Thanks for the tip- I'll have to switch over to 30W I think... any tips for removing the oil from an SU? I was thinking I could carefully remove it with a little clear hose.

-Will

SAE 20 oil is thin, while SAE 50 is thick. Thin oil will allow quick reaction of the piston, while thicker oil will reduce the bouncing of the piston on rough roads & on hot days, but will reduce the speed that the piston can react to throttle opening, & this can affect the performance, particularly when the weather is cold.

I used SAE 30 oil in mine because
1. I always had some oil left over from the last oil change
2. I am too miserable to go & actually buy some 20 weight oil.
3. I prefered to dampen the piston movement a bit more to help stabilise the mixture better while operating at highway cruise on what we laughingly called "highways" I did a lot of mileage on rural roads back then.

Even in deep winter, i used the 30 weight & drove steadily untill the whole engine was fully warmed up.

The way i remember it, many people also used Auto trans oil. Dexron was popular from memory.

Hi, Thanks for the link to the article! I used 20w oil in my carbs and it seems like pretty heavy-weight stuff. Should I use lighter oil? The wording is a bit confusing in the article because I thought that 20W is heavier than 30W

Here's what the article says:

The oil reservoir in the suction piston rod in which the oil damper plunger is equipped should be topped up to the level periodically every three months or 5,000 km (3,000 miles) with thin engine oil of preferably SAE 20 but not thicker than SAE 30.

Here's a very good article on SU carb operation and tuning clicky. It's based on the 510 carbs but they're almost identical to yours. Good luck
Michael

Hi,
The carbs are Hitachi SU's, from a 1400GX in New Zealand I was told.

What brand carbs do you have installed?

Hello Everyone,
My Datsun ran yesterday for the first time since the summer! I have swapped out the old A10 for an A14 bored 1mm over, with stock cam, MSD ignition, A15 swirl-port head and exhaust manifold, and a set of SU-type GX carburettors.
The engine seemed to be running okay... no exhaust past the manifold though, so VERY loud!... I had to fiddle with the adjustments on the bottom of the carbs (the jets, I believe) and the timing and it was running best at about 15 degrees BTDC, but the carbs didn't seem to be working too well. I had gone through them and installed new gaskets, fuel bowl valve, cleaned them out and made sure that the needle didn't bind when the piston moved up and down. I also added 20w oil to the dampers, which I read was the right weight on the internet, but it seems quite heavy! The carbs were doing some backfiring, and coughing up a bit of fuel mist onto my firewall (the engine is in my FWD Datsun Cherry Estate) especially if the engine missed.
So I was wondering if any of you had tips for tuning up a pair of SU carbs for someone that has never tuned, or owned a car with SU Carbs before. Also if you have any tips about how I should adjust the timing, or anything else to get the most out of this setup I would really appreciate it!

Thanks!
Will