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

greg brillus

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 .
 
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