Timing issues

[Daz1968]

I have built my mk2 998 Cooper to as near to downton no4 touring spec as I can, have used a nice ported head along with twin h4 carbs using springs and needles from the Downton tech section on here, I just have a little problem with light throttle acceleration, it pinks a little. If I retard timing then I get other issues. I have been looking at other downton conversions on coopers and both the one that was sold from New Zealand and the 997 in the restoration section on here appear to have the vacuum advance disconnected, I am reluctant to do this but could my issue be the vacuum advance over advancing on light throttle. I think I will get my distributor checked at h and h as they are local to me just in case anything is out of spec, or maybe something needs changing for modern unleaded fuel.
Anyone know for sure if vacuum advance was disconnected on the conversion or can offer any advice to solve this.
Car is running pretty good to be honest apart from this and it’s something I don’t like to hear.

Thanks.

[Hipwell]

What timing have you got?
Have you tried disconnecting the vac advance?
Vac advance ported from correct location?
Timing marks accurate?

[Daz1968]

Thanks,

My timing was set at tdc as per touring conversion data sheet, but I have now been adjusting it to try to solve the problem, the vacuum advance is connected to the correct port on underside of left hand h4 carb with the correct copper tube.
I will try it without vacuum advance working as it does seem to be fine on idle and full throttle it’s just like the vacuum advance is advancing the timing on light throttle too quickly. Not sure if they can go weak with age. Distributor is correct 998 cooper unit 40955f, I have 9.5:1 compression, standard cooper cam and big valve ported 12g295. Car pulls very well for what it is no flat spots and revs pretty clean, it’s just this part throttle over advance that is worrying me.
If I retard ignition to stop the part throttle issue then it is so far retarded that the car won’t start properly, sounds like flat battery due to firing too far before tdc.
I am pretty confident the issue is the distributor and it was a used buy that I have not used before.
I would rather run with vacuum advance to help cruising

[111Robin]

If you have a vacuum hand pump connect it to the vac unit, run the engine at idle and check advance with no vacuum applied. Then slowly apply vacuum and note the increase in advance vs applied vacuum. Keep going until you stop increasing the advance. You can then compare the values with those marked on the vac unit to see what it's giving you. You can then connect a vacuum gauge to the port and see what vacuum you're getting at part throttle. This will at least help you to see where you stand. Also check what maximum mechanical advance you're getting at high revs with vacuum disconnected. Armed with the data you will at least be able to assess where you need to be going.

[Oneball]

If I’m reading that correctly you’ve got the static timing set at TDC?

So it’s pretty retarded to start off with. Are you sure it’s not 180 degrees out?

It also sounds like you’re getting retard and advance confused.

“If I retard ignition to stop the part throttle issue then it is so far retarded that the car won’t start properly, sounds like flat battery due to firing too far before tdc.”

If you retard the timing you are moving it later in the crankshaft’s rotation. If you’re at TDC at the moment you will have moved it after TDC.

[Daz1968]

It’s defo not 180 out as car runs fine under most conditions, if I turn distributor clockwise is this retarding the ignition, just i have tried to turn it this way to stop the part throttle pinking but before the pinking stops the car is difficult to start, if I reset it back to tdc everything runs fine apart from a small amount of pinking only on part throttle acceleration, cruising and full throttle is fine, even under heavy load. I am not an expert with ignition timing. I will call h and h on Monday see what they advise but will try with vacuum disconnected to confirm it is what I think it is.

[Oneball]

If you turn the dissy clockwise you’re advancing the timing.

[Daz1968]

Think I understand, the manual states that turning clockwise retards the firing point, but this actually advances the ignition timing. It is firing more in advance of tdc I think. So the vacuum advance actually retards the firing point further before top dead centre, so in order to try to stop the pinking I have to turn distributor anti clockwise,
I have tried a number of settings though so will get the distributor checked over to ensure is working as it should be.

[Oneball]

What manual are you looking at? Turning the dissy clockwise advances the firing point.

