What’s the best oil for them. I’ve been using 3-in-one SAE20 it works great but i have to add every few hundred miles about 600 cause the car starts to act up .. is that normal .

well i didn't even know you have to oil them. where does the oil go?

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694

I use SU carb oil. MSA sells it. zcarparts.com The oil goes in the black plastic caps on the top Mike. Now there are alternatives, I just haven't tried any. You can find that answer searching online, or someone here might now. From what I've heard the thinner the oil, the better the response. Hope this helps.

ah ok. cool. i will have to check it out. learn something new everyday.

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694

I've exclusively used 10wt 3-in-1 sewing machine oil for more than 45 years (I had Healeys and motorcycles before I had my Z) and never had a problem. It's cheap, has a handy nozzle which shuts tight and doesn't leak, and the can is the perfect siZe to carry with you in the Z.

SUs require oil in the tubular reservoir under the black plastic thumb caps in order to dampen the action of the vacuum piston. Just don't over-fill them. Yes, it's completely normal to have to refill them that often; even more often if you really romp on it for long periods. I've refilled them 2 or 3 times a week when necessary.

Sportscars require frequent minor maintenance. As Jaguar used to say in the 1960s: "If you think you can just buy a sportscar and forget about it, forget about it".

Mike, when you've topped off the oil damper reservoirs, you'll immediately notice smoother carb action.

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1970 240Z

ok Frank. i will get some oil for them.

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694

Only fill to the top of the little reservoir tube; the part the piston fits into. Any more than that is a waste.

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1970 240Z

Frank (10wt 3-in-1 sewing machine oil ) is that the black bottle. I use the 3 in 1 in the blue bottle.

what happens if you over fill?

Here's a diagram of how much oil you need. You're only trying to top off the little tube reservoir the tiny "shock absorber" piston fits into. Fill to the level of the arrows. When you put the tiny piston back in, it will probably squirt out some oil, but then you know for sure the reservoir is full.

I have accidentally overflowed the reservoir several times (probably drunk) and the excess oil "went away" quickly. I suspect it got sucked into the engine and burned. Overfilling is more just a waste of oil than it is a danger to the car.

All we're trying to do here is dampen the movement of the suction piston inside the suction chamber. The chamber is dry and the piston springs very freely up and down inside it on a very bouncy spring, carrying the needle in and out of the jet. If the suction piston is allowed to 'bounce' or fluctuate, the carb feeds the engine a constantly varying degree of fuel.

Picture fuel trying to flow thru a "donut hole" (the jet). An inverted "traffic cone" (the needle) slides in and out of the donut hole and either slows the fuel or lets it flow more. If our traffic cone is allowed to bounce, the fuel flow will never be constant. So all this little piston in a tube reservoir is doing, is acting as a sort of shock absorber to keep our traffic cone from bouncing in the donut hole. When it runs out of oil, our "shock absorber" is dead. (All you dirty-minded people out there keep your similes to yrslf, pleaZe).

Dave, I usually just buy the red and white can of 3-in-1 10wt oil, but slightly heavier weights will work, too. I think it's mostly a personal preference thing ~ I've never had any trouble with the 10wt sewing machine oil.

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1970 240Z

Back in the day, guys used everything from 10 wt. oil to shock absorber oil for MG and Sprite shocks. Depends on how quick you want them to open , WITHOUT GETTING STALLING AND HESITATION from them opening too quick.
Irv Rich

Right, Irv.

The Haynes Datsun Automotive Repair Manual for the 240Z says to use SAE20 weight engine oil. I've never personally known anyone who used that, all preferring to use lighter weight oil for better performance.

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1970 240Z

how about using some vegetable oil? .......

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Mike Tubiak
1978 Datsun 280Z - HLS30-438694

Whatever works!

I can barely undrstnd this bloke, but I can recogniZe and follow what he's doing with these actual British SUs.

Our Japanese made Hitachi SUs are actually better in some ways than these original Brit carbs, but they are identical in appearance and function for these purposes.

http://youtube/0Wb4b2Xrhr8

Please note the very bouncy spring which can cause the vacuum piston to pogo around in the vacuum chamber if it is not dampened. The spring and vacuum work against each other. The spring wants to push the vacuum piston down (restricting fuel flow), and vacuum wants to lift the vacuum piston up, (increasing fuel flow). Unless we dampen the operation, the vacuum piston can bounce up and down much too often causing weird operation.

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1970 240Z

10 wt is thinner than SAE 20?

Yes. The "weight" of any oil refers to its viscosity, or how easily it flows. The lower the number, the less viscous the oil is. The lighter the oil, the better it flows.

Each 'weight' has different advantages for automotive lubrication purposes. Oils today are usually 'blended' multi-weight (such as "10W-30"). That shows they have 10 weight oil for winter use, blended with 30 weight oil for summer use.

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1970 240Z