G'day forum members,

I know I have discussed this before however I had some developments and need some final advice.

The Car
Reconditioned A+ 998 converted to unleaded (most likely a Metro engine from around 1985)
RA40 exhaust system with extractors ( bought as a stage one kit)
Twin 1 ¼” Carby’s with ABC needles
Pancake filters
65DM4 distributor with the GLC143 coil
Fuel is delivered through an electric pump through a filter king regulator at 3.5psi
Fuel bowl levels are fine.

I have 2 options with this car.

I can set the car at 5 degrees BTDC and the car will idle perfectly but it will not drive well.
Or
I can advance the distributor off scale, I would guess 30 degrees, and the car will run excellently but will idle like rubbish.

At 5 degrees, when the car is driven, will struggle like the engine is labouring under its own load. The car sounds like it wants to die and car stumbles like its running out of fuel. So in saying that the fuel side of things are fine. I can rule this out because I can advance the timing and the car runs fine.

I can’t find a happy balance between the two.

Until now I have focused on the electrical side thinking it may have been the ignition system. Everything on the electrical side stacks up and other than the timing side of the electrics it all seems to test correctly.

On advice from a retired carby guy I was told that the issue is that the Carby is not getting rich enough, fast enough. He based this on 2 main reasons.
1. When idling perfectly at 5 degrees when I lift the piston in the carby 1/32" the engine wants to die where it should slightly increase in revs
2. When the car is struggling I can pull out the choke and the engine improves to a near perfect level

He recommended that I get needles that have a slightly higher start point to get the carbys the correct mixture from the start.

So has anyone had a similar situation that they have managed to sort out? and more importantly can anyone recommend a needle that will give me a higher start point? I sure that selecting a needle that gets really rich towards the end of the range will also cause a whole new set of issues which also hope to avoid. I have looked over dozens of needles however I really need some guidance from people who know how they perform not just what looks richer on paper.

Thanks to everyone that has help out so far. It has been helpful and got me to this point which I hope is near the end.

Have you looked at the total advance of the dissy and the advance curve.
You may have 14 degree advance plates and have a curve that is still advancing at 5000rpm.

Is the advance on the distributor working correctly I.e. Checked with a dial back timing light and what is the curve? And how confident are you with the timing marks on the flywheel?
I use a colour tune and it works pretty well at determining rich/lean profile as there are a number of tests you can do. Sounds like it could be a combination of timing/ advance and mixture and the best I can think of is confirm timing and advance is correct then look at mixture?
Cheers
Rod

_________________
1967 New British Racing Green Mk1 Cooper S, 1967 Lake Green 1275 MG Midget, 1969 Jet Red / Crystal White Mk2 Cooper S, 1972 Gambier Turquoise Clubman GT (ex police), 1972 Camino Gold Clubman GT, 2009 JCW Challenge Edition, Megane RS265, Clio RS220.

Thanks for the feedback. I don't know what the curve is I will be honest. I can get it to idle at 5 to 10 degrees at the flywheel. It idles well at this point including using the colour tune to get the mixture spot on. So I can get it right on 5 degrees, a nice Bunsen blue colour using the colour tune , a even note at the exhaust and a consistant rpm. However while this sounds all good I cannot lift the carby piston 1/32" without the motor to die, also as soon as I drive, near unmeasurable speed at the speedo, the engine starts to labour. It struggles in all gears. As I said before if I pulled the choke out while its struggling like this the engine revs come up and the car powers forward. I guess this is reason why I am looking at options away from the distributor to see if it's something more like the mixture past the idle setting.

Maybe the 65dm4 will never work right on my car.

Can someone give me an idea of a more suitable distributor based on the car specs above?

On the side of the dizzy there will be some numbers what are they. Google them to see if the dizzy is for a 1300 or 998. If its the 1300 type then theres your problem. They had too much advance for the 1300 engine let alone a 998. If its wrong you will need an A+ 998 dizzy. The 998 ones are quite rare as was the 998 metro. Hope this helps

You also mention abc needles in a set of twin 1.25 su carbs. They are floating needles. They should have fixed needles like M. This could also be your problem.

Sorry for the multiple reply. Using my phone as
pc is having issues.

You must disconnect the vacuum advance pipe and block off the carb end then set timing on a 65d4 dizzy.

