carb tuning

[Ron Kwas]

Arcturus;

I hate to hear you have so much difficulty...I would like to come back to the wiggly Metering Needle, and compare it to the hard MN...bottom line in terms of mixture is that when Dashpot is lifted that little bit for idle, the same OD should be blocking Jet Orifice for both hard and wiggly MN, resulting in an equal amount of fuel being dispensed...so this goes back to the position in Dashpot of the MN in Dashpot...please confirm this...you might also measure the MN OD at some distance from bottom Dashpot surface and compare that between hard and wiggly MNs...finally, confirm OD is what you believe it should be based on MN specs. MN taper, Dashpot lift at idle, and therefore height out of Jet orifice (0.100") determine idle mixture...!

Good Hunting!

[Vintagewrench]

Originally Posted by 960kg

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

So true - will one of these plugs hold up to road use for a while?

If so how about using a mounted camera under the hood to record one of these plugs while driving at different speeds? Then change it to each of the other cylinders one at a time and then you will have an interesting record of the burn colors. Doing this on a chassis dyno or rolling road would be easier.

Or, take it out and warm it up first, and find a good road w/little traffic. Pull over in a quite spot and set up the Colortune on #1 and run it though the gears up to a constant speed. Go back to where you started, change plug to #2 and later #3 & #4 and run all at about the same speeds and rpms as you did the first time and you will know exactly what you mixture looks like through the range.

Another method is what I and others use on racing cars: Warm up the engine first and then put in a new set of plugs of the correct heat range. Run it though the gears up to a constant speed and then push in the clutch and shut the engine off at the same time and then coast to a stop and check the color of the plugs for an average record of the run.

To find our what you mixture is like at the speed you drive at most of the time, put the plugs back in and run it at that speed for several miles and shut it off as you did earlier and check the plug colors.

Color info here: https://www.ngksparkplugs.com/about-...d-a-spark-plug

http://www.verrill.com/moto/sellingg...colorchart.htm

[arcturus]

Well, that's it sorted for the time being. Getting there slowly.Runs a bit fluffy between 10K and 15K rpm. starts to get better at 20K, at 30k picks up its skirts and starts showing a leg and at 40K hang on, up to 50K.I would like to try the KF needle if I can get a springy one.

[arcturus]

Just had this from Burlens


Thank you for your enquiry. The sprung needles available for the 100 thou HS6 jets range from the BAA needle to the BHD needle and the KN needle. There is no 100 thousand KF needle available. You can purchase the profile charts showing the diffferent profiles of each of the needles.

[amazon69]

Is this not why the jet is so far down? The unsprung needles are 0.090 but the sprung ones are wider at 100 thou therefore you need the jet lower? My unsprung needles are 1.2mm below the bridge.

[arcturus]

Hi again, just returned after my Christmas treat in posh hotels and great wine. The car runs fine but is lumpy now between 10 & 20K. It was much smoother before so I think that I will return it to it's earlier position.
Also noticed this for the first time. The position of the ridge on the dash pot neck differs between carbs although the dash pot will only fit in one position.

[arcturus]

Read this whilst browsing SU carb adjustment
couple of decent donations as it is so useful. If you use the site, then please make a donation – it is well worth it.

Needles come in a very wide variety of profiles for both the fixed and bias sprung (Pic 8) types. The biased sprung (swinging) needles are very much longer because they were initially developed for the 2-inch SU fitted to export Jaguars to achieve minimal emissions and safety reasons. To simplify and minimise stock numbers, the same length was used for all biased sprung SUs from 1.5-inch upwards. Consequently the needles used in the smaller carbs only use a very short section of the needle

This could account for the 18 flat adjustment.

BTW the mileage I expect to do shouldn't make wear a problem