New Zealand Datsun Club

cartbed a12, just rekitted carb over the weekend (in retro spec I shouldnt have, its caused more problems that it was worth, should have just replaced the seal/gasket that was buggered.....but anyway)

now it will surge/stumble at idle (its fine when dirving, smooth as kks mum nether reigons). not all the time, but probably over 50% of the time. It is alot rougher then beofre I pulled the carb apart so short of pulling it apart again is there anythign else it might be? I have the mixture screw set at two turns out (as per manual) so should I have a little play with this to see if it tightens up the idle?

Would a vacum leak cause it? and is it worth looking at the ignitions side of things as well?

Cheers

vacum leak will cause it to do this, as you suggested.
I wouldnt get to involved with the ignition side of things unless you are 100% sure that its not carb, you could end up chasing 2 seperate issues if things go awry.
generally anything electrical will get worse when driving under load not better.
How much fuel in the side glass of the carb, if its to full it could choke things up and cause poor idling as well, be worth checking.
apart from these things, you may need to strip down again and check that some crap hasnt made its way into the system.
make sure to that the gaskets are sealing properly, some times the top plate of the carb can be warped,and when pulled apart and put back together the top doesnt always seal together with the bottom, if this is the case you may have to strip the top of the carb, and sand the bottom of the plate on a very flat surface, ie a piece of 10mm steel plate, and some 400grit wet and dry sandpaper.
i hope that makes sense to you, if it looks like the top is warped a little, DONT overtighten the screws to try and pull it down, as you will strip the threads.
hope this helps, let us know how things go.

Sweet thanks.

I checked the fuel level in the glass when I put it backtogether yesterday and it was way to high so I adjusted it and now it sits perfectly in the middle.

I actaully reused the old top gasket as the new one wouldnt seal and was pissing fuel out the side.

the hose that attaches the to manifold below the carb (I think its for the PCV valve or whatever its called) is pretty shoddy so will check/replace that.

Beaver I'd have a fiddle with the mixture screw before tearing everything apart, 2 turns is a guide, Mr Nissan put it there because he knew that as the engine aged it would need adjusting Screw it in till it stumbles then out till it settles down. These things are pretty simple, not too many vacuum hoses to check Spraying carb-clean around suspected leak areas can show up faults as Carb-clean won't burn and takes the place of the oxygen.

Oh yeh for sure, will have a fiddle with it. So screwing in makes it richer or leaner?

beaver wrote:Sweet thanks.

I checked the fuel level in the glass when I put it backtogether yesterday and it was way to high so I adjusted it and now it sits perfectly in the middle.

I actaully reused the old top gasket as the new one wouldnt seal and was pissing fuel out the side.

the hose that attaches the to manifold below the carb (I think its for the PCV valve or whatever its called) is pretty shoddy so will check/replace that.

did you adjust the fuel level before or after the top gasket was leaking ? the gaskets can get very brittle, although if there are no leaks then I guess things must be ok, however the fuel may shut off when level is reached, and therefore not leak, but a split gasket would have a tedancy to let air in affecting the fuel mix.

beaver wrote:Oh yeh for sure, will have a fiddle with it. So screwing in makes it richer or leaner?

Been a while Beaver, but pretty sure in is leaner.
All the best

classicdat wrote:

beaver wrote:Oh yeh for sure, will have a fiddle with it. So screwing in makes it richer or leaner?

Been a while Beaver, but pretty sure in is leaner.
All the best

pretty sure as well that in is leaner, are you doing this with the airfilter off? as when its put back on it could effect air/fuel ratio a bit.
as it tends to allow less air through, may be a good idea to adjust it with filter on.

2 doors wrote: did you adjust the fuel level before or after the top gasket was leaking ? the gaskets can get very brittle, although if there are no leaks then I guess things must be ok, however the fuel may shut off when level is reached, and therefore not leak, but a split gasket would have a tedancy to let air in affecting the fuel mix.

I was thinking that myself just this morning, and Im 99% sure it was leaking before and after adjusting the float level, and not until I put the old (cork) gasket back on that it stopped.

Thanks for all the tips, ill have a play with the mixture tonight (with the filter on) and see if it helps, as well as check the pcv hose.

had a quick play, wound it in slowly until it started running worse then wound it out until the idle smoothed off. sound about right? idles much nicer but it still seems real 'boggy' until about 2000rpm