14 replies to this topic

[David Oldcorn]

This is my first time here and my first time on any forum, so sorry if it is repetative or nothing new.

 

We have a 998 1988 Mini. The previous owner has fitted a Fletcher LCB exhaust to twin boxes at the rear. It pootles around fine on the whole, but wouldn't respond to a sudden open throttle and it was a bit rough until driven hard. On the whole, it became quite civilised if I pulled the choke out a bit.

 

Initially I went over the points and condenser and replaced them (the points were pitted). A small improvement.

 

But it was still a bugger to drive (especially when we were using it for our son to learn in). As an experiment, I replaced the AAC needle with an AAU, and there was a marked change, but as I expected the plugs eventually furred up, really quite black. So I set about the Colourtune. Couldn't get it back to a blue flame, and when I replaced the AAC, it took a week of timing/points/another condenser to get a driveable car: we are back to square one.

 

Now... I am about to take out the waxstat and replace with a new non-wax jet, on the basis that I have no idea if the original jet is worn. My own fault for not really looking at it hard enough when it was out of the car.

 

New gaskets front to back on the carb.

 

So my questions:

 

this carb should work with the AAU - why not?

what should the timing be? I have a manual that asks for 8 btdc, but the car is set to 16.

would another needle suit? I don't want something that sets your hair on fire, just good throttle response.

 

I am also considering drilling extra holes in the panhandle air box, just to get this thing to breathe.

 

 

Thank you for reading all that.

 

David.

 

PS. not completely new to this, I have driven Minis before, learned to drive in one, but all my engine work has been on twin carbed Triumphs...  might raid a spare carb for a needle or two.

 

 

 

 

[KernowCooper]

If you drill holes in the box it will make the problem worse, what you have is a car with a modified exhaust and its running weak thats why when you pulled the choke it ran better, as you have found out by changing the needle, and just this week one of the most respected Mini Tuners/Engineers who's on TMF AC Dodd remarked 95% of the engines on the AAC run weak and the AAU run BORE WASH rich. What you really need is a custom needle, maybe you can do this yourself or need a rolling road session?

 

Timing are you checking this at 1000rpm with the vacuum pipe disconnected and blocked? if so 16degs is way to much advance, and I'm surprised its not pinking if its set like that?

[David Oldcorn]

Thank you Kernow Cooper.

 

16 btdc came with the car, I have it down to 12 at the moment. All the breather pipes are clear, timing set with the vacuum off. I'll be going over everything again this weekend, when the weather is dry and we aren't looking after our grandchild. I always saw it as a weak setting, it is hard to hit the compromise between reasonable throttle response and black plugs.

 

The extra holes planned for the air cleaner came from a suggestion on another site, they would be on the intake side of the filter.

 

Custom needle? This is new to me: how do I set this up?

 

And lastly, Kernow? where are you? I am in Penzance, can you suggest a good rolling road please?

 

Thanks very much,

David.

[carbon]

+1 for Kernow Cooper's comments, sounds very similar to other recent thread.

 

Also check what damper spring you have fitted, if you stick with the AAC then I would recommend getting a new red damper spring before customising your needle profiles.

[alex-95]

I think it was AAA that runs bore wash rich, AAU lean. 

 

It's a long way but  there may be a rolling road shootout in Launceston coming up with the cornish mini club but hasn't been confirmed yet. This should make the cost of tuning cheaper. I think it's about £70 normally. http://www.srdengines.co.uk

[Ginge620]

I had the same problem. Previously has waxstat jet, RC40 DTM centre exhaust, 3 to 2 to 1 manifold + HS4, AAU needle. Never ran well. Poor throttle response like yourself. Switched to static/normal jet, LCB manifold and a fletcher single side exit exhaust, still using the AAU needle and did a simple colour tune. Now runs much better, throttle response is instant. Hope this helps.

[David Oldcorn]

Thank you everyone for this. I have priced up the non waxjet as a way to go. I have just had new glasses and may actually be able to see things like the jet a little better now. Was going for the 2 x 1p soliution, but realised this might be waste of time if the jet was actually worm...  although doesn't seem likely if I am getting a weak mixture.

 

The thing about drilling holes came from here I think:

http://www.calverst....tuning_bolt-ons(stage_one).htm

the holes drilled to accomodate the AAU needle. Does the page in this link make sense as far as the holes go?

 

Can anyone let me know what the timing btdc should be please? and the final idle speed once this thing is being civilised?

 

Thanks,

David.

[carbon]

David,

 

I wouldn't bother replacing the jet unless it's really worn. In fact with a swing needle jet you may be better sticking with a nicely 'run in' main jet.

