56 replies to this topic

[ACDodd]

I think you need to go back to basics with this thread. too many cooks and all that. You also need to dispense with the so many flats crap. The only way you can get this running is a baseline.

Verify that the TDC timing mark is actually TDC.

Then set the point gap to 0.015" (if point are fitted).

Then set the timing to 10 degrees BTDC at 900rpm. Vacuum disconnected. The reconnect the advance.

Verify that the mechanical advance is working using a strobe light and post up the timing figures at 1000, 1500, 2000 2500, 3000 up to 5Krpm.

Ensure that the carb piston bottoms out on the bridge and that it is not being held open,

Empty and then refill the dashpot with 20W/50 engine oil.

With the engine running, turn the mixture so that it is 1 flat away from running uneven. With the AAA needle fitted Rev the engine. If the problem is still there fit the AAC needle and reset the mixture to 1 flat away from running even (lean), rev and let us know what the results are.

Do you have access to a gas analyser?

AC

Edited by ACDodd, 01 January 2013 - 01:39 PM.

[carbon]

 SU Carb Adjusting Nuts.JPG   31.15K   8 downloadsHapy New Year! Hope you're making some progress. In addition to the suggestions by AC Dodd here is some info which might explain why you're having to adjust the jet down by 24 turns before it will even start.

There are two types of HS jet bearings, coarse and fine. These are listed in the Burlen catalogue (good old print version 12.25, page 173) as :
1. AUC8460-AUC8461 centering jet & nut (fixed needle) - coarse 26 tpi thread
2. JZX2075-JZX1183 centering jet & nut (fixed needle) - fine 40 tpi thread
3. AUD3414-AUC8461 non-centering jet & nut (fixed needle) - coarse 26 tpi thread
4. JZX1182-JZX1183 non-centering jet & nut (fixed needle) - fine 40tpi thread

The Burlen catalogue states that fine thread versions were introduced for more precise adjustment with emission controls, and also that the 12 flats down initial setting for tuning purposes applies to coarse threads.

Not sure if there is a specific 'changeover date' for going from one type to the other, more likely they were both produced from early 70's onwards depending on the local requirements. There is also a slight difference in the shape of the adjusting nut, if I can work out how to post a picture I will put this up as well.

For the 'emissions control' carbs with the fine 40 'threads per inch' thread then this would need 3 full turns (or 18 flats) for initial setting. If you have a vernier caliper would be worth checking how far beneath the bridge level you jet is sitting, should be about 2 to 2.5mm but in practice can be quite a bit more to get the motor running sweetly.

Edited by carbon, 02 January 2013 - 09:33 PM.

[dklawson]

Thank you for that excellent research Carbon! That is exactly the type of information needed to explain 2 vs 3 turns of the jet adjusting nut.

[80sMiniCity]

Here’s an update on the progress:

When I start the car the plugs will carbon foul (really bad) after 1 minute of idling. They fowl so much some plugs develop a miss and spark sporadically. I assumed it was the leads at first. I replaced the following, none solving the carbon fouling issue. The leads, cap & rotor on the 65DM4 (off a Metro), coil, then replaced the 65DM4 with a 59D4 with new points and condenser. The plugs still foul after a minute of idling. I have 2 sets of new Champion RN9YC gapped to .6mm. If I put a new plug in any cylinder it fouls and starts to spark sporadically after 1-2 minutes. The extra needle I had was a AAG not an AAC so I sent it back and am currently waiting on an AAC and AAU. Not much more I can do until I get the two needles.

Edited by 80sMiniCity, 03 January 2013 - 08:14 PM.

[Shifty]

Are you still on the red jet?

When I changed mine I had the change the choke arm as well, did this come as part of your kit?

[80sMiniCity]

Yes, I had to change the choke arm when I switch between the Fixed (red) and waxstat jets. The red choke arm is part of a SU kit BFS701SUL. I think I found out what the problem is…

I have the fine thread jet bearing. That’s the original one that came with the car. When I put the AAA needle in, regardless of what jet is installed, only 12 flats to get it started. That’s 6 flats for the older coarse type jet bearing. That’s too rich of a needle for my engine, so it runs too rich and carbon fowls the plugs at idle. When I put the AAG needle in it took 24 flats to get it started. Again 12 flats on a coarse jet bearing, about where it should be. I sent back the AAG so I can’t put it back on to test. I’m waiting on an AAC and AAU needle. I don’t have a gas analyzer. A Gunson G4125 would cost $280 (£174) here in the USA.

From what I found out on the “jet centering” issue here after talking to shops that rebuild SU carbs. When using a spring needle either on a HS4 or all HIF carbs you don’t need to center the jet. It will always be centered. The only time you center a jet is with a fixed needle in the piston of a H, HD or HS carb. I spoke to 4 shops and they all said the same thing.

[Scott@minispeed]

For a stage 1 998 we would normally recommend an AAU needle. The AAA that you have is miles too rich for a 998 and is usually used for stage 1 kitted 1275 GT and other 1275 engines using a single 1.5" Carb either HS4 or HIF38. You are correct that you do not centre the jet on carbs with spring loaded metering needles.

[sonikk4]

I thought the plug gap for points fitted engines is 0.6mm. Closing this up surely will create more issues??. having seen this size mentioned in three different manuals surely must be correct or is this through experience??

[80sMiniCity]

I found this in the Haynes manual.

Carburettor models

System type

All except 1990 on, 1275 cc models . . . . . . . . . . . . . . . . . . . . . . . . . Conventional contact breaker ignition

1990 on, 1275 cc models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lucas electronic ignition

Distributor - contact breaker ignition

Type:

All models except Cooper S Mk III:

Early type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lucas 25D4

Later type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lucas 45D4, 59D4 or Ducellier

Cooper S Mk III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lucas 23D4

Direction of rotor arm rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anti-clockwise

Contact breaker points gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.35 to 0.40 mm

Dwell angle:

Lucas 23D4 and 25D4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60º ± 3º

Lucas 45D4:

Non-sliding contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51º ± 5º

Sliding contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57º ± 5º

Lucas 59D4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54º ± 5º

Ducellier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57º ± 2º30’

Firing order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3-4-2 (No 1 cylinder next to radiator)

[sonikk4]

That is the contact breaker points gap not the spark plug gap which should be 0.6mm. That is the gap i am on about.

[80sMiniCity]

I had the spark plug gap set at 0.6mm when using both the 59D4 (points) and 65DM4 (electronic) dizzys and both stock and Sports coils. The plugs still fouled after a minute or two no matter what dizzy/coil was used.

This is what Haynes has for Spark Plug gap:

Spark plugs:*

Type:

All models up to 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion RN9YCC or RN9YC

998 cc engine models, 1987 to 1989 . . . . . . . . . . . . . . . . . . . . . . . Champion N12YCC or N12YC

998 cc engine models (1989-on) . . . . . . . . . . . . . . . . . . . . . . . . . . Champion RN12YCC or RN12YC

1275 cc engine models (1990-on) . . . . . . . . . . . . . . . . . . . . . . . . . Champion RN9YCC or RN9YC

Electrode gap:

All Champion plug types except RN9YC and N12YC . . . . . . . . . . 0.8 mm

Champion RN9YC and N12YC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.6 mm

HT leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion LS-02, boxed set

*Spark plug types and electrode gaps are as recommended by Champion Spark Plug. If alternative plugs are used, refer to their manufacturer’s

recommendations.

[lrostoke]

I've got mine set to 0.9mm running electronic ignition and Lucas gold coil.