i have no idea what to do engine has no power at all. i checked the vacuum, manifold vacuum, which is 15 lbs@idle. when i rev it the guage drops to zero and when i let off it goes to 25 and drops back to 15.when on carb vacuum port,where i hook vacuum advance,@idle the guage reads zero. when i rev it it pulls 20 to 22 lbs+. when i let off it drops back to zero. i bought a crane cam adjustable vacuum advance with weight springs. initial timing set @ 12*. with vacuum advance disconnected,it reaches maximum advance at 1700-1800 rpm.i want to know at what rpm i should start to get advance,and what rpm i should have full advance. right now it seems to be getting too much advance at low rpm because it seems to be trying to fire against itself.until rpms pick up past 2000 rpm. it is a points distributor and dwell is set at 32*. how much vacuum advance should i have? how should the distributor advance? should i test my mechanical advance first? how should my vacuum advance work? i need lots of help i do not understand the principles of advance all that well. thanks,Josh :ball:
Josh, everything sounds normal as far as the vacumn goes. I am assuming you have a timing light. What springs do you have in the dist. now. Mechanical advance is built into the dist. and the rate at which it comes in at is altered by the springs and weights. I like to run the medium springs with about 14 degrees initial. This should give you about 32-34 degrees of advance all in by 2200 RPM. These springs bring in advace around 1000 RPM or so. It sounds like you have the light sprins in now. You will start to see advance at around 600 RPM with these. As for vacumn advance it is mostly for ecomy. When you are at WOT there is no vacumn, therefore no vacumn advance. As for the amount you need to run, it is trial and error. Keep incresing untilk you hear pinging under normal throttle. When you hear pinging back it off a little.
I think you mean 15 Inches of mercury, not Ibs. Automotive vacuum is measured in inches of mecury. The vacuum is working the way it all should. 1700-1800 is to early for full advance. Use a stronger spring... keep going up in spring streght until the knocking goes away. Probally going to be somewhere in the 2500rpm area, but depends on your exact setup. When you are tuning the mechanical advance, leave the vaccum diconected (and pluged at the carb). Once that is tuned with no pinging, then hook up the vacuum advance. Then run part throttle while driving. If you have pinging then tighted up the advance diapragm adjustment until it stops the pinging. Also use the advance limiter that comes with the kit. I just used the max amount of limitation.
Advice on timing a 340 Ok folks with a 340 modified! First thing degree the cam! If it is aftermarket performance cam Next check your valvetrain assy. particular the pushrods lenghts new cam may call for different lenght pushrods. Also check rocker arms for worn tips. Next go with double roller timing chain. I lov it. when degree cam make sure you do not have to retard the timing it so retard it with the timing chain. Most double roller have marking for +- 4 degrees. My timing was sensitive after my rebuild, but I finally got it. My intial is 10 degrees after ten my mark floating due to the mechanical timing of new weights,center weight,bushing, springs. I have a total of 34 degrees. Its all in by 2500 my cam is mild it 210 @.050 with .47 lift on both in & ex. I am using 15 degree vaccum advance, but I have an advance button on the bottom of the distributor to limit it. My car ran like crap with the stock distributor curving, but know it leave 2 car lengths worth of tire tracks when pressing the accelerator on 195/50/15 tires in 1984 Monte Carlo SS. I knew my engine had power but the timing was missing it up now I like wow! I can't wait to get it to the track.
