• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Vanishing dashpot oil?

Share this page

M

Money_Pit

Jedi Hopeful
Offline
Seems my dashpot oil is vanishing? At this rate I might have to purchase by the barrel. If I do that I'm worried that it will create a sudden high demand and they'll have to increase gas prices to cover shortage. I'm topping it up daily based on car sputtering. Your help in this matter would be greatly appreciated!

DT
 
If you have the standard SU carbs, there is no place for the oil to vanish.

When you fill the dampers the oil level should be just a little below the top of the INNER tube (down inside). Over filling will just cause the excess to overflow into the piston chamber. Mysteriously vanish until it reaches the proper level.

The dampers have a one way action, resistance when the pistons rise, no resistance when the pistons drop. You can easily check the action by filling the dampers, when inserting the cap with damper sleeve you should feel some hydraulic resistance. When you pull the cap back up there should be noticeably less resistance.

You could also check the damper action by raising the slides with your finger. Hydraulic resistance to raising, no resistance when lowering. The sliding brass sleeves act as one way hydraulic valves. They might need cleaning.

If the dampers are operating as described, your problem is likely to be something else. Maybe the mixture is set too lean.

Damper oil can be any viscosity or type that works for you. 20 wt motor oil is frequently used. If the pop back is truly being caused by the dampers, you can try some heavier oil in them.
D
 
Thanks Dave

I purchased 2" carbs from DW and I just changed out the carb needles to UN's (as advised by DW) since I'm running with DWR8 cam (I was getting quite a bit of sputtering at low end) After changing the needles I reassembled and put daspot oil in (maybe a fraction to much) and the car ran great! Next day car starts sputtering again at low end again so I add more daspot oil and it runs great again? What's up???

DT
 
With that cam/carb combination, a certain amount of lower rpm misbehavior could easily happen.

Possible cures would be heavier dashpot oil, richening the jet adjustments, & changing the distributor centrifugal advance curve. ie. More initial spark advance, & a quicker lower rpm advance, while limiting the maximum mechanical advance.

Something like 15 crankshaft degrees initial at idle, 25 degrees at 2500 rpm, & 35 degrees maximum at 4000 rpm.

Also heavier carb springs might help. I think the three spring weights available for the 2" carbs are - red/green = 11.25 oz, - lt. blue/black = 4.5 oz, - lt. blue/red = 18 oz. I don't know which springs you have installed now but you could go up to the next heavier step.
D
 
Back
Top