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Mk1 Concentric bad starting from warm


Bill Thomas

Well Known and Active Website User
VOC Member
Years ago as a Car Mechanic, I used to go on breakdowns To find mostly women had the choke out, Because they always start it with the choke out !!.
Reminds me of my Dad, Went to the doctors, The Doc' says this is to stop your headache ,Dad said, I don't have headaches, Doc says you will after you take these other pills.
They are putting so much junk in this Petrol, And we all know it's not good for us, We were better off with a bit of lead. Cheers Bill.
 

Len Matthews

Well Known and Active Website User
VOC Member
The thing is Greg, I have only been out the once, This year, And with me giving it a good flood, I can't fault it,
YET !. If it would only stop peeing oil from where the Macdougleator goes in, It would be Perfect !.
Gave it a good clean up and it looks Super.
Now Comet time, Cleaned it up last night and it's looking the Bizz.
I wonder if it's going to be good this year ?.
Might try and get out later.
Have Fun, Bill.
Bill, in your post you mentioned McDougalater. I had a spate of starting problems until I ditched the car alternator I had used for years. As you know car type alternators need battery input to start charging.Mine was robbing power from my ignition coil hence the starting problems.I'm now using an Alton which requires no battery input.
 

greg brillus

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VOC Member
I put small insulator spacers between the cylinder head and manifolds, but I don't think it did much. Perhaps the spacers need to be quite thick to have more affect. I think this is an offshoot of the modern fuels, where it appears that the top end volatile properties of the fuel boil off quickly. This explains Steven's comment about the need to enrichen the mixture on a hot engine, something that was not needed with leaded fuel. The experimenting to get it right can drive you nuts at times, and can cause havoc with your right leg too.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have them on the l/ning, And my special with Dellortos has a nylon sleve where they fit over, Always thought the carb was too cold !,Very strange. Cheers Bill.
 

Normski

Well Known and Active Website User
VOC Member
It may be as Greg says, heat from the head transferring into the carb body and vaporising the fuel. Tickling would put a fresh lot of cool petrol in to counteract this. That would explain the contradiction of flooding helping a hot engine to start. Triumph specified a thicker o ring than the Amal one for the carb to manifold fitting which along with some stepped studs and rubber bits meant that there was no metal to metal contact between manifold and carb. Even after a good thrashing you could feel the heat difference either side of this with the carb being cool - set up like this there was never the fear that a quick stop would lead to starting troubles. On my Egli I've monoblocs with 1/4" Tufnol spacers but there is still some slight metal to metal contact through the mounting studs, it's on the job list to insulate those too. As an aside I've never had carb icing with a Brit bike but it has plagued some oriental ones.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Morning Norm, I have had icing with my E.I. flat slide carbs from USA, Only at slow running, I guess it's when the air speed is so high though a small gap, They were on Rubber mounts like Amal Mk2.
I think Amal said you have to run richer with this new petrol, But I have found you have to lean the carbs off or it fouls the plugs, I might have got that wrong !!.
I wish I had not sold my T.T. carbs, They just needed leaning off, But I didn't understand what was going on !.
Glad Steven and Norm are backing me up, I thought I was going Mad, Why has this not been in print before.
Cheers Bill.
 

Normski

Well Known and Active Website User
VOC Member
Is the engine using any oil Bill? Could you be leaning it off to make the plugs hot enough to keep them clean of oil? ( I think you mentioned that possibility in a post above) What happens with the next grade hotter plug?
 

Bill Thomas

Well Known and Active Website User
VOC Member
I thought you might like this Bill, it's from the blue'un in 1956View attachment 21971
Thank's Mac, They were good times, I think we have all drunk a bit of that, When getting petrol out of a tank !.
It was still good in the late 70s, I ran my Special with 12 to 1 pistons on the road and track, Was doing 110 mph over the finish line of 1/4 mile standing start 12.5 seconds.
I have had a taste of this new stuff !, They say I should be Dead.
Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Is the engine using any oil Bill? Could you be leaning it off to make the plugs hot enough to keep them clean of oil? ( I think you mentioned that possibility in a post above) What happens with the next grade hotter plug?
You might be right, It's not too bad Norm, Old type Race pistons, 10 thou gap. I tried 7 thou and locked it up on the M4 Playing with a HondaKwaki I am running Champion N5, Now gone over to N9yc, Don't really want to go any hotter, In case it holes a piston, Any colder, stops in 20 miles.
Cheers Bill.
 

