Hi. i have a 1965 A65 twin. when i bought the bike it had a wassel carb on it, i was also given the amal 389 67 carb that was supposed to be the original. wanting to keep it as it came out of the factory i stripped the carb and cleaned all the parts in a sonic cleaner. put a new gasket set on it and fitted it, set the mixture screw to standard, the bike started first kick and ticks over nicely, but does not like much choke, the plugs are black and sooty. t ticks over lovely, and pulls off well, but when out for a long run it seems to splutter mid range, when i give it full throttle it clears and runs nice, and as soon as i settle to a 40/50mph cruise speed it goes back to slightly spluttering, if i drop a gear so the revs are higher it seems normal, my pilot jet is a 25 and the slide valve is a 3. 1/2. i was thinking of buying a 4 and trying that, any suggestions please.

You haven't got a washer under the float valve seat, either that or the seat and float needle are worn so giving a rich mixture.

I fitted a new float valve and no washer under it. just a fibre washer
the float valve is working ,i did check it.

sorry i got a tad confused, new to all this, there is a silver washer under the float valve chamber, not a fibre one, when i put a rubber tube over the filler and 2 holes either side and blow with the float valve pushed up gently no air can pass, so i assume petrol can not pass when its closed either.??

Remove the washer, no fuel will come out. By removing the washer you will lower the fuel level and weaken the mixture and no doubt will solve your problem.

ok will give that ago cheers.

despite what looks like a washer ,it is actually part of the float valve case and cant be removed.

Hello tige,

Have you checked the needle position?  Even if properly positioned, sometimes during fitting the slide etc. back in the needle can be pushed up a notch.  The little clip can get a bit weak with age.  There is also the likely hood that the carb. is worn internally so upsetting the standard settings.  It may be worth tweaking the pilot screw as well as checking/lowering the needle.  I have a 'Colortune' kit that lets you see the colour of the combustion whilst you make adjustments - worth a try if you can get one.

Dave.

I will have a look at the needle, and try dropping it and then do a plug check. the carb worn theory may be a more likely scenario, i will try a number 4 slide as ive ordered one anyway, if i get no joy, i will try a new amal. thanks for the advise all.

Sometimes, it is easier and cheaper to get a new carburetor than to keep buying and replacing parts on an old carb body. I found that out several times in the past.
Used Hitchcocks who are very good and will jet and set up carb for whatever bike you tell them. Also very quick service!

Yes you are probably correct, However because i already have the slide i may as well fit it and drop the needle a notch and try it. do you have a link for hitchcocks, Just in case i have no joy.

I use Surrey cycles for all of my amal purchases. Very knowledgeable as that is all they deal in. Vert quick delivery and reasonably priced.

Just had a look on surrey cycles £208.00 each, Hitchcocks £170.00 some big price differences. Fitted the slide i ordered and dropped the needle a notch, just want a dry day to take it for a run. will come back with results if any. then think about a new one if i get no joy, thanks again for advise.

 

I go direct on line to AMAL. also very good will jet etc to specific request/type.

Turn round is not brilliant, but I think improving again again now.

Mike

UPDATE. been out for a run this afternoon and all good, rides smooth now mid range , had to turn the air screw in half a turn as it was now popping on de acceleration, now runs sweet . many thanks for all the help and advise.