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MG Midget and Sprite Technical - Weber DGV set Up?

Hi All,

I haven't had a need to post a question in a while, but I have started messing with things again and have hit a problem. I bought a used Weber DGV and pierce intake as a unit. I was told it came off a 1275 midget. I cleaned it up and rebuilt it and for the most part it runs fine utill it is in forth gear and i give it some gas. It stumbles all over its self then if I back off it recovers and I can slowly give it more gas. What can cause this? I have adjusted the timing and the mixture and it helped, but still the same problem. I think the jets may be to small and I have searched the web trying to find a reference for the right jets for a 1275 with no luck. Even on this site I have found several threads asking about this, but the thread always goes in a different direction and the question never gets answered. Does any body have an idea as what might be happing? Just a little information it is a 1275 borred 40 over.

Thanks in advance for any help.
james caddell

I have the same problem but with a 1098 and not necessarily in 4th, it stumbles on immediate acceleration then recovers and off you go. Accelerator pump inducing too much richness, maybe? I don't know. I too need to settle this or put the SUs on, which I plan on doing anyway. Sorry, no help but I hope to learn something.
J Van Dyke

The very first thing you must do is check if the throttle pump is working, look into the throats of the carb and twist the throttle does it spray fuel into the engine?

Next the weber DGV is a progressive choke carburettor that means that it uses the small side for light running, say upto 60/70 miles per hour and then for more speed and power uses the big choke sounds like the large choke is poorly jetted. Check the throttle pump first then remove the jets and state their sizes?
Robert (Bob) Midget Turbo

James, I'm not sure this will help as your symptom seems to be at higher speeds/fuel requirements, but as per J Van Dykes post:

<< it stumbles on immediate acceleration then recovers and off you go >>

If you lean out the idle mix screw the stumble will lessen. I happily discovered this while hooked up to the GasTester. the factory setting was WAY too rich, 8 or 9 ppm IIRC, after adjusting it down to ~ 0.5 ppm I got the pleasant touch of backfire/rumble on overrun I was looking for, with the unexpected added benefit of (almost) losing the stumble at acceleration.

R
Richard 1979 1500

Interesting. I adjusted mine with the this process:
http://redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm
but while I can get it run bad when leaning out the mixture screw, it never seems to get too rich, at least I don't notice it running different as I back out the screw. Just tonight I went for a run and I could barely detect the hesitation at all anymore. Not to say the g force flattens you against the seat but overall it's running pretty well, not sure what's different. I really should put the SUs on for fun though. I went through them this winter, not rebuilt, just cleaned and ensured the jets were centered and the pistons matched and moving freely. I'm dying to see what they do, shouldn't much of an issue to pull the carb/intake as a unit and swap in the other, I'd like to think a 15 minute job.
J Van Dyke

FWIW, while fussing with the Weber DGV, I placed a vacuum gauge on the ported vacuum (distributor vacuum) connection then gave the engine WOT from idle. the vacuum went from ~4 to ZERO, very briefly, before running up to ~11 at ~4000 rpm. Don't ask me what this means, but I find it interesting that the vacuum blip seems to mimic the engine stumble at acceleration.

R
Richard 1979 1500

I think you make the most vacuum at idle and very little at WOT. As you accelerate it should go from 6 to 0 then recover a bit at speed I believe but 11 at 4000? That's not right. Should be making a lot less vacuum at 4000 rpm then at idle...as I thought I understood it?
I did confirm my accelerator pump is squirting gas.
J Van Dyke

Wouldn't claim to know what's "right", just passing on observed data. It was what it was.

R
Richard 1979 1500

I don't claim to know what's right either, not by a long shot! But 11 at 4000, yikes, your vac advance would be kicking in right when you don't want it, wouldn't it?
J Van Dyke

I was under the impression more advance at higher rpm was proper. FWIW I am running the "Flame Thrower" distributor (Moss part #143-116) with it's "improved advance curve" with static timing set at 16BTDC. At 4k rpm, total advance with distributor vacuum connected is 32BTDC. Overall performance is pretty good for an engine approaching 80k miles.
Richard 1979 1500

This thread was discussed between 20/05/2009 and 23/05/2009

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