Midget that runs too rich

[BKRTEE]

I rebuiltthe engine & carb on my 76 Midget a couple of years ago and can't get the barb to run any leaner by adjusting the allen screw inside the carb. As I recall, I think the original needle was a bit longer than the new one that replaced it; but at the time being new to all this, I just tossed it in favor of the replacement. The former electronic ignition was replaced by points before I bought the car. Could I have the wrong needle even though the catalog specified the current one? How can I get the correct needle if that's the case? There is no specific tag on the Stronberg carb (150), so I'm not even sure if it was the original one meant for the 76. Any thoughts?

 

[jcatnite]

You might be in a bind on the carb deal. If it is the original carb, then you need a 44A. What type of choke is on the car? If the choke circuit is leaking by then there is nothing you will be able to do with the needle to keep it from running rich until you fix that. Other then the carb, the engine will run extremely rich if your spark is weak to the cylinders. It could be time to check the plugs, points, cap, and condensor to make sure that they are all performing up to par. I have never been able to totally tune the richness out of my 76 but I have been able to get it to where the plugs are nice and tan unless I let it idle extensively then it starts to richen up. I would take it a step at a time and rule out the ignition first.
JC

 

[BKRTEE]

Thanks for the observations. I've pretty much exhausted all those options except trying another needle. I decided earlier today to go ahead and order a 45Q that's supposed to go on the 78-79 models. It seems the only other logical option since the other two needles are for California cars. I did notice this evening when I pushed the choke all the way in, it was not quite driving the carb armature completely home (off about 1/8"). I readjusted the cable at the locknut to correct. It's raining this evening in the wonderful Northern Ohio area, so no way I was going out. We'll see if there's any improvement manana.

The car has and still is running pretty well. If I can lick this, that's the last problem...until the next one!
But that's the charm of an MG!

 

[jcatnite]

Oh my mistake. I thought that all the ZS150's after 76 used the 44A. Let us know how the new needle treats you!
JC

 

[BKRTEE]

Installed the new 45Q needle in place of the 44A this evening. I leaned it out about one turn. With no exhaust analyzer, I'm at a bit of a disadvantage to tell the difference in mixture. The car seemed peppier as I took it out. One good sign: the idle came down to where I can adjust it. I was unable to get it under 1200 rpm before with the screw all the way up. Now it's in the range of 750-900 where it should be. Guess I'll run it for awhile on the highway then take a look at the plugs.

 

[jcatnite]

That is the best way that I've discovered to check the mixture ratio. The only thing is, it doesn't tell you that much about how it is idling. I have a colortune 500 that I have tried with varied success. Theoretically, if the ratio is proper at highway speed, it should be close when idling but I think any mismatch is magnified down at idle.
JC

 

[Simon TR4a]

I think you will need new plugs to get any meaningful information, you can't read plugs that have been in use.
So get a set of 4, change one at a time, after each change you can compare.
Since you changed other settings (choke) you might want to go back to the original needle at the end for a cross check.
Also, an old, dirty air filter could contribute to the problem, though I guess you thought of that.
Simon.