Just filled both of my Hitachi refurbished 3 screw SU Carbs with 3 in one  motor oil (Blue and White label). The Temperature here in Panama is 33 degrees Celsius, very hot indeed! The car is running okay, but at first gear sometimes hesitates back and forth. The idle was set to 1000 but does not keep the rpm steady. It lowers to 900 or rises to 1,100 RPM. Sometimes if stuck in traffic it can lower to 500 and could stall.

 

Is this caused by the kind of damper oil? the timing was adjusted to 10 degrees Celsius and the Camshaft is a Schneider 274F (1800 to 6000 RPM)

 

Any recommendations? Both carbs are fully adjusted and fine tuned.

Have you tried using search for help with this?

If it helps I just did, does this look familiar...

http://www.classiczcars.com/topic/49287-damper-oil-for-hitachi-su-twin-carbs/?hl=damper

Mr. Matsuo recommended 20W for temperate climates and 30W for hotter climates.

When your 20W runs out, try 30W.

btw please PM me or email with pictures of the 311 cam when you can. Thanks!

Swapped the damper oil  with Castrol 10w 30 engine oil. Results:

 

1. Idle still not perfectly steady. Sometimes lowers to 600 RPM;

 

2. If i make a harsh brake stop, the car engines shuts down.

 

I am really fed up with this situation. I sprayed carb cleaner and could not find any vacuum leak nowhere.

Edited March 29, 20159 yr by jalexquijano

Oil only affects transitions when accelerating and decelerating.

It will not affect idle.

I'm pretty sure that's straight 30 weight. Not multi weight. A lot of folks use ATF.

 I ran Marvel Mystery Oil in mine the first couple of years & ATF for the next 20 years, year round. I never found a reason to change. That said, I haven't been able to figure out why some SUs have trouble using ATF.

To anyone. Is it the internal clearances, tuning or something else that's making the difference?

Mark

Ztherapy sells SU oil. Why not use what they recommend? I've got a couple bottles of their oil and it seems a heck of a lot thinner than 30wt. oil.........but about the same consistency of 3 in One machine oil ( in the little squeeze cans ).

Edited March 30, 20159 yr by Diseazd

If the piston rises too fast (thin oil), the fuel droplets fall out of suspension and the constant velocity drops. This makes a lean bog. Bumps in the road can also cause fuel changes.

The opposite happens if the oil is too thick: the piston rises slower, the air rushes through faster through a smaller area (not CV) and it pulls more fuel. This makes a rich bog.

Well i managed to fix the problem by pulling each of the NGK BP6ES spark plugs, cleaning them with a wire brush and electronic contact cleaner, spraying contact cleaner to each of the terminals of the distributor cap and pertronix ignitor. I also filled up a Little bit more of Castrol 10w 30 engine oil in each of the carbs. Retuned each carb and balance them raising the fast idle screw to 1,500 RPM.

 

I set the idle mixture knobs in each carb to 3.5 turns and the idle RPM to 1,000 RPM.

 

At the moment no backfire or engine shut down. I will keep testing tomorrow and keep you posted! I need to sort this idle issue first before i install the AC system.

 

Question: Are these NGK BP6ES spark plugs pregapped from Factory? or will i need to get a feeler gauge? If so what is the gap?

Edited March 30, 20159 yr by jalexquijano

Plug all of the vacuum ports you can. Any place on the manifold that uses vacuum. Distributor, emissions and the brake booster. Plug them all. See if the idle is more stable. You could have a bad booster, leaking dash pot on the distributor or some other concealed vacuum leak. Use rubber caps with clamps or put a bolt in the hose with a hose clamp. Dying when coming to a stop made me think of the brake booster...

Charles

I will test again today! 2 days ago it was keeping the idle up! I thought the carb cleaner spray test was enough! It the car idle changed, then there could be a leak!