Warning....Newb Carb Question

[mally002]

Ok, after you quit laughing help a non-mechanic out with hopefully a simple question......

I just (finally) got the roundtops on the 73, After getting everything hooked back up I went for the first start, wouldn't start so I pulled off the air cleaner to shoot a little starter fluid.

After pulling off the air cleaner I noticed that when looking into the carb you see a metal cylinder on one that you can move up and down with your fingers and the other one is open, the cylinder is up and you can't move it.

I admit I know nothing about these carbs, I was in hopes of just bolting on and starting...sort of a plug and play if you will. I know that one of these is wrong.....but which one....help please.

If this makes no sense I'll try and get a picture.

[gogriz91]

Take the screws off of the bowls and lift the bowl off. You should then be able to gently take the cylinder off too. Take some carb cleaner and clean off the cylinder and the interior of the bowl. The needle attached to the bottom of the cylinder should be reasonably straight too. Hope this helps, I'm no SU rocket scientist but this is the gist of what I do twice a year as a form of lazy SU tuneup.

[Bruce Palmer]

Correction: The needle should be very straight.

The rest of the thought is good. Douche out the dome and clean the outside of the piston so it slides freely. Take out the plunger and clean out any oil that is in the tube and replace to the fill line in the tube with fresh ATF, then go do the other carb. It is fairly important that both piston rise and fall at the same rate. After re-installing the piston raise and drop the piston to insure nothing is in a bind (needle to nozzle)..... If there is some binding move the dome slightly and re-tighten....

Are these carbs unknown to you?? If so, a lot of gains can be made just with a good cleaning.

There are very few sources of 30 something year old Hitachis that wear the mantle of "plug and play" and there are variations even among those.

[FHPTOM]

Randy, again I forgot to advise you of another thing to do. I drained the oil out of the carbs when I cleaned them and did not want to ship them with oil in them. Or like Bruce said, just use ATF.

Sorry, they really should have been just hook up and turn on. I ran my car right before I took them off so that I knew my car was set before I put my new triples on.

Tom

If you need anything else for your car and I have it,I will send it to you free for all the hassle you are having with the carbs.

[mally002]

Thanks Guys,

Tom, I think it's more my entry level skills that are the problem....:stupid: Thinking back you did tell me about the oil, I'm just so new at carbs I wasn't sure exactly how these worked. I really do appreaciate the SU's, but if you have a spare engine in perfect condition feel free to ship it to me....

It's all becoming a great learning experience, I just wish my Haynes manual or the restoration book had more details on doing engine work...any recommendations on another book?

Again thanks for all the advice....and the carbs Tom.

Randy

PS....ATF?

Edited October 2, 2008 by mally002

[blue 72]

If you are interested in learning about how the SU carbs work then there are plenty of resources.

Try this one for instance:

http://www.jetlink.net/~okayfine/sutech.html

[xray]

Des Hammill's "How to Build and Powertune SU carbs" is indispensable.

http://www.amazon.com/Build-Power-Tune-Carburetors-Speedpro/dp/190370698X/ref=sr_1_1?ie=UTF8&s=books&qid=1222911299&sr=8-1

amazon says it's out of print, but check MSA and Ebay

Monroe's "How to Rebuild..." book:

http://www.amazon.com/Rebuilt-Your-Nissan-Datsun-Engine/dp/1931128030/ref=pd_sim_b_3

Honsowetz's "How to Modify..." book:

http://www.amazon.com/Modify-Your-Nissan-Datsun-Engine/dp/1931128049/ref=pd_sim_b_4

All excellent reading. Buy them from Black Dragon, MSA, amazon etc.

Edited October 2, 2008 by xray

[Sailor Bob]

Automatic transmission fluid

[JonnyRock]

ATF is short for Automatic Transmission Fluid. It's similar to motor oil, but lighter weight. It's typically red in color, but I think I've seen green. The ATF level in the carbs should be checked fairly regularly as well, since it's essential to proper carb function.

[mally002]

Mine has 10w 30......should I drain and refill with ATF or is the 10/30 ok?

I did remove each dome and clean, and then filled with oil. Both cylinders move up and down with ease, but after the oil was added it has resistance which I assume is normal.

What will happen if I over filled the dome's? To me it's hard to get each carb dome with the exact same amount of oil. Do you guys use the lower mark on the thumb screw or add so many cc's. If a set amount when empty what is it.

Thanks,

[MikeW]

The resistance is not only normal but it's the desired effect. The purpose of the oil is to keep the piston from moving too fast. The weight of the oil obviously matters here. The factory recommends 20W but people have claimed success with other weights.

This is what I've used:

http://www.3inone.com/products/motor-oil/

Not only is it 20W but it comes in a very convenient bottle that makes it easy to add just the right amount to the carbs as it doesn't take much. It's also readily available in stores whereas if you go to an auto parts place looking for a quart of 20W you'll have trouble finding it.

[blue 72]

There has been some discussion on which weight is best for which driving and in such and such environment. I'm sure you could search and find some of these threads.

As for filling, you don't want to overfill the pistons because it will overflow and leak down into the carb bodies. My general rule of thumb has been one capful of ATF (cap from a standard 1 quart oil bottle). Just make sure the levels are close on each one. It isn't an exact science, just as long as they rise and fall at the same rate.