carb tuning

[arcturus]

KN sprung needles. Looks to me that they can only be fitted on way. I might try different needles later, when I sort out this problem.

[arcturus]

Derek, I pulled the domes and checked the needles etc. Everything seems OK .
Re set each jet to full up and unscrewed each 12 flats,that's two full turns. At that it would start with full choke but just. Unscrewed each one, one flat at a time and runs best at three full turns, 18 flats.I think that the filter is a red herring as I made all adjustments with filter off and barely any difference with filter replaced. I will probably try out KF s in the new year.
Swede and German. Which setting do you use on your wind gauge? I was using meters/sec' or are they all basically the same?
Derek. In my earlier posts I said that I turned the flats down, that was a mistake. I turned them up. I don't know which thread is used on the jets but three full turns shouldn't amount more than a couple of mm. Don't have a spare jet to try.

[Derek UK]

I've never heard of anyone needing to use a setting of 18 flats down. With the domes off, wind the jets up until they are both level with the top of the bridge. Start your flats down from there. When you just wind up the jets with the domes on you don't know where the jets end up relative to the bridge so equal flats down under those conditions can have the needles mismatched. With the domes off you can try and wind the jets down 12 flats and then measure the drop with the thin end of a digital caliper. Try it again with 18 flats. I think that you will find the drop at 12 is more than 2mm and therefore even more than that at 18 flats. Sometimes the jet holder that screws into the carb body locks up before it is fully home when you screw it in. If that happens you can't raise the jet high enough to get it level with the bridge. Burlen didn't have an answer for this when I asked them at Beaulieu.

[arcturus]

I don't want to disturb anything again Unless necessary. Can you tell from these photos if it's OK or not?

[960kg]

Originally Posted by arcturus

I don't want to disturb anything again Unless necessary. Can you tell from these photos if it's OK or not?

The reason you are so many flats down is because the jet is too low too start with ...it has to be flush with the alloy bridge....your pictures show it too low?

Any model of motor with SU`s will be correct within 1 1/2 to 2 full turns down of the jet.....Use the lifting pin by 1/32" to give the correct mixture for each carb.

The rear cylinders should not be richer, if anything the front will be on the same setting as these are nearer the water pump and so run colder so in practice need more fuel.

Colortune i have read some good reports but always read the actual plug color on coming back from a run ...colortune are idle only.

Are the pistons returning down with the "famous" click or is one sticky?...jet not central.

Upon correct mixture given by the lifting pin on each carb ....when fitting the air filter it gives enough richness to be just right for better acceleration.

It is normal in Winter with these type of carbs to go richer by one flat because of the colder air intake.

[arcturus]

It seems to me it ends up being in the same place. Yes i'm starting from higher up but the needle relative to the jet will still be the same? What I thought was the top of the Jet was the seat.I take it that this what is meant.

[Ron Kwas]

Arcturus;

That sure looks like flush with the Venturi Bridge to me!

I understand that the "Swinging Metering Needle" never got installed on Volvos from the factory...it seems to me that a one-piece MN combined with a proper jet centering, will beat a MN literally dangling in the breeze, and making contact with jet any time it wants to (which can only lead to wear!) every time!

See also: http://www.sw-em.com/SU%20Jet%20Bear...be%20Notes.htm

Good hunting!

[960kg]

Originally Posted by arcturus

It seems to me it ends up being in the same place. Yes i'm starting from higher up but the needle relative to the jet will still be the same? What I thought was the top of the Jet was the seat.I take it that this what is meant.

In this post the jet looks correct but in your other one which i have put up the jet is too low.

The jet has to be the correct height to start with despite you saying the needle relative to the jet will be the same as the Air Flow will be different to the fuel amount??

[arcturus]

This is how it came back from it's overhaul in January of this year. This was the first time I had reason to check it after altering it for the inspection. It has been running fine. As a matter of interest would I be able to install a "fixed" needle in this configuration. I would like to try a KF but the Burlens one are all regular solid fix.

[arcturus]

Re-set everything as per' and quite honestly it doesn't seem to run as well!