Ok heres a dumb ? Do I want timed or full vacuum on my 78 el camino? using a EDL 1406 carb.What rout are you guys on the the site going timed(ported) or full vacuum advance? Thanx guys.. MSD HEI with vacuum advance..

Looking at the front of the carb, use the small port on the left. The one that's alittle higher up(above the throttle blades).

You definitely want the timed vacumn port to your distributor advance. If you use full manifold vacumn you will have full vacumn advance at idle and other high manifold vacumn conditions. This will most likely cause detonation on small throttle accelleration. In the '50s and '60s GM and other manufacturers used full manifold vacumn connections to the distributor advance in order to get full advance at high vacumn cruise to improve fuel mileage. Detonation wasn't much of a problem with rich mixtures, cooler running engines and higher octane fuel. With the beginnings of fuel emissions in the '70s the engines could not use all that advance without detonation so the timed vacumn port on the carburetor became the standard connection for vacumn advance.

The weird thing is ,when I do put the hose on the timed vacuum advanced side my idle and throttle response is terrible,and when i put it on the full vacuum side the throttle response and idle are 150% better.What gives? Help me out fella's I just dont get it..

I bet your initial timing is retarded. When you hook up the vacumn advance hose to full manifold vacumn you are advancing the timing 10-15 degrees or more. Try this--plug the vacumn advance and advance your initial timing 15 degrees from where it is now.

ok that part does make sense, going to try that right know Ill post results to you in a few.And thanks for not laughing at me..

I bet your initial timing is retarded. When you hook up the vacumn advance hose to full manifold vacumn you are advancing the timing 10-15 degrees or more. Try this--plug the vacumn advance and advance your initial timing 15 degrees from where it is now.

you were right, that made a big difference.know what do you think about the advance springs ? right now im at med. blue spring and light silver spring MSD ..

Do you have a dial back timing lite? If you don't, beg borrow or steal one because it will help you to setup your distibutor advance curve. A second choice is to use a regular timing lite and a calibrated tape on the harmonic damper. Disconnect and plug the vacumn advance, you can reconnect it after you check and set the initial and mechanical advance. You want as much initial timing as possible, start at 12 degrees. You want about 38 degees total advance all in by about 2400 rpm. You can change the springs/weights/stop to get the necessary advance. If your engine can take a little more initial advance without pinging or "kickback" on starting go ahead and advance the timing. I think that you'll find that
somewhere between 12-14 degrees initial and between 36-40 total at 2400 rpm will give you the best performance. You can reconnect the vacumn advance to a timed port and this will give you upto about 50 degees total but only at cruise, high vacumn.

Ok thanx Ill try that also

Guys, I was about to post a similar question, some of which have been answered. I am runnning a EDL 1406 also and am using the full advance port(right side). My questions is, what are the proper steps to set the timing. I have a spec sheet from my engine (350ci) that recommends 36-38 degrees of total timing @ 2500-2700 RPM. What should the initial timing be? Also, is initial timing set w/out vacum and in drive or at idle? I was told by a friend that I should purchase timing tape for the 8in. balancer and that the timing cna be read at 2500-2700 RPM. I am running a HEI Dist. w/ a Super Coil, all Accel. Thanks for the help. I am looking forward to making this Elky run to its fullest.

Your initial timing should be in the 10-14 BTDC area. You need to adjust the advance curve on the distributor to give you the 36-38 degrees at 2400-2500 rpm if you cannot give the engine enough initial advance. In other words you check and have only 34 degrees at max distributor mechanical advance (increase engine speed until it stops advancing). You can then increase the initial advance 4 degrees to get the required 38 degrees. If maximum distributor mechanical advance occurs above 2400-2600 rpm you have to recurve the distributor. You can probably run 12-14 degrees initial advance without ping or engine kickback on starting. Always disconnect the vacumn advance when making these adjustments and NEVER try to make these adjustments while the trans is in gear.
You can play around with the initial timing and distributor advance but most small block Chevys run best at 12-14 initial and 36-38 maximum.

Thanks Mrapii,
I was thinking of setting the idle RPM when in gear. My next question is how how does one recurve the distributor? I am quite a novice with ignition work. Thanks for the help.

Be very careful when adjusting things with the engine running and in gear. When I was young and foolish, many many years ago my 1964 Buick station wagon ran me over and almost killed me when I was adjusting the idle in gear.
Anyway you can get a advance kit at JEGS (http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=113185&prmenbr=361). It comes with complete instructions.

Recurving is easy to do but it does take alot of trial & error.

I recurved my MSD with the two light springs and it starts, accels.. and runs alot better..

We've gone through this "ported or full" question several times on HR.com. We even had two published articles that reached two different conlcusions, but both recommended manifold vacuum. Go figure.

Anyway, our conclusion was to use manifold vacuum.

I disagree, using full manifold vacumn is just asking for detonation due to excessive ignition advance at the wrong time. Use the timed port, that is why all carb manufacturers include them on modern carbs.

I guess we'll have to agree to disagree.

My distributor is set up for the initial timing and centrifugal timing to equal around 36 degrees and be all in by 2500 rpm. At WOT, the vacuum cannister is adding additional timing if it is connected to ported vacuum. That would put me over 50 degrees advance (depending on the cannister) and into detonation land.

First of all 50 degrees advance under the right conditions will not cause detonation. At a steady cruise light load 50 degrees will add fuel mileage and not cause detonation. Too much advance under load will cause detonation; now under WOT of course manifold vacumn drops and if the vacumn cannister is connected to manifold vacumn the timing will retard but the problem occurs under light throttle load conditions (throttle tip-in). Momentarily the timing is too advanced and detonation occurs. Unfortunately I was at a new car dealership during the mid '70s and got a lot of first hand experience with this problem.

I totally agree there are times (idle, crusing) when an engine can handle more than total timing (initial plus centrifugal). I can also see the possibility of detonation at light throttle when connected to manifold vacuum. However, I'm still hung up on the 50 or so degrees (initial, centrifugal, and vacuum) at WOT when connected to ported vacuum.

Somewhere I read that manifold vacuum was standard until the advent of pollution equipment, i.e. EGRs. Then the manufacturers went to the ported. Does that make any sense? That would have been about the same time as the compression ratios fell into the basement.

MI2600, I think that we might be misunderstanding how the timed vacumn port (sometimes called spark port) works. The port is located above the throttle plates so at idle there is little or no vacumn. As the throttle plates open vacumn increases but the vacumn doesn't increase immediately not until 1500 or more rpms. At part throttle cruising speeds the vacumn will be highest and the vacumn will increase to the maximum, just when you need it. At WOT when the plates are completely or almost open (heavy acceleration) the vacumn drops to zero or near zero and there is no vacumn timing, just when you don't need it. Now you cannot test in your driveway because the engine is not under load, you need a chassis dyno or actual road conditions. Historically many American car makers went to timed port advance in the early '50s although General Motors and Chevrolet in particular used manifold vacumn at least until emission standards became serious in the early '70s. Some manufacturers (Ford in particular) used a double vacumn advance cannister with both manifold and timed port push-pulling rhe advance plate. Prior to the early '70s when engines had to run lean and hot and fuel was of a higher octane engines ran ok with manifold timing to the vacumn advance. Try the timed port and I think you can tune your engine for better acceleration.