16 replies to this topic

[CdnAustinAmerica]

1976 998 Canadian mini - came with a 43d currently has a minispares 45D unit C-27H7698 in it with 37H8414MS vacuum advance on it. Carb is running an AAU needle at this time and was rebuilt by someone proper a year ago,Cylinder head is a rebuilt unit fitted two years ago (not the smog pump head) and earlier this year I fitted 1.3 cooper rockers and new shaft. Compression is 150 across the board and it still has the cast iron one piece manifold.

Timing is currently set to 7 btdc at 1000rpm - timing set through clutch housing viewport

 

Been fiddling with it as much as I can to eliminate this issue, vacuum advance will make the car ping just enough to be audible at speed and part throttle, also sometimes on lift from light throttle as well. Even running it without vacuum advance seems to cause pinging briefly - usually for a split second after a gear change under spirited acceleration. Manifold gasket was just replaced to be sure, and I soldered the overrun hole in the carb butterfly which helped a bit.

 

Any insight would be greatly appreciated. Never had the vac hooked up for this reason

 

 

Carb has 20w50 in it, lighter oils made full throttle response better but made pinging worse, carb jet is set a bit rich as well, but it might still be leaning out and causing this problem?

Edited by CdnAustinAmerica, 05 June 2023 - 04:42 AM.

[cal844]

You need the carb tuned to work with the engine and fuel used

[Lplus]

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected.  I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

 

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio?  Has the head been modified and/or skimmed?  Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers?  All those can cause detonation.

[CdnAustinAmerica]

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected.  I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

 

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio?  Has the head been modified and/or skimmed?  Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers?  All those can cause detonation.

 

 

Plugs are NGK BPR6ES, I run 94 octane as its ethanol free, the head is stock but might have been skimmed slightly, the engine internals are stock so its around 8:1 I think? , maybe a bit higher. There is some carbon build up on the pistons but I ran some combustion chamber cleaner through it, was temped to try the water method but I am hesitant if thats actually safe even when done properly.

This was a smog pump car originally - came with a 43D 41404 - the original distributor had a maximum advance of 10 with a conservative curve but the springs are probably quite a bit weaker now - I threw it in after cleaning and lubricating it and it was worse than the newer unit, timing setting on it was a bit jumpy compared to the new one which is very steady, both were set at 7 btdc

[timmy850]

What’s the mechanical advance like at the RPM you're having issues?
How much advance is the vacuum adding?

[Lplus]

 

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected.  I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

 

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio?  Has the head been modified and/or skimmed?  Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers?  All those can cause detonation.

 

 

Plugs are NGK BPR6ES, I run 94 octane as its ethanol free, the head is stock but might have been skimmed slightly, the engine internals are stock so its around 8:1 I think? , maybe a bit higher. There is some carbon build up on the pistons but I ran some combustion chamber cleaner through it, was temped to try the water method but I am hesitant if thats actually safe even when done properly.

This was a smog pump car originally - came with a 43D 41404 - the original distributor had a maximum advance of 10 with a conservative curve but the springs are probably quite a bit weaker now - I threw it in after cleaning and lubricating it and it was worse than the newer unit, timing setting on it was a bit jumpy compared to the new one which is very steady, both were set at 7 btdc

 

The 41404 was set up to have no vacuum advance, possibly because of the smog pump?.  The theoretical mechanical curve was 3 deg at 800 distributor rpm, 6.5 deg at 1400 distributor rpm and 10 deg at 2000 dist rpm.  It still might be worth checking the curve of the Minispares unit.  I'm assuming your 94 octane is our 98/99 octane so that should be just fine. and the plugs and compression ratio shouldn't give pinking either.  Most odd.

[CdnAustinAmerica]

What’s the mechanical advance like at the RPM you're having issues?
How much advance is the vacuum adding?

I'm just going off the flywheel timing marks, doesn't it only go up to 15? Just a standard stroboscopic light, no fancy readouts or settings. How would I check it?

With the vac advance on it seems like it can happen even below 2000 rpm for the part throttle issue. Don't know how much this vac unit adds, but its less than the one that came with the distributor as ordered from minispares.

[CdnAustinAmerica]

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected. I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio? Has the head been modified and/or skimmed? Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers? All those can cause detonation.

