74Runneer

I have a 318 mild cam, eddy 600 cfm carb, headers, stock heads, street master intake. Everything else stock I think. I ran a timing light and it was 5 degrees before tdc where its supposed to be stock, but it has a cam so does that sound reasonable? I also hookhooked up a vacuum gauge and it was reading only 12 in hg (rocking between 11 and 13) that's a sure sign of a leak right?

74Runneer

Okay so i was spraying around with the can of carb cleaner and i found that the hose from the distributor to the manifold has a leak in it and also the carb gasket has a hole in it. Do you think that fixing these two issues could bring the vacuum up to normal?

74Runneer

This is at 700 rps

moe7404

a small variation in vac reading is ok. that sound like the mild cam is working fine. i like the chrysler stock AFBs, are set right. for a eddy carbs at idle it sounds fine. BUT they dont know how to set rods and jets. i dont have time to go into that now. if you can find my other posts about eddy carbs that will give you more info.

TVLynn

Would definitely help. I would try 10 degrees on the timing. The cam will change the idle vacuum so it may not read what you think. Maybe 16 after you fix the leaks.

74Runneer

Moe- yeah i saw your post about rods and jets, im getting a jet kit and ill follow your advice , thanks.

Ill fix those leaks then adjust the timing and see how she runs.

Archer

74 -

OK, you have a hose from the manifold to the distributor???
That should be a ported vacuum, and unless there's something weird going on all manifold vac lines are full vacuum, not ported. You'll have to figure out where there is a ported vac on the carb.

With the hotter cam:
You may need more advance on the timing.
That vac reading may be normal. The hotter the cam the lower and less stable the vac reading.

Archer

bremereric

After you fix your leaks use your vacuum guage to determine your best vacuum reading while rotating the distributor. That will set up your timing at idle. You may have to lower your carburator's idle when your done.

440roadrunner

You likely need more initial advance You likely need to either replace the distributor with an aftermarket which has an adjustable mechanical advance, or have your old one re-curved so that it has a SHORTER mechanical curve.

There is some argument, but most of us run what is known as "ported" vacuum advance, which means that the port provided on the carb has no vacuum at idle. This is opposed to manifold vacuum which gives of course full vacuum advance at idle.

In you searches for this, keep in mind that people refer to "crank degrees" and "distributor degrees." Most old-school manuals which list dist. specs show "distributor degrees" which are half of crank degrees. GENERALLY a performance curve for a mild cammed engine might be 12-17 degrees initial, with 16-20 in mechanical advance. This would give you "under power" IE WOT somewhere in the 34-38 degree range. You will at that point have no vacuum with the throttle floored.

The vacuum advance then is added to the iniitial + mechanical, so (example) 34 total + vacuum might give you as much as 55 degrees under light load cruising. Many Mopar stock distributors have the advance stamped on the mechanism, but this is DISTRIBUTOR degrees. One stamped 15, example, is THIRTY crank degrees, a typical "smogger" which has a very long very slow advance.

74Runneer

I'm not sure but I think I'm having to run the carb super rich to compensate for the vacuum, does that sound right? Ill fix it then adjust everything again. Whats a ported vacuum?

74Runneer

Okay sorry, my distributor hose hooks up to a port on the front of my carb near the idle mixture screw.

440roadrunner

Which side? Google your carb model, or here is the Edelbrock manual for AFB carbs

https://www.google.com/search?num=40...hp.ycDp-70pt5k

You normally have two ports on a Carter/ Edelbrock 4bbl, one is manifold, one is ported. Simple. Hook a vacuum gauge to the port at a dead "properly adjusted" idle and see if there's any vacuum there. You should also be able to tell simply by (at an idle) hooking up, unhooking, hooking up the advance can hose. A manifold port should dramatically affect the idle

74Runneer

Its hooked up to the left side which is the ported side, not the full time vacuum port. What does this mean???

Okay i have no clue if I have a stock distributor or not or if its adjustable or not. Should i just type the part number in google to see what it is? I dont know what mechanical and initial advance are? Im guessing one is the timing light reading?

Archer

74 -

Don't over complicate this stuff.

Yes, you need a timing light.

Disconnect the vacuum advance line at either end.

