77ricbaez

I know there are a billion threads out there regarding ignition timing. And believe me, I've been reading A LOT of them: "set b/t 36-38* @3000rpms" or "set ignition timing a bit more advanced than stock" or "advance till it pings then retard" and then I saw one guy say that Oldsmobile engines like a lot of initial but not too much total, and that 30* total timing was better than 36*

And believe me I, I've been tinkering with the timing for a while. Initially when it was tuned (not by me) it was sitting with waay too much timing. The vacuum can was hitting the firewall, it was advanced as far is it could physically go.

Then I retarded it to 24* initial, just 4* above stock, with about 36* total. Mileage was a bit better, (in the 11.5 range) still a bit low for this car. I expect to pull 15-17 mpg since I drive about 2/3 highway and 1/3 suburban.

BTW Yes, my vacuum advance is working, it's providing 14* advance and I have it hooked up to full vacuum.

Anyways, then after a bit, I advanced it to 26* initial, 38* total. Mileage fell to (10.5).

So my question is, what do you guys run on your smogger olds 350s to get the best mix of economy and efficiency? Is stock (20* @ 1100) really the most optimal setting? I just tuned it according to stock specs, we'll see how it goes.

I cannot get better than 11 mpg, I drive 25 miles per day, 2/3 on the highway going 60 mph on average. I seldom get caught with traffic, and when I do, it isn't too bad. I do not have a lead foot. I do not understand, I should at least get 15 mpg maybe better, even with California's E10 (I swear I cannot find ethanol free in Southern California).

Spark plugs are perfectly fine, I just pulled them to check the condition, no abnormal deposit. Fuel ratio is perfect, a bit lean at 14.8. I checked the spark plug wires resistance and condition and they were fine. Carburetor was rebuilt 2 years ago, still running smooth. No major mechanical problems. Engine still runs strong.

svnt442

A lot of the problem is the crap gas in CA. My 2004 S10 dropped almost 5 mpg when I moved here from Il in 2008, and it was immediate.

77ricbaez

Really? I thought the E10 had only a 3% loss in efficiency.

shiftbyear

Good post, cars with EGR systems are hard to diagnose. I don't know what the engineers did so far as cam timing, ignition timing, and jetting to get the cars thru emission regulations. Some engines just don't respond to tuning tricks. Unrestricted exhaust (duals) may help a little, just guessing. Good luck.

oldcutlass

Your engine will tell you what it likes. Since you've been tinkering you've discovered the best settings for performance vs fuel economy. You already answered your own question. As far as the position of the vacuum can, it can be changed by pulling the distributor and moving the rotor 1 tooth, reinstall, and readjust timing accordingly. You will have to turn the oil pump shaft to get it to line up so you can drop the distributor back in place.

77ricbaez

Bump

So I think my problem all along was running 87 octane fuel. Using a timing of 20° @ 1100 rpms hurt my fuel economy and performance so I put it back to 24° @ 1100, this gave me a total timing of 36° @ 3000 rpms and so far my economy is looking good, I'm running shell 91 octane (highest here in California) and so far I've driven 80 miles and the needle is still relatively close to full. Usually itd be around 3/4. I noticed it burns cleaner, I used to get a strong smell of burning gunpowder after coming off the highway. Now it smells like a modern car. I think I've solved my issue, we'll see what I average this tank

oldcutlass

What is your total timing with the vacuum advance hooked up. Should be somewhere between 50 and 55.

77ricbaez

Yep I've got 50°, 14° vacuum.

oldcutlass

You should be good to go, doubt it will be better. As others have stated the E10 ain't helping either.

Ozzie

This may not be current, and may not be near you.

https://www.pure-gas.org/index.jsp?stateprov=CA

77ricbaez

So far no ethanol free here in California, but I have tested different brands of gas and my car really liked Sinclair, 76 and Shell. I filled up at a new gas station, I think it's ethanol free from what I've read but we'll see.
Also​​​ sorry to bump again but I'm just not sure about the octane I should be using. Currently I have it dialed in at 36° by 2500 rpms and 54° cruise timing. The motor is 8:1 and I'm running 91 but honestly i might be wasting money, maybe I could get away with 87 with such low compression what do you guys think? Another issue is that I've never heard spark knock so I don't know what it sounds like, though if I were to guess it'd sound like a diesel?

RRB

Burning gunpowder smell or is it kind of a sulfur smell? I'm going to guess the latter. Your 77 has a catalytic converter but also has a non-feedback carburetor which generally run rich causing the cat to get hot and throw off this smell.

With fuel economy numbers like yours, I suspect the carb is set to rich either just the idle screw adjustment but possibly the float level setting is too high. If the car had normal acceleration, I don't think timing is all the cause for your low fuel economy. I realize you said your AFR is 14.8 to 1 but with all due respect, how did you measure it?

Also, disconnect and plug the vacuum hose to the egr valve. Engines of this era run best when this is disconnected. The engine will have more power and fuel economy should increase too. However, re-install when you get it smog tested every two years so you will pass the NOx portion of the test. I'm in SoCal too so know what it takes to keep these smoggers going.