Plugs are NGK BPR6ES, I run 94 octane as its ethanol free, the head is stock but might have been skimmed slightly, the engine internals are stock so its around 8:1 I think? , maybe a bit higher. There is some carbon build up on the pistons but I ran some combustion chamber cleaner through it, was temped to try the water method but I am hesitant if thats actually safe even when done properly.
This was a smog pump car originally - came with a 43D 41404 - the original distributor had a maximum advance of 10 with a conservative curve but the springs are probably quite a bit weaker now - I threw it in after cleaning and lubricating it and it was worse than the newer unit, timing setting on it was a bit jumpy compared to the new one which is very steady, both were set at 7 btdc

The 41404 was set up to have no vacuum advance, possibly because of the smog pump?. The theoretical mechanical curve was 3 deg at 800 distributor rpm, 6.5 deg at 1400 distributor rpm and 10 deg at 2000 dist rpm. It still might be worth checking the curve of the Minispares unit. I'm assuming your 94 octane is our 98/99 octane so that should be just fine. and the plugs and compression ratio shouldn't give pinking either. Most odd.

So if it kicks in at 800, would it have been better to time it at idle, 600-700rpm? Isn't the rest of that curve fairly tame? Or is it alright for a stock 998?
It was for the smog pump, original head had ports in it and a massive pump with a different radiator too, long since removed, still had the head on it when I bought it. Also had a heater in the carb spacer and extra vacuum ports on it which were used for smog stuff. All blocked off now.

Should I email minispares? Or is there a section on their site I can check?

[CdnAustinAmerica]

So I decided to double check if my TDC is indicated correctly and as far as I can tell this mark is basically where it is, does that mean my timing marks are off? I tried setting the idle to 5 degrees btdc and it *almost* eliminated the pinging at part throttle... however reducing it further yielded no further improvement. Also I managed to get the mixture set correctly, very slight rise and then fall when just touching the carburettor piston.

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Edited by CdnAustinAmerica, 06 June 2023 - 02:38 AM.

[Lplus]

 

 

 

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected. I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio? Has the head been modified and/or skimmed? Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers? All those can cause detonation.

Plugs are NGK BPR6ES, I run 94 octane as its ethanol free, the head is stock but might have been skimmed slightly, the engine internals are stock so its around 8:1 I think? , maybe a bit higher. There is some carbon build up on the pistons but I ran some combustion chamber cleaner through it, was temped to try the water method but I am hesitant if thats actually safe even when done properly.
This was a smog pump car originally - came with a 43D 41404 - the original distributor had a maximum advance of 10 with a conservative curve but the springs are probably quite a bit weaker now - I threw it in after cleaning and lubricating it and it was worse than the newer unit, timing setting on it was a bit jumpy compared to the new one which is very steady, both were set at 7 btdc

The 41404 was set up to have no vacuum advance, possibly because of the smog pump?. The theoretical mechanical curve was 3 deg at 800 distributor rpm, 6.5 deg at 1400 distributor rpm and 10 deg at 2000 dist rpm. It still might be worth checking the curve of the Minispares unit. I'm assuming your 94 octane is our 98/99 octane so that should be just fine. and the plugs and compression ratio shouldn't give pinking either. Most odd.

So if it kicks in at 800, would it have been better to time it at idle, 600-700rpm? Isn't the rest of that curve fairly tame? Or is it alright for a stock 998?
It was for the smog pump, original head had ports in it and a massive pump with a different radiator too, long since removed, still had the head on it when I bought it. Also had a heater in the carb spacer and extra vacuum ports on it which were used for smog stuff. All blocked off now.

Should I email minispares? Or is there a section on their site I can check?

 

I should have added that there is no advance below 150 distributor rpm, so that's zero advance.  Also for the avoidance of doubt the degrees quoted are distributor degrees not engine degrees.

 

That curve is correct for the canadian 998.

 

My Haynes manuals don't give a static timing for the canadian 998 so it might be worth asking around for that info.  It is possible to time at cranking speed if someone knows the correct static timing.

 

If I want to ask Minispares a question I use the contact form on their site and they usually get back quickly.

