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350 Timing

27K views 260 replies 13 participants last post by  cobalt327 
#1 · (Edited)
How many times have you guys been asked this? Well, I have read some pages and posts but I just don't know for sure.

Just got my jeep fixed. Had to replace the pick up coil and ignition module in the distributor. I did not do this myself because I just didn't have the time. When I picked up my jeep from the shop it ran but not like it use too!

When I got home it did not idle low enough to hear the mild cam. I adjusted the idle set screw 1/2 a turn and that did the trick. But it still didn't run like it use to although I did not expect that adjustment to make it run better, just like to hear the cam.

I noticed that when I would accelerate it would hesitate. Well a few months ago I checked the timing and it was set to 16deg. I thought that was awful low, piston position, but I left it alone. I decided to check it again since the parts were installed and figured the mechanic probably readjusted the timing. Yeap, the timing was reset to 4deg. Ouch! As I adjusted the timing back to 10deg, for a starting point, it idled up but still hesitated when accelerating. I adjusted it various placed but it didn't run right until I adjusted it back to 16deg. Thus I had to adjust the idle screw another 1/4 turn to get the lopping sound. Vacuum at idle is now about 10 psi.

My distributor is an Accel 71100E which is a high performance distributor with a hefty price tag!

So does 16deg sound right for a performance engine? It sure don't run right set at a lower number.

Engine insides are unknown but here is what I know,
Chevy 350 crate Casting #10066036
Stock heads - I think 993 8.5-1 but unknown pistons
Stamped rockers
Supposedly mild cam
Edlebrock carb and Intake Manifold



 
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#3 ·
southshore30 said:
Nice! good to see another Jeep guy on here. I have the same motor. Same casting number. Just freshening up my motor now and doing a restore on my Jeep. Yours looks great. What are you running for a trans? Can't wait to drive mine. The suspense is killing me.
I have a 700R4 "K" case with manual lock-up switch!
Here is a video of how it sounds. Something for you to look foward to! Flowmasters.


http://www.youtube.com/watch?v=eRj7K1OIVVs
 
#6 ·
Blue84JeepCJ7 said:
The vacuum at idle, with lope, may be 8 1/2 instead of 10. With a 700-800 idle its more like 10. I will have to check it all again today and rite it down!
Be sure that the TOTAL timing (mechanical plus initial) is at or below 34-38 degrees so it doesn't detonate at WOT conditions in the upper rev range where it's hard to hear.

You can run more initial advance, up to the point that you have run-on when you shut the engine off, or hard starting due to the advanced timing. Just adhere to the (about) 36 degree total advance.

A good way to do it, is to set the total to, say, 36 degrees. Then see where the timing is at when idleing. If the timing at idle w/the total set to 36 degrees is below the 14 degrees BTDC that the engine likes, you will need to limit the total advance to a setting that will allow you to run the initial timing you need. On your Accel distributor this is a piece of cake to do, thankfully.

I would suggest running the vacuum advance from a full-time (manifold) vacuum source at the base of the carb.

You already know the drill for adjusting the idle mixture screws and setting the curb idle, so I'll skip all that.

If you don't have (or want to check the accuracy of) a dial back timing light, take a couple minutes and MAKE A TIMING TAPE.

If you have any doubt as to the accuracy of your timing marks on the tab and damper, the drill for DETERMINING TDC is also available.

Good luck, and that Jeep's a real looker!
 
#7 · (Edited)
performance tune up instructions:

http://www.gnetworks.com/v4files/barrygrant/Ign timingwithimages.pdf

at idle rpms a carb needs about 12Hg absolute minimum to make a half way decent "atomized" mix...

at 8-10 Hg idle and rumpity rumpity (bad idle mix on purpose) you are dripping liquid gas into the cylinders and that is not a good thing (washing the oil off the walls and contaminating the oil and fouling the plugs)....

stock or mild cam with a dual plane manifold is (ideal) 18Hg at 700rpms with 10-12 base...
sounds like you have a signifigant vacuum leak if 14-16 base only shows 10Hg (or your vac gauge is reading way way off calibration)....

just fyi:
a typical (268 duration) street performance cam with a dual plane will show 15Hg at 700-800 with 14-16 base,,,,10Hg on that cam means there is a "inhale" problem...

a open plenum manifold will cause low Hg,,,if you have one get rid of it....

edit: there are more good articles on that Barry Grant Demon carb site...
 
