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Concentric Mk1 Fuel Starvation

b.l.hayward@tesco.net

Website User
Non-VOC Member
BACKGROUND:Just finished the rebuild on my twin (basket case so was not running previously) and have fuel problems (I think). I have no previous experience of Concentrics Mk1's so don't know if they have any foibles or age problems! Have used 276's, Monoblocs, TT's and GP's and have NEVER had the problem below. Bought the Concentrics from a club member several years ago and have dismantled and cleaned them prior to fitting but have not renewed anything.
SYMPTOMS: Turned on the juice and did the usual carb tickle (3-4 pushes) and started kicking - nothing. This went on for a while with nothing happening - not even a cough! Tickled the carbs some more (actually until petrol started to drip from the float bowls) and it fired up, ran for a bit on one and a half cylinders and then settled down to life as a 500 single! If I blipped the throttle it seemed that both cut in. Felt the pipes and No2 was hot and No1 was cool. Tickled the carbs again and found the float bowl for No1 was empty (ie the tickler did not make contact with the float bowl until I tapped it quite hard up and down against the stops). Fired it up again, ran as a twin for a while and then went back to being a 500 - But with lots of spitting and coughing from No1. If I tickled No1 whilst it was running, this stopped and it chimed in. Occasionally, No1 would be the hot pipe and No2 the cool one! So it seems to me that petrol is not flowing easily into the float bowls, somehow - any thoughts other than I wouldn't use Mk1's!
OTHER INFO: I have fitted new Spares Co fuel lines and taps and the mag has been rebuilt and retested ok (I originally thought I had an intermittent spark causing the problem but I don't) - so I think I am left with a petrol feed problem which should be so simple to fix it's driving me round the bend!
 

Henry Martini

Well Known and Active Website User
Non-VOC Member
Concentric MK 1 Fuel starvation

Hi, As a quick guess it sounds like you need to look and check the float levels but I cant tell you what they should be.
Regards, Henry Martini
 

methamon

Well Known and Active Website User
Non-VOC Member
Concentricity!!!!!!!!!!!!!!!

Hmmmmmmmmmmm. What about; Turn off both petrol taps. If the bowls are fitted with drains, drain the bowls, alternatively remove bowls and drain / dry out; replace & re-connect bowl banjo bolt. Turn on petrol do not touch ticklers, leave for a minute. Turn off petrol, remove bowl banjo bolts and tie pipes out of the way. Both bowls should be full of petrol. Carefully remove bowl screws whilst suppporting the bowl and see if the bowl is indeed filled with petrol. Repeat for the other bowl. If one of the bowls either doesn't have enough or any petrol, possible causes are (not enough fuel in tank - are your carbs fed from one tap each or linked?) blocked or obstructed pipes, blocked filter at banjo, blocked banjo blockage above float needle or as the other gent mentioned incorrectly set float height but I recollect that the floats are plastic and the needle prongs are non adjustable?:)
 

overthehill

Active Website User
Non-VOC Member
i run mk1 concentrics and have been very happy with them - I also have to tickle them until petrol comes out before starting from cold so this is normal.

It sounds like a sticking float which only drops down when you press the tickler.
have you checked that the gasket between the bowl and the body is not catching on the float?
also check the needle valve as the rubber tip can perish - although this usually results in flooding it could cause it to stick closed.
If you run standard fuel lines you do need both taps open in my experience - better safe than sorry anyway - the last thing you want to do is starve one pot of fuel while overtaking a GSXR down Glen Coe.:eek:
 

sidmadrid

Well Known and Active Website User
VOC Member
Had similar symptoms some time ago after a rebuild.
My mk1 concentrics were fitted with brass float needles with Viton tips, after much head scratching I concluded that the brass needle valves were too heavy, the fuel was always shut off. Depressing the tickler pushed the float down and allowed fuel into the float chamber, but as soon as you took your finger off the the tickler the fuel was cut off, no matter what the level of fuel in the chamber. {Hope you under stood that.}
Anyway I fitted nylon float needles and problem solved. sid
 

ksbundy

Active Website User
VOC Member
Concentric carbs

There is an article called "Bushmans Carb Tuning secrets" on a website called www.jba.bc.ca It explains the operation of Amal concentric carbs very well and also includes information on setting the float heights.
Hope this helps
KS
 

biggles

Website User
Non-VOC Member
Hi.
Thanks found it this time good article. I am however not overly fond of Mk 1s
As they don't last very long especially if there is no air cleaner fitted.
I note however that Surrey Cycles now supply a plated brass slide for them which should go some way to overcoming the problem.
Cheers.
Biggles.
 

mercurycrest

Well Known and Active Website User
VOC Member
Hi.


I note however that Surrey Cycles now supply a plated brass slide for them which should go some way to overcoming the problem.
Cheers.
Biggles.

Hi Biggles,
You wouldn't have a website for them would You? I tried to Google
Surrey Cycles UK from here and got pages full of petal cycle shops. Sounds like plated brass slides are just what I need for Wifey's Outfit.
Thanks, John
 
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