October 21, 201411 yr Author Ok Larry and all other helpful people, another one for you........... She's up and running but pretty poorly in that she takes a lot of kicking and the plug gets wet. When she fires she will run at higher revs but not low down, like bogging. Got to be a carb issue as the ignition system has been rebuilt ,but I bought her as a non runner so no benchmark to go from. The owners manual for this 248 gives details of a Bing carb, but the one that's on her is a Mk 11 concentric Amal carb. I've had it apart and cleaned it to an inch of its life, thought it was the slow running/ pilot jet but that's fine. Thought it may be the float height letting to much fuel in but I can't see any tangs to alter, not like on other carbs, is there a way to set these or is it just , buy a new one. Any help is appreciated, even the Amal site doesn't recognise the 248 as having an Amal carb fitted just the 247, but 348s did I believe. Have I got the wrong carb????????? Thanking you all in anticipation of speedy cure. Dave. Edited October 21, 201411 yr by chappo
October 21, 201411 yr No Bings on Montesa trials. You need an Amal 2627/411 with 150 main jet, 20 idle jet, 106 needle jet, 2B1 needle, and 3 cutaway throttle slide. But the symptoms you describe are more likely to be electrical. I'd check the ignition point.
October 21, 201411 yr Author Thanks Kingscorpian, I have replaced the points and condenser, moving it to the frame near the coil. The coil is brand new, the stator has been rewound, new plug cap and plug, Timing set to 2.5 mm BTC, points at .04mm. It starts but won't run at low revs, I feel it's going to be something simple when I find the problem. The original Montesa 248 manual I have with the bike says it's a Bing carb and gives all the settings. When I moved the condenser I have ground it to a bare part of the frame ( painted rubbed off ), and spliced the condenser wire into the black and white wire from the stator which then goes to the spade connector on the coil. Very annoying .
October 21, 201411 yr Chappo, The Amal on my 247 was so worn I couldn't get it to run at lower revs. Bought A new Mikuni already jetted from the twin shock shop !!! Them job done ..... Ran like a dream until all of the engine bearings have decided to growl their heads off !!! Rebuild time !!! Good luck The wobbler
October 21, 201411 yr Author Thanks Wobbler, That may be the way ahead, just going to go over the electrics again first. Dave.
October 22, 201411 yr Dave, Hope to be of help, the PM will explain my problem. Best of Luck Larry Edited October 22, 201411 yr by lbhbul
November 12, 201411 yr Author Hi guys, been a month or so since I was able to do battle with my love/ hate 248 Montesa. Still having issues. As previously stated in this forum,she has been virtually rebuilt apart from splitting the mains crankcases, as there was no need, the mains and crank are in good order. She still refuses to run on the Amal concentric carb. I've sent off for a full rebuild kit which has been fitted, float level set etc. She fires up fine and will run on choke but slightly hesitant, then drop the choke and it runs for 30 seconds or so and then if you open the throttle it just dies. I've split the pet cock and cleaned the filters, fuel gets through fine , the tank vent is fine, just seems like it's fuel starvation. All the electrics are fine, rewound stator, new coil, new condenser ( now at the top of the frame ), new points, new plug and cap, good blue spark. HELP ........................
November 12, 201411 yr Dave Does sound like fuel, the symptons you describe if it were a Mikuni; clogged pilot or passages I am no authority on square Amals. Hopefully you can get a spare to try, and eliminate your carb. Do not go buying things. Later on Larry
November 13, 201411 yr The spark plug is dry? Could it be a damaged rubber adaptor? It sounds like if you need more fuel / less air to get a proper mixture once the engine is warm.
November 13, 201411 yr Author Thank you for the replies, just checked the plug and it's wet, which is back to electrics . Just ordered an inline spark plug checker that'll be here on Tuesday. But saying that all the electrics are new from rewound stator, to the condenser, points , plug cap, plug, ignition is 2.5mm from TDC. I'm missing something really basic here........................ Will repost with results of spark plug analysis , see if it's sparking in the barrel, it's sparks really well externally, strong blue spark. Thanks guys. Dave.
November 13, 201411 yr Dave It makes no sense for the plug to be wet, as it seems we run out of gas without choke. Check your PMs. Larry
November 14, 201411 yr Author Wil do Larry. The only thing I'm presuming is that the engine dying is electrical not fuel and is still drawing fuel but not firing,hence wet plug?????
November 15, 201411 yr Hi on my BSA which has an amal carb I find that I need to have the strangler ( choke ) on for a lot longer than you would think, definately longer than thirty seconds If I open the throttle fast there is fuel starvation but after about five mins I can un strangle and it is all good, I have also in the past had "new" components and "refurbished " stators etc that were just not good! also brand new plugs and caps and points that were faulty out of the box? If you can find someone local with the same bike running well it would be good to ask if you can try your new parts on his bike. Cheers
November 20, 201411 yr Author Thanks Allyboy, It's quite possible, going to get a spark plug tester (today) to see if the plug/ electrics are failing under compression. From there it's back to basics and testing each component in turn. Very, very frustrating. Dave.
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.