626 Concentric idle circuit ?

[A10 JWO]

What are the problems if this section of the Amal is blocked, novice speaking. I have symptoms of no starting and fuel starvation when I push start it.
I am willing to learn in my retirement.
Ta Colin

[Billybream]

Hi Colin.
My tip is clean and clean again, all jets, orifices and pathways, very useful is Amal,s web page : http://www.amalcarb.co.uk/

[iansoady]

Older Concentrics didn't have a proper idle jet (just a bushing) and the very small passage to this gets blocked up very easily. It's worth trying an ultrasonic cleaner, and blowing high pressure air through all the passages.

[A10 JWO]

Hi
Pulled it down again and set an air line on it. Started first kick but boy is it rich, thin black smoke. I have read that I need to screw the idle in and 1 and half turns out. Tried that still rich. Tried screwing it in a bit more and it cuts out. My Haynes does not cover Concentric set up ???
Ta very much.
When it did cut out fuel spat out the venturi at the back of the carb ( bigger hole not the main intake )

[Triton Thrasher]

Screwing the idle mixture screw inward makes it richer!

[A10 JWO]

I read that the old monobloc was the opposite way round. Will try that in daylight, thanks.
Colin

[muskrat]

 G'day Colin. The first of the concentrics had a pilot jet screwed in the body at the back of the float chamber. Most use a #25 jet. The later ones had a fixed jet inserted as Iansoady says. This jet is 0.016" and is at the bottom of the pilot screw hole. Have a look down the hole, if you can see brass it has that jet. Use a oxy tip cleaner to clean it. The later type still have the thread for the screw in jet. Has been known for people to drill out that jet and use the older screw in type so if you have the later type make sure it's still 16thou.
Cheers

[Triton Thrasher]

I read that the old monobloc was the opposite way round. Will try that in daylight, thanks.
Colin

On Monoblocs and Concentrics, the screw restricts air, so screwing it in enriches the pilot mixture.

[iansoady]

I think it was something exotic like the TT or RN where it worked the other way round.

[Topdad]

if the bikes been stored for a while and seeing as it was ok and then developed a problem I'd check the tank for rust ,if present it can block or restrict the tap filters ,worth checking , could could be that you're curing the fault short term but not getting rid of the real problem, this happened to mine during the first month,also even the petrol cap vent hole, regards BobH.

[bsa-bill]

I'd check the tank for rust ,if present it can block or restrict the tap filters ,worth checking

My thoughts too Bob which is why I suggested checking fuel flow but maybe I didn't make clear you need to let it run for a while into something like a half litre or more container as you can sometimes get an initial rush of fuel through the pipe then it will slow down as  stuff around the filter/s will collect and restrict flow, can't recall Colin's findings though

[A10 JWO]

The fuel appears to be clean from the tank now. I will put the needle on the middle notch in lieu of the bottom one albeit I thought that my richness problem was the idle not the main jet, am I right so far ?
Ta Chaps
Colin

[chaterlea25]

Hi All,
Colin,
This link may help, http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=11

On some bikes fitted with concentrics I have found it necessary to "ream out" the pilot bush to 0.020 or a shade more
as the carbs could not give enough air/fuel mix when the screw is in too far
the symptoms are spitting bach under initial acceleration !!!!
The recommended mod for concentrics on Vincent twins also calls for cutting away part of the  brass bush that surrounds the throttle needle in the venturi !!!!

Give me a Monobloc anyday !!!!!!!

HTH
John

[A10 JWO]

Thanks chap.
Moved the needle to the middle setting. Cleaned all the jets out with Car Plan carb cleaner and it runs and rides like new. The bike has only done 2 miles since rebuild and the oil is quite dirty, is that normal. I intend to change it at 50 miles of running in.

What a great forum.

Colin

[metalflake11]

Yes, it is normal for the oil to get dirty quickly after a build. Others on here may have different ideas but this is what I recommend.
1/. Ride 25 miles away from home, head back and drop the oil on arrival home. Don't go over 40mph and don't open the throttle more than 1/4, but allow the engine to rev out. ie light load/maximum oil pressure.
2/. Change oil after 500 miles, no faster than 50mph. From this point start increasing throttle opening gradually.
3/. Change oil at 1,000 miles. I take my oil tank off at this point and run a full jet wash cycle through it and re-fit. (I actually have two tanks, one dry and ready to go on and the other in the wash, so to speak.)
4/.Change oil 1,000 miles.
5/. Change oil and clean the tank again after another1,000 miles.
                                        Rob.