Amazon: - '67 P220 SU adjustment - Page 3

gjr0 · Aug 14th, 2023, 22:43

The cam is an Iskenderian Z-66-005. Lift is 0.293 " on both intake and exhaust. Duration is 268° for intake and exhaust. At 050" lifter rise the duration is 244°. Overlap is 52°.

blueosprey90 · Aug 18th, 2023, 01:58

Not sure what carbs you have or whether this humble advice might be helpful.

My experience is limited to SU H4 and H6 carburetors. I have never had any success whatsoever fine tuning with the lifting pins. Perhaps I am unable to hear. I've had a little better success using the carb balancing wires to lift the dashpots (basically mimicing the lifting pin) - but still don't really tune this way.

Generally, I measure the distance from the bridge to the jet. Right now, I'm running the H6s at about .085" - but the range I use is in the .060" to .090" range and then tune by looking at the spark plugs.

If you can set your carbs to a distance in this range and see how the car runs. Then when you stop, and it's idling to say 2,000 rpm, shut the car off and re-measure. The distances should not change, and then I would say that your high rpm idle is a binding in the throttle linkage as Ron has suggested. Loosen up the linkage between the two carbs and make sure the throttle shafts move freely, can't be pushed down when the car has the high idle. If the shafts are misaligned, one may be hanging up.

You may find it worthwhile to complete disconnect your choke linkages while tuning.

Are you also sure you are running on both carbs. I've had a situation where one jet was blocked by the cork packing - except it wasn't cork packing.

Consider setting up the carbs individually. See here.

https://mgaguru.com/mgtech/care/cf120.htm

Also see here from around 4:50

https://youtu.be/4nvGLgO6pj0?si=7w0YRjhrXqDmYinC

gjr0 · Aug 18th, 2023, 02:19

Solved ?

It turns out that the Idiot's Guide to Tuning SUs doesn't work for these carbs (HS6). It may work for HS4s but that is to be determined.

Starting at 1 1/2 turns out and adjusting for maximum idle speed on both carbs (+1 flat) makes for a stable idle. I'm not sure my old dwell tach is up for resolving small rpm differences but as of tonight it works.

I'll have to go back and work through all the set up again, just because, but it is much better. Thanks for all your ideas and help.

Now, on to the other items on the to do list.

Derek UK · Aug 18th, 2023, 12:19

My first reply, post #4 appears to agree with you.

Aug 14th, 2023, 22:43	#21
gjr0 Junior Member Last Online: Today 02:22 Join Date: Aug 2023 Location: Delano, Minnesota USA	The cam is an Iskenderian Z-66-005. Lift is 0.293 " on both intake and exhaust. Duration is 268° for intake and exhaust. At 050" lifter rise the duration is 244°. Overlap is 52°.

Aug 18th, 2023, 01:58	#22
blueosprey90 Master Member Last Online: Today 16:33 Join Date: May 2017 Location: New Milford, Connecticut	Not sure what carbs you have or whether this humble advice might be helpful. My experience is limited to SU H4 and H6 carburetors. I have never had any success whatsoever fine tuning with the lifting pins. Perhaps I am unable to hear. I've had a little better success using the carb balancing wires to lift the dashpots (basically mimicing the lifting pin) - but still don't really tune this way. Generally, I measure the distance from the bridge to the jet. Right now, I'm running the H6s at about .085" - but the range I use is in the .060" to .090" range and then tune by looking at the spark plugs. If you can set your carbs to a distance in this range and see how the car runs. Then when you stop, and it's idling to say 2,000 rpm, shut the car off and re-measure. The distances should not change, and then I would say that your high rpm idle is a binding in the throttle linkage as Ron has suggested. Loosen up the linkage between the two carbs and make sure the throttle shafts move freely, can't be pushed down when the car has the high idle. If the shafts are misaligned, one may be hanging up. You may find it worthwhile to complete disconnect your choke linkages while tuning. Are you also sure you are running on both carbs. I've had a situation where one jet was blocked by the cork packing - except it wasn't cork packing. Consider setting up the carbs individually. See here. https://mgaguru.com/mgtech/care/cf120.htm Also see here from around 4:50 https://youtu.be/4nvGLgO6pj0?si=7w0YRjhrXqDmYinC

Aug 18th, 2023, 02:19	#23
gjr0 Junior Member Last Online: Today 02:22 Join Date: Aug 2023 Location: Delano, Minnesota USA	Solved ? It turns out that the Idiot's Guide to Tuning SUs doesn't work for these carbs (HS6). It may work for HS4s but that is to be determined. Starting at 1 1/2 turns out and adjusting for maximum idle speed on both carbs (+1 flat) makes for a stable idle. I'm not sure my old dwell tach is up for resolving small rpm differences but as of tonight it works. I'll have to go back and work through all the set up again, just because, but it is much better. Thanks for all your ideas and help. Now, on to the other items on the to do list.

Aug 18th, 2023, 12:19	#24
Derek UK VOC Member Last Online: Today 15:34 Join Date: Jul 2006 Location: Chatham	My first reply, post #4 appears to agree with you.

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