Yellow versus red in the HIF

linearaudio · Post by **linearaudio** » Thu Oct 22, 2009 9:40 pm

Am I the only one to be prompted to use the yellow (8oz) spring in the HIF38 by WINSU, rather than the standard red (4.5oz) rate?

I was suffering an 'orrible erratic tickover/low pick-up with the red spring, Using the "standard route" 940 head etc.
Switching to the yellow spring sweetened the whole lot up, but took the "snap" out of the acceleration, and made heavy weather of the top end. The red spring was measuring 4 1/4" long, so I carefully-ish strtched it to 8". Now has a stable tickover, good "snap", and doesn't run out of steam at the top!
Was my red spring over-short? Why does WINSU guide me toward the yellow one? I tried various permutations of manifold etc, and it still threw it up!

Post by **bmcecosse** » Thu Oct 22, 2009 9:56 pm

Never had to change a spring -I think you proved the point! The carb needs to be set to open wide just before max air flow is reached - ie max revs with throttle full open. I suspect the yellow spring held it down too much. The lighter the spring - the more it will act like a 'weber' carb - only problem is over weakening on acceleration. The piston is held down by weight/spring/damper - so adjustments to all three items have an affect. You seem to have yours well sorted - well done !