10 replies to this topic

[IainR]

I have noticed that the dash pot oil in my carb disappears quiet quickly, even when the car is laid up in the garage. When I do start the car up is creates a huge cloud of smoke, so I guess its leaking into the inlet manifold and then through the engine.

Will a carb service or rebuild kit solve the problem or is it a replacement carb / dashpot / plunger the remedy?

[dklawson]

Please explain what you mean by the oil is "missing". A lot of people misunderstand how much oil is supposed to be in the dashpot and how high to fill it. A couple of the manuals have published some misleading information so they don't help the situation.

Take a look at the picture in the following link.
http://www.mgbexperi...hs4-section.gif

Look at the "grey" material labeled by callout #7. Note that the grey material extends upwards, above the removable plunger barrel but does NOT go higher than the top of the inside tube. Several of the manuals imply that you fill the reservoir ABOVE the tube, stopping about 1/2" below the threaded opening... that is wrong. Note in the picture that the level is about 1/4" to 1/2" below the top of the inner steel tube. If the oil is filled higher than that level, the excess oil will seep down between the vacuum dome and tube... where it will be sucked into the engine and burned.

[IainR]

Thanks for the link, it appears that I have been filling it up too much, I top it up to just below the threads for the cap - by the diagram obviously far too high.

Ive got my Dad to thank for this, 30+ years ago when I used to checkover my Mothers Morris Minor he always said to top it right up.

Thanks again.

Edited by IainR, 08 February 2011 - 01:00 PM.

[Shifty]

You can fill it up as much as you like, it just finds its own level!!

[ma11b]

a silly question while on the subject but what oil should i use in the dashpot?

[Dan]

SU dashpot oil, or 3 in 1 seem to be about best for most applications. Changing the oil grade can be part of tuning the carb.

[ma11b]

cheers dan

[Big_Adam]

I use motor oil. Found 3in1 to be too thin for me. Each to their own though it seems.

[charm_muppet]

I tried 3in1 but was far too thin, I have a 1098 with a stage 1 kit. I changed to engine oil 20w/50 and this helped a great deal. When I took my car to T&M in Colchester to go on the rolling road, Ray (the Mini man!) suggested using gearbox oil in the summer as the oil will 'thin out' due to the heat.

[mk1leg]

When at Slark race engineering for a rolling road test last Sept He found a problem with the dashpot plunger and advised me to get a new plunger as this was affecting the performance du the the ware..............I did change it and it has improved less topping up................

[bmcecosse]

The thinner the oil -the better the throttle response - the piston can rise more easily, and this allows more air into the engine and off it goes! However - if this results in the engine going too weak it will obviously 'gasp' - so you may need to set a richer mixture to cover this. It's a balance - you need to discover what suits you best. I found my car ran best at Sprints with NO damper plunger in the carb - but it was set very rich and would have been close to undriveable on the road.