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Tips
Tips

Which Dashpot oil ?

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bighly

bighly

Jedi Knight
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I don't even remember what I put in my dashpots a few years back when I first put bighly on the road. Probably whatever the manual said. Everything is working well but I would like a bit more pep in the pickup. I assume this has been discussed but couldn't find it by searching keywords. So I assume a lighter weight (higher number) produces quicker piston lift with a trade-off of less dampening at higher RPMs. I have 1-3/4 carbs with thermocarb on a toggle switch on my 1960BT7. What I am looking for is an explaination of what weight oil corresponds to what behaviour. And is it worth it to change. Ah and how does one drain dashpot oil?

Tracy
 
I'm sure there are suitable substitutes, but I have seen places like Victoria British and others who sell "SU Carburator Oil" especially made for the purpose.
 
To remove the oil just take the domes off and remove the pistons and turn them over. Four screws each easy. No upset to any adjustments.
 
[ QUOTE ]
To remove the oil just take the domes off and remove the pistons and turn them over. Four screws each easy. No upset to any adjustments.

[/ QUOTE ]

BUT only do one at a time to avoid mixing up which piston goes with which dome, as they are matched,
 
For that matter, you don't have to remove the pistons from the domes. Just remove the cap and turn the whole assembly over.
Or, you can put a small hose on a syringe and suck it out without removing anything other than the cap.
Do not , I repeat, do not use your wifes turkey baster for this!!
Jeff
 
Oh the Turkey baster. Excellent Idea!! /ubbthreads/images/graemlins/devilgrin.gif Except I think it melted in the oven while I baked painted parts. /ubbthreads/images/graemlins/lol.gif

I take it you are speaking from experience.
 
/ubbthreads/images/graemlins/lol.gifYes, I am. Also on the list of don'ts are don't use the turkey roaster for an oil drain pan, and don't use the Pyrex measuring cup to mix the two stroke gas/oil for your dirt bike.
Jeff
 
Tracy,

A lower weight has a LOWER number.

The "standard" oil is SAE 20. people have used everything, & I do mean everything, imaginable. I use ATF which is equivalent to SAE 5-20. This gives a little more consistent operation over a wider temperature range than straight 20 wt. The special dashpot oils usually consist of 20 wt in a special bottle at around $20 per quart.

The key to oil weight is in the throttle response. The dampers take the place of accelerator pumps on conventional carbs. When the throttle is quickly opened the dampers resist lifting the piston too quickly & momentarily cause a richer mixture to prevent quick throttle opening flat spots in acceleration. Damping at higher rpm is a small secondary consideration.

Too light oil lets the pistons open too quickly & hesitation, spitting, or flat spots occur. Especially when the engine is cold. Too heavy oil slows piston opening to the point where an over rich condition on acceleration can occur & also gives a bit slower throttle response. Each engine & climate condition has it's own optimum oil requirement. The standard 20 wt is a good compromise. It's kind of like "what kind of beer do you prefer?"

You can get the oil out by sucking it out through a small tube. Or just remove the pistons & pour the oil out.
D
 
I almost hesitate to mention this, but I have run different viscosity oils between front and rear carbs to get them to function correctly.
I'm guessing this may have been due do a difference in clearances between the pistons and suction chambers on each carb.
Jeff
 
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