Wanta Start Sometin?
How to start an engine that either has been sitting for a long time or you have never seen run before.
All "SI" (spark ignited) engines or "SI Piston" engines share something in common. They only require three items to run.
However, there are conditions on each of the three. Compression must be sufficient for a specific engine. For example, most engines only require about 125 PSI to run except for a few like the 850 Fiat that requires 200 PSI. Some small aircraft engines can use much less then automotive engines. Another variation is "Side Valve" or "Flat Head" as they are called, can have lower compression than most "OHV" (Over head valves) or "OHC" (Over head cam) engines. So you should look up the specs for the engine you are testing.
How you test the compression is important too. To get an accurate compression test you must have the throttle open. "No air in = No air to compress" Some engines are more critical than others. For example, at a dealership I worked at we had MG and Jaguar and we took on the Lotus and the Alfa Romeo car line. Back then Lotus and Alfa had side draft Weber carburetors on them. I had worked on a few of these cars before this dealer took on the lines so I was a little familiar with several of the models. One of our mechanics got one of these cars to work on and it had a miss and it was standard procedure to test the "Three Items". I heard him say that it only had 50 to 60 PSI on all cylinders and I seen the car drive in and if it only had that much compression I knew it would not start or run.
I knew the side draft Weber carbs would not allow much air in if you didn't open the throttle when doing a compression test so I went over to him and asked him to run the test again and as he started to run the test I opened the throttles. So it is important to open the throttle on any engine when doing a compression test. Also, you should let the engine turn over at least 4 or 5 revolutions.
Fire (spark) is next. The conditions for "Fire" are that it be a good spark and be at about the correct time. This was easy for us because we had a "Scope" but we also had a preliminary rough test that we could perform that didn't require any test equipment. We removed all the spark plugs and attached the plug wires to the plugs and laid the plugs on any metal part of the engine so we could see the plugs. Then we would put our thumb over number one plug hole and spin the starter and watch the number one plug. The spark needed to be thick (about as thick as the lead of a pencil) and blue in color. A weak spark would be thin like a hair and colored yellow or orange. When the plug sparked it would make a "Click" sound. When the piston came up on compression on the number one cylinder it would blow our thumb off of the plug hole and make a "Pop" sound. The reason we had our thumb over the plug hole was to hear that "Pop" sound because if you are watching the spark and hear it "Click", it seemed as though the "Click" was causing the "Pop". Meaning if we heard "Click" - "Pop" or "Pop" - "Click", it was a sure sign the timing was off. When the "Pop" and the "Click" were at the same time, we knew the timing was close enough for this engine to start.
One day I had an MG connected to our scope and was checking the ignition system and an old man was watching me. Back in those days customers could come into the shop and watch a mechanic work. He seemed interested in the patterns on the screen so I explained them to him. He said he was a mechanic back in the days of the Ford model "T" and "A" and he didn't have any equipment like that. I showed him how I could use the scope to kill a cylinder while it was running and watch for an RPM drop to roughly see if each cylinder was pulling it's load. He said he had two ways he could do that. One was to just short out each plug with a screwdriver and listen for an RPM drop. We did that too when the scope was being used and we wanted to check for a dead cylinder. I couldn't think of a second way so I had to ask how else could he do that. I had an older MG Midget that had exposed caps on the plugs so he proceeded to demonstrate. He put his fingers on the exposed part of the plug wires while it was running. It startled me as I didn't like to get "Bit" by a plug wire and here he was with a finger on all four plugs. He said he could tell if one was not firing as well as the others that way. Back then a Lucas coil would be producing from 25,000 volts to 35,000 volts depending on the plug gap and it was not bothering him at all. He would not be doing that on today's ignition systems.
Next is fuel and I learned something from that old man on this too. All engines need a combustible fuel available to the combustion chamber and in roughly the correct air/fuel ratio. When we had an engine that would not start we first asked if this car has been stored or just recently quit running. If it had been a running car we would pull the choke on and try to start it before removing the plugs and look at the plugs to see if they were wet. Then after the fire test we put the plugs back in a tried to start the engine by spraying either starting fluid or something like WD-40 into the intake when spinning the engine over. If it started but only ran for a second or two or as long as we sprayed in the intake, we knew there was a problem with either fuel supply or the carburetors.
