MG Midget Forum

My car has 25D4 distributer and based on data sheet the timing should be 13deg B.T.D.C at 1000 r.p.m.

But if I adjust it to 13deg D.B.T.D.C the car sounds running low and shaky I can tell the r.p.m also drops to 850. But if I adjust it to 22deg B.T.D.C looks like car is running better with a 1000 r.p.m. Any idea?

did you disconnect vacuum to adjust? You should. I get mine close then play it by ear from there. Adjust to where it runs best.

Yes, it was disconnected.

What I do is set the timing and the rpm to spec, so if your rpm drops at 13 degrees BTDC increase the idle and back off the timing until you have both set correctly together. Don't forget that when you set the mechanical advance at idle with the vacuum disconnected the advance will change when you connect the vacuum up again. After you reconnect the vacuum you can always reset the idle to where you want it. After I set the idle advance I always check the maximum total mechanical advance, I look for around 32 - 34 degrees BTDC total mechanical advance for a stockish 1275. Then I see if it runs right. To me, it's the total maximum advance that matters the most, that is what can cause detonation and hurt things at full throttle and higher rpms going up on-ramps and such. Advance at idle pretty much is all about idling smoothly, advance at low throttle and rpms is all about smooth acceleration and running around town.

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Brian Evans, Tatamagouche, Nova Scotia
1961 MG Midget G-AN1-L218, 1964 Mini Traveller, 1979 MGB LE Canadian edition.

I'm getting better rpm at 22deg vs 13deg that is what I mean. Let's say the rpm is 1000 at 22deg but when I go to 13 deg (spec) rpm drops to 850.

That's likely because your carb idle screws are not set correctly. First I'd set the timing to spec and then raise the idle by adjusting the carb idle screws. Then repeat until you find the sweat spot, where you get 1000 rpm at 13 btdc. Timing adjust followed by carb adjust is the proper order of operation.

It sounds like your aftermarket cam is also advanced. Go with it. Some 1275 cams require the timing be set as high as 28 degrees at idle to compensate. Put it wherever the engine is happy!

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jeff@advanceddistributors.com

I'm not sure about my cam but my ignition is electronics.