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
Supposedly mild cam
Edlebrock carb and Intake Manifold
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.
Here is a video of how it sounds. Something for you to look foward to! Flowmasters.
12 BTDC is a good starting point, your hesitation may be coming from your carb. your vacuum sounds a little low, the mixture may need adjustment.
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!
performance tune up instructions:
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)....
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...
Thanks guys, I'll get to reading some more!!!
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.
I am going to ge read up on those links you posted. Until I get back maybe this helps. When I rev up the engine the timing mark on the flywheel is almost, if not right at, straight up and down, Top of centerline reference to the flywheel. Timing marks are about 2 o'clock.
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:
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)....
Thanks for all the info guys, I'll keep reading and tinker with it in the morning!
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. ;)
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)
"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)
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...
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