needle depth

glennhuff · Post by **glennhuff** » Fri May 12, 2006 11:22 pm

Trying to get my carburetors adjusted. When I replace the needles, how far do they go into the pistons? Do they bottom out, or do I line up the bottom of the shank with the bottom of the piston? Anyone know for sure? The carburetors are the only thing keeping the roadster off the road now.

Glenn

Post by **spl310** » Sat May 13, 2006 7:31 am

The information that I have is that the shank should line up with the bottom of the piston.

Conner · Post by **Conner** » Sat May 13, 2006 8:16 am

Because needles, nozzles, carb bodies, and pistons may vary and you want the needles have the same exposure into the nozzles (bottom/point of needle) rather than in the pistons (top/shaft of needle), I used the following procedure to set my needles:

1. Loosen the set-screw on the piston.
2. Loosely install the needle into the piston.
3. Drop the piston into the body and push it all the way down until the needle bottoms out in the nozzle (holding the nozzle up tight against the body), forcing the needle upwards into the piston.
4. Remove the piston and tighten down the set-screw to secure the needle in place.

Pictures and the full write-up are here: http://www.mydatsunroadster.com/2005/08 ... embly.html.

Post by **Linda** » Sat May 13, 2006 10:51 am

It also depends on the kind of needles you are using. The ADQ needles which I have,are set differently. Even when I had stock needles though it was suggested that it is possible to slightly extend the needle from the standard "flush" position to change the carb running, but I can't remember exactly what that does...maybe richer/leaner? Anyway you might want to try.

Linda
68 1600

glennhuff · Post by **glennhuff** » Sat May 13, 2006 1:04 pm

Thanks guys. I'm going out to the shop right now to finish the carb assembly. I'll let everyone know when I drive it.

glenn

Russell Roach · Post by **Russell Roach** » Sun May 14, 2006 5:49 am

Glenn,

Running a racer I have my carbs apart on a regular basis, I have found the easiest way to set needle height. Take a feeler guage the type you would use for valve adjustment.

Use one of the thicker blades and turn the blade on end instead of flat like you would to adjust the valves use that as a straight edge and put it across the the neck or where the needle widens so the screw can hold it in the piston.

When the widened part and feeler guage are flush with the bottom of the piston, tighten the screw and you are set That needle will be exactly in the position you need it.

Linda to answer your question the more you extend the needle out the leaner it will run.

Russell

keith0alan · Post by **keith0alan** » Sun May 14, 2006 8:08 am

Hello all,

The normal needle setting is shoulder flush with the face. Setting it out primarily leans the idle mixture. On the ADQ I found that setting it flush left the idle a little richer than I wanted but there was no other needle that was better. By setting it out .012" the idle leaned out without a noticable effect on the high end. Going out about .020" made it lean enough to pass the smog test.

keith

glennhuff · Post by **glennhuff** » Sun May 14, 2006 10:51 am

So what's the difference between putting the needle down (extended), and moving the nozzles up? I set my needles flush, and it seems to run a bit rich, and idles fast. Can I fix this by adjusting the nozzles, or do I need to move the needles?

glenn

keith0alan · Post by **keith0alan** » Sun May 14, 2006 10:30 pm

Idling fast and running rich are seperate issues.

For the idle make sure the linkages are free and back off the idle speed screws.

On the 1600 all the Nissan needles tend to run rich at idle and lean through the middle and on top end. If you adjust them so they run right at speed the idle is way rich. As the needles and nozzles wear it only gets worse.

With the needles flush and the mixture knobs all the way lean, if you are still running rich at idle the needles and nozzles are most likely worn out. Dropping the needles might make it better depending on how bad they are. Sometimes either the needle will get bent or the nozzle will be out of center and the nozzle will wear oval. The only fix for that is a new needle and nozzle.

glennhuff · Post by **glennhuff** » Tue May 16, 2006 8:32 pm

Thanks for the expert advice Keith. With new nozzles and M39 needles, it still runs rich at an idle just like you said. I can live with that, but this whole fast idle thing has got me puzzled. With all of the linkage unhooked, and both throttle stop screws backed clear off, it idles at about 1100 rpm. Maybe I should check my tach.

glenn

keith0alan · Post by **keith0alan** » Wed May 17, 2006 8:11 am

Pull the carbs off and make sure the throttle plates are really closing. Also chek your timing. If it is way advanced it's hard to get the idle down.

Post by **itsa68** » Wed May 17, 2006 5:40 pm

Also check those choke cables for slack to make sure they are not accidentally withdrawing the fuel nozzles.

I dont know if the float valves would raise the idle if they are leaking slightly.

Anyone?

Ray B.