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Mk1 Concentric bad starting from warm


Bill Thomas

Well Known and Active Website User
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.
 

greg brillus

Well Known and Active Website User
VOC Member
Bill, If you find you are kicking many times and not firing it is a good idea to stop and remove the plug to see if it is wet (flooded or too rich........Float level or similar) if not then you are too lean. i find it is a fine line between too lean or too rich as you know they all behave differently. Most Mk 1's respond to tickling till they dribble out the button............Only other thing could be if the slide cut away is too large even a small change here will affect how it behaves, and the slide numbers differ from each model of carb too...............;).
 

Bill Thomas

Well Known and Active Website User
VOC Member
Cheers Greg, But we are talking about a hot engine, Everything tells me not to flood it, I am too old to do all this kicking.
This is a L/ning spec motor, Starts first time after stopping for petrol, Runs below 40 mph easy, Ticks over nice,
Pulls like a train !, Compared to a standard bike .
Mk2 Robinson cams.
I had to hand cut the slides, Weak, Or it will wet the plugs, Might be a bit oily, Old Specialloid, Race clearance.
Rita ign'. Very strange. Cheers Bill.
 

greg brillus

Well Known and Active Website User
VOC Member
Bill, I found most Brit bikes with amal carbs like no throttle when starting from hot, this can be difficult when you swing down on the kickstart lever, as your hand tends to open the throttle. Cheers...........Greg.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Morning Greg, I know what you mean, But I have been playing with all sorts of carb's for years, We even made our own Wal Philips type fuel injector.
This bike never spits back, ie weak, Even on cold days, And yesterday was Hot for UK.
I know it's this Petrol, And they say they are going to put more of this stuff, Pee !!, In it in years to come.
Cheers Bill. P.S. Happy Birthday Marcus.
 

vibrac

Well Known and Active Website User
VOC Member
Morning Greg, I know what you mean, But I have been playing with all sorts of carb's for years, We even made our own Wal Philips type fuel injector.
This bike never spits back, ie weak, Even on cold days, And yesterday was Hot for UK.
I know it's this Petrol, And they say they are going to put more of this stuff, Pee !!, In it in years to come.
Cheers Bill. P.S. Happy Birthday Marcus.
Have you tried Esso top brand Bill they are the only petrol company with the guts to say ethanol free on their web site.
However I should add that I have recently had reports that some paint removal problems have still been noted with even this brew (who knows what other stuff they add) when I get a chance I will do a ethanol check in a jamjar
 

Bill Thomas

Well Known and Active Website User
VOC Member
I have got one of those, But it's not on my normal ride, I like to leave the house and fill up 1/2 a mile away,
Don't want any running out of petrol !.
It gives me a chance to see if the bike is OK before going too far, Silly habit I know, But that's who I am !.
Cheers Bill.
 

Albervin

Well Known and Active Website User
VOC Member
Modern fuel is weird. I have standard carbs on my B Rap. with 190 main jets and 3 1/2 slides. Cold, I lightly tickle front carb, find the correct stroke and kick through with a bit of throttle. Fires almost every time. If not then next kick is with full throttle and that always works.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Tis Strange, My 28mm concentric slides are out to nearly 4, Tried going back a bit and break down in about
20 miles, I can't do messing at the side of the road, Looks bad with a Vincent !.
With in 1/2 an hour, 2 people asked me, How much and how long have I had it !.
I said to one of them, 53 years, And she said I must have bought it New !.
I can't bring myself to try Full Throttle, I saw Harvey do it on youtube, With his A Twin.
Funny thing is, My knackered Comet, Flash spec, Will start fine, With all sorts of Carb'.
Ron's Comet likes Full choke Mk1 concentric, I even put chokes on mine and it did work sometimes.
Anyway, I can still ride !, Magic. Cheers Bill.DSCN0015.JPG
 

