New SU user...switched from Dual Mikuni to HS6 (latest version with butterfly return springs)
HS6 mounted on much modded B20 (no spacers) monkeyfied extra return springs from butterfly ear to top of head...

Currently running, accel seems fine...decel seems "delayed"??? Is this function of piston return spring, or too heavy damper oil (using ATF)???

Am used to immediate decel that Mikunis gave...

Do the throttle flaps in your HS6 carbs have decel valves?

The 1968 HS6 came with decel valves in the throttle flaps and the spring that holds them closed frequently goes bad and we have to solder the flaps closed.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com

My butterflies are solid pieces of brass. One closes tightly enough I can't blow thru it(with my hand cupped on the outlet), the other leaks just a little. I was thinking the piston springs might be a little weak, and the pistons don't close fast enough (once throttle is released, and butterflies close) but being a newbie to SU. maybe ATF is too viscous). I'm used to the near instant RPM drop when a Mikuni Slide closes...

A small point - the British car manuals I use recommend "engine oil" in the SU dashpots. I have always used 20/50, same as in the sump!

Ian F

I lied...

It accelerates great in the garage...on the road, it has no power and spits back thru the carbs at about 3000...timing? Running at 14BTDC at 1200 straight line to 20 at 2000 (123 programmable) Will be installing Wideband Air/Fuel meter tomorrow...

Have no Idea...whatever came with the carbs....but the tips are thicker. Have a pair of KD's I got from CVI sitting on the bench...

The needles may be marked on the stem part that clamps into the piston. If not marked and you can measure the diameter at the top and at the tip (measured in inches) I may be able to help ID them with an old SU reference book I have. From my memory (for what it's worth--I'm 75 now) the ZH needles referenced by Planetman is noticebly thicker(leaner) than the others. I recall DX needles being in my '68 144S B18 (that model had a 10:1 compression ratio - 115hp from the 108 cu. in). - Dave

Which metering needles are you using, KD, ZH, DX or SM?
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com