I was adjusting the mixture on this MG Midget and the old man was still watching and I explained the procedure used on SU carbs and he said he had a way to get the mixture at idle correct on most any car in his era. He set the idle as low as he could get with the throttle stop screws and then turn the mixture screw which ever way made the RPM go up or smooth out. Then he set the idle back as low as he could and readjust the mixture to raise it up. He quickly arrived at a very low idle and if he turned the mixture screw in either direction it would die. He then set the idle up to specs with the stop screw.
He was using the fact that with the engine so low it was laboring to keep running which required the most horse power from the mixture. So when it was not the correct mixture it would not idle. His theory made cense so I tried it on the Midget and then checked the mixture and it was right on the money. Later I tried it on several other brands of cars and later in years I even tried it on several different types of fuel injection cars and it worked every time and I was able to confirm it with the use of CO equipment. So when you think because you can work on high tech fuel injection systems and use the latest test equipment you can still learn something from a Model "T" mechanic like I did.
If you have established that it is a fuel problem, the next step is to find out if it is fuel supply (Tank, Pump, Filter or lines) or it is the carburetor/s or the fuel injection system.
The first test is fuel pressure. This requires a gauge connected to a "T" in the fuel line up close to the carb/s or injection rail. Most MGs and Triumphs need about 1.5 to 3 PSI and fuel injection systems require different pressures depending on the type of system and brand of car from a low of 14 PSI on up to 80 PSI on other systems.
If the fuel pressure is correct for the brand and model car but there is no fuel getting into the combustion chamber, you need to open up the carburetor for carburetor equiped engines to see why the fuel is not getting into and out of the main jet system. If it is an injected car, you need to test an injector with a "Noid" light or in the case of a CIS injection system just pull an injector and hold it into a can or jar and activate the fuel pump and open the disk in the injection system housing.
As with anything else, there are exceptions to all rules. Once I received a MG Midget that came in on the hook that had sat in a garage for a year or two and the owner had done all the normal stuff to get it into running condition. Cleaned the fuel system from tank to carbs and put in new ignition parts, set the timing and confirmed a good spark at the correct time, changed oil and filter, adjusted the valves and did a dry and wet compression test that showed the combustion chamber was good as well as rings. New battery and guess what! No start. Even with starter fluid into the intakes.
I couldn't get it to start either and even went back over all he had done to confirm he didn't miss anything. It had me stumped too. I tried one thing that he didn't do and that was I held my hand over the intake of one of the carburetors and spun the starter and found no vacuum. At first I didn't understand this because I did a compression test and it was good. I put a vacuum gauge on the intake and as I spun the engine I noted a little vacuum at first few spins but the vacuum then went down to nothing as it spun.
The culprit was mice. They had built nests in the exhaust pipe stopping it up completely. The compression was building in the exhaust pipe and while the valves were in "Overlap", the pressure in the exhaust was blowing back into the intake destroying any vacuum.
A partially stopped exhaust will usually run at low RPM and go flat at high RPM or high loads.
Another odd "No Start" is the Series III XJ-6 Jaguar. In this case everything checks out OK but no start. I learned this one early in the life of the Series III. and had to make use of the cure several times as a hot line answer man for mechanics.
We had a good customer that I had become acquainted with over a few years and I knew he was sharp on all British cars. He had a customer with a Series III Jag and it came to him with several problems including a bad battery. He made all of the repairs and installed a new battery. Result, no start. he checked everything to make any engine run and still no start. He called me and explained the problem and what he had done to check for the fault.
I told him to put a jumper battery on the car with the new battery and he said that was a waste of time because the new battery was even load tested to be sure it was good. I urged him to try it so he did and called me back as it had started and he couldn't believe it. He had installed a new standard low end battery in the car and it would spin the starter fast so he assumed it was ok.
The Series III had an odd problem of requiring a "deep charge" or "diesel" battery to start.
Other odd "No Start" cars were on an 850 cc Fiat. We had a "no start" and a compression test of 135 PSI. This is normally enough to start an engine but it would not start this Fiat. We looked up some other specs and found that it should have 200 PSI on a compression test. This is much higher than most cars have but needed on this small engine. Another "No Start" on a Fiat was when one came in on a hook with a bad starter motor. One of my mechanics installed a new starter and the starter would spin the engine fast but it would not start no matter what he did to correct it. After several tries with the help of another mechanic, the other mechanic noted that the engine was rotating in the wrong direction. Fiat had different models that used the starter on opposit sides of the flywheel thus they turned backwards and the bolt patterns were the same so when the parts man gave him the wrong starter it bolted in but turned the engine backwards.