Or are you talking about the knurled wheel rather than the dissy body?

[Hipwell]

How can the engine run with the timing 180 out?

I feel a timing light is needed here.

[Daz1968]

I have never had an issue with static timing before and usually leave a little loose and tweak a little on the road so it runs at its best, my issue is part throttle which I think is the vacuum advance unit. I just didn’t know if h4 carbs pulled a stronger vacuum than hs2 hence pulling advance more. I had noticed the two downton coopers I have seen pictures of have the unit disconnected hence the original question. I agree it wouldn’t run 180 deg out. I will try with unit disconnected and as the distributor is old will get it checked to standard spec, hopefully then I can get it all set up.

Thanks for advice

[Oneball]

How can the engine run with the timing 180 out?

My brain was off on one.

[Oneball]

Where is the vacuum take off on your new carbs?

[Daz1968]

It’s in standard location on underside of carb body, appears close to butterfly. I will hopefully have a reply from h and h tomorrow and if the turnaround time isn’t to long will take it in to be at least checked and adjusted to standard spec. I know what I am working with then.
I don’t want the body of distributor blasting as it has 50 years of patina and don’t want to lose it. Their normal reconditioning service returns a brand new looking distributor.

[Oneball]

Can you read the numbers on the vacuum advance unit and see if it’s the correct one?

[111Robin]

Just buy a cheap dial back timing light then you can check what both mechanical and vaccum advance you have as i described. Static timing is just to get the engine running, it's pretty meaningless for anything else. If you set it at 30 to 32 degrees before tdc total (ie. this is the sum of maximum centrifugal and additional advance achieved by rotating the distributor)at around 3000rpm, vacuum disconnected) you should be good. Then reconnect the vacuum unit and see how it runs. Setting things to the figures quoted in the original manuals won't necessarily be the best running a non standard spec engine on modern fuel. With a dial back timing light you can pretty much plot the advance curve to see how it looks but ultimately you want that 30 to 32 degrees maximum at high revs.

[Hipwell]

Just buy a cheap dial back timing light then you can check what both mechanical and vaccum advance you have as i described. Static timing is just to get the engine running, it's pretty meaningless for anything else. If you set it at 30 to 32 degrees before tdc total (ie. this is the sum of maximum centrifugal and additional advance achieved by rotating the distributor)at around 3000rpm, vacuum disconnected) you should be good. Then reconnect the vacuum unit and see how it runs. Setting things to the figures quoted in the original manuals won't necessarily be the best running a non standard spec engine on modern fuel. With a dial back timing light you can pretty much plot the advance curve to see how it looks but ultimately you want that 30 to 32 degrees maximum at high revs.

Totally agree with this, I had a friend with an 80's Mini, set up with the light bulb method, thought it was perfect, I checked it, over 40 degrees at idle, and a big hole in the head gasket. You can't account for wear or dynamic effects with static timing alone.

[seandoyle]

PM sent.

[Daz1968]

Thanks all for advice, I have checked plugs tonight and colour suggests a correct mixture, even though I had set it up with a colourtune so was pretty confident it was ok, the vacuum advance is correct unit for 998 Cooper, I have spoke to h and h today and will be taking distributor to them tomorrow to be checked if it is to correct spec, then they will advise any changes based on my engine spec sheet I have to take with me, hopefully all will be sorted as they have enough experience to get it right, will update when I have it returned and fitted, but hoping all will then be ok, The 998 cooper distributor I have is over 50 years old and purchased from eBay so is an unknown quantity, at least by sending it off I can be assured everything is as it should be.

Will purchase a timing light to set it up.

[Daz1968]

I gave my engine spec to hand h ignition services and they have checked it over and made a few changes. They informed me that mine was advancing to early, also vacuum advance not working correctly, all done for £40 plus vat, will fit the weekend and see how it runs, if it works which I am hopeful it will then it’s money well spent. For a 50 odd year old part it was in reasonable condition and needed no further work but a full recondition is £155 if needed.
Will update after trial run.