As per previous post on this matter Bazz, ABC needles are far too rich. Get hold of some EB or GG needles, pretty standard for 997/998 Cooper. May not be perfect but it will run much better. Also piss off the distributor and beg, steal or borrow a Cooper S one to see the improvement. Then you should be on the right track.

The cooper s dizzy wont fit as the engine is A+.
But it would have 10 degrees of advance which works very nice in a 998 engine with modern fuels. I run one in my Moke.

If this also helps M is a 998 rich needle Eb normal mixture.

Yes, you are correct Kiwi. M is a touch richer but anything would be better than ABC.

I've never had much to do with A+ engines. Are you sure the dizzies are different and the Cooper S can't be fitted.

Thanks, I was thinking so far that the ABC needles were not rich enough but your suggesting that they are too rich. Of course I only based this on the points above about the choke and caby piston which seems to suggest more fuel or a richer fix was needed.
I am getting to stage where I think the 65 is not right. I think the cooper and A+ distributors are different so i assume I need something like the 59d4. Maybe someone would like a swap a suitable distributor for a 65dm4 ( most likely for a larger engine)

Pull the dizzy out and post the numbers. I will be able to tell you if its wrong. Late model 998 plus engines where 65dm4. I would start with the needles. An abc needle is floating needle and was never fitted to 1.25 su carbs. Someone would have had to modify the carb piston to make them fit or the needles. I would leave the dizzy and sort the carbs first then the dizzy.

"......An abc needle is floating needle and was never fitted to 1.25 su carbs. Someone would have had to modify the carb piston to make them fit or the needles.."

Never is a very strong word.... fixed or floating is irrelevant. All 90 thou SU needles belong to the same set and are interchangeable. Each type of needle has its own type of collar that fits into the same hole in the piston...

There are a lot of other dodgy comments on this thread IMHO... for example "He recommended that I get needles that have a slightly higher start point to get the carbys the correct mixture from the start." Basically all 90 thou needles "start" ie are 89 or 90 thou thick at the base. Its the "shape" of the needle across its full length that makes it work for your engine.

While there are Mini Savants who can tune a car by sound or smell, they're very thin on the ground these days (the Works minis were never dynoed - at least not until they brought some to Oz to run at Bathurst ; ). These days you need a dyno - or an air fuel meter and someone who knows how to drive it.

A few years ago I bought a distributor from Aldon. Those guys are (or were) the world's experts on Mini dizzie tuning. I gave them my engine specs and they promised they would build a dizzie with a custom curve that would solve all my problems. The first run on the dyno demonstrated how far you (they) could be wrong...

i wouldn't be pfaffing about with all this "expert" advice. Take it to someone who knows their onions, pay the money and have it done properly.

Cheers, Ian

[quote="1071 S"]"......An abc needle is floating needle and was never fitted to 1.25 su carbs. Someone would have had to modify the carb piston to make them fit or the needles.."

Never is a very strong word.... fixed or floating is irrelevant. All 90 thou SU needles belong to the same set and are interchangeable. Each type of needle has its own type of collar that fits into the same hole in the piston...

There are a lot of other dodgy comments on this thread IMHO... for example "He recommended that I get needles that have a slightly higher start point to get the carbys the correct mixture from the start." Basically all 90 thou needles "start" ie are 89 or 90 thou thick at the base. Its the "shape" of the needle across its full length that makes it work for your engine.

While there are Mini Savants who can tune a car by sound or smell, they're very thin on the ground these days (the Works minis were never dynoed - at least not until they brought some to Oz to run at Bathurst ; ). These days you need a dyno - or an air fuel meter and someone who knows how to drive it.

A few years ago I bought a distributor from Aldon. Those guys are (or were) the world's experts on Mini dizzie tuning. I gave them my engine specs and they promised they would build a dizzie with a custom curve that would solve all my problems. The first run on the dyno demonstrated how far you (they) could be wrong...
1524.23

i wouldn't be pfaffing about with all this "expert" advice. Take it to someone who knows their onions, pay the money and have it done properly.



I should have been more specific. No floating needles where fitted to a 998 mini engine. They where fitted to Mg 1300s with a AAP needle is where the twin carbs may have come from. The M needles where fitted to the cooper which is pretty close to the engine mentioned and I know works well on a 998 mini engine because its a factory needle


For reference I looked it up the floating needles in the Su specifications carburetters and fuel pumps 1963 onwards mannual I got from bmc when it closed down.