MGB: No ignition advance visible - FIXED! Update....

Hey guys-

Now that I have the steering/suspension sorted out I am working on "performance issues" with my 77B.

She is quite gutless at speed so I decided to start by checking the ignition timing. I set her (at 1000 RPM vacuum advance disconnected) to 12 degrees BTDC. Then I re-connected the vacuum line and re-checked the timing.

NO CHANGE. I revved the engine while watching the timing with the strobe - NO CHANGE. Still at 12 BTDC even at about 2500RPM.

This can't be correct can it? I would expect a lively timing mark as I revved the motor, but there it sat at 12 degrees.

This could explain the logy behavior, too I would suspect.

What say ye?

Ren

Ren:

Disconnect the tubing to the vacuum module on the distributor. Take the distributor cover off and rotor also for better visibility. Then use a length of 1/4 inch surgical tubing and connect one end to the vacuum module and suck the air out from the other end. (Not a joke). You should see the distributor plate move slightly each time you apply a vacuum/suction. Under the distributor plate are a set of weights that move by centrifugal force and they may be stuck. Yes, the advance should move as you rev up the engine.

Hi Ray-

Yes, I already tried a version of what you suggest. With the car idling I connected the tubing to the vacuum advance module and sucked on it while I watched the timing mark with the strobe. Nothing. No movement from12 BTDC.

Furthermore, it seemed as though the diaphragm in the module may be leaking as I was able to draw air through it when sucking on the hose.

Does the mechanical advance do much above 1000 rpm? I thought it may be already "maxed-out" at this engine speed.

Thanks for your ideas, guys,

Ren

If your 77 is like my 78 it has a 'module' on the trans that connects to this little vacuum advance thing. It will only give you advance in 4th gear. The vacuum advance 'switch' is on your pedal box with wires and vacuum hoses connected to it. I don't remember the correct name for it, but look back in the archives under-- vacuum advance. You should find plenty of info there, I did! Here's what it looks like unattached from the pedal box.

TCSA=Transmission controlled spark advance. This works to advance the engine timing when the tranny is in fourth gear. BUT, if he disconnected the vacumn hose at the distributor and attached a seperate hose and applied mouth suction (vacumn) and nothing happened, I would say that the vacumn advance unit on the side of the distributor is bad.

Anyone know of why I suddenly am having a severe knock from my engine, and now I can't turn it over? Recent oil change, level fine. I have a 74 rb mgb. Thanks

Yeah, it could be a bad vacuum advance unit, but I replaced all the vacuum hoses on mine in order to get the whole system working right. You could have OLD vacuum hoses that are making the car not get the vacuum to the dizzy.

Thomas, start a new thread.

Ren, it sounds like your vac unit is shot and the advance mechanism is stuck. ALL the advance happens from 1000-3500 rpm, and you should see the timing jump almost 30 degrees on that distributor. Its time for a rebuild or a replacement.

Hi Jeff:

I hear that you are the man when it comes to distributors, so I suspect I'll be sending this one your way soon. In the meantime here is what I did...

The PO replaced the original 1977B dizzy with a 25D from a junk engine. He apparently never even checked it - just stuck it on.:eyeroll:

I pulled the 25D off and it was absolutely filthy. I gave it a clean-up. The vacuum advance was stuck solid, but I got it cleared and it seems to work now. The mechanical advance was also stuck, so I disassembled it, cleaned and oiled it and now it feels OK. The points were SHOT, too. [color=#0000FF]It's a miracle that this thing ran at all[/color]. I put it back on with the bad points and now she won't even start, so tomorrow I'll get some new points and give her another try.

One question:

Is the 25D vacuum advance meant to use manifold vacuum or ported vacuum?

Thanks,

Ren

Jeff can set how you like
i think it better to sense from carb as that senses carburetor demand vacuum vice manifold vacuum

but i am probably wrong

BEE & VEE @ Hammers and Spanners discusses this , And probably says which a 25d is set for , prby dunna matter with yours it is slack and wore out anyway..

http://www.mgb-stuff.org.uk/ignitionframe.htm

Ok, so after a night's sleep everything seems clearer sometimes...

As I said, last night I removed the filthy, old 25D dizzy with the stuck vacuum and mechanical advances. I cleaned it up and un-stuck the advances and reinstalled it and the MG would not start. I was pooped and went to bed.

This morning I looked at the dizzy and realized that I have placed the condenser wire terminal on the wrong side of the insulating bushing on the points spring. :eyeroll: I reassembled it correctly and gave the points a clean-up and re-set. I turned the key and she just purred! I.set the timing to 12 BTDC and snugged her down.

I went for a quick test drive of about 10 miles and the MG now goes like the proverbial "scalded ape"!

I will still be sending this dizzy off to Jeff once the weather sets in hard, but in the meanwhile, I'm drivin' this thing!:thumbup:

Thanks for your encouragement throughout.

Cheers,

Ren

Dont ya just love it when a plan comes together?!

Good job Ren. Remember this lesson. Everything on this vehicle is 32 years old and no telling what "experts" have worked on it prior to you.

You can't go wrong coming to this site for guidance...

[quote="Kats Bee"]
Dont ya just love it when a plan comes together?![/quote]

That I do!

I went out this afternoon with my son driving the MGB for the first time (he's 24 years old ) and he put the "B" through the paces revving to 4500+ when shifting, etc, and that little motor didn't miss a beat.

It always impresses me how much of a positive effect cleaning and lubrication can have on machinery.

I have ordered some new points, condenser, etc., for the dizzy in the hopes of improving reliability - though she has not let me down yet (knocking on wood).

Next project - new steering rack boots/bellows/seals/whatever they're called - and lubing the rack. I'll keep you posted.

Ren