New Zealand Datsun Club

Been a while since ive updated, as of late i have bought a recond U67 head for my l20b as well as a set of SU carbs with manifold

I pulled the motor out and ripped her all apart and replaced main bearings, piston rings and my water pump.
i have got the motor all back together but am not really sure if my SU carbs are in proper operating condition.

They didnt look too bad internally but after alot of cranking it fails to even fire once. is there an easy way to loosen the timing chain again without having to take off the crank pulley and front cover? i think my head is 180 degrees out from my bottom end atm

any feedback would be greatly appreciated

The cam turns at 1/2 crank speed, so is 180 degrees out as well as 360 out or 0 if you like. With a chain you can be any number of degrees out, but if you are sure you are timed to 180 or 0 degrees, the only thing that it can be 180 out from is the distributor, check which plug the rotor is pointing at when the cam lobes are down rocking on # one cylinder valves. If you are 180 out you can do several things to remedy it, one remove the leads from the cap and refit as required, or remove the oil pump and dizzy drive and refit drive 180 degrees around, this can be tricky to get right but just takes trial and error. (you will need to remove the dizzy to do this, just check the angle of the drive and judge the off set to be 180 degrees out when you have refitted it (looking from above)).
Sorry a bit wordy, hope you get the idea.
You can remove the cam sprocket by wedging the cam chain tensioner with a spacer, (eg piece of wood the right size to jam the chain against the guides and fit all the way to the bottom sprocket) this can go all wrong if you don't get it right causing the removal of the front cover etc. but can facilitate adjusting cam timing if needed.
Hope this helps, all the best.

classicdat wrote:The cam turns at 1/2 crank speed, so is 180 degrees out as well as 360 out or 0 if you like. With a chain you can be any number of degrees out, but if you are sure you are timed to 180 or 0 degrees, the only thing that it can be 180 out from is the distributor, check which plug the rotor is pointing at when the cam lobes are down rocking on # one cylinder valves. If you are 180 out you can do several things to remedy it, one remove the leads from the cap and refit as required, or remove the oil pump and dizzy drive and refit drive 180 degrees around, this can be tricky to get right but just takes trial and error. (you will need to remove the dizzy to do this, just check the angle of the drive and judge the off set to be 180 degrees out when you have refitted it (looking from above)).
Sorry a bit wordy, hope you get the idea.
You can remove the cam sprocket by wedging the cam chain tensioner with a spacer, (eg piece of wood the right size to jam the chain against the guides and fit all the way to the bottom sprocket) this can go all wrong if you don't get it right causing the removal of the front cover etc. but can facilitate adjusting cam timing if needed.
Hope this helps, all the best.

Cheers mate, i got it sorted. had to stuff around with the oil pump thing to get the dizzy pointing to the right place and now my engine starts! and it also runs!!
but now ive run into another problem.

the twin su carbs i put on just keep revving without me giving the car any gas whatsoever, it just revs straight up and i need to kill the engine before i do damage to anything. anyone had a similar problem? or someone who knows alot about su carbs?

Is there oil in the dash pots?
where are the throttle stops on each carb set to?
How is the cable connected? Does it have tension on it?

Yeah i made sure to put oil in, ill take a photo tomorrow morning so you can see anything obviously wrong. there is no tension on the throttle cable and the stops dont look high enough to rev it that high
i think the throttle stops are still set to stock

could be the needles are sticking in the dash pots.

Wind the throttle stops out till they don't touch, counting the turns, if that solves the problem just adjust them back up when you balance the carbs, if not readjust them back down and keep looking.

i do know that the lil pistons in the carbs are opening fully as soon as the car starts which i dont think is ment to be happening

They shouldn't be doing that.
I used to have a pair of SU's on an L20B in my old sunny coupe. It used to stick with fast idle, and run lke crap often. I took it to see a mate of mines dad who is well versed in Pommy SU's. He gave them a quck tickle up for me, (Cleaned the inside of the dash pots, equalised the spring lengths, changed the oil, and synchronised the butterflies) and it ran so very very sweetly after that. Never ever needed the choke, and if driven gently it was soooo economical. I dunno what he'd charge someone off the street to do that, but If you get stuck I can give you his work number.

Id say that would probably be the best thing to do, is he in chch?