickover is that if you're used to doing a BMW and Triumph that's not how a Vincent should sound, it should sound uneven. I found the best way for me was to fit the manifolds with take offs for vacuum gauges. Don't use the dial type they are too sensitive for out big slow revving cylinders, I have the Gunson ones with stainless rods in, I also had the same problem when I first got a big Ducati Darmah, it also makes balancing them so much easier.
 

Old Bill

Well Known and Active Website User
VOC Member
Mark, some thoughts; replace HT Leads readily available from car parts shops, ensure good seal between manifold and carb, plumbers ptfe tape perfect for this, ensure carbs are as vertical as possible (if tilted it will affect float height). Are the new carbs set as per the old units in respect of throttle cutaway, jet sizes and needle position? From what you have stated it sounds like a weak mixture but other issues can cause a similar effect. Achieving perfect carb balance is only possible with vacuum gauges and don't forget the two stage rule, balance at idle and at raised slides to synchronise cable lift. As Bill Thomas has written the idle speed will vary considerably from cold to hot engine temperature. In Know thy Beast Eddie Stevens tells us that the rear cylinder needs a richer main jet, interesting theory. My experience has been that the rear carb sometimes requires raising the needle one notch or a richer slide either a 3.5 or 3 in extremes but if using a richer slide return the needle to mid position and set the slow idle just after start up when you can open the throttles with no choke and no spit back, when warm the motor will probably idle a little quick but at least it wont stall at an inappropriate time! Finally remember that as other guys who know far far more than l have said no two Vincents are the same and yes they are temperamental even in the hands of experts like greg, hey ho...
 

greg brillus

Well Known and Active Website User
VOC Member
The trick to tuning an engine for idle speed and mixture is for the engine to be at a nice temperature, neither cold or too hot........You should start the engine and ride the bike not more than 3 to 4 km's around the block, then return to the workshop and get to work quickly.........If the engine is quite warm it is a good idea to have a good sized electric fan at the ready to help keep some air flow over the engine. It pays to keep the bike as upright as possible as well, especially with the original side bowl carby's as these will give a poor reading of the engine if a side stand is used. If you have all the correct tools at the ready, and preferably sat on a stool or low bench very nearby, this helps very much........An engine that starts and runs quite well from cold with no spit backs when the throttle is opened quite quickly is a general indication that the mixture is probably on the rich side.......this is not a bad thing, but it could cause sooting of the plugs.......Despite the differences from modern fuels to old leaded fuels, you can actually get quite good plug readings......You really want the outer steel ring/body to show a light sooty black appearance, with the center electrode area a tan/grey sort of color........If the plug total area is very sooty black, then the mixture is too rich........this is probably an issue with too small a slide cut away, or else the fuel height is too high........Worn needle jets can cause this too, and they don't need to have much wear to cause a rich mixture.........needles themselves actually don't wear much at all, suffering more from mechanical damage if the needle is allowed to pass down the wrong hole in the top of the jet block, the grooves do wear over time as well. Plugs that are oily wet are a sure sign of excess wear in the guides or mechanical failure of the guide and its lock rings, another very common cause for oil on plugs is the oil feed at the rear of the liner is too high in relation to the piston rings, thus feeding oil within the rings, this was a problem right from the factory from what I have seen........Right'o its time for a cuppa tea...........Cheers.
 

Old Bill

Well Known and Active Website User
VOC Member
Greg, you have explained the process in a clear and precise manner especially with regard as to warming the motor and yes l forgot to mention the fan, as a side note, steve at Maughans has said the same re cylinder oil feed locations, reckons the position varies between singles and twins. Should keep Mark busy now!!
 

greg brillus

Well Known and Active Website User
VOC Member
Thanks Bill....... On the 229/289 new carb's, I modify them before installing them to any bike now........I always check the idle circuits and usually trim the slides from a number 4 to about a 3 1/2 to get a bit more fuel in to them.......Going to a number 3 will be too rich........It might seem stupidly obvious, but I also pre set the throttle opening on both carbs before I install them, so the opening at the front/engine side of the slide is about 12 to 13 mm in width.......This is easier to explain than to quote a height figure.........Another simple tip for checking that the carb/bowl is level, with the bike vertical, either on a bike lift or on the rear stand........Stand in front of or behind the bike about 4 or 5 feet and look along the side of the bike down level with the carby and you will quickly see if the bowl is up or down........All these simple checks will help in getting a quicker result with the tune up process........Running any type of air filter will richen the mixture as well........This can be good and bad.......The foam ones that slip over the bell mouths from the VOC spares co work well and probably cause the least restriction, the looks might be a bit ordinary, but any air filter on a Vincent look a bit out of place. I put some lovely paper element air filters on my Rapide years ago, it was completely unrideable........Would not have even made it out of the shed............
 

Old Bill

Well Known and Active Website User
VOC Member
Bang on greg, lets hope Mark can sort his carbs now, cant think of anything for stock carbs that hasn't been covered. Those VOC filters l keep in my consumables box, the damn things are forever falling off! Still like the look of a long bellmouth with wire gauze filters almost as much as the large glass of malt whisky that's in my hand, cheers all
 

Bill Thomas

Well Known and Active Website User
VOC Member
I will drink to that, Cheers !.
I see the new Bikes you don't have to use the clutch for up or down !,
But Vincent's you have to Ride !,
So No taking your hands off the bars, And watch out for the Pot Holes !!.
Cheers Bill.
 

Old Bill

Well Known and Active Website User
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
 

Mark Stephenson

Well Known and Active Website User
VOC Member
Funny and likely having the benefit of truth...
I wonder if uneven firing of a Vincent Twin makes it harder ?,
At one time with Mk1 concentrics , I soldered the head of a key into the screw head,
Of the slow speed screw, Adjusts the slide, And if in traffic for a long time I could just
Turn it up or down a touch on the front carb', Worked well !,
As I said the heat of the big lump of a Twin goes up quick, More so on a hot day.
To me it's a wonder these things run at all :D .
 

Mark Stephenson

Well Known and Active Website User
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

New Website 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 Website 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.
 

vin998

Well Known and Active Website User
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 Website 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

Active Website User
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 Website 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

Active Website 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.
Thanks for that ,I will gap the plugs back
 

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