1969 MG Midget car idles only when manual choke engaged

  • 1969 MG MIDGET
  • 4 CYL
  • 2WD
  • 22,996 MILES
I just bought a ’69 Austin Healey Sprite MK IV, 1275 engine. It's the sister car to the Midget but your website didn't list Austin Healey as an option.
A previous owner(s) replaced the original SU carbs with a Weber DGV 32/36 two barrel. The problem is I cannot get this car to idle without the manual choke almost fully engaged. As soon as I back off on the choke and try to disengage it the engine sputters and simply stalls out. Of course, while the choke is engaged it’s racing like crazy (over 2000 RPM). The car may have been sitting in storage for a while so I tore the carb apart, purchased a basic weber rebuild kit, cleaned it good and reassembled. In the process I changed the needle valve assembly that controls the float and accelerator pump diaphragm (because those parts of what came with the kit so I assume they tend to wear out quicker). I changed the fuel filter and added a fuel stabilizer to a fresh fill-up of gas. But it didn’t do any good. The car is behaving exactly the same way as before the rebuild. Since it’s behaving the same way now as before I rebuilt it then I assume that I didn’t make any screw-ups when I rebuilt it and put it back together.
I adjusted the idle mixture screw and the throttle idle adjustment screw every which way and followed the instructions as best I could to set idle but the result is the same. The carburetor seems to be locked in this “choke cycle", for lack of a better way of putting it.
I also changed the plugs just to cover myself and to be sure that there's a good healthy spark, although it acts like it's really a carburation issue.
Is it possible that there are problems associated with installing aftermarket non-SU carbs (especially weber) on the 1275 engines of this particular year?
I've also read from some blogs that webers are best tuned by a pro or very experienced amateur but I assumed that was meant for the more complex multi-barrel carbs. This is just a simple 2 barrel that sits atop of 1275 four banger! Maybe I made the wrong assumption and it's more complicated than I thought!
I’m stumped! Any ideas what this could be? I admit that I’m a novice and I apologize if I didn’t use quite the correct jargon in explaining my problem but as an owner of two Miatas (that I love also), carburetors are a whole new world for me although I admit that I’m really enjoying it! I loved tearing apart that carburetor. It was fascinating! Now if the car would only idle properly!
Do you
have the same problem?
Thursday, November 4th, 2010 AT 3:57 PM

1 Reply

First thing to do is take some chokecleaner anspray around the baseof the carb and inlet ports for a vacuum leak. Tyr to get eh engine to run ata loweri idle though. You really shouldn't need apro for tuning this carb. The webers they are talking about are the side draft and the dual down drafts not yours. Your sis a simple crarb that is very similar to waht was used on a pinto many years ago. A couple of things you have to check first is check your dwell or points. You can do that with a feeler gauge, but if they are burnt replace those as well as the condensor. If you can check for a loose distributor shaft. Make sure when you change the points to put some lube on the dist cam so the points don't wear out. Then go to the carb, recheck your float adjustment so it's not to low and the float issn't sinking in the fuel. You can throw the float in some gas and see if stays on top if it sinks you need a new one. Then when it's together yo go for the adjustments. Make sure that the idle screw isn't set to low for onething. Then lightly seat the mixture screw, not tighten it down like a regular screw. Then back it out 1 & 1/2 turns. Use either a tach or vacuum guage and go for the highest vacuum or highest idle speed, then turn down your idle screw. One thing though, check the screw where the needle and seat rides asi've had one loosen up onmebut they are fairly reliablae carb. I've had one for the past 7 years with no problems at all. Of course this enginemay have a large or high lift, long duration cam that is causing this as well. And have fun with that SPRIDGET
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Sunday, November 7th, 2010 AT 8:58 PM

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