blk79nj

Hello, I know this was covered before. I attempted to search for this but I was unsuccessful, so I decided to post it.

I have a bone stock 79 L48, automatic with the stock HEI distributor with a new cap and rotor. I have had the car for a while, and it runs OK on the highway, but.. when you get into the secondaries.. it boggs down.

So I want to get it to run better, so I started with the timing. I have a craftsman timing light, the kind with dial on the back. After showing my son how it works... I had him sit in the car and give me some RPM's so i could take some readings. This is of course with the vacuum advance line removed and plugged with the engine warm. Here is what I came up with:

I set the initial to 6 based on some old Chilton's manual I have...

650(idle)=6
1000=10
1500=14
2000=20
2500=21
3000=23
3500=27
4000=27

Does this look correct, or is there something wrong? If this is good...I'm going to move on to the carb. If this needs some work, my plan is to fix this first then move on.

Any help is appreciated.

scottyp99

Looks fine to me.....but you can do a lot better with a recurve kit and a new vacuum advance canister.

Scott

7t9l82

dial in 2 degrees more at idle drive it , if its better dial in 2 more and so on.when it starts to run bad or lose power back it up 2.
get Lars's tuning papers. and use them.

Blue79

It looks low. Total timing should be more in the 34-36* range. Rebuild the distributor first, then re-time and let the initial timing fall where it may. I have the exact same set-up as you and now it starts immediately, no cranking on.. and more responsive overall. Can't pass emissions any more at this setting so get through that first. And, timing should be 'all in' by 2800RPM or thereabouts. Read the Lars paper at the top of the forum. Happy motoring

blk79nj

Thank you for the responses. I will review the Lars paper

Sounds like I will re-curve the distributor, then play with the initial timing to get the it up in the 34-36 range.

I will be on vacation this week, so it will have to wait until the next.

I'm not worried about emissions, in New Jersey with Historic Tags there is no inspection.

cardo0

Like Blue said get it all in by 3000rpm. U can use a stethoscope and listen for knock as u increase rpm. If u hear marbles in a coffee can then back off a couple degrees.

bluedawg

I like to power brake for a brief second facing up hill, but not break the tires loose this will usually cause it to ping if the timings not right. I haven't listened with a stethoscope at idle while increasing idle speed, how far out would it need be to ping in park? I'm only asking cause I found a stethoscope at a garage sale and bought it.

cardo0

Good u asked as it brings up a overlooked situation. The OP will be setting his curve while parked so he can easily listen between adjustments there. U should be able to make your timing curve (mechanical only, w/o vac adv connected) within 1 degree of detonation (once detonation detected/heard back off 1 degree). If u have good working vacuum advance U then need to subtract out your vac adv to make your total adv < the detonation curve u just made. Without a good functioning vacuum adv u are on your own.

The OP will be setting his timing curve while in park and thats a good place to start while he gains experience before he moves on to methods with better results. Yes a long shallow grade is preferred to load the engine but a knock sensor would be more useful for that and MSD sells one for reasonable price.

BTW u dont need a fancy medical stethoscope but a cheap Hobo Fake $10 automotive stethoscope works well enough.

lars

The compression on a 79 is so low that you can't get it to detonate unless the timing is grossly over-advanced. If you set up a '79 within 1 or 2 degrees of detonation, you're probably over-advanced by at least 10 degrees, with a massive power loss from the over-advanced condition. Set total timing to 36. This will be best power, performance and drivability. The OP can achieve this by simply taking his original setting as first posted and advancing the timing 9 degrees. This will produce 36 total with 15 initial, which is a near-perfect setup. Let it go at that. He can gain a little performance by installing some slightly softer springs in order to get that total timing all-in by 3000 rpm instead of 3500, but this change is very minor, and will not likely be noticeable.

Lars

blk79nj

Thank You to Lars and everybody else for you assitance. I really appreciate the help.

I am away this week, and when I get home, I will advance the spark to get it to 36 degrees.

I will then follow the procedures to insure that the vacuum can is working/connected properly and to insure that I'm getting up to 52 degrees, but no more.

cardo0

Lars is right. I cant figure a subsitute for using a load bearing dyno to find max brake torque (MBT). Once torque stops increasing adding adv does nothing and timing adv should be returned to MBT.

I think the OP needs to try a few (proven?) curves and drive it to find what is best for him.

blk79nj

FOLLOW UP

Just got back from vacation at the beach.

I went out, and bumped the initial timing up to 15 degrees without the vacuum advance attached. Gave it some RPMs, and the total is 36 at about 3300 or so.

I then reattached the vacuum advance can, the idle increased, so I decreased it down to about 650.

I then checked the timing again, and it was at 27 with the vacuum advance attached, so it's giving me about 12 degrees.

Doing the math... 36 mechanical + 12 vacuum gives me 48. I kn

LB66383

You can go through the hassle of tracking down and installing a different vacuum canister to get the total to 52*, but in the end I don't think you will notice the difference of those 4*.

blk79nj

I did a run last night, it pinged a little on the 1st to 2nd shift at about 5500 rpm.

At this point I will leave it and see how it goes. If I do make a change, I will back it off by 2 degrees.

It bogs/hesitates at lower RPMs, but not as much as before. I am going start tuning on the Q Jet, but if I need help I will create a new thread for that.

r16678

Mine is idling good at 32 degrees before top dead center, is my distributor no good? thanks

resdoggie

Is that with your vacuum advance hooked up?

calwldlife

i would have started with the carb

r16678

No I capped my vacuum advanced

r16678

I just had the carb rebuilt by Rod's Carb shop in Phoenix

resdoggie

32* btdc at idle is way too much with the vacuum advance disconnected. Before you tweak the carb, you need to get your timing sorted out.