greg brillus

Well Known and Active Website User
VOC Member
Bill, I think the Mk 1 and 2 Concentrics can tend to suffer from a float level that is too high. Modern fuel atomizes very readily which could cause partial flooding. A larger cut away can make an engine harder to start. If the carb is worn you might consider replacing it with the newer premier model, as Amal hardly sell any of the original spec MK 1 Concentrics anymore. I don't believe they are expensive to buy either. Cheers......Greg.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I never liked the Mk1 s, but she runs so good at the moment.
I have just bought a pair of second hand Mk2 s, To me they are a Proper Carb' with Proper Chokes,
I am very pleased with the one I have on the Comet now, Just need to get Manifolds etc, Might get Ron to get them on Open Day at the Factory. If they make the twin go better, 30mm !!, Not sure I will be able to handle
all the Power! Cheers Bill.
 

erik

Well Known and Active Website User
VOC Member
flooding when engine is warm shood be contraprductive.what is about the ignition?if the magneto is weak this poor warm starting is a symptom.mostly the capacitor is behind his best days.regards Erik
 

Bill Thomas

Well Known and Active Website User
VOC Member
I know what you mean Eric, Which is why I have never done it before.
I have been a Car and Motorcycle Mechanic for many years.
The Ignition is Rita electronic, Not a Mag'.
Nobody was more surprised than me when it started and it did it again half an hour later.
I agree with Greg, That the weak slide may be some of the trouble, But I have tried slightly richer and it wets the plugs, So I had to try something else, I have also tried altering the float level.
Maybe a better Carb' I hope the Mk2 Amal, May fix it, But for now it seems to work. Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Now you have me !, I know nothing about electrics, I don't think the systems made for Vin's are very good.
If they were good, I think you would be able to run bigger plug gaps, Like cars.
When I needed an ignition for my ex L/ning, The only thing on the market was Rita, I hate it but untill it packs up it will have to do.
I now have a spare "D" Distributor, For next time !.
I have the same fault with my Special, With "D" distributor, But with 36mm Dellortos, I have a proper choke.
None of my Bikes Spit back when cold, So I don't think the slides are too weak.
Same on that Bike, If I go richer, Plugs foul in short time.
I think we all agree that the pilot setting on Mk1 concentrics are not good, Some like jets some not.
Brother Ron's won't work with them, Mine won't work without !!.
Cheers Bill.
 

erik

Well Known and Active Website User
VOC Member
my opinion is:if you have a weak spark,and you will have it all over the range ,you can Forget carb Tuning.the first thing to check is the ignition.under compression and heat the spark is different from if you screw out the plug and look at it.and when the ignition works perfect and the Timing is correct,then you start Tuning the carb.best regards Erik
 

Bill Thomas

Well Known and Active Website User
VOC Member
It's only when it's been standing for a short time after a run, The bike goes too well apart from then.
I have tried 12v twin coil, But it's now back to 2x 6v, It seems to prefer that, Rita told me to try a Twin coil 12v.
If it's still in trouble when I am 90, I will have to sell it !. Cheers Bill.
 

greg brillus

Well Known and Active Website User
VOC Member
I'm not sure you are alone there Bill, I've found my bike start straight away after a fuel stop. But if you stop for say 20 to 30 minutes, then you can have trouble. I think it is the heat soak from the engine that Percolates the fuel in the carb. So is it rich or lean for the next start................:rolleyes:..............Cheers............Greg.
 

Bill Thomas

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.
 

ClassicBiker

Well Known and Active Website User
VOC Member
Bill,
I know it seems counter productive to flood a warm engine but my '72 Triumph Daytona has always required a good flooding to start when hot. It has run RITA since the early '80s. In fact it ran the original 12 volt coils until last year. When it started to exhibit what Erik is referring too. I think Greg is correct it is heat soak vaporizing the fuel. I had a '66 Triumph TR4A that would not restart when hot unless I made the mixture extremely rich. I cured that problem by having the radiator re-cored. That brought the temperature right down.
Steven
 

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