Hi,
My Datsun is running again for the first time in a while, but there are some problems... It starts quickly and idles at a rather low speed, with the idle and choke adjustments set where I believe they should be, but after a few minutes of running the car starts coughing gas back through the carb throats and smoke starts coming out of the crankcase breather filter. If I try stepping on the gas or getting the car to move, the coughing problem gets worse and the engine loses power and stalls. The exhaust looks okay (not white or black... pretty much invisible.)
Does anyone have any ideas what the problem could be? It's an A14 with an A15 swirl-port head and 2 Hitachi SU's.

Thanks for your time!
Will

Try doing a compression test.
If the comp is down. Put some a little bit of oil in the cylinder & comp test it again.
I the comp come up it is a piston ring problem. If the comp stays the same it will be a valve problem. If your still not sure put compressed air in the sus cylinder. If you hear air leaking through the carbys you have a leaking inlet valve. If there is air coming through the exhaust you have a leaking exhaust valve. If you have air coming out through the radiator you have a blown head gasket. But in your case that sounds unlikley
Hope this info helps you. Good Luck.

maybe you are just running the carb lean?
try adjusting/tuning your carb

good luck

sounds exactly like the problem i had a couple days ago...

check the points gap is opening enough. Really simple to check... might save you a lot of time.

It worked for me!

Thanks for the reply!
When I put the engine in my car I used the electronic ignition from a '78 F10 and a MSD 6AL ignition box. Maybe I should check the air gap?

-Will

Thanks for the reply!
I'm new to SU carbs- is there a way to make the carbs run more rich other than by turning out the choke adjusters on the bottoms of the carbs?

-Will

Next time you start it and it's idling, push up on the pistons. There should be a little pin with a spring under each carb. If the engine speeds up it's rich if it slows down it's lean.
Also those pistons in the carb should move freely from top to bottom. You should be able to reach into the carb (engine off!) and push the piston up then let go and watch it drop with a "thunk". Both carbs should move the same.
The screw thing on the botton adjusts the overall mixture of the carb. It moves the nozzle (hole that the needle is in) in relation to the needle. You should be able to adjust the idle mixture with this adjustment.
Off idle, when the pistons/needles move up, it's the profile of the needle that changes the mixture.
SU tech pages
Try this link. I've had to read and reread it several times as well as other pages i googled.
edit: I turned the screws/knobs on the bottom all the way in, marked them, then turned them back out. I counted how many turns so that both carbs were the same. Mark the knobs so you can see the marks when you lean in to adjust them. Drive around... half turn in... drive some more ... full turn out... etc

Hi,
I tried to lift the pistons and drop them, and they did go down with a "thunk" before I added the oil. Now that I added the oil there is resistance when I press up on the piston (It still goes up though) and when I release it it drops slowly to its regular position... too slowly to make the "thunk" noise. Is that normal?

Thanks,
Will

I don't know what's right. Mine are hard to push up with oil also, but I think they drop faster than they go up.

We found that when tuning su's, the best way to get them to run sweetly was to pull the piston out and give it a quick going over with some 1200 wet and dry sandpaper(wet with ditergen). Do the same with the bore, only lightly on both then reasemble.

For quicker throttle responce, we used sewing machine oil. Worked like a dream