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MGB Weber DGV setup on 74 MGB

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crazymagman

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I've got a 74 MGB and I just put a Weber DGV manual choke carb on. With the idle screw backed all the way out, it still idle's around 1000rpm, and I'm fouling out the plugs while idling. I've adjusted in the mixture screw and I think I only have it a half turn out right now if I recall.

Do I need to pull it off and adjust the floats, or what should I do next?

HELP!!!!
Mike
 
AIR LEAK.
 
Is it a new or old carb?
 
First: I'd suggest dosconnecting the choke actuating cable and making certain the linkage is "home". Fouling plugs at idle indicates a LOT of fuel is getting thru, in spite of the high RPM. Check for air getting thru the gasket at the base of the carb and manifold gasket by spraying with WD-40 or about anything you can aim. Water in a squirt gun will work. If there's a leak the idle will change.

Throttle link should have a stop with a screw adjustment, it should allow the blade to be completely closed when wound back. If that is done as the engine idles at 1000 RPM and it doesn't lower idle, the choke is suspect, as are vacuum leaks.
 
I agree with you 100% on all your possibilities Doc. But if it's a used carb, it's just possible it's set up for another application. My CJ-7 Jeep had a DG Weber on it but the bores were larger as were the jets. Setting it on the bench next to one I have for a "B", they look identical. Just another thought. Irregardless, I also think he has a vacuume leak.
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Right, Paul. But goin' for the "easy stuff" first, jets and internals if "gross" problems aren't found. Weber use idle jet(s) to meter fuel volume thru the mixture screw, it can be adjusted fairly close if all else is as it should be. Closing the throttle blade(s) & choke to the "off" position should slow it down to tick-over if there are no vacuum leaks, regardless of jetting size errors.
 
Thanks for all the replies. It is a new carb. I'm going to change out the exhuast manifold first as it is a 74.5 GT and the new intake does not mate up to the exhaust manifold very well as the intake is for pre 75 cars. I made some shims to mount it, but I may not be compressing the exhaust gasket enough to seal it. A guy from work gave me his '73 exhaust manifold, so I'll try to get that on this week and see if that helps, and if not, then I'll go after the items mentioned above.
 
I had the same problem with a Weber manifold set up. The manifold casting was thicker than the header flange. I believe the original cast iron exhaust manifold is thick enough to mate up with the Weber casting. I made step washers to overcome the miss match. After all that work, I scraped the Weber idea and went back to SUs. I don't like Weber down drafts on MG engines, as they have an inherent lag or pause when starting from a dead stop. JMHO.
 
The manifold would be the culprit. Where it ~doesn't~ smush the gasket. Weber uses an accelerator pump for the first throttle app. Should be an instantaneous rush to RPM. If the RPM at idle is as high as described, the manifold/gasket seal is the first of "The usual suspects".
 
I had a problem with my DVG at first. Finally figured out that you turn the mix OUT to lean, not IN. Could this be a part of the problem?

Guinn
 
Finally got it all mounted back up with the correct manifold, and also found my choke cable was hanging up on the linkage, so it would never fully open, thus holding the idle higher and continually dumping in a little more fuel.

Now I've come across a new problem....No spark......
How frustrating. Did the 74 1/2 GT's have a ballasted ignition system? Currently I have a Crane XR700 and a Lucas Sport Coil on it that were installed in 2001. I didn't have any problems with not having spark until two weeks ago when I finally set the car back on the ground to drive it for the first time in two years......
Any ideas?

Mike
 
Is the red LED flashing on the trigger box when you turn it over? If not make sure your Cable is firmly seated in to the optical pickup lead. I'm pretty sure you need a ballasted coil with the XR700.
 
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