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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
 

Mark Stephenson

Well Known and Active Website User
VOC Member
Folks--Success!!! I now have a solid idle at stops and I no longer have "petrol surge" where the bike dies at quick stops.
#1. Fix: tighten throttle stop screws on 276s half a turn.

Contributors: 1. Adjust float bowls more/less at 90 degrees from Carb 2. NKG B6's @.18

Need to replace my BTH Spark Plug leads next as casing melted (touched fin).

Thanks for all the help!!!

Mark
 

chankly bore

Well Known and Active Website User
Non-VOC Member
Note also. The way the H.T. leads go is clearly shown in "Richardson" photographs. The lengths must be, for Lucas magnetos, 26 1/2" and 28 1/2". If they are then clipped correctly they will never touch any fins!
 

MartynG

Well Known and Active Website User
VOC Member
Its a shame to see someone who has been a forum user since 2007 - thats FOURTEEN YEARS - who also badmouths the VOC and refuses to pay for a VOC membership continuing to have free and unfettered access to our valuable resources and our community

What ever happened to ethical behaviour?

Martyn
 
Last edited:

genedn

Well Known and Active Website User
VOC Member
Its a shame to see someone who has been a forum user since 2007 - thats FOURTEEN YEARS - who also badmouths the VOC and refuses to pay for a VOC membership continuing to have free and unfettered access to our valuable resources and our community

What ever happened to ethical behaviour?

Martyn

Personal grievances are best left off the forum. Regardless whether you are right or wrong.
 

Mark Stephenson

Well Known and Active Website User
VOC Member
Folks
I found fault in retiring my original 276's for new 276's. Neophyte move--old 276's "3" throttle valve and top notch needle position for new 276's with "4" throttle valve and 2nd notch needle position. I noticed the bike ran lean...hesitated why I did the compare. I did not give Coventry Spares the throttle valve spec because I knew not.

(All of this got started when I went to a dual twist grip throttle and new cables which I am happy with)

I have a "3" on order from coventry. Question: how does one know beyond trial and error to figure the right # throttle valve? Could you do a compression test and correlate to throttle valve # required?

Thanks

Mark
 

Old Bill

Well Known and Active Website User
VOC Member
Mark, l hate to say l told you so but see posts 23-26, its rare to find two Vincents the same but when tuning there is an awful lot to check, compression, valve clearances, ignition function are all contributing factors. However in this case a straight swop of carbs initiated the fault so it gave a big clue as to where the problem lay. Incidentally three and half slides are generally about right with a standard exhaust but you may need to run the rear carb with the needle in half rich position.
 

greg brillus

Well Known and Active Website User
VOC Member
Never had a Rapide run with number 3 slides.....way too rich.......Sounds like something else wrong I would say.........Perhaps if the old carbs run # 3 slides it could be because the float level is too low.......the lower large cap nut that holds the jet block within the carb body has been available in at least 4 different heights from what I've seen..........the only factory Rapide specified to run a number 3 slide is the front carb on a series "A". This is only to aid in "drawing" the fuel required from the horizontal carb to bowl arrangement........The "A" front carbies are something else again to set up.
 

Old Bill

Well Known and Active Website User
VOC Member
Mark, the old carbs were running 3 slides with the needle in full weak position on both front and rear? As Greg says probably too rich hence the needles in full weak position to compensate, however l have found that the rear carb often requires a richer setting than the front which is usually obtainable via needle position. Suggest three and a half slides with needles in mid position, if the rear spits back a little when warming engine try needle in half rich position. Being sandwiched between the two cylinders the front carb warms up quicker whereas the rear carb being somewhat isolated takes longer hence the possible need for a richer setting. That's my theory anyway, might also explain why the Comet usually requires a richer slide? Oh the joys of Vincents!!
 

MartynG

Well Known and Active Website User
VOC Member
Folks
I found fault in retiring my original 276's for new 276's. Neophyte move--old 276's "3" throttle valve and top notch needle position for new 276's with "4" throttle valve and 2nd notch needle position. I noticed the bike ran lean...hesitated why I did the compare. I did not give Coventry Spares the throttle valve spec because I knew not.

(All of this got started when I went to a dual twist grip throttle and new cables which I am happy with)

I have a "3" on order from coventry. Question: how does one know beyond trial and error to figure the right # throttle valve? Could you do a compression test and correlate to throttle valve # required?

Thanks

Mark
Hi Mark, These AMAL related documents may provide some help
 

Attachments

  • premonobloc booklet.pdf
    1.5 MB · Views: 9
  • Tuning guide cutout.pdf
    760.9 KB · Views: 7
  • How Those Amals Work.doc
    43 KB · Views: 7
  • Carburettors__the_things_you_have_always_wanted_to_know.pdf
    223.7 KB · Views: 6

Mark Stephenson

Well Known and Active Website User
VOC Member
A bit of AMAL History
Martyn...thanks so much. I can't wait to read these!!! Amal ships the first doc with their new carbs that I ironically bought from John Healy:). The tuning guild will take some further reveiw. Look forward to it.

I am excited to see what the "3" will do on my new 276's. and use these guides to tune away.

Mark
 

Mark Stephenson

Well Known and Active Website User
VOC Member
Retail is retail and johns prices would be almost the same as burlens. Shipping in the us from conventry is much, much faster and cheaper than the uk. Shipping speeds would only be exsabated by COVID.
I have bought the carbs from John. Pricing comparable. Appreciate the service. Shipping from UK dodgy and he puts Cookies or Chips in each package:). Have "3" Throttle Valves coming on Monday!!!
 

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