February 28, 20215 yr Hi, Just nearly at the end of Restoring my 198A. And I have a problem with the Amal Carb. I cleaned it out after soaking it in parrafin for a couple of weeks and fitted service kit to the carb but the bike will not fire up off the carb. If I tip a little fuel down the plug hole she fires straight away. I have fitted a new needle valve and checked the float is operating correctly, that is shutting off the flow of petrol when bowl is full. I fitted a new needle in the same position as the old one i.e in the middle grove of the 5 grooves.And if anyone has a list of the correct numbers for the jets that should be in the carb that might help. Any help or advice would be appreciated. I have been advised to bin the Amal and buy another carb but I would like to keep the bike original. Thanks in advance.
February 28, 20215 yr Hi - Amal Concentric Mk. II 27mm. Slide #3 cutaway Main jet 150 Needle jet .106 Pilot jet 20 Cold start jet 40 I suspect your problem lies in the idle circuit (smallest orifices block the easiest) and if it's been lying about unused for a long time I doubt that soaking in paraffin would do any good as far as cleaning it is concerned. You need CARB cleaner ! in aerosol form, preferably. A combination of this, and compressed air if available would be much more effective. Failing this, you may have to resort to using an ultrasound cleaner. But don't ditch the Amal just yet.....
February 28, 20215 yr Has it got any cold starting device..? They used to have a second slide, either operated by cable or just a plunger on the top. My Ossa MAR is very reluctant to start when cold, I have to hold the tickler down for 10-15 seconds after the fuel starts leaking out of the float bowl, so that some goes directly into the crankcase to richen the start. Once the engine is warm, it fires up first kick. .
March 1, 20215 yr Make sure that all parts are correct for your 198A. Even though they look the same they might be different between 2/4-stroke and between Mk1/Mk2 carb. Besides that there are specific parts for some models. Std 2-stroke needle for a series 2900 carb should be marked 2D1 while they for a series 2600 carb should be marked 2B1. Also check that your jet holder is of the correct type and that the air jet is of correct size. Lot of information here www.amalcarb.co.uk.
March 1, 20215 yr 11 hours ago, phiggs said: Has it got any cold starting device..? They used to have a second slide, either operated by cable or just a plunger on the top. What you are describing is an earlier Mk. I Concentric, or Monobloc type instrument. This is a Mk.II, which has a " bypass" cold start control - a carb. within a carb., if you will. This also does away with the need for a tickler.
March 1, 20215 yr Author 20 hours ago, lorenzo said: Hi - Amal Concentric Mk. II 27mm. Slide #3 cutaway Main jet 150 Needle jet .106 Pilot jet 20 Cold start jet 40 I suspect your problem lies in the idle circuit (smallest orifices block the easiest) and if it's been lying about unused for a long time I doubt that soaking in paraffin would do any good as far as cleaning it is concerned. You need CARB cleaner ! in aerosol form, preferably. A combination of this, and compressed air if available would be much more effective. Failing this, you may have to resort to using an ultrasound cleaner. But don't ditch the Amal just yet..... Hi, Thanks to all for the input. I have stripped and checked the carb again! It is jetted with the same as specified above. Given a good clean with carb cleaner and a can of compressed air. I found 2 blocked jets. The needle Jet in the bottom of the carb body and the Cold start Jet which took some finding in the bottom of the float bowl. The numbers on the Carb are "L 2627" and 401. 4 new jets on order so we will see how we get on at the weekend. Cheers. Edited March 1, 20215 yr by Old Gezzer Add Photo
March 2, 20215 yr Looks like a nice carb, I haven't got any of those on my relics. The old Monoblock was notorious for having a rich incident, on most scrambles bikes way back then. The only cure was to lay the bike on the ground whilst it sorted out the mixture. Happened to at least two bikes every Scrambles meeting. .
March 7, 20215 yr Author Hi, Firstly many thanks to all who gave me the helpful advice. Next, Rebuilt the carb after cleaning with Carb Cleaner and fitting 4 new jets as per Lorenzo's advice. Bike now starts, runs and ticks over. The tickover screw is fairly well nearly screwed all the way in. The needle is in the middle of the 5 grooves, If I lift the needle one groove will it give me better use of the tickover screw. 2nd Question, Where do I need to be with the Air Screw? As a starting point how far should I screw it out from it been fully screwed in? When should I know if it is correct and running sweet? Thanks in Advance.👍 Edited March 7, 20215 yr by Old Gezzer Spelling!
March 8, 20215 yr I used to run a 25 pilot with the Amal. I found the air screw was barely one turn out with the 20. With new parts fitted they run fine and require very little tuning/fiddling. The slide, needle and needle jet do require replacing periodically as they are prone to wear, particularly the needle jet and tuning becomes impossible but this does take some time to happen.
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