HD8 drop test time in seconds

[AUSMHLY]

HD8 vacuum drop test

Hello all,

When performing a vacuum drop test with the HD8 carburetor piston and suction chamber, how many seconds should it take?

The two ventilation holes should be plugged (ear plugs) or taped (masking tape) over first, for an accurate reading.

Testing a pair of carburetors in a BJ8, if they don’t have the same drop time, what difference in time is acceptable?

Would there be a difference in performance if the drop test result was quicker or slower?
Example: better/worse gas milage or quicker/slower acceleration?

Here’s a link to a video about how to perform a drop test.

Thank you.

 

[Dandare]

I have seen 5-7 seconds stated for 1.5"-1.75" throttle but can't see a figure for 2".

The factory stance was that a fast piston drop, if markedly so, gave a richening effect over standard tuning and vice-versa..."sometimes even taking the general mixture strength outside the range normally given by the standard needle"

Danny

 

[John Turney]

5 - 7 sec is correct for all carbs larger than HS2. http://sucarb.co.uk/technical-carburetter-maintenance-settings-hs, Section 9 C. Both, if one has two, or all, if one has more, should be the same.

I would think a slow drop would result in the piston being lifted higher, causing a richer mixture.

 

[Rob Glasgow]

I'm guessing the speed of drop in this test is only to determine the consistency between both carbs. Once the masking tape is removed and springs reinstalled in the domes, those piston come down pretty fast, only restricted by the dash pot oil. So if the test drop for both is close to the same then anything in the 5 to 8 secs. Would be OK.