With the car idling, take a timing reading off the #1 plug wire and write down the number. That's the initial reading or initial advance, and 10 - 15 degrees is normal.

Have some one bring the engine to about 3000 RPM and take a reading. That's your total advance (initial + mechanical. Total should be about 32 - 34 degrees, but with your cam, can't say for sure.

Repeat the exercise with the vacucm line reattached. Note differences in the initial and total advance numbers.

Beyond that, you can take timing readings every 200 RPM and plot the results to get your timing curve, but that may or may not be necessary.

Archer

74Runneer

Why repeat with vacuum line attached?
Also it only goes 10 degrees before and after tdc. Do i have to buy some timing tape or could i just make my own?

Archer

74 -

The vacuum should add to the advance.
If you can eye ball it, tricky but can be done, or you can do the math and mark the balancer at 10 degree intervals, that way you are always reading off the zero line.

Putting a degree tape on a motor that's been in service ain't fun, since the surface of the balancer has to be squeeky clean.
Don't ask me how I know.

Archer

74Runneer

Yeah ill just measure the distance of 10 degrees and mark up to 60 degrees in 10 degree intervals on some painter tape. then line it up with 0 and put it on and take a razor blade and mark each 10 degrees. I think that should be good enough.

74Runneer

Alright I adjusted my timing today and i moved it to the max vacuum. So now my timing is around 12-14 (my reading is cut off at 10) btdc. I adjusted the idle back down to normal running condition (around 700 rpms) and found that my vacuum was at 15 in. (This is up from the bouncing 11 that it was before). It drives and accelerates nice but im noticing that it runs at a higher rpm. Is this normal? Does this information sound correct? Thanks

Coronet 500

Before that question can be answered your total mechanical advance must be found as suggested by Archer. Setting initial timing by vacum is fine, but it is only for idle quality not for higher rpm performance and preventing detonation.

If you keep advancing without knowing your total you could cause damage.

440roadrunner

OK Archer whatever you say LOL

74Runneer

Okay my problem is that I can only see 10 bdtc. Any advance beyond that is covered up and no tape could help because I think the timing chain cover covers it.

74Runneer

After I adjusted the timing today i took it for a cruise and i noticed my acceleration was a lot better and it was running a lot smoother. It was 83 degrees out today and i was running it pretty hard and i didnt notice any pinging. Is there another way to check what the total advance is?

Coronet 500

Turn the crank by hand so 0 lines up with tdc, mark damper at 10. Move so new damper 10 mark lines up with 0 on cover, mark at 10 (this will be 20). repeat 2 more times to have 40. Not completely accurate but you should get an idea were you are.

74Runneer

Okay i think that makes sense to me, Thanks ill try that!

74Runneer

Okay so i tried marking the damper 40 degrees at 10 degree intervals but it didnt go well, It was very hard to measure and mark them accurately. So when I reved it up to what i thought was about 3000 rpm (i was by myself), the original mark moved about 40-45 degrees from tdc. I feel like none of this is accurate at all, but does any of this make sense? Is there a way to check what total advance i have by taking the distributor apart? thanks

Coronet 500

Easiest with timing light and described by 440 and Archer. Even as innacurate as you think, it sounds like your 10-12 initial plus a stock 30ish = 40-45 WAY too much. You could buy a cheap circumference or peewee tape, measure all the way around the damper then do the math. 1/9th of total or total times 0.111 = 40 degrees. Redo with no vacum advance, off and plugged.

74Runneer

Okay I think ill just buy a distributor with adjustable advance. Maybe get one that is marked 10 or 12 for a total of 32 to 36.

440roadrunner

Keep in mind that traditional shop manuals and distributor guys talk in DISTRIBUTOR degrees which are half of crank degrees.

If, therefore, you want a dist. with an advance of say, 20-22 crank degrees, be absolutely sure that the specs you read specify either or the other 11 dist or 22 crank, etc.

That was the point of the factory weight I posted above. That weight is distributor degrees. That weight is a long smog curve.

440roadrunner

I wouldn't want to overcomplicate it, as Archer can't understand, I guess.

74Runneer

Yep I caught that, I'd get one with 10-12 distributor degrees which is 20-24 crank degrees. So when I add my initial timing in the total timing should be around 35. Is this right?