Hugo Myatt

Well Known and Active Website User
VOC Member
When I swapped the standard but worn out original carbs on my Rapide for Mk 11s an established Vincent expert made me two beautiful inlet stubs that connected them directly to the heads. However I discovered that stopping for an interlude of one pint of fine ale was sufficient to make the machine a pig to re-start. Two pints and it was raring to go again but I would not be as the looming threat of the Road Traffic Act would be hanging over me. I reverted to less grandiose stubs with the Amal rubber connector and the problem disappeared. I reckon the rubber connector acted as an insulator against heat transfer and prevented the vapourising of the fuel in the float chamber. With the original standard carbs the float chamber was semi-remote and on a long arm so that heat transference was not such a a problem.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Give me a clue Hugo, Am I going to get stuck at the Pub, Joke, I don't drink.
Surely with a Mk2 It will have to be rubber mounted ?.
I have just ordered a pair of Club Shop stubs, They look nice, 2 front heads type, Fairly short.
Cheers Bill.
 

Hugo Myatt

Well Known and Active Website User
VOC Member
Bill, as long as you only take circular rides you'll be all right.

On a practical note it pays to renew the rubber connections regularly as they eventually crack and then leak air. Also, as KTB recommends, use wider Jubilee clips than those supplied. I think mine are 12mm. Mk11s were intended to be additionally supported to some part of the bikes anatomy using the two threaded holes at the top of the carbs. This isn't really possible on the Vincent due to a lack of suitable fixing points, which means they waggle about more than on most conventional machines. I think it is this that leads to the degrading of the rubber connectors.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I think the Mk2 s are much lighter than Mk1 s, Better metal etc.
Just got my Inlet Stubs from Club Shop, Very quick, Many thanks Jayne and Ian.
Now have to get all the bits that were missing, The Bloke said they came off a Shadow !,
If so, Shadows don't need Main jets, Float needles, Slide spring and special big washers to hold the needles in place, Choke lever, Some screws to hold the float bowl on etc, What Fun !!.
Don't watch this space !, It will be ages before I get it running on these. Cheers Bill.
 

Daytonanorton

New Website User
Non-VOC Member
Just got back from first ride of the year, Gave a lot of thought to bad starting over the winter.
Just picked up a pair of Mk2, Bit of a joke, When I looked inside , Half the bits are missing, Don't buy unseen bits !!.
Anyway,Because of this rubbish Petrol, I have to run weak, Or the plugs will foul.
Back to Mk1,s, I have not been flooding enough !!. Partly because I don't like petrol all over my nice clean engine.
And a life time of a mechanic say's I should not !.
So on a hot day, Down on the coast, Quick chat, Then time to restart, I am being watched !, Gave it a real good flooding, Thought this is never going to work,
Starts first kick, Went round the bay a bit more, After a short stop, Same thing, First Kick, I can't tell you how much I have been kicking this bike these last few years,
Since I took my T.T. carb's off.
Learning All The Time !!. Cheers Bill. P.S. I have not touched the Carb's or Plugs etc over the Winter, Left old petrol in there.
Hi Bill, I've just joined this forum so I can give you some feed back. I have just finished building a Daytona spec norton dominator and have exactly the same problem with poor starting as you (and yes the excessive flooding technique works for me too), however looking in to this a bit deeper when I flood the float bowls no fuel actually gets out of the flat top spay tube so no fuel gets down the port into the engine. Having done some research on different spray tubes fitted to mk1 concentrics I found there were 4 types and one of them appearently was designed for the 850 commando which has a cut out on the engine side of the spray tube allowing the fuel into the port when the float is flooded. I read somewhere also that one of the reasons for this was that the larger capacity motor had a lower compression ratio and less suck to draw the fuel in to prime the cylinders - sounds very familiar doesn't it! So I have brought a couple to try and will let you know if it solves the problem. Also I believe that my shallow down draft angle is probably not helping as all the commands are steeper and most of the early commies have either single carb of 2x smaller ones so more suck - not 2x 30mm drain pipes like I have , Kind regards Sarah
 

Bill Thomas

Well Known and Active Website User
VOC Member
Good luck, All Bikes are Different, I tried the spray tube mod' for 4 strokes, Didn't work for me.
Now a Fan of Mk2, But as Stu told us, The Slides can stick bad, If the wrong type.
Funny, The Comet 500cc single, Seems to start and run well, What ever I put on it !!, And that Bike is the most worn out of them all !. Cheers Bill.
 

Chris Launders

Well Known and Active Website User
VOC Member
As regards Mk1s and float levels I had an instance last year of fuel starvation, I had the float level set with the float level .080 (2mm) below the face of the float bowl and a brass needle with Viton tip, so I couldn't understand what was happening as I had a good flow to the carb, I called Amal and was informed that with modern fuel the float should now be set level with the top of the float bowl and they have found that unless the float actually lifts the needle the brass one is too heavy to be lifted by the petrol pressure alone so now recommend an alloy needle with Viton tip. The latter was the problem I had, the float was hitting part of the float bowl before lifting the needle but was taking pressure off it so some fuel was getting through, enough for steady riding but anything over 60mph and it was being starved.
 

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