#10 · (Edited)
My carb is an Edlebrock 1406 (?cfm)
Intake Manifold is also Edlebrock and its the Dual Plane #2701

I readjusted the idle to were it sounded normal (no tach) (no rumpity rumpity) and it checked out to be 13 1/2 Hg on my vacuum. Fairly steady with maybe 1/2 Hg variation.

Distributor vacuum is connected to the left side vacuum of the carb and my vacuum gauge inside on the column is connected to the right side vacuum port on the carb.
 
#12 ·
13.5Hg is enough for the Edie to make a decent atomized mix at idle....
(the Edie independent idle fuel circuit doesn't work well at all at 8-10Hg)
1406 is 600cfm and that's fine....
your going to have to have a tach to set up the centrifugal advance....
you have know the mechanical advance is set correct first for 34-36 at 2900rpms (approx) (with the vac adv disconnected and plugged) and then test your specific vac unit to know how many degrees your vac unit does add....

hint: screw in the idle rpms adjust screw on the linkage to hold it at 2900rpms to set the 36* then just plug in the vac advance and read the new total,,, if it says 50*'s then it is a 14* added by the vac unit

the left nipple is the "timed port" which is no vac adv added till the throttle blades move (at about 1000-1200 rpms) so presently at idle your base timing is the only timing
your vac gauge is hooked up to the manifold vac port,,,fair chance you will need/want a "T" in that line to hook up the vac adv unit also on that manifold port so idle timing will be base plus the vac unit which will be alot more idle hg....
messing with the vac adv is the none critical last step (try both ports pick the one you like)

it sounds like from your post,,, you need to measure the diameter of your damper then go to the store and buy a $7? Mr Gasket timing tape for that diameter which has all the individual degrees from -10 to 60+ marked on it....

80%+ chance,,, once the timing is set correct the carb will be happy but for future refence here's the complete carb manual:

http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

1406 is factory set up abit more for mpg than performance but should be fine if you do indeed have a mild cam ,,,cross that bridge when you get to it (90% of the performance is due to timing,,,10% in the carb)....
 
#14 ·
On your 1406 carb, the full time (manifold) vacuum port is the LEFT (drivers side) port.

You said earlier "Distributor vacuum is connected to the left side vacuum of the carb and my vacuum gauge inside on the column is connected to the right side vacuum port on the carb."

If the vacuum gage is set up this way, and the left and right references are correct, you have the vacuum gage set up on the ported vacuum port. This will not give a correct reading at idle!

This also would mean that the distributor's vacuum advance is on the manifold vacuum port- this would be fine... but I have the feeling that your references are as you face the engine, not as you sit in the car. If this is the case, try putting the vacuum advance line onto the drivers side port and see if the vacuum at idle improves. You will need to lower the curb idle if it was on the ported side before.

This can be confusing- you (and the others here) need to refer to all "left" and "right" as if you were sitting in the seat of the vehicle, OR specify "as you face the engine or carb", or words to that effect.

Better to just say "drivers" or "passenger" side, that way there's no question as to what side you're talking about.

But bottom line, if nothing else is said, "left" is always the drivers side and vice versa.

BTW, your 1406 is a 600 CFM carb. ;)
 
#15 · (Edited)
cobalt,
good point,,,I should have written "facing the carb" left is ported/timed....
rule #1: assume nothing!!!
I did assume he was facing the carb (and the illustration is facing the carb)

Blue 84,
"assume nothing" includes telling you that you will need a timing light...
I assumed you have one because you referenced base numbers not typically marked on a stock damper....
(there are some aftermarket performance dampers that do have base degrees marked out to 18 so you can be setting the base without a light)

comment:
setting up ign timing is not a "tinkering" project at all....
"best" performance setting is darn close to the motor detonation point so you have to do small precise changes steps...
the spark event is only microseconds duration and you are trying to deliver the spark when the piston (which is moving at 100's of feet per second!!!) is at a exact precise location in the bore ATDC...
 
#16 ·
good point,,,I should have written "facing the carb" left is ported/timed....
rule #1: assume nothing!!!
I did assume he was facing the carb (and the illustration is facing the carb)
Ah ha! I am an aircraft mechanic (and pilot) so everything I refer to as well as most aircraft mechanics and pilots, is from the pilot's position UNLESS looking at a diagram. IN this case I was referring to the diagram FACING the carb references. Can get confusing huh?


