xxxtreme22r

While reading through the service manual, I came across something that has confused me quite a bit. I know that to set timing you remove and cap off the vacuum advance and set to 0 degrees @ 950 rpm on a 22r CARB which makes perfect sense. Then it says to replace vacuum advance and check timing between 10 -14.



However the manual also mentions that mechanical advance starts at 600 RPM and at 750 it is .2 - 1.7 and then at 1100 RPM it is at 2.9 - 4.4. What I am seeing is that around 950 mechanical advance is somewhere between 1.7 and 2.9. And then goes on to say max vacuum advance is 11.5 - 13.5 not 10-14.



While talking to ENGBLDR, they had mention with the 268 cam and their new stock style head to set the timing for 5 1/2 to 6, which I am assuming is @ 950 RPM with vacuum advance capped off.

Can someone explain to me why this timing diagram differs from the timing procedure? Afetr rebuilding and breaking this rebuild of mine, i want to be sure the mechanical and vacuum advance is working properly on the distributor. Just not sure what the values should all be.

Thanks.

xxxtreme22r

Wow, I either asked a really dumb question or a really good one. 57 looks and no replies.

waskillywabbit

iTrader: (-1)

No help here. I always just take mine to my mechanic who worked on these things when they were new.

xxxtreme22r

I can do the work, but i just found it confusing that it looks as though the manual contradicts itself.

yodta

I think the separate advance numbers you're seeing are just specifications on how much actual advance is built into the distributor under the different advance mechanisms, i.e., mechanical and vacuum. I don't think it has anything to do with where you set your timing; it's just there to tell you what provisions are built in to the distributor and when each is active, whether separately or in combination under certain conditions.

Basically, what you do is disconnect and plug both the idle and normal advance hoses from the distributor. Set it to 0° at 950rpm max, and you're all set. If higher than 950, more mechanical advance is coming in, and the timing will be off when you reconnect the vacuum advance.

One very important thing to check here -- make sure your vacuum advance diaphragms are not torn. if they are, your engine will never time correctly. the quick way to check this is to put the rear most vacuum hose back on after you set your base timing. it should jump to between 10-14°. if it does not, then your vacuum advance is damaged, and you should replace it. this is not uncommon, and I recommend replacing the entire distributor; it's actually cheaper than buying just the vac. advance I've found. I bought mine from Advance Auto. Here's a link.


do keep in mind the info EB has passed along. I'd start with the stock spec. and see how it works for you, and then gradually start adding more base timing and make sure it doesn't ping. if it does, you can help some of that with running premium fuel. I have to run it in mine.

hope this helps.

xxxtreme22r

that clears most of it up, so if I am understanding this correctly then that 0 base timing it actually between 1.7-2.9 BTDC plus the mechanical advance of the distributor. I am pretty sure that the vac advance works as i do notice a change in rpm when disconnecting the vac lines.

yodta

don't factor in all that stuff. just set it to the spec -- 0°

"pretty sure" isn't the same as knowing exactly how much. if you're really interested in proper tuning, I'd also be interested to see your timing numbers after you connect each vacuum hose, the idle advance first (rear port of dist) and then the normal advance (front port).

I'm curious to hear whether the diaphragm is still good and whether it fully advances to the specced range of 10-14°

xxxtreme22r

Will do, once this motor is together I do plan on checking that as the motor and distributor did have 172,000 miles on it. Proper tuning is what I am after which is what led to this thread to begin with.