Just as the title says, my mixture screw on my Nikki doesn't seem to do anything. The carb is stock. I rebuilt it a few months ago and turned the screw out three turns. It ran so I didn't mess with it. But now I've got the urge to get some more done to the car. Last night, I removed the rat's nest to fix a vacuum leak I couldn't find. Got that done and the idle was up to 1,500. I decided to finally afjust the mixture and idle but I turned the mixture screw in slowly waiting on the motor to "stumble". But I turned it quite a bit and finally ran out of "adjustment". I backed it back out about five turns or more and didn't notice any changes at all. I must have messed up something during the rebuild but it ran pretty good for the few months I drove it. What might my problem be?

Also, during my time of trying to adjust the carb, my buddy noticed that my cat was glowing pretty bright towards the back of it. That was after a spirited 5 minute drive and another couple minutes of idling after. I'm not overly concerned with this as I need to check timing and mixture anyway. But if it's still does it after it's getting a testpipe.

The car is a mostly stock '83 GSL with Carter fuel pump and pressure set to 3.5-4psi and removed rat's nest.

 

Adjust the idle to 750 rpm. Then you'll see the mix screw making a difference.

 

cdrad is right (I've never said that before! -laughs-)

The idle mixture screw only affects the idle circuit in the carb. You're not in the idle circuit until you're below 900rpm or so. So use the idle speed screw to get yourself down under 900 and you'll be able to adjust with the idle mixture screw.

Now if you can't get under 900rpm, you most likely have a vacuum leak. Cat glowing is also a sign of a big vac leak. Find that leak and you'll have much more success.

Jon

 

Ok, I was thinking that mixture would help bring the idle down to where it belongs. It seems I need to adjust the throttle cable a bit as the idle screw isn't lowering the idle. When it had a vacuum leak, the idle was about 900 but rough. Now that the leaks are fixed, I stay at 1500.

Also, the cat must have been clogged, I drove it in to work today (about 10 minutes, mostly coasting), but it wouldn't rev above 4k. I hollowed the cat, which is a bitch to do, and it revs fine and feels so much better throughout the revs.

But I'll mess with the idle first and report back

 

My mixture screw doesn't work either (at my 700 rpm idle), but I think it may have something to do with the fact that the threaded section on the needle valve is bent.

 

There is also a thread, I believe in the FAQ section, where that knucklehead Sterling explains blow by blow how to tune the 7 in terms of playing with the mix and idle screws, the sequence, and all that. Then there's of course the manuals.

@ Box Man: yes, that would do it too.

 

I was thinking about building my own sterling-clone (send off some parts to the man so he can work his magic, and I assemble the rest) but since I got shafted trying to buy a replacement carb, I might just go with a RB manifold, and an Edelbrock 500 carb instead. Hooray discouragement.

 

That's probably the same explaination I was going by for the tuning. Carbs used to confuse me but thanks to you guys, I prefer them.

The cats must be restrictive as hell on these cars. After I gutted the cat, I went for a drive to warm it up to mess with the carb and this little 1.1L hauls ***. I even thought it felt pretty strong before. I love the rotary more and more each day.