"assume nothing" includes telling you that you will need a timing light...
I assumed you have one because you referenced base numbers not typically marked on a stock damper....
(there are some aftermarket performance dampers that do have base degrees marked out to 18 so you can be setting the base without a light)
The damper only has one "dash", "mark" or "line" nothing else. But I do have a timing light.

comment:
setting up ign timing is not a "tinkering" project at all....
"best" performance setting is darn close to the motor detonation point so you have to do small precise changes steps...
the spark event is only microseconds duration and you are trying to deliver the spark when the piston (which is moving at 100's of feet per second!!!) is at a exact precise location in the bore ATDC...
Understood. I may have used the word incorrectly.

THANKS AGAIN!
 
#17 ·
cobalt327 said:
On your 1406 carb, the full time (manifold) vacuum port is the LEFT (drivers side) port.

You said earlier "Distributor vacuum is connected to the left side vacuum of the carb and my vacuum gauge inside on the column is connected to the right side vacuum port on the carb."

If the vacuum gage is set up this way, and the left and right references are correct, you have the vacuum gage set up on the ported vacuum port. This will not give a correct reading at idle!

This also would mean that the distributor's vacuum advance is on the manifold vacuum port- this would be fine... but I have the feeling that your references are as you face the engine, not as you sit in the car. If this is the case, try putting the vacuum advance line onto the drivers side port and see if the vacuum at idle improves. You will need to lower the curb idle if it was on the ported side before.

This can be confusing- you (and the others here) need to refer to all "left" and "right" as if you were sitting in the seat of the vehicle, OR specify "as you face the engine or carb", or words to that effect.

Better to just say "drivers" or "passenger" side, that way there's no question as to what side you're talking about.

But bottom line, if nothing else is said, "left" is always the drivers side and vice versa.

BTW, your 1406 is a 600 CFM carb. ;)
I mis-informed on my locations, I have them correct...sorry!

Also, I noticed the 1406 was also available with a 800 cfm but I doubted seriously I had that one. Actually there was no question about it but I just had to discribe it with a (?)
 
#18 · (Edited)
Blue,
I'm still concerned about the Hg (is the rotating assembly healthy)

do this test for me:
warmed up on a level road downshift 3rd to 2nd at about 50mph with no gas pedal and read the vac gauge...
post the results please...

a stock or mild cam motor will read 24Hg+ and steady if everything internal (rings and valves etc) is sealing correct...
25-26 is "excellent" sealing...
it's not a conclusive test for sealing because we don't know what cam is in the motor...

reads low?
next step is to measure the actual cam lift at the rockers with calipers for a decent clue to what the cam duration actually is...
(with a big cam you need to write down the downshift Hg when the motor is fresh,,,for a initial reference point)

edit: LOL,,,now I am confused,,,is the vac adv hooked to ported or to manifold???

on manifold the mechanic may well have backed it down to only 4 base because the vac unit is adding plenty of degrees even at only 10Hg...
 
#19 ·
Blue84JeepCJ7 said:
the 1406 was also available with a 800 cfm but I doubted seriously I had that one. Actually there was no question about it but I just had to discribe it with a (?)
Not to put too fine of a point on this but the 800 CFM square bore Performer carb was either a 1412 or -13, depending on choke type.

The Thunder AVS series 800 CFM are 1812 and -13.

BTW, the 1406 is set up w/a leaner calibration, more for mileage than performance. If you see a lean condition, obviously you can change the jets and rods easily.

Just as an example, using this same carb on a fairly mild SBC, primary jetting had to be changed to 104 jets and 75x37 rods front and back.
 
#20 ·
Blue84JeepCJ7 said:
The damper only has one "dash", "mark" or "line" nothing else. But I do have a timing light.
I don't know how deep your pockets are, or whether you enjoy making things instead of buying them, or how valuable your time is, but the link on page 1, post #6 is for making a timing tape out of a piece of masking tape. Takes maybe 5-10 minutes to do. This allows you to use a non dial back-type timing light to see the timing at values not covered by the OEM tab.

The damper itself can be marked at 36 degrees (or any other values you might want) while the tape is still fresh.
 
