G12 1964 MAJESTIC NON IDLE ON ONE CYLINDER

wayne fields · Post by **wayne fields** » Sat Nov 18, 2006 8:55 pm

HI ALL.HAVE JUST REBUILT THIS MACHINE , AND AM HAVING A PROBLEM GETTING IT TO IDLE ON TWO CYLINDERS.SOME SPECS :

FITTED WITH TWIN AMAL CONCENTRIC CARBS
1 LH AND 1 RH
9OO SERIES
VALVE TAPPETS @ 6 THOU
POINTS @15 THOU
TWIN COIL SYSTEM
TWIN POINTS NEW
CYLINDER PREASURES 135 PSI LH AND 132 RH
NEEDLES IN RICHEST POSITION OR LOWEST SLOT
NEW N4C CHAMPION PLUGS
NEW HT LEADS

I CAN SET UP THE RIGHT HAND CYL TO RUN AS A SINGLE SPOT ON . BUT CANT GET THE SAME OUT OF THE LH SIDE MOTOR JUST STOPS WHEN THE RH LEAD IS PULLED OFF. HAVE SWITCHED OVER IGN SIDES TO NO AVAIL. SO BOTH SIDES ARE OK .THE MOTOR SEAMS TO RUN OK WHEN I OPEN IT UP. EVERY NOW AND THEN I CAN HEAR THE MOTOR FIRE ON BOTH AS IF IT WANTS TO..HAVE CHECKED ALL GASKETS O RINGS ETC ARE NEW. I TEND TO THINK THAT MY PROBLEM IS CARB ASSOCIATED. THE MOTOR IS THE EASIEST STARTER, ONE KICK EACH TIME , HOT OR COLD

ANY HELP WOULD BE GREATLY APPRECIATED AS I HAVE RUN OUT OF IDEAS.

WAYNE

Don Madden · Post by **Don Madden** » Sat Nov 18, 2006 9:44 pm

Could be a blocked pilot jet. The early concentrics & the Spanish made 2 stroke type have a removable pilot jet located just above the float.

The later type has a non-removable brass jet pressed in. The jet is pressed into the far end of the drilling under the pilot adjusting screw.

In any case, The pilot jet is fed by a passage from the bowl gasket surface to the bottom of the bowl. That is turn is fed fuel by a small port which, being in the bottom of the bowl, tends to get clogged.

Remove the screw & blow compressed air into the orfice. In cases where that doesn't work, I made a tool by pressing a #80 minature drill bit into a slender, (1/8" I think), rod that will enable the bit to ream out the jet.

Don't get carried away with the bit, you don't want to damage the jet.

Some report success using a small copper wire but the required size is very flexible & the jet is a long way inside, making it quite a fishing expedition.

Also clean out the port & passage that feeds the idle jet. The bowl gasket must seal the joint around the passage.

Sometimes I wonder why they replaced the monoblock, which regulates well & gives little trouble. Easier to work on, too.

Cheers, Don.

itma · Post by **itma** » Sat Nov 18, 2006 10:19 pm

is there a balanve pipe between the manifolds?
on twin carb triumphs the trick, as I remember it as to nip up the balance pipe and tune each carb as one before setting up the balance

lawrence · Post by **lawrence** » Mon Nov 20, 2006 10:58 pm

Could be an air leak at the manifold if the nuts have been overtightened. I always use Wellseal here and take care not to nip the nuts up too hard or the flange is distorted.

My preferred option would be a blocked jet. I had a pair of new 930 amals and the slides stuck so had to be rubbed down to fit. They sometimes ran very unevenly and eventually the trouble was traced to a piece of sprue that occasionally blocked the pilot jet. Sad that 'new' doesn't always mean 'properly checked and correct' on classic parts.

Worth stripping the carbs and blowing them out with carb cleaner (from Halfords) even if new.