Advance issue

[gprimm]

Just completed a 6 month redo of my small block Monte: Eddy RPM heads, roller rockers, 2.5" Pypes exhaust, GTA steering box, 12 bolt with a 3.42 posi, 700r4, tubular rear control arms, etc. LOTS of stuff.

 

Well, it would run fine at idle but when driving it would surge. Last night put a timing / advance light on it and it idles great at 15 degrees but when I hit the throttle it would advance alot and could not see the mark.

 

At a car show tonight before leaving, I plugged the vacuum advance to the distributor (has lighter springs). Guess what? It runs great now. No surge and it will light the tires very nicely.

 

I don't think I can continue running with the advance plugged, but what do I do? Put heavier springs back in?

[420ponies]

gprimm,

On my Monte I use a timing /advance(dial) timing light .I too have lighter springs in the distributor(HEI).I run about 12Degress at idle (vacumn unhooked and hose plugged)and 40degrees total (vacumn hose attached)at 3000rpm's.I have a holley 750vac.secondary and run off the lower base (full vacumn)port.I've tried the upper metering vacumn port and have had the same issue like you.Is your vacumn advance on the distibutor a adjustable style?that style will limit the amount of advance in the distributor.It has a little allen wrench bolt inside the vacumn advance canister port.Hope this helps.alot of smallblocks run 34-36 degrees total advance,mine just likes the 40!

[wallaby]

Agreed. The springs aren't going to make a difference with your issue...they are speed sensitive and only control the advance relative to engine speed. The vacuum advance is LOAD sensitive, and controls the advance relative to throttle opening and engine load by sensing the vacuum level. When the two systems work together, they regulate the advance by sensing both engine speed and load. You shouldn't have full advance unless the engine is running over 3000 rpms and at light load with high vacuum levels.

 

It sounds as if you simply have the vacuum line hooked to the wrong port on the carb. I also get best result by using manifold vacuum from the base of the carb or the manifold itself.

[gprimm]

The vacuum advance line is hooked up to The ported vacuum on the right side of the Eddy carb. The full time is on the left side. I believe I had it on the full side but after watching the Eddy online tuning videos I put it on the ported side as they did. The distributor worker fine before. I will book it up to the full vacuum side. My son drove it to work this morning. Thanks.

[stangeba]

Try both and see what works better for your car. With ported you have no vacuum till after the throttle plates are opened allowing for perhaps lower idle setting if you run into a "run on" or dieseling problem. Use a simple vacuum gauge to check the source. (more advance at idle, like with manifold vacuum vs ported vacuum, will increase idle speed)

Here is a tech article about vac advance, my boss has written.

 

Vacuum advance and why you need it

[Montemedic]

Bruce, that is a great article. Thanks for sharing it with us.

[201fireman]

I have been trying to figure out where to run mine as well. I also found Bruce's article very interesting. Just another thought for discussion. The instructions that came with the Edelbrock I bought say to hook to ported vacuum on emission controlled engines. I believe it stated to go to manifold vacuum for non-emission controlled engines. I am not sure why this is but found it interesting. Can anyone shed any light on why? Just curious.