Ok, Now the car is through its MOT I need to nail the poor running, what I thought was a carb issue is more likely a timing issue. Issue I have is poor running and backfiring through the carb. I had put this down to lean running. However having gone all the way in on the mixture screw this is still present, I know I need to sort timing before the carburetion, but I didn't have access to a timing gun until this weekend.
basic spec is –
1330 Mg metro engine in 71 clubman.
Minispares EVO1 cam
Aldon Yellow AYPV
HIF44 BCE needle
Pipercross Cone filter
I have replaced the ignition system with fresh points/condenser/rotar arm & Dizzy Cap. Points gap is .015
I timed the engine at idle, but I don’t seem to have any advance tooth/comb markings on the crankcase, I have a TDC marker on the crankcase and a dot on the pulley, so I am not sure how I set the advance. I am guessing it should be about 8 deg so 2 teeth on the advance comb if it was present. Now I have a timing gun with an advance knob. As a test I set the advance knob to zero and then timed the engine (Vac line removed and blocked) at about 1000 rpm, fluctuates between 950 and 1050, it was showing zero advance, so the TDC marks were lining up, am I right in thinking that this means the engine is running with no advance at idle?
To time it correctly given I have no advance timing marks to line it up with, is it just a case of setting the timing advance knob to 8 and then timing it and adjusting the dizzy until the 2 marks line up? If that’s the case am I then ok to set the idle to 4000rpm, set the advance knob to 30deg, time it in for that, and then test drive it under load to check for pinking?
Or am I misunderstanding the function of the advance timing knob?
I have read the below and that’s what I understand and took from it.
Let's start with the obvious and basics. There should be a red lead. Connect that to a source of +12V (perhaps the solenoid). The second lead will be the black one and it goes to a good, bare earthing point, preferably on the block or head. The inductive clamp lead goes around the spark plug wire for cylinder #1. Look carefully at the clamp. There MAY be an arrow on it. The arrow should point towards the spark plug.
Start learning to use your gun WITHOUT the advance knob. Turn the knob until the its pointer lines up with its zero mark (turn the advance function OFF). Start the car's engine, point the gun at the timing marks (presumably on the front of your engine) and squeeze the gun's trigger. The strobe should fire each time #1 spark plug fires. This will appear to freeze the relationship of the pulley to the pointer. Read what's going on with the timing marks.
If it's necessary (or you want) to adjust/change your ignition timing, stop the engine and loosen the bolt(s) securing your distributor to the block. JUST BARELY LOOSEN, you don't want the distributor to move at this point. Restart the engine and set the idle speed where your specs say it should be (disconnect and plug the vacuum advance line also). Point the timing light at the pulley and read the relationship of the pointer and the mark on the pulley. Determine if you need to advance or retard the timing. While still firing the timing light, use your other hand to gently twist the dizzy and you'll observe the timing mark on the pulley moves relative to the pointer. Stop when the marks are where you want them then tighten the distributor clamp again.
That's the basics. Now let's move on to using the advance knob. Let's say you have a spec that says your distributor should be giving you an increase of 20 degrees of timing at 3000 RPM. Start the engine and read where the idle advance is using the light as set above. Write it down. Now add the 20 degrees to the idle timing you observed (say you measured 8 BTDC at idle and you add 20 to that for a total of 28 degrees). Turn the advance knob to 28 and point it at the crank pulley. The mark will be NOWHERE close. Now bring the RPM up either using the throttle or the idle screws. When you hit 3000 RPM the mark on the pulley and the zero mark on the pointer should be close to alignment if the advance is working properly. Remember... I made up these numbers. Look up what's right for your engine.
Now let's talk about timing your car to it's maximum advance. Most cars can stand about 32-35 degrees of TOTAL ignition advance. To set this on your engine, disconnect and plug the vacuum advance as mentioned above. Set the gun's advance dial to 32 degrees. With the dizzy clamp loosened, bring the engine RPM up to 4000 RPM using the idle screws. Fire the timing light at the crank pulley and note where the marks are. Turn the dizzy until the zero mark on the pulley lines up with the zero pointer mark, then tighten the dizzy down. Reduce the idle speed to "normal" and use the gun to see where your idle advance is after setting it at 4000 RPM. Write it down. Reconnect the vacuum advance and take the car on a test drive. During the drive put the car under heavy load. Try accelerating uphill in a gear that's higher than called for (a hill that's best taken in 3rd, put the car in 4th and floor the accelerator). If you hear pinging, pull over and use the timing light (at idle will be fine) to retard the timing 2 degrees. Repeat the load testing... retarding the timing in 2 degree steps until you no longer hear pinging. At that point, measure and record your advance at idle.
You have now used your advance timing light to set the maximum ignition advance your engine can handle for its mechanical condition and accounting for the fuel that you buy.
Note that in all the cases where you're using the advance knob... you're using the scale on the advance knob to measure the degrees of advance. You're lining up the zero timing marks on the engine and measuring the degrees of advance based on the knob position on the gun instead.
Edited by 28hodge, 24 January 2018 - 11:40 AM.
