[Super Chevy]

well i have fixed my problem with the missing while cruising and the detonation, i got a re-curve kit, and when i got the cap and rotor off, there were no springs! they both broke, found them in pieces. so all this time i have been running full advance at all times, so i installed the weakest springs in kit, got everything back together and it wouldn't idle, so i turned up the idle and took it for a ride and it ran horrible, well originally to compinsate for all the detonation i was getting (from the broken springs i didnt know about) i retarded the timing until it was gone, so when i put the springs in, the timing was way to retarded and thus would not idle and caused it to run so horrible, so i advanced the timing got the idle where i wanted it, and now it runs amazing . i cant believe it was such a simple problem and it explains alot, because all of a sudden the car just would not run right. i also installed a timing marker but i cant use it, my 305 dampner has the timing mark at around the 12 o'clock position, and my marker is at 2 o'clock, so im just gonna get a dampner cover. well i just thought id inform u guys that my problem is fixed.

[rifraf]

Yea,that would do it,right on for ya,say,now try your different vacuum ports for kicks when ya get board,keep in mind you will have to re-time it though,the switch will change your advance at an idle,if it doesn't,your horns bad to. Also they sell degree tape that sticks on the balancer,just be sure to know how large your diameter is.

[Super Chevy]

im gonna order the balancer cover soon, once i get that ill start testing things, hopefully before it gets too cold out, i hate winter. ive been doing alot of reading on this stuff and the ported source seem to be the way to go, thats how i have it right now.

[batman09]

Super chevy,
Here is a really good article about timing and vacuum advance.I have my chevy on full manifold and it runs really well!!!I used to run it on ported.I have alot more power of the line.Check out this article it may change your mind. bmhttp://www.73-87.com/7387garage/drivetrain/hei.htm

[fried_guy]

I'm going to have to say use full manifold vacuum. And the reason is this...

GM used to run all their cars on full manifold vacuum from the factory. Then stricker smog standards came into play and GM had to reduce emissions. To combat this they set up ported vacuum for advance. Why? It's really quite simple. Setting the timing more retarded heats up the exhaust more. Hotter exhaust gasses = better emissions. With this done, the engines would still have that top-end power and only lose some power at idle.

The quicker the advance curve comes in the better... so logically, the more you have at idle the better.

Also, the ONLY difference between ported and full manifold vacuum is at idle. As soon as the butterflies of the carb start to open and RPM and vacuum pick up, the ported port acts like it's a full vacuum port.

Check out this post...
http://www.chevelles.com/cgi-bin/for.../4/20095.html?

[batman09]

Fried guy,
That is 100% correct!!!!Ported was only invented for emissions control.If you have a car that does not require smog.Run full manifold!!BM

[Tmod]

Originally posted by fried_guy
Also, the ONLY difference between ported and full manifold vacuum is at idle.

That is not true as I did a test on my truck and during part throttle cruising with the truck doing 35 MPH the full manifold vacuum was 17" and the ported vacuum was at 7".

[fried_guy]

Sheesh, sorry, let me rephrase...

The only difference between ported and full manifold vacuum is at idle some at part-throttle.

The more closed the throttle is, the less vacuum there is... to a point. For example, at 3/8 throttle ported it would be the exact same as 3/8 throttle manifold... anything under that and there would be less vacuum on the ported than there would be on the full manifold. (I just used 3/8 as an example... it really depends on a lot of factors).

Advance is very good to have... especially at part-throttle. If too much advance is given from full manifold vacuum then get an adjustable vacuum advance canister.

[Super Chevy]

thanks guys for all of your help and those are very good links, i am now ordering the adjustable vac advance can, and im gonna put new bushings in my weights, mine are worn. im also gonna go with the full vacuum port, it makes the most sence to me now.

i am switching my carb soon to a Holley 1850, it has one vacuum port, do u know if its full or ported vacuum?

[rifraf]

Not so fast guys,until you see what a vacuum gauge is doing under a load,you may want to re think what you now believe,its a whole different story than how it seems revin it up in neutral. You will notice if you hook a gauge to manifold vacuum and view it from inside the car that when you step the peddle down,especialy climing a hill where it is lugging,the vacuum will drop to almost full zero,this is a bad thing when you consider what you are trying to accomplish,note also when you let up on the gas and say downshift it will send the needle skyward. The purpose of the advance is to aid in accelerating beyond the idle circuit. There are ways to make it function the other way,but for me,the reasons are only those that appeal to folks who are running inadequate fuel and have things set up to benefit more typically from a mechanical advance apeal,but use that methode as a bandaid,just ask yourself why else a performance only carb would label the ported vacuum"dist",its not to pass the sniffer,also,some of the highest noted builders use this method and have clearly stated as I will,efficiency is power or the other way around,they are one of the same. The obviouse comparison would be if your car runs good with 68 jets,would you go to 90s? All I suggest is to try it bolth ways,and remember to re time it between line switches,I think you will find what I say to be true.

[fried_guy]

I, personally, prefer full manifold, but I think either way will work for you if you tune it right. Whatever works best for your car works best for your car... not mine. Test and tune.

[Super Chevy]

well tomorrow i pick up my new parts. let the test and tune begin!

[rifraf]

Hey,will you update me on the results? Thanks

[Simo]

Originally posted by rifraf
Hey,will you update me on the results? Thanks

rifraf,,
I reckon your on the money
Vac can be set for most conditions ,ie ,,around town touqe , more seriouse,, or full tire tearing...

Vac tells many messages to many ears,,..

ie ,,computer,

Please tell me when to spark and pour the correct amount of beverage down my throat and when to take a breath,,.

Carb vac asks,,.
please tell me how to burn this fuel att correct spark time att different degs att revs and load,,..

[Tmod]

Originally posted by rifraf
Not so fast guys,until you see what a vacuum gauge is doing under a load,you may want to re think what you now believe,its a whole different story than how it seems revin it up in neutral. You will notice if you hook a gauge to manifold vacuum and view it from inside the car that when you step the peddle down,especialy climing a hill where it is lugging,the vacuum will drop to almost full zero,this is a bad thing when you consider what you are trying to accomplish

When I tried my little test that I did I was driving around with vacuum gauges inside the the vehicle with my wife watching them both on acceleration and steady state cruising.

I am getting the impression that you are saying that when climbing a hill under full throttle low RPM with the engine lugging that you want full vacuum spark advance. This is crazy as the engine is in such a loaded state it will more then likely ping all the way up the hill.

I have tried both ported and full applied to the canister and I can say that around town and general Highway cruising that the truck runs better with full manifold vacuum applied. When I start climbing a hill yes the vacuum does go down but that's what the engine needs.

Just my .02

Tmod