65 replies to this topic

[icklemini]

Ah but the thing is the screw backed right off. Not had this happen before usually the timing doesn't alter that much at tick over.

Accelerater cable too tight and holding the lever off of the idle screw perchance?

Vac advance will alter the timing the most at idle... as thats where theres the most vacuum to advance the timing...

[mrmeds]

If the engine is already built and in the car why are we talking about cam timing? Yes... you can set cam timing with the engine in the car but it's a lot more work and if the cam seems to be doing its job, is it worth it?

As for the ignition timing, once you put on a stage x head and type y cam, the OEM tuning specs for the engine should only be considered a starting point.

I know of no situation where an engine performs "better" when the timing is retarded. My advice continues to be very similar to what BMecosse said. Bring the engine up to about 4k RPM then set the timing to about 32 BTDC. Return the idle speed to "normal" and test drive the car by putting it under load (such as accelerating uphill in too high a gear). If you hear ANY pinging and/or knocking, retard the timing about 2 degrees and repeat your test drive. Keep doing this until NO pinging or knocking is heard and you will have the max advance your engine can take for its state of build and the fuel you are using.

by the way, stop worrying about the vacuum advance. Its job is to give you fuel economy at part throttle (such as cruising). Under those conditions it does advance the timing. When accelerating (wide open throttle) vacuum advance is NOT happening. During acceleration the advance is purely mechanical and is handled by the advance weights under the breaker plate. (Mechanical advance for power, vacuum advance for economy).

set my timimg to 32 at 4000 rpm ..... but looks like this leaves me with 20 at 1000 idle ... does this sound normal 

 

 

 

have 998 wuth cooper twin carb conversion and CA2 cam

[68+86auto]

 

If the engine is already built and in the car why are we talking about cam timing? Yes... you can set cam timing with the engine in the car but it's a lot more work and if the cam seems to be doing its job, is it worth it?

As for the ignition timing, once you put on a stage x head and type y cam, the OEM tuning specs for the engine should only be considered a starting point.

I know of no situation where an engine performs "better" when the timing is retarded. My advice continues to be very similar to what BMecosse said. Bring the engine up to about 4k RPM then set the timing to about 32 BTDC. Return the idle speed to "normal" and test drive the car by putting it under load (such as accelerating uphill in too high a gear). If you hear ANY pinging and/or knocking, retard the timing about 2 degrees and repeat your test drive. Keep doing this until NO pinging or knocking is heard and you will have the max advance your engine can take for its state of build and the fuel you are using.

by the way, stop worrying about the vacuum advance. Its job is to give you fuel economy at part throttle (such as cruising). Under those conditions it does advance the timing. When accelerating (wide open throttle) vacuum advance is NOT happening. During acceleration the advance is purely mechanical and is handled by the advance weights under the breaker plate. (Mechanical advance for power, vacuum advance for economy).

set my timimg to 32 at 4000 rpm ..... but looks like this leaves me with 20 at 1000 idle ... does this sound normal 

 

 

 

have 998 wuth cooper twin carb conversion and CA2 cam

 

 

Anything is possible, the distributor new or old could be defective. Get it tested on a distributor machine. You could pull it apart and inspect it but since you are asking the question you won't know what's correct.

 

I assume you had the vacuum advance disconnected when checking the timing.

Edited by 68+86auto, 19 August 2024 - 12:27 AM.

[mrmeds]

yes ... no vacuum advance - not fitted at al;l on my twin carb set up

 

 

and im using an elctronic ignition in my distributor ... part number below .... does tyhat make a differnce

2. PSK-D10-75

thanks for all the advice as ever !

Edited by mrmeds, 19 August 2024 - 05:09 PM.

[68+86auto]

yes ... no vacuum advance - not fitted at al;l on my twin carb set up

 

 

and im using an elctronic ignition in my distributor ... part number below .... does tyhat make a differnce

2. PSK-D10-75

thanks for all the advice as ever !

 

The electronic part doesn't change the advance curve. At least that distributor is listed for 1275 and not one size fits all so it should at least have some kind of specific curve, not a random one.

There's many possibilities of what's happening such as:

- it's not manufactured with much advance

- it could still be advancing after 4000rpm

- it's advancing too early.

- your test method is incorrect somehow

 

It could be functioning as designed, who knows what someone decided the optimum curve is to sell. What you need to do is determine what timing you want and then either modify the distributor to suit or determine exactly what the distributor is doing and set your timing as a compromise. The distributor needs to be tested at small intervals between 0 and maximum RPM.

