Still stuttering

[gatsby989]

Greetings all,

Had an issue a few weeks ago where my moggy was "stuttering" or not quite firing right, causing loss of power and a jerky sort of motion. Then it just died and wouldn't restart. I replaced the condenser, points, and rotor arm, and it came right back to life. However, it still stutters. It only does it when accelerating, but doesn't seem to (or is not detectable) if accelerating hard. It doesn't seem to do it all the time. When it's warmed up, it does it less.

I've since replaced the distributor cap and spark plugs as well, but no change. I've also discovered that the vacuum advance does not seem to be working at all. I have a new unit on order, but I'm afraid it will take 2-3 weeks to get here. In the meantime, any ideas on what could be causing this? My (limited) understanding of vacuum advance is that it is most active when you are NOT accelerating, so the fact that it's broken shouldn't cause the stuttering. Is that correct? Is this perhaps a timing issue? If so, is it worth fiddling with before I get the new vac unit?

Any help would be appreciated. Thanks!

[bmcecosse]

It could be the timing - make sure it is not over advanced at the moment (as compensation for failed vac unit) since this could lead to pinking..... Could you not get vac unit locally?? Same dizzy in Spridgets and MGBs.... What colour are the spark plugs?? And what oil do you have in the carb damper? About the only thing you haven't changed in the dizzy is the 'low tension lead' - may be worthwhile getting a new one. And make sure the COIL connections are nice and firm/clean.
Edited to change crazy mention of 'dizzy' to 'carb'......

[gatsby989]

I will check the timing and the coil leads / connections. The spark plugs are sooty black around the edge, and mostly fawn on the nose and the lead, with some black there too. I know it is running a bit rich. Do you mean what oil in the carb damper? (I'm not aware of any damper on the dizzy). I have a weber carb, so there is no damper.

I should have mentioned that I actually replaced the whole breaker plate assembly, including the little leads. It is not exactly the same as the old one, but everything seems to fit as before. I could pull all the new components off and refit the old breaker plate assembly.

I could get a new vac unit sort of locally (california), but it would cost over $100 just for the vac. I needed to order some other things they don't have in stock, so I just ordered a bunch of stuff from Bull Motif.

[bmcecosse]

Sorry yes - moment of madness there (heatstroke I think..) of course 'carb'. But I didn't know weber carb - obviously the problem I think!! What model is it - how is it choked/jetted??

[gatsby989]

It's a 28/30 DGV carb. The PO put it on, and I've put in a smaller idle jet (but haven't fooled with the other jets yet) to help with the richness. Did that last summer, and it's still a bit too rich, but better than it was. But the stuttering is a fairly recent problem. I haven't done anything with the carb since last summer. It has a manual choke.

Also, how the heck do you check the timing? I can't see the timing marks. Do you have to actually take the whole front grill / radiator off?

[bmcecosse]

Why would you want to 'check' the timing? Any past guidance on ignition timing settings is now hopelessly out of date due to the very different fuel we have these days - especially where you are..... Just advance till you hear a little pinking when accelerating in top gear - and then take it back slightly till it's 'not quite' pinking. Personally I would deep 6 the weber and fit a nice 1.5" HIF 38 SU carb..... on an unheated alloy inlet manifold. Hang on - that's exactly what I have on my car!

[gatsby989]

Well, I think (hope!) I got it sorted. After replacing just about everything else, I replaced the plug leads, and so far (knock on wood!) no more stuttering. Boy I wish I would have tried that first! On the other hand, I learned a lot in the trial and error (lots of error) process. I'll drive it a bit more and see how things go. If all seems well, I'm going to try the new vac advance unit (arrived in record time!) and hopefully it will be even better than before.

Thanks all for your help.

[JOWETTJAVELIN]

Keep the old parts (condensor, rotor arm, plugs etc) as spares or use them again - they're not throwaway units like everything on modern cars, and can be cleaned up to give much more service.

[mike.perry]

Replace the old parts one at a time and road test. If you get any problems you can identify the faulty part then bin it.