SkylinesSuck

I'm just doing general tune up and restore stuff to my '75 Salon w/350. It seems to get pretty terrible gas mileage (like 150 miles to a tank) and one thing I was looking at is the vacuum advance on the side of the dizzy. If I blow through the vacuum line into the advance diaphragm, shouldn't it eventually stop me from blowing, similar to blowing in to the cruise control diaphragm? If I blow into it now, I can keep blowing just like the tube is open at the other end. Would this indicate a blown diaphragm and if that is the case, would that hurt power/mpg? Lastly, anybody got a few quick tips on changing them if it is busted?

**Just for reference, I have already changed the cap, rotor, ignition module, plugs, air filter, fuel filter, oil, coolant, ATF check, and probably a couple other things. Still poor gas mileage. I am trying to figure out scrounging up a tach so I can check/set the timing, but I came across this potential problem first.

MDchanic

Yeah, your advance diaphragm is bad, though usually you suck on the line instead of blowing into it.

Order a new one from AutoZone (you could get an adjustable one and tune it in if you want, but if your engine's original, a stock one should be fine).
It's held in by two screws - remove screws, unhook from poInts plate, install new one.

- Eric

SkylinesSuck

Perfect, thank you. I did suck also, but i was trying to dodge comments that I knew I'd probably get from statements like that The stock one from Autozone actually says "out of stock" when you go to check out so I might grab the adjustable one. In the mean time, should i plug the hose?

There is somebody on island that said they bought the wrong dizzy for a chebby that needed one for EFI IIRC, and the one they bought was for an older model that had the vacuum advance on the side. Might this one work, or do they all have different timing curves?

SkylinesSuck

BTW, this is what I was looking at from autozone instead of the stock one since it isn't in stock:

http://www.autozone.com/autozone/par...uestid=1836556

Look okay?

oldcutlass

That is more of a performance vacuum can, be advised you may have to set that up!! If you are inexperienced with mechanics, I would go with the stock original unit, which is less expensive and will work fine for your stock application!

Also check and make sure your mechanical advance is working properly with a timing light!!

SkylinesSuck

I'm for sure not new to working on cars, but I am new to stuff this old. Dizzy's and vacuum advance stuff is WAY before my time. I'll see tomorrow if I can use that stock replacement from somebody on island though. I just wonder if I should cap it off in the mean time though.

How would I go about checking to see if the mechanical advance is working?

oldcutlass

Basically, with a timing light you would see if your initial timing is somewhere between 12-16 deg before top dead center. Then with the timing light shining on the mark, rev the engine up to about 3500 rpm and it should read 30-34 degrees before top dead center. You will probably need an adjustable light to perform this. If youo do not have an adj light then just see if it moves smoothly from initial to somwhere on the balancer based on raising the rpm's slowly! If it moves then the advance plate and weights are operational.

If the vaccum line is disconnected, and plugged it will not operate.

MDchanic

... But DO plug the vacuum line until you replace the diaphragm, or it's just a big vacuum leak.

- Eric

BlackGold

Just to be clear, Eric means you should plug the vacuum source, which is probably a port on the carburetor or elsewhere. You don't have to plug the line going to the vacuum advance can.

oldcutlass

No we mean plug the tube (line) going to the vacuun can, usually a bolt, screw, pencil, will do!

SkylinesSuck

Why would I plug the line going to the vacuum can? That's busted and is just a big leak anyways, right? It is not a source of vacuum. The line coming from the carb however is pulling vacuum and causing a leak when hooked up to the busted advance. Maybe I'm missing something though. All this old stuff is new to me :-)

I just picked up the dizzy from a local guy. it's an MSD unit with an adjustable vacuum advance and probably some other whiz-bang features. I'm going to see if I can just swap vacuum advances for the moment since I have no tach which would be needed to reset the timing.

oldcutlass

You need to plug the rubber line! Whay not pickup a vacuum can from the parts store, probably about $20. Two screws and your done!

SkylinesSuck

The rubber line is plugged.

I'd love to swing by autozone and grab one, but I'm in Japan :-)

MDchanic

Surely you're busting his chops.

I didn't think I would have to specify this, but I should have said
"... But DO plug the vacuum line from the carburetor or the intake manifold until you replace the diaphragm, or it's just a big vacuum leak (and don't worry about the now-unused distributor vacuum diaphragm, you don't need to plug THAT."



- Eric

SkylinesSuck

Here is the instruction sheet to the dizzy I bought. I want everything to look stock, but I think you won't notice it hiding behind the air cleaner.

SkylinesSuck

So the more I'm reading on the internet, the more I am wondering. Will this cheby distributor fit on the Cutlass?

507OLDS

Just leave the vaccuum advance unhooked,and plug the source on the engine.Let the distributor advance itself mechanically.You can get some performance gains this way,and you could pick up some mileage.

oldcutlass

No it will not. Just run without a vacuum advance and order one off the internet and fix when you get it. As I and others have said, the engine will run without it!

