I took my 1936/7 model 18 out for a run yesterday. It ran well at speed but was obviously running very rich. The 1.1/16 276 Amal is pretty worn but I think it may have the wrong needle which has 5 settings (like my Commando). On return I checked the plug which was soot black after 10 miles on open quiet roads. Reading through the book it seems that the correct needle has only two settings but I apprerciate the five setting needle could be a development. Does anyone know the details for the correct needle? Any other advice on running very rich, which has developed without me knowingly changing anything, would be appreciated. Thanks
I've a couple of bikes with 276 type carbs, both have needles with 5 settings.
If this has occured without you changing anything I would suggest a blockage in one of the small airways in the carb.
It's a straightforward job to give it a strip down, clean and a blow out with an airline and see if that cures it.
In addition to Ian's comments, if the fuel level is too high, it will run very rich. Is the float ok, i.e. not part full of fuel? Is the float needle or seat damaged or got dried fuel on it? It does sound like a carb clean out will be needed soon.
I've just removed a needle from my bike and measured it.
The overall length is 3.2"
It is 0.1" diameter at the top.
There are five grooves, the centres between the top groove and the bottom groove are 0.25"
It has a No. 6 stamped on about 0.56" from tbe top.
Hope this helps
Are there any markings on the main jet?
Thanks everyone. I will look at the main net tomorrow.
.. the main jet only has any effect at or near wide open throttle.
The main jet wouldn't cause a sudden change in performance unless it either became blocked or unscrewed.
IF all the airways going through the carb are 100%clear, with no muck stuck near the air screw or pilot jet, check the fuel level. Only a month ago my 650 was running excessively rich throughout the range, but before 'laying up' it had been perfect. As part of its recommissioning, I had ultrasonically cleaned the carbs, blew everything through with an airline, installed new slides and a new 'stay up' float. It turned out that fitting the new float had raised the fuel level over 1/4" higher than it should have been. Rectified the issue and it now runs right as rain with lovely milk chocolate coloured plugs.