QFAD fitted with HS2 SU Carb

[Steve Keohane]

Hi all,

Pleased to report QFAD 's conversion to a HS2 (11/4") carb (fitted with a ABC needle and 3 in ! oil in dashpot)) is progressing well. The engine fired up fine and once warmed up I had a go at setting the idle mixture. Still on a learning curve, but manged to achieve a reliable tick over ok - needs fine tuning.

Went for a test run; engine pulled well (no spitting back or hesitation); but bogged down when pedal 'floored'. I replaced the 3 in 1 oil with 20/50. Much improved but still bogged when floored.

The engine is running rich through the rev range and is difficult to start when hot; so will pop into Burlen Services to source a leaner needle and heavier spring.

All in all very pleased

PS thanks to all those who have offered advice - naturally always open to more pearls of wisdom!

[Geoff Ryall-Harvey]

Try a weight in the dashpot - a very large washer is ideal.

[david]

you can tune the SU needle by measuring on a piece of card at the side of the needle 1/8th measures and then remove the dashpot plunger and put in a piece of dowel..mark that with similar 1/8 marks from the top of the carb..run the engine -no need to drive it and when it flutters or stalls-read the mark and apply to the needle in a pillar drill and fine emery.
once done to the length of the needle, it is set for your engine.
info from the Doug Hammill tuning sU carbs book...
It worked for the Triking superlite racer...with a morris marina 1700cc carb on a tuned 1200cc moto guzzi engine.

[Steve Keohane]

Hi David and Geoff,

Thanks for the advice. I tried the AAC needle with a new yellow spring (trying to achieve a baseline). Interestingly the original spring had no colour marking and was an inch shorter?

Mixture wise the AAC was better - engine pulled cleanly from low rpm (vast improvement on my Solex) and the mid range felt solid; but I need to undertake a longer run to really confirm final view. The new yellow spring was an improvement - but will experiment with washers to see the effect.

Regarding attempting to re-profile the needle ( i have the Doug Hammill tuning SU carbs book). - I will speak to a car mechanic mate who has experience of SU's.

All in all well pleased with the progress thus far.

Steve

[Steve Keohane]

Morning all.

QFAD SU tuning is getting very close now. Running an ABS needle with a green spring and qty 2 12mm washers (underneath the spring). The Engine pulls well at all rpm and does not bog down. It is still running slightly on the rich side - but better that than running lean. I am particularly pleased with the low rpm pick up as this was a major issue with my old Solex (I think my old carb was just worn out - I had tried many different jet mods, reset float heigths and butterfly adjustments etc to no avail.).

Looking forward to the weekend for another batch of testing - hopefully the weather will hold.

Steve

PS must remeber the sunscreen as my nose is beginning to suffer from all this sunshine!

[Geoff Ryall-Harvey]

Steve - glad to see you're making progress.