MDchanic

Olds Distributor:


Chev. Distributor:


It'll stick out of the hole too far .

- Eric

507OLDS

I wouldn't bother ordering one.Just run it without it,and leave it that way.

SkylinesSuck

Thanks for the pic MD and damn


It's a daily driver so I'm going to need to do a little better than 9 mpg which is what it currently gets. I found this:

http://cgi.ebay.com/ebaymotors/_W0QQ...KQ3aMEWNXQ3aIT

and ordered it last night. The vacuum nipple isn't curved like mine, but hopefully that's the only difference.

MDchanic

So you got yourself an AR-12 unit. That should be right for your car.

Here is the fundamental interweb source document for GM vacuum advance units. You can see how the different units vary in their specifications.

This'll be a cheap an easy fix, and should improve your gas mileage, but if you're getting only 9mpg, something else is wrong, and this won't bring you to 20 (though I think these cars never did much better than 14 to 16, if I'm not mistaken).

- Eric

507OLDS

I get 12-14,depending on right foot position.

SkylinesSuck

That link was immensely helpful, thanks. After reading a bit, it appears the "AR-12" is the most universally street car friendly, but the article says the Olds actually calls for a "AR-12" which appears a bit more aggressive in it's advance (if I am reading that correctly.)

While I had hoped for a little better than 12-14 mpg (I do 25 miles round trip mostly e-way 5 days a week), 14 is still a better than I get with my 3 cylinder .66L Suziki Jimny (think Samurai) due to my 31" Super Swamper tires

MDchanic

Unfortunately the mid-seventies cars were pretty much all pigs.

It was the perfect confluence of cheap, plentiful gas, no fuel economy standards, and the beginning of crash standards (which added weight) and pollution controls (which initially destroyed efficiency). It took a few years after the fuel crisis (was that '73?) for fuel economy to trickle into production cars. If I recall correctly, even straight six Mavericks got about 16mpg.

- Eric

SkylinesSuck

Yeah, perfect storm. I'd add to that the 70's affinity for ginormous styling. All of that was before my time though, so I can claim innocence

Still, I'm hoping with a light foot, free flowing exhaust, and not 36 year old bead style catalytic convertor (yes it's still on there) I can get as much as possible.

oldcutlass

Still, I'm hoping with a light foot, free flowing exhaust, and not 36 year old bead style catalytic convertor (yes it's still on there) I can get as much as possible.[/QUOTE]

Ohhh, I bet if you replace that converter, your fuel economy would increase dramatically !!

MDchanic

I bet that if he even begins to remove that converter, the Japanese authorities will sense a disturbance in the force, come arrest him, obtain a confession, and lock him up .

- Eric

507OLDS

You could leave it in a large parking lot,and some illegals will remove it for you.

SkylinesSuck

Ironically they actually wouldn't mind me messing with the converter. The whole reason this car was "easy" to bring over was that it was made before 1976 (Dec '75 baby!) and doesn't have to meet their emmissions standards. Newer cars have to go through a much more exhaustive (no pun intended) import process that happens in Tokyo first. My car came straight to Okinawa.

So you really think it would make a noticable difference yanking it off? I would be happy to replace it with a modern free-flowing cat (or two if I can get duals.)

SkylinesSuck

Incedently, like MDchanic said, they are strict about cat's in general. The motorcycle cops are notorious around here for carrying collapseable poles that they extend and jam up your tail pipe to see if you have a cat installed and if it's been hollowed out.

MDchanic

Never mind installing a modern cat, just install a "test pipe." No problem there, since you're emissions exempt, though if you did it here, it could potentially subject you (and possibly me for advising it) to an $11,000 federal fine.
Since you're not in the US though, we're both safe .

- Eric

SkylinesSuck

Just an update. I installed the "AR-12 unit" which isn't as aggresive with the timing advance, but it still got me up to around 11 mpg which is around 200 miles to a tank. Not gut wrenchingly terrible. I still think I need to check/set the base timing (need a tach for that which I don't have) and maybe play with the carb a little more, but I think I can get a couple more mpg out of it. I'm also looking at one of those mechanical advance kits, but I'm not sure if they do a whole lot for part throttle operation and if you need 93 octane for that or not. Anyways, problem fixed and it helped mpg's, thanks all!

66ninetyeightls

Just get a decent timing light. It will gave an RPM readout on the light.

olds 307 and 403

Get rid of that converter! I took mine off my 81 Delta 88 after a Mercury Mistake owned by a co worker beat me. I had way more power and helped mileage some. Put on dual exhaust, if you are emissions exempt. You can simply set the timing around 20 at idle. I have seen anywhere from 13 to 22 at either 1100 or 2200. I believe I got the best mileage on the Delta's non CCC 307 with 19 at 1100 rpm. Tried all different settings. I ran 22 initial in my Olds v8's which does help part throttle. An advance timing light with a tach is nice to have.