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Fluid for carb damper

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TonyPanchot

TonyPanchot

Jedi Trainee
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Ok now I could use a suggestion for the fluid for the carbs as they appear low

thank guys for all the help as I had a hard drive failure and my backup is 5000 + miles away

one good thing is that my 3 chest roll away finally arrived
albeit the drawers were a bit jumbled :thirsty: fixed that
 
I use ATF in my SUs
 
SAE 20 is about ideal for SU's in most climates.

You can mix your own by blending a splash of light sewing machine oil with engine oil, or use Penrite SU Carburettor Dash Post Oil supplied in a 125ml plastic container.

Viv.
 
Mystery marvel oil.
 
I'll put in another vote for SAE 20.

Not immediately obvious, the damper oil provides an analog to the accelerator pump function on a fixed venturi carb. The heavier the oil, the bigger the 'squirt' (mixture goes richer when you first open the throttle wider), which, up to a point, provides crisper throttle response.
 
Hi Tony,

There are a ton of opinions as you already have several & they`re all good.

Personall; Without having to mix, guess which is the best; I bought a bottle of "Moss Motors" pre-mixed, pre-formulated, specifically designed to our Carbs.

Yes; Its expensive but I`ve had my little bottle for yrs. now. So; No guessing games here. Never had any problems.

Regards, Russ
 
Whatever you put inna crankcase at oil change. :wink:
 
DrEntropy said:
Whatever you put inna crankcase at oil change. :wink:
Click to expand...

thditto.gif
 
TR3driver said:
I'll put in another vote for SAE 20.

Not immediately obvious, the damper oil provides an analog to the accelerator pump function on a fixed venturi carb. The heavier the oil, the bigger the 'squirt' (mixture goes richer when you first open the throttle wider), which, up to a point, provides crisper throttle response.
Click to expand...

Never really thought of that, but makes perfect sense.
 
toysrrus said:
Personall; Without having to mix, guess which is the best;
Click to expand...
FWIW, I selected SAE 20 after experimenting on my own car (TR3A with stock SU H6 carbs), in it's particular condition, to see which I liked best.

I had already made a gizmo that worked well for sucking out the oil: cheap air-powered vacuum pump plus a Mason jar for a liquid trap and a probe from thinwall brass tubing. Tried ATF, MMO, 3-in-1, plus motor oil from 5W30 all the way to SAE 40.

The differences were fairly subtle, meaning none of these is really "wrong", but I found that the thinner oils gave a bit of "lean bog" where the engine didn't respond for a bit after you open the throttle; while the SAE 40 actually made the throttle kind of 'twitchy'. I settled on SAE 20 as the best overall compromise (which indeed seems to be very close to the tiny bottle of genuine SU damper oil I was given at some show).

YMMV of course.
 
Wow thank all:smile: now that I can source locally (20 Wt.)
 
Hi

I completely acknowledge SAE 20 is the most widely recommended. However, in practice I have been using SAE 30 non detergent and feel it give just that tad bit more initial enrichment upon acceleration. This results in slightly better (I feel) throttle response without feeling "twitchy". Either way, I'll admit it's an extremely fine line. Can't go wrong with either.

Bob
 
I'm with DOC on this. whatever I have for the crankcase is what I use for the dampners.
 
I did my own "experimenting" there as well. I felt the thicker oils (SAE 40 & 50) didn't allow the piston to open fast enough during the acceleration period, which is usually just a few seconds. I liked the feel with AFT, which is usually equivalent to a 5W-20.

I also had to "rich" the carbs up by about 1/2 turn based on plug color with the ATF. I figure that was because the throttle is almost constantly being manipulated while driving (unless on the freeway) - give a little gas, ease up, repeat. Since the carb piston damper is actually a little check valve the piston will drop quickly when the throttle is eased, then encounter the viscous resistance to opening when reapplied. With a thicker oil the piston takes more time to equilibrate its position, which then might not be achieved before the next time the throttle is eased. The fuel mix will then be more rich than with a thinner oil.
 
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