I have a 1962 A65 with the correct AMALMonobloc carb fitted the bike was running great except it was running quite rich tried tuning but still running rich so decided to renew the internals of the carb bought a repair kit from Burlen also new throttle slide. Replaced main and pilot jet needle jet and new needle new air screw new float needle new gaskets. When I came to start it needed full choke to start which is unusual also could not close the choke until it warmed up otherwise it cut out. the bike keeps spitting through the carb also banging in the exhaust. It runs better if you screw the air screw right in but as soon as you screw it out about 1 and half turns problems start. I cannot get it to tick over for more than a few seconds it sounds like petrol starvation. I did lower the needle from positon 3 to position 2 when it was running rich but to no improvement it is still in position 2 I have conflicting settings AMAL says position 3 but another book says position 2. I did not think that the needle position 3 or 2 would give me the problems I am having advice would be appreciated please.
Thanks for the quick reply the gaskets are new I did check the pilot jet but no blockage I will tomorrow check the float level. The reason I bought new parts was when I got the bike it had a Concentric carb on which was no good I obtained a correct Monobloc but do not know how many miles it has done and being unable to cure the very rich running I decided to renew the internals. The bike was starting and running great just could not cure the rich running.
I have had another go today to solve my problem, I started by checking the float level which proved to be okay. I took the carb off and completely stripped it down checked everything blew compressed air through to clear any possible blockages then rebuilt it fitted it and on start up nothing had changed still spitting in the carb and banging in the exhaust, the only way I could get it to run was to screw the mixture screw in as far as it would go. So I took the carb off again and swapped all the new parts for the original old parts and the bike is now running again, using the Gunsons colourtune I can get it to tick over correctly but showing yellow which is rich, screwing the mixture screw in I can get it to turn blue but the tickover is a bit fast and I cannot slow it down because the throttle adjuster is not touching the throttle valve. I have tried adjusting both throttle adjuster and mixture screw but cannot get a satisfactory result. Where do I go from here. The bike has Pazon ignition but the problem is not ignition it is I believe a carb problem.
I think the slide, gaskets, and fit are ok. You may have too fat a main jet, worn out main jet, or the needle adjustment is incorrect. However I think its a timing issue because when the color tune shows correct your are too fast at idle.. 1. Start with the cable adjustment at the top of the carb. You need to make sureh the slide all the way down then slowly bring it into tune. 2. Ignition may be to far advanced. You need to strobe it at the primary side to make sure. Yes its a hassle because the early A65 did not come with an ispection plate to check this. I remove the primary cover, then use a hose to hold the chain tensioner in place while I run it. Or you can just run it as is and retard the Boyer ( that would be the easy fix) Good luck Richard
You may have too fat a main jet, worn out main jet, or the needle adjustment is incorrect.
You could remove the main jet from this carburetor and the bike would still run properly right up through, and slightly beyond, one half throttle! At idle the needle has absolutely no effect on carburation.
The symptom you speak of when you have to turn the pilot air screw all the way in to get the bike to idle screams to me that the pilot jet is some how blocked: one of the orifices is blocked or it has too small an jet orifice.
With all of the old bits installed, swap out just the NEW pilot jet into the body. Make sure it seats fully and try just that one change. John
Thank you John I agree with what you are saying. I have had the bike out for a short run this morning and it is running perfectly, but the plugs are still showing a very rich mixture. Now going back to the beginning I tried to cure the rich running by lowering the needle from position 3 to position 2 but that made no difference so I decided maybe the needle and the needle jet are worn. So I bought an overhaul kit from Burlen which included new needle and jet also new pilot jet main jet mixture screw float needle and throttle slide. Now on fitting the new parts the bike would not tick over unless you screwed the mixture screw right in also when opening the throttle there was spitting in the carb and popping in the exhausts. I removed the carb stripped it down checked everything blew through the jets and holes in the carb with compressed air rebuilt it up and refitted but it made no difference, so I again stripped the carb but removed all the new parts and fitted all the old parts and the bike is now running perfectly except it is still running rich. What I intend to do now is when I get the time I will try fitting just the new needle and needle jet and see how it goes. I am tuning the idle mixture with a Gunson Colourtune when I first started it, it was showing yellow which is rich but if I screwed the mixture screw out over which should weaken the mixture it did not change but when I screwed it in over it turned blue which is correct. If you increase the revs it turns yellow but at idle it settles down to blue. I still cannot understand why after fitting the new parts the bike will not run correctly and have checked that they are the correct parts for my carb.
In a way of explanation why your old parts run well, but the plugs appear rich is typical of an AMAL that has some miles on it. The one thing that wears in these carburetors is the needle jet. It is the jet controlling fuel delivery at throttle openings used most. As it wears the fuel mixture gets richer. This is normal and these needle jets should be considered wear items just like oil, tires, spark plugs and points.
Main jets on the other hand don't wear, although they can get blocked with deposits, and pilot jets don't wear, and again can get blocked. Both of these conditions cause the bike to run lean. So it doesn't surprise me the bike runs with the old jets, but the plugs are black (there are a lot of other reasons the plugs are black and these might need to be explored).
Forget the color tune as your ear is just as good. The drill for any AMAL is Main jet first, but as we can look in the manual for the proper size main jet we do not need to make a high speed open throttle run down the high way. I can expand upon this, but lets move on to the second thing you MUST TUNE. The pilot air screw and pilot jet (or what is the main jet for the idle carburetor). You tune the pilot jet/air screw so the screw: 1. Is as close to 1 1/2 turns out from seating. 2. That the idle speed falls of if it is turned in or out from the 1 1/2 position. You adjust the size of the pilot jet so the needle ends up sitting at 1 1/2 turns. Why 1 1/2 turns? It has to do with air velocity going through the orifice created by the tip of the air screw and hole in the body. To small, and the air velocity is too fast. To large and the air velocity is too slow. Like the main venturi you are looking for something around Mach 0.3 or 0.4. Once you get this right you move up to the slide cutaway and then needle needle jet.
Now we all make mistakes, and Burlen is no exception, but it is rare these days. They have assembled a dedicated group and quality control has been a top priority. But when faced with the proper bits, and a carburetor that will not perform properly it is time to check things. And as you are relying on the flame color and not the air orifice I would either get a plug gage to measure the pilot jet, or leave all of the old parts in the carburetor and just change the pilot jet. I cannot over emphasize the importance of the proper operation of the idle carburetor (pilot air screw and pilot jet) in the overall operation of the carburetor.
Make one change at a time, and start at the beginning, and that is the pilot air screw and size/operation of the pilot jet.
Now, no one is perfect! After a modest start some 10 years ago, Burlen finally assembled a group who are dedicated to making the best AMAL possible. One of your new (and new NEVER always means good) might be out of spec. It is possible and you need to sort it out on piece at a time. This can be done with plug gages, or by changing ONE thing at a time. HTH
Thanks John for the time you have put into your reply and I will do as you recommend. As it stands now the mixture screw is about 11/2 turns out now the bike is running perfectly. This all started some time ago after the restoration I must have fitted a couple of dodgy plugs the bike was missing when warmed up so I fitted some new plugs and the missing was cured but I noticed that the plugs were showing signs of very rich running I left it for a few months bike running really well then checked the plugs and still running very rich so decided to try and cure it hence the problems I am having but I will do as you suggest and take it one step at a time, thanks again for your time.