[Lplus]

yes ... no vacuum advance - not fitted at al;l on my twin carb set up

 

 

and im using an elctronic ignition in my distributor ... part number below .... does tyhat make a differnce

2. PSK-D10-75

thanks for all the advice as ever !

Firstly 20 degrees at 1000 rpm sounds too high, espectially with no vacuum advance, but then 32 degrees at 4000 may be completely wrong for your engine - the person you quoted was just making a general recommendation.

 

Personally, I'd go for about 10 degrees at 1000 rpm as a reasonably safe starting point and ask the supplier of your distributor what mechanical curve has been built in.  Mechanical advance distributors have limited options since only two springs of varying length and stiffness are used and a final end stop, so the curve is highly unlikely to be perfect at all rpm and also can vary widely between different setups.

[mrmeds]

just for bit of background ... engine was rebuilt by minisport  jan 2022 with cam and dizzy supplied by them . they were the folks who recommended the 32 at 4000, but they didn't say how that would effect reading at 1000.

Maybe i'm just rubbish with a timing gun !

Will try and set it again over next few days.

[mrmeds]

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****

 

 

 

feel like giving up

[68+86auto]

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****

 

 

 

feel like giving up

 

Many people set their mixture too rich, you might have too?

 

Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

Edited by 68+86auto, 22 August 2024 - 04:27 AM.

[mrmeds]

everything was running fine until about. a. year ago- it had been up to minisport - and I got 38 mpg on the 200 mile trip home, and could pull up to 80 mph on motorway easily. But then the distributor broke , I replaced it with exact same spec, or got the local garage too. Since then its run like a dog , eating fuel, Tried several different places but no one seems to be able to set it up right. Hence me trying to do it myself .... but I'm worried Ive messed it up now. Oil pressure has started dropping nnnow at 1200 rpm when hot....

Have given up and getting a bloke who specialises in classics to have a look. Also have horrible clunk sounds and  weird vibrations. Hoping it isnt something major- the engine only has about 6000k on it since rebuild

[mrmeds]

 

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****

 

 

 

feel like giving up

 

Many people set their mixture too rich, you might have too?

 

Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

 

the mixture seems all over the place. It was running really rich when I got it back from garage after mot a few months ago- seems like I set it- test with lifting pins, and checking colour of spark plugs - then a couple of weels later its rich again

[68+86auto]

 

 

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****

 

 

 

feel like giving up

 

Many people set their mixture too rich, you might have too?

 

Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

 

the mixture seems all over the place. It was running really rich when I got it back from garage after mot a few months ago- seems like I set it- test with lifting pins, and checking colour of spark plugs - then a couple of weels later its rich again

 

 

Or you have an ignition issue.

[mrmeds]

 

 

 

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****

 

 

 

feel like giving up

 

Many people set their mixture too rich, you might have too?

 

Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

 

the mixture seems all over the place. It was running really rich when I got it back from garage after mot a few months ago- seems like I set it- test with lifting pins, and checking colour of spark plugs - then a couple of weels later its rich again

 

 

Or you have an ignition issue.

 

spark plug gaps ?

[68+86auto]

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****
 
 
 
feel like giving up

 
Many people set their mixture too rich, you might have too?
 
Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

the mixture seems all over the place. It was running really rich when I got it back from garage after mot a few months ago- seems like I set it- test with lifting pins, and checking colour of spark plugs - then a couple of weels later its rich again

 
Or you have an ignition issue.

spark plug gaps ?

Could be, what have you set them to?

[mrmeds]

 

 

 

 

 

reset to 12 degree at idle at 900 rpm.... still running  rough as a sack of badgers, fuel economy a bit better - but still ****
 
 
 
feel like giving up

 
Many people set their mixture too rich, you might have too?
 
Unfortunately there are so many possibilities for issues that nothing can be suggested without further info. Add a photo of the carb and engine bay and we might be able to spot an issue. Getting the readings from an exhaust analyser would help a lot in a diagnosis. But before you go changing the fuel system you need to be sure the ignition system is perfect and from what you've said, it isn't.

the mixture seems all over the place. It was running really rich when I got it back from garage after mot a few months ago- seems like I set it- test with lifting pins, and checking colour of spark plugs - then a couple of weels later its rich again

 
Or you have an ignition issue.

spark plug gaps ?

Could be, what have you set them to?

 

0.040  as i've got a sports coil ... as advised by minisport