MG Car Repair: carb tuning, coolant line, coolant system

Question
QUESTION: Hi, did that compression test (150 psi across all four cylinders); fixed some
vac lines and put new gas in...vroom! It runs! Thanks. It idled decent, bit
shaky upfront, not bad--blipped the gas and it drops just around 750 rpm
'ish. Ran it for about 5 mins once and 2 mins later. Checked oil level; ok since
last change. Exhaust cleaned up pretty good (tiny bit of smoke the first time)
Temp normal, oil pressure between 50-60. No leaks anywhere. Need
probably to set up the carbs(?) and "burp" the coolant system. This is where I
need some help. Carbs--not much of a clue (except my tear down and clean I
did). The coolant system<this confuses me> I have a cross-flow rad
probably from a 1500 and a 1275 engine. Rad side of hose(s) are larger then
inlet to block and outlet from the t-stat housing a-top of the head. So the
coolant line from the thermostat housing to the rad has a homemade bump
up (welded "barbed pipe fittings") and the same with from the bottom/side of
the rad back to the block. On that side, (rad to block) I have another step
down with also a "tee" fitting  attached to run a hose to the heater core.
Another line runs from the core to the back top of the block. Currently, I have
that valve closed. I have a overflow tank attached to smaller line off top of
rad. No real way to fill coolant system however without disconnecting the
hose off the t-stat housing and using a funnel to fill the rad and attached
lines. I filled around 3 liters...bit shy. So, to get any air out, I don't have the
typical :screw-type fitting to "burp" the system. I am guessing I can
disconnect the hose from the heater core (attached into t-fitting - welded on
top of step down fitting) which is the line that runs from side/bottom of rad
to block to try to remove air locks. Figured if I take the cap off the overflow
also this would help with that? Also, can the overflow be used to add coolant
(top up) system. i.e: does the system pull coolant back from the overflow>?

I guess top different quests here...thanks.

Jon-George (76 Midget)

ANSWER: Hi Jon,
Normally a cooling system that has a pressure cap with an over flow line off of it to an expansion tank will retrieve coolant from the expansion tank (if it has the correct kind of pressure cap)(one that is a pressure cap but will not hold a vacuum)
If you just have a radiator with no cap but does have a small expansion tank with a pressure cap on it. This type of system will also draw the coolant from the expansion tank back into the radiator as the coolant cools and contracts providing it has the same type cap as the first system.
As far as getting air out of a system you need to open up the thermostat and examine the base of the thermostat to see if it has a hole or a small valve called a giggle valve. If it has neither you should should drill a small hole in the base (flat area outside of the main valve). The hole should be a 1/16th to 1/8th inch. This should solve any air pockets getting trapped especially when filling.
Let me know.
As far as the carburetor goes, the 76 Midget has a single stromberg carburetor and the adjustment for mixture is in under the top cap down into the oil with a 3mm Allen wrench. Clockwise richens the mixture and counter clockwise leans the mixture. If there was no oil in the top be sure to put some in. About a table spoon is enough.
Howard

---------- FOLLOW-UP ----------

QUESTION: i actually have the twin su carbs on mine>...
the ones with the conical plastic floats in it..HS2's?
will not drilling the small hole on the outside of the valve area not cause leakage
and a problem with the system?

Answer
Jon, you don't drill it in the cover. Only in the thermostat plate. This prevents an air lock at the thermostat and allows you to completely fill a radiator without removing hoses etc. It also allows a small amount of coolant to bypass the thermostat as the engine warms up thus keeping a circulation of heated coolant access to the thermostat operating bulb. Assisting the bypass hose in keeping a flow of first heated coolant before the thermostat opens. If you don't feel comfortable doing this, be sure to remove the thermostat housing to fill the radiator on a first fill up.
Howard