 

What is essential to change is the needle if there is any ridge or other signs of wear about 3 - 4 mm from the top shoulder. If the needle is worn in this area then you will be able to set up the idle mixture OK but as soon as you come off idle it goes weak.

 

Are the needles you have new or used?

[David Oldcorn]

Hello Carbon,

 

The AAC came on the car, looks OK, the AAU is new. I am about to go out and and check the timing/idle again (now I have new glasses and can actually see!), so I'll check the AAC on this fine and sunny day. What it is to have new eyes.

 

The plan is the remove the waxstat eventually, either with a replacement or by the 2 x 1p fettle. In view of what you last posted, probably the latter. A lean running AAC doesn't suggest a worn jet to me.

 

I have an unused pancake air filter/foam insert, which came with the car, unused, and I am going to see if this will physically fit on the carb today. If it does, I am going to set the carb up with the AAU, the pancake filter, withe timing at about 10 btdc, idle at 800. I would be grateful for advice on the timing and idle speed.

 

Thanks,

David.

[cal844]

Try 10° BTDC and 850+-50

This is what my 1989 998 and my 1993 1275 are set at, both run spot on

Both have stage one kits (with KnN style filters) both cars are fitted with 65DM4 dizzies and GCL143(evivalent as Unipart are defunct)
The only differences are exhaust bore sizes:

998 has an HS4 with AAU needle
2 inch bore single box DTM back box

1275 has::
HIF with AAB needle
1.75 inch LCB
2.25 inch link pipe
3 inch back box

HTH

Edited by cal844, 17 August 2015 - 10:01 AM.

[jaydee]

You said you wanted to give a try at colourtune, not as good as a gas tester but you can get some decent results with it.

Once you set the timing, 10 degs will be fine but this needs further fine tuning, use the AAU needle in the carb dont bother with the AAC.

Keep a reminder of your needle position in the piston every time you have to remove it and reassemble, being a bias needle it will always wear, but keeping it always in the same position means you wear the needle only at one point at the front so it gives less problems as it wears down.

Use the colourtune in a dark environment, will be difficult to see anything out of it at direct sunlight on a sunny day..

To adjust mixture, with engine warm, fit the colourtune, rise the idle at 1000 rpm, and adjust mixture until you see a nice blue flame which turns yellow-orange as you blip the throttle, it should look a lighter blue if you keep the throttle open at a steady 3k rpm (if white, turn mixture nut clockwise a flat start try again). Set the idle speed back to 850-900 rpm. After any big adjustment run the engine at a steady 2500 rpm for about 20 seconds to clean chambers and plugs and get a better reading. Do not use the colourtune plug for more than 2-3 minutes, after that let it cool down.

Once done you have set mixture to a decent idle, but it may turn out that AAU can be lean at full throttle conditions, if so try thicker oil in the dashpot like a 20w50. If picks up better with the 20w50 but acceleration feels slow, you just need to reprofile the needle, at this point you best bet would be to get it rolling roaded.

Good luck

Edited by jaydee, 17 August 2015 - 10:35 AM.

[jaydee]

Forgot to say, those little shiny pancake filters are useless and make setting correct mixture almost impossible, you have a strangled carb inlet and a wide open exhaust, you'll get better results by using the standard air box and filter at this point....

[David Oldcorn]

Read that a bit late... oh dear, but the shiny pancake filter is on, got the blue flame, and everything else OK across the Gunson test sheet. Timing at 10 btdc, idle at 800. AAU needle. The dash pot spring seems to be a red one, but precious little colour on it. Dashpot oil is 3:1.

 

It sounded better than it has for a long time, so we took it for a test drive. Largely OK, but sluggish under load and up hill, with what sounds like an occasional spit back through the carb. When it struggled like this when we first got the car, pulling the choke out a bit helped, but not this time - it just ran rough, which is what I expected.

 

A quick look round the distributor this afternoon. And a little thought on those pennies. And a different dash pot oil.

 

I am trying to track down a rolling road in Cornwall that is good with Minis.

 

Thanks,

David.

[David Oldcorn]

The timing had wandered off, it was down at 0 btdc, reset to 10 dbtc, now runs a treat. Plus grey/brown, regular idle, and smooth accerelation. Good enough to get the learner behind the wheel and probably drive to a rolling road.

 

Will look at the dash pot oil and the filter later this week.

 

Thank you for all you advices everyone.

 

David.

Edited by David Oldcorn, 17 August 2015 - 05:43 PM.

[ACDodd]

Yes AAU needle is better than AAC but usually still runs too lean at part throttle. The AAA usually runs too rich. The whole point is actually in some cases the AAU can also be too rich. You have to see what your individual setup actually needs to get it to fuel correctly. Needles do not work the same in all setups!

Ac

Edited by ACDodd, 19 August 2015 - 05:52 PM.