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Dash pots


daverclasper
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These are basic CD 150's on Vit Mk1 2Litre.

A few questions please.

Can oil get lost in normal running and if so how often and how?.

Can the pistons and/ or bore in the carb be worn causing oil lost over the top  therefore also limited damping.

If dash pots are low can this cause a bit of pinking, due to running weak?. Or ambient temp (use car all year).

 Asking, because  every now and then (few weeks), engine develops a little bit of pinking.

Have been retarding timing slightly on the vernier, about 10 clicks when this happens.

Wondered if crank pulley was slipping a bit, though looked at timing recently statically (not got gun), and was only 3.5 degrees BTDC!, which  seems a bit retarded.

Using tesco 99 oct.

I know it's an old car and runs well, so happy anyway, but interested. 

Any advice great please.

Cheers Dave 

 

 

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Dash pots on strombergs fixed needle air pistons do tend to lift oil, over the top, not much will be worn as theres not much comtact

Low oil weakens acceleration mixture and weak wont generally make her pink under load

I would suggest you check the vacuum capsule , if the internal returnspring has failed you get too much vac advanve at the wrong throttle

opening  , its not easy to check the timing ring , yes if the bonding has gone it can give duff readings.

Ikewise weak centrifugal springs in the dizzy will advance too early

3.5 is much too low 8 to 10 is more normal

Can you fit a vacuum gauge  set tiing to give 18 to 21 ins hg.  Or just use ears and turn dizzy to give fastest  idle and back it 

Off  a little ,  ,   as you advance the idle will speedup.it must be retarded to be 200rpm less that best  or there abouts.

Your on the right fuel, , dashpot top up is normal

Pinking at 3,5 is not normal

Pete

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It may be worth taking some advance readings at different rpms. I did this recently when changing distributor springs to get back to something resembling the factory advance curve.

Do it with vacuum disconnected, and record the actual figures at (say) 800, 1200, 1500, 2000 etc up to 3000ish when the advance should reach max. My distributor was at max advance from 1000rpmish, so hopeless. New springs corrected the issue, economy and drivability greatly improved!

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if you use the data in the workshop manuals just check the small print  many a dizzy test data is Decelerating  and falling vacuum 

which will confuse the results as building the revs gives a very different hysteresis compared to slowing down from hi revs

Pete 

 

 

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3.5 BTDC is to far retarded. 6 to 10 would be about right. You can test if its the vacuum unit by disconnecting it and blacking off the pipe into the inlet manifold.

The vacuum unit is an economy device which advances ignition under light engine loads.   

It maybe worth trying another brand of Super Unleaded fuel to see if you have a bad batch.

Dave 

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Thanks everyone. few questions please.

I have a vacuum gauge. Can I rig it to the manifold stub (will have to use a bit of hose and jubilee clips, this ok?) , where the PCV valve hose goes on, then remove the the PCV from the rocker cover stub, so the crancase can breathe?.

Does the vacuum capsule have to be disconnected AND blanked off?.

Pete. those vacuum figures are just for idle?.

Thanks, Dave    

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Dave, Things to do first.

1/ Try a different brand of Super Unleaded fuel.

2/ If you want to test for pinking without the vacuum unit in use then you have to disconnect it and blank off the vacuum pipe coming from the carb to stop air entering the inlet manifold.

Thanks,

Dave  

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Any tapping in the manifold will work , you could use the pcv take off but would only use it as a temporary to use a gauge and replace the pcv again afterwards

Any piped vac gauge needs a short squashed tube to dampen the fluctuations , just squeeze a tube with pliers till the needle is steady

Yes 18 to 21 is at idle ,

Soon as you open the taps it will drop, in a high gear at full throttle it can drop to 0  and deceleration go up to 30-32

Cruising 10 to 15  is a general expectaion.

Dont use the dizzy vac take off this works completely the opposite to manifold vacuum.

 

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