 

Short of the minispares distributor having a weird advance curve i can't see anything you are doing would lead to detonation. The only time I had an engine that pinked in standard form the problem was carbon build up from burning oil producing hot spots, only a rebuild sorted that ( it wasn't a mini)

[timmy850]

I would say that there’s only a small chance that your distributor still has the same advance curve as new, and less likely that it’s the right curve for modern fuel

The best way to check what you have now is to use a dial back timing light and measure the advance curve every 1000rpm. Once you know that and the advance at the problem rpm (plus how much advance the vacuum gives) then you might be able to figure out the problem

[Lplus]

I would say that there’s only a small chance that your distributor still has the same advance curve as new, and less likely that it’s the right curve for modern fuel

The best way to check what you have now is to use a dial back timing light and measure the advance curve every 1000rpm. Once you know that and the advance at the problem rpm (plus how much advance the vacuum gives) then you might be able to figure out the problem

His distributor is a minispares one, so it almost certainly won't have exactly the same advance curve as the original when new, or even when worn.  The question is, what curve does it have.  Your suggestion of checking with a dial back timing light is one good way of finding out.

Edited by Lplus, 06 June 2023 - 09:28 AM.

[CdnAustinAmerica]

The '76 998 came originally with the 45D4 41418 set to 7degrees btdc at 1000 rpm vac disconnected. I've no idea if the Minispares distributor has the same mechanical advance curve as the 41418, it might be worth asking them.

Further questions come to mind - fuel grade? Plug type and heat range? compression ratio? Has the head been modified and/or skimmed? Has the engine been fitted with high compression pistons? Is there a lot of carbon build up in the combustion chambers? All those can cause detonation.

Plugs are NGK BPR6ES, I run 94 octane as its ethanol free, the head is stock but might have been skimmed slightly, the engine internals are stock so its around 8:1 I think? , maybe a bit higher. There is some carbon build up on the pistons but I ran some combustion chamber cleaner through it, was temped to try the water method but I am hesitant if thats actually safe even when done properly.
This was a smog pump car originally - came with a 43D 41404 - the original distributor had a maximum advance of 10 with a conservative curve but the springs are probably quite a bit weaker now - I threw it in after cleaning and lubricating it and it was worse than the newer unit, timing setting on it was a bit jumpy compared to the new one which is very steady, both were set at 7 btdc

The 41404 was set up to have no vacuum advance, possibly because of the smog pump?. The theoretical mechanical curve was 3 deg at 800 distributor rpm, 6.5 deg at 1400 distributor rpm and 10 deg at 2000 dist rpm. It still might be worth checking the curve of the Minispares unit. I'm assuming your 94 octane is our 98/99 octane so that should be just fine. and the plugs and compression ratio shouldn't give pinking either. Most odd.

So if it kicks in at 800, would it have been better to time it at idle, 600-700rpm? Isn't the rest of that curve fairly tame? Or is it alright for a stock 998?
It was for the smog pump, original head had ports in it and a massive pump with a different radiator too, long since removed, still had the head on it when I bought it. Also had a heater in the carb spacer and extra vacuum ports on it which were used for smog stuff. All blocked off now.

Should I email minispares? Or is there a section on their site I can check?

I should have added that there is no advance below 150 distributor rpm, so that's zero advance. Also for the avoidance of doubt the degrees quoted are distributor degrees not engine degrees.

That curve is correct for the canadian 998.

My Haynes manuals don't give a static timing for the canadian 998 so it might be worth asking around for that info. It is possible to time at cranking speed if someone knows the correct static timing.

If I want to ask Minispares a question I use the contact form on their site and they usually get back quickly.

Short of the minispares distributor having a weird advance curve i can't see anything you are doing would lead to detonation. The only time I had an engine that pinked in standard form the problem was carbon build up from burning oil producing hot spots, only a rebuild sorted that ( it wasn't a mini)

Yeah I guess I'll have to get a new timing light, my haynes says 7 btdc at 1000 rpm for Canadian minis.

Anyone have any luck with using water to get rid of carbon? I have some combustion chamber cleaner as well.

Any feedback on where my TDC is based on that picture?

[Lplus]

That looks like about 2 deg btdc.

 

The fact that retarding the timing helps does make me question the part of carbon in the problem.  That said taking the head off to clean it isn't the most complicated job.  You can also measure the combustion chambers and the piston bowl to be certain the compression ratio is as low as you think it is.

[panky]

A weak mixture can also cause pinking.