Getting your Isetta carburettor to work right by john jensen
Here is a series of steps to follow to get your engine to run normally. Seems like very couple
years I have to go through most of these steps to clean my carb. My fuel tank is well sealed
with no tank rust for 20 years, but additives or impurities resembling rubber cement may form
when fuel remains in the tank for a long time. Recently I removed my fuel valve and installed
a different one. There was little or no sandy matter in the fuel tap when I removed it, only
some fuel goo clinging to the inlet tubes.
The pot metal Bing carb does tend to form deposits of alkali, oxides or calcium. Cleaning it
out every year or two is a good idea! If you go through the following steps, most likely your
carburettor will work fine for you, if there is no physical damage to the carburettor If, after
doing the following for your fuel system and carburettor, you should probably investigate the
electrical components, timing and valve adjustments. Your accelerator and choke cables
should move freely, too.
fuel system remove internal fuel-
where possible fine screen on each inlet tube is a good idea valve should seal properly in
the “off” position test by blowing through inlet tubes fuel line no in-
flow use sediment bowl only verify that you get a respectable trickle from fuel line air-
canister new paper filter carburettor removal disconnect slide piston and choke piston check
that cable-
carb from engine carburettor cleaning remove dirt and grease with kerosene and a brush
remove caps, jets and air-
container drop the carb and all the parts in the mix, slosh it around after 20-
hot water into the bucket until clear add some dishwashing detergent and slosh that rinse
again, same way check float chamber and caps for residue carefully remove all the parts
from the hot water to dry a can of spray air will help to remove water in carb assembly check
slide needle, replace if pitted check float needle, replace if pitted visually inspect jets to see
that they’re not clogged the slide needle jet can become oval from vibrations replacing all
jets is a good idea install the jets fairly tight in the correct locations add float needle and
secure float in slot use new gaskets on caps and filter bowl assembly replace soft rubber tip
on choke piston install air-
pressed paper gasket at intake manifold install carb snugly to intake so no air can leak in set
slide needle with key at 2nd notch down from top install cable through slide piston fit slide
piston into carb and secure top insert choke piston and secure top adjust top fitting to remove
slack from choke cable fuel hook-
sediment bowl see that the float rises slightly tap the float needle gently to see if the float
floats no fuel should be leaking out the overflow hose fuel should not rise above the float
secure the float cover secure air filter intake hose to carb start-
out idle screw to let slide piston reach bottom screw idle screw in to raise slide piston 2mm
or so valves adjusted, timing set, plug ready transmission is in neutral don’t touch the
accelerator during this process turn key to “on” and then to “start” it might start in one or two
turns if not, pull choke out slowly 1∕2” to 3∕4” while cranking it should start within a few more
turns if not, stop cranking after 10 seconds if it starts, it may begin to run rough as it warms
up shut the choke “off” and let it idle to warm up warm engine adjustments adjust idle to
1000-
from accelerator-
if it doesn’t run..... I would look for problems with the timing, check that you have a spark,
and double-
condenser, plug, and plug wire.
My new engine seems to start immediately, first revolution, without choking. My former
engine required choking, but that was also a different carb.
Your Isetta should start right up and run well for you.