Test Runs

Due to the radical design including the cooling system, the air start and the carburetors, it is necessary to run tests on the starting, temperature and drivability of the MG.

The first test run of the engine was just a circle around the yard to warm it up and then some stationary running in the yard.

The first thing noted was that I was able to take it off choke very early which was an indication that the carburetors were still too rich. Especially at the lower RPM. By leaning out the idle mixture screws I was able to get it to idle but it required a very closed adjustment to do so and as the RPM was raised slightly the mixture was very rich with black smoke out the exhaust. The DCNF Weber has a "Idle Jet" that not only feeds the idle circuit but controls ports for just off idle. I had also drilled these jets too but by too much.

Throttle response was very good at mid range with a slight puff of black smoke. This was the accelerator pumps adjustments were also slightly on the rich side which I prefer. The high RPM range was good with no black smoke and good throttle response at high RPM. This was an indication that the main jets were close to correct. This was a relief as I had drilled the main jets out an extensive amount. So much that two more size drills would have reached the size of the passage ways in the carburetors that fed the main jets. Which would mean that these carburetors could not be used due to the volume of fuel needed by this engine.  I did a fuel volume test at a high RPM range and found that the fuel use was 16 gal per hr. (this is a normal amount of fuel used by a 265 HP engine.) This is encouraging as I would be happy at anything just over 200 HP.

Originally the carburetors were completely wrong because they would not run the 308 Ferrari they came off of. According to Weber the idle jets should have been .55 mm but these were .45 mm. So I ordered new Idle jets of .60 mm and would start from there. Not having a good selection of very small drills I also ordered a drill index box of small drill bits.

I did find why the Webers were taken off of a new 308 Ferrari that could not be delivered due to the carburetors. Ferrari had installed a float needle and seat smaller then the main jets thus causing fuel starvation. The Ferrari mechanic could not spend the time finding out why the carburetors would not run the new 308 so he just put four new carburetors on the car which corrected the problem. The faulty Webers were stored in the dealership loft for years when I purchased them at a discounted price. I knew that I needed to alter and jetting anyway so I finally found the problem after a lot of work.  I had built in a few problems of my own when I used "Safety Foam" in the gas tank and not having any experience with the foam I made the pocket for the tank pick-up pipe too small and the foam would not drain sufficient fuel so the pocket was sucked dry by the fuel pump. Even after all that was corrected I found that the one electric fuel pump could not pump 16 gal per hour so I had to put two pumps in, which then raised the fuel pressure too high so a fuel pressure regulator had to be added.

On the second run in the yard I started to map the cooling system's temperatures with a thermal gun when I fouled the spark plugs with the over rich mixture at the lower RPM range so the car was put away until I could get the Idle jets. However, I decided to road test the car after just a half lap around the yard.

I ran the car hard through the gears and noted that the clutch and 5 speed gearbox were smooth and worked well. However the brakes were not up to par with the rest of the car, so I figured that I would work on them after the car show. I drove the car about 3 miles and turned around and went back to the garage. I ran it through the gears a few times and even scared myself a couple of times.

It was still fouling plugs when idled down so I put it up and would wait for the new idle jets to come in.

I had entered the MG in the local British car show and the new idle jets came in the mail a couple of days before the show. So I cleaned the plugs and installed the new idle jets and tried to start it. However the engine was locked up solid. I removed the spark plugs and found that #1 combustion chamber was full of water. Evidently I had blown a head gasket on the hard road test and didn't note it as it didn't indicate any overheating. The time between the road test and the new jets came in was long enough time to fill the cylinder with water from the cooling system.

I removed the one head and could not see where the head gasket was leaking. On a car driven a lot on the street, it is easy to spot any leakage, but on an engine that only run a short time and only about 5 or 6 miles it is not easily noted where the leak is. I will now have to clean the head and block and use a straight edge and feeler gauges to look for any warpage of the head or block.

While the head is off I have decided to upgrade the compressed air start system by changing all of the 1/4 inch pipes to 5/16 inch pipes to increase the volume of air available to each cylinder for starting. As it is now it requires 200 PSI in the air tank to spin the engine fast enough to fire the direct ignition system.

I also removed the air distributor to see if it was ok and I found that everything looked good except one point and that was my design of the cam that operated each ball valve. I will use my lathe to make a different design cam and valve system. My existing cam was brass and it operated small pins to open each valve. For the amount of use there was too much ware on the brass cam so I have decided to make a steel cam and have it operate ball bearings so as to distribute a larger load area.

So over the winter I will upgrade the air start system, correct the coolant leak and work on the brake system.  After I get the car performing better I will drive it on the street some. Then I will tame the exhaust note down a little.

Page 16

Home Page