#21 · (Edited)
red65mustang said:
Blue,
I'm still concerned about the Hg (is the rotating assembly healthy)

do this test for me:
warmed up on a level road downshift 3rd to 2nd at about 50mph with no gas pedal and read the vac gauge...
post the results please...

a stock or mild cam motor will read 24Hg+ and steady if everything internal (rings and valves etc) is sealing correct...
25-26 is "excellent" sealing...
it's not a conclusive test for sealing because we don't know what cam is in the motor...

reads low?
next step is to measure the actual cam lift at the rockers with calipers for a decent clue to what the cam duration actually is...
(with a big cam you need to write down the downshift Hg when the motor is fresh,,,for a initial reference point)

edit: LOL,,,now I am confused,,,is the vac adv hooked to ported or to manifold???

on manifold the mechanic may well have backed it down to only 4 base because the vac unit is adding plenty of degrees even at only 10Hg...
edit: LOL,,,now I am confused,,,is the vac adv hooked to ported or to manifold???
Vacuum advance is connected to the "ported" port.
Vacuum Gauge is connected to the "full time" vacuum port.


downshift 3rd to 2nd at about 50mph with no gas pedal and read the vac gauge...
post the results please...
Deceleration from 50mph, from 3rd to 2nd, with foot off the gas was dead on 25Hg
 
#22 ·
cobalt327 said:
Not to put too fine of a point on this but the 800 CFM square bore Performer carb was either a 1412 or -13, depending on choke type.

The Thunder AVS series 800 CFM are 1812 and -13.

BTW, the 1406 is set up w/a leaner calibration, more for mileage than performance. If you see a lean condition, obviously you can change the jets and rods easily.

Just as an example, using this same carb on a fairly mild SBC, primary jetting had to be changed to 104 jets and 75x37 rods front and back.
No problem either way I don't much about them. Here is what I saw on Edlebrocks website.

#9906 Edelbrock Reconditioned #1406 Performer Series Carburetor 600 cfm, Electric Choke

#9963 Edelbrock Reconditioned #1406 Performer Series Carburetor 800 cfm, Electric Choke

On the carb base, front, passenger side (hehehe) is the part number 1406. Beside it is stamped 1963. Don't know what that means!
 
#23 ·
Blue84JeepCJ7 said:
No problem either way I don't much about them. Here is what I saw on Edlebrocks website.

#9906 Edelbrock Reconditioned #1406 Performer Series Carburetor 600 cfm, Electric Choke

#9963 Edelbrock Reconditioned #1406 Performer Series Carburetor 800 cfm, Electric Choke

On the carb base, front, passenger side (hehehe) is the part number 1406. Beside it is stamped 1963. Don't know what that means!
I'm thinking: Typo!

No biggie either way, at least as far as the gasket kits go- AFAIK, the gaskets are the same for all the Carter-type Performer carbs.
 
#24 ·
25hg test results pretty much confirms it has a mild cam
(many many miles from now when that same downshift test shows 23 it's time to start thinkin' bout a rebuild)

12 base plus 22 centrifigal all in at 3000 plus 10-13 vac adv is a very common and safe starting point....
"best settings" depends on your specific car weight/tires size and rear gear ratio

if the timing changes doesn't improve the idle Hg,,,do check that the carb base and intake manifold are torqued to their correct values...
(25hg downshift results means they are the only 2 possible vacuum leak sources left)

click on each graph on this link tells you the typical best idle hg at what rpms with that much cam duration...
(I'll be happier when your motor shows 15+ at 700)

http://www.compcams.com/Technical/DynoSheets/

800cfm 1406 is definitely a typo...
being a aircraft mechanic I expect you will like the Edie,,,because,,,each change has a "known" exact change result....

cobalt,
please do continue to point out any errors I make on any thread....
my brain is broken...
"use it or lose it" is why I post on this board
 
#25 ·
red65mustang said:
please do continue to point out any errors I make on any thread....
my brain is broken...
"use it or lose it" is why I post on this board
I'd much rather look at it as keeping us on the same page- me included. There's already enough ambiguity in this hobby/profession to go around, IMHO. Anything to lessen the uncertainty. :)
 
#26 ·
About the Vacuum begin low, I ran a mild 350 Chevy in my Jeep, similar to yours.

350 Chevy
ported 993 heads, 8.5:1 compression
Crane Powermax 272/284 camshaft
Headers.
Edelbrock Torker intake.
Holley 600 4bbl carb,

I was running with 17" hg vacuum at idle, 600-700 rpm, if i remember correctly.
So to me it seems like you could adjust your mixture a little.

Best regards
 
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