- Sun Oct 11, 2020 11:48 am
#93471
I've had two enfields with amals, they both did stuff like this. I took the one off my 350 in the end because it eventually wore out so badly, it was unuseable. I'm working round the issues with the one on my 612 but to be frank, once I have my trials bike up and running properly, I'm going to look into fitting a Mikuni.
They seem to have a "clunky" transition from idle to slow running. Both of mine will either cut out as you come to a stop or (more annoyingly) idle normally then cut out as you try to move away after being stopped for a bit. Not every time mind you but often enough to be a pain in the arse and to make you tend to hold it off the idle stop at junctions with the throttle if you might want a quick getaway.
One thing I have noticed is if you park them on the sidestand with the engine running, it exacerbates the problem which does seem to imply fuel level or float movement has something to do with it.
Both of them also had (have) issues with the float/needle valve function which I actually suspect are more of a design issue than anything. For example, on both of mine, if they are parked up with the float bowl full for any length of time more than a week, they won't fill when tickled. to the extent i sometimes have to disconnect the fuel line from the tap and blow down it. I'm going with this being the needle valve sticking in its seat because the tickle button physically moves the float and this can be the only possible reason it wouldn't fill with fuel at this point. I replaced both the float (with an "unsinkable" one) and needle valve/seat on the last one and it still did it. I now turn the fuel off and run the engine for a bit to run the fuel level down before parking up which entirely prevents this happening.
I must say, I've turned into an Amal hater based on the fact when you put the VM carbs back on, normal service is resumed. The above aren't the only reasons.
In the interests of being useful, here's a couple of thoughts for stuff you can look at.
Check the inflow on the carb isn't obstructed in any way. I have a feeling (not based on any real evidence I will admit) that when the bowl is nearly full and the fuel rate slows, it doesn't take much to stop the fuel flowing in, leaving the fuel level somewhat below the desired level. I also find they are reluctant to work properly on the idle circuit unless properly full and stopping from full-chat perhaps brings that issue to a head? I also find mine is much less likely to do it if the tank is over half full (generating a bigger head of pressure?). I also have a nagging suspicion that it doesn't happen dusing normal running because the engine vibration prevents things "sticking".
One thing is the tap, does it have sufficient flow? Some of the indian taps have badly aligned drillings so the outflow isn't everything it should be.
There is a seemingly unecessary filter screen on the filling banjo that can be replaced with a fibre washer. Also check the fit and finish of the drilling the fuel goes into the float chamber through. I've seen pictures of ones partially obstructed with a piece of swarf that wasn't de-burred when it was drilled and the seat fitted on top.
The float bowl itself isn't indexed/dowelled and is only held on with two screws which introduces a degree of slop in the system. The float itself can catch on the edge of the bowl or a slightly protruding gasket. There were witness marks on the alloy to this exact thing happening on the one I had on my 350. When fitting, you can push the bowl away from the moving side of the float slightly as you nip up the screws.
I also wonder if heat may be an issue. Mine is certainly more likely to cut out if I stop after a more spirited run. I do wonder if the heat from the engine is vapourising the fuel and dropping the level. I find I need to tickle the 612 to get it to start after even a 5 minute stop if the engine has been hot. I think this is a known issue because they come with two insulating spacers on the mikcarbs and our hosts also sell tunfol carb spacers.
I'm so suspicious about this fuel filling issue that I have spent more time that I really should be spending looking and listening. For example, I notice that when you turn the fuel on and everything is working correctly you can hear a faint buzzing/fluttering sound (a bit like a spun penny rolling to a stop) as the float bowl approaches full caused by the needle valve rattling against/in its seat before fully closing. I've never heard this sound on a jap bike or mikcarb.
I'll admit I have even considered the logistics of fitting a fuel pump but decided I will live with the idiosyncracies of the thing for now and put the time and money I would have spent on that towards setting up a mikuni.
