Hi Charles,
Since the piston is part of a "closed loop" feedback system, it will hunt or
flutter around it's balance or set point. In this steady state mode, the
dashpot works to filter out this hunting and stabilize the piston. The
thicker the oil, the more dampening to the control loop.
Upon acceleration, the dashpot retards the otherwise rapid rise of the
piston in response to the increase in vacuum. This increases the velocity of
the air past the fuel jet and temporarily enrichens the fuel mixture
providing a similar effect as an accelerator pump. The thicker the oil, the
more "accelerator pump" action is achieved.
If the oil is too thin, fluttering at steady throttle opening will occur as
well as stumbling upon acceleration.
Too thick an oil and you will get overly rich and sluggish acceleration.
The owners manual for my '74 Midget calls for engine oil in the dashpots.
I think most of this is mostly correct. Hope it helps.
Richard
'74 Midget (undergoing Arkley conversion)
'58 Morris Minor 1000
'68 MGBGT
At 10:36 AM 3/13/00 -0500, you wrote:
>But what is confusing me is that unless the spring is going bad, the piston
>ought to remain at the same level while at a constant speed. Since my
>dashpots go through half of their oil in about a week or two, I'll be
>experimenting. A representative from a local parts vendor suggested using
>ATF, so that if a problem developed that caused dashpot oil to be consumed
>rapidly, the resulting smell (stench) would indicate the driver.
>
>If the oil is too thick, doesn't it also impede performance by making the
>mixture adjust more slowly?
>
>As for the 3-in-1 that I use, its best feature is that it comes in a small
>can that fits conveniently behind the frame member in the boot.
>
>Regards,
>
>Charles
>'74 Midget
>'68 Sprite
>cdsorkin@ix.netcom.com
>Bloomfield, NJ
>
>
>
>-----Original Message-----
>From: shawn tobin <suhs2@hotmail.com>
>To: cdsorkin@ix.netcom.com <cdsorkin@ix.netcom.com>
>Date: Monday, March 13, 2000 9:43 AM
>Subject: dashpot oil
>
>
>>I have used Marvel Mystery Oil like some suggest but I believe it to be too
>>thin and allows the carbs to flutter. My car seems to run best with 20W50
>>synthetic in the dashpots. This weight of oil is recommended in the
>Bentley
>>manual and in owner's manuals. You may like a lighter grade but some
>weight
>>of motor oil works best for me.
>>
>>Also, on constant speed question, I have done a couple of the Vizard mods
>on
>>my carbs to increase airflow. After modding them, I put straight Marvel in
>>them and adjusted the mixture for idle. I found a sputtering flat spot at
>>2000 to 3000 rpm even at constant speed. Richened the mixture nuts--same
>>problem. Put in 30wt and the problem subsided. Now I'm back to 20w50 and
>>the car runs great. Don't exactly know why.
>>
>>PS get some Royal Purple--you'll love it.
>>______________________________________________________
>>Get Your Private, Free Email at http://www.hotmail.com
>>
>
>
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