Carby Dashpot

Post by **David53** » Mon Jun 29, 2009 6:45 am

I recently rebuilt the carb and (silly me) forgot to put oil in the dashpot before fitting the Oil Bath air cleaner. As the Oil Bath air cleaner sits RIGHT over the dashpot you can't get the top of the dashpot off to top up. So I managed to get the lid slightly off and drizzled in some sewing machine oil. question is - is this oil too light? Should I replace with engine oil? Getting a few flat spots at low revs. Taking off the air cleaner is just a bit of a pain! (Done it so many times recently)

Post by **bmcecosse** » Mon Jun 29, 2009 7:23 am

I prefer thin oil - we call it 3in1 - your oil should be fine. It's probably running a bit weak - richen it up a flat or two and see what happens.

Post by **David53** » Mon Jun 29, 2009 9:43 am

Yes that's the stuff, 3 in 1. I managed to get a reasonable amount in I think! Kind of hard to tell - how full should it be?

Post by **mike.perry** » Mon Jun 29, 2009 10:35 am

Just below the top of the piston you can see inside when you take cap off. If you overfill it, it will sort itself out.
Give the piston a final lift and drop check before you refit the air filter.

Mon Jun 29, 2009 6:34 pm

3 in 1 might be a bit thin if you have re-conned the carb. i Used 3 in 1 fine until I cleaned up the carb and the removal of 20 + years of crud meant everything moved to quickly, changing back to a thicker oil seemed to sort everything out.

Post by **alanworland** » Mon Jun 29, 2009 7:46 pm

I found 3 in 1 was ok with a cold engine, but hot it was worse than water! it let the piston rise far too rapidly and the mixture went weak (huge 'flat' spot) I drained and replaced it with 20/50 engine oil and it has been fine ever since!

Post by **mike.perry** » Mon Jun 29, 2009 10:04 pm

it has been fine ever since

Until the alarm starts

Post by **bmcecosse** » Mon Jun 29, 2009 10:28 pm

The idea of the thin oil IS to lift the piston quickly! This allows air into the engine - it's what it breathes! Years ago it was all the rage to modify the piston to make a 'quick lift' dashpot asembly. The thin oil is a kind of half-way stage. Yes - you may need to richen it up slightly - but throttle response and general acceleration will be better.

Post by **David53** » Tue Jun 30, 2009 11:12 am

Well, I think I'll have to nite the bullet and pull that %^&&$#@ Oil Bath air Cleaner off again and have a proper look as I have no diea how much oil's in there now. How I envy you folks with the later air filter!

Tue Jun 30, 2009 1:00 pm

The problem for me as i seem to recall.. 15 + years ago was that yes it lifted quickly but dropped quickly too and a bit too quickly and the car just kept dieing.. yes maybe a tune up would have resolved the issue but using a thicker oil also cured the problem.

Post by **bmcecosse** » Tue Jun 30, 2009 1:19 pm

It doesn't matter how much oil is in there - any excess just spills over and is sucked into the engine.

Post by **katy** » Tue Jun 30, 2009 3:43 pm

Now you fellows have me thinin' about what oil to use in the dashpot.
I don't have 3in1 oil so I put in 10W30 which we have lots of, but maybe it's too thick?
I'm thinking about changing it to ATF, which is quite thin.
BTW, I was looking for 20W50 in town yesterday and didn't find any.

Post by **bmcecosse** » Tue Jun 30, 2009 4:55 pm

Probably because it's COLD there most of the year!

Post by **alanworland** » Tue Jun 30, 2009 9:53 pm

Burlen Fuel Services do sell a 'SU' oil for the dashpot, never had any but I believe it is quite thin.
My handbook suggests SAE 20, it also goes on to say (in bold!) that a heavy lubricant should not be used!
I'm sticking to my 20/50 engine oil.
Mike, the alarm has been rewired so that it cannot go off or immobilise whilst on the move! I think it was all too clever for the old girl as the (pulsing) distributor feed upsets it.

Post by **alex_holden** » Tue Jun 30, 2009 10:21 pm

I'm using the SU dashpot oil. It starts out slightly thinner than 20-50 when it's cold and gets much thinner when the engine is hot. Perhaps something like 10-40 multigrade engine oil would give more consistent results.