I just bought a 1971 coupe 454 it was idling at 1500rpm in park and 800rpm in drive. When you put her in reverse the solenoid vacuum valve advances the idle(not a problem)but the vacuum valve open /or closes and moves the points plate, the points move(back and forth) off the vacuum created off the carb base plate and it moves with the cam lobeing of the engine, she then surges 600 to 1200rpm right before she dies in reverse. Shift her into Drive and the vacuum valve slams or open and the points plate returns to its starting point and does not move with the natural lobeing of the engine/cam....................you can watch the point /plate advance through a adjustment door in the dist cap, if it was not for this reverse idle problem I would have her running like a swiss watch!!!!!!! can't wait for the book to show up and show me what I have forgotten and should remember.

Any guesses as to why the points in drive don't move and she idles a smooth 700 but in reverse the vacuum pulls the points and she surges with the cam idle???????

Thanks guys it will be a while before my brain get's back into the mine set of the 70's vacuum technology and what book would be a good purchase for this year Carb and motor.

:crazy:

 

checklst -
First, there is no vacuum valve in the system that opens or closes - I assume you're talking about the vacuum advance control unit...(?)

You have a few things/problems going:

1. First, your idle speed is very high. You should be running below 1000 rpm in neutral wth a 650-750 rpm idle speed in gear. You may have some carb issues that prevent you from a proper idle.

2. Second, you should not be running the vacuum to your vacuum advance control unit off of manifold vacuum on that car (hose should not come off the carb baseplate). Switch the vacuum hose to the ported vacuum source on the carb (nipple on the carb coming out of the front, driver's side of the carb in the middle of the float bowl). The ported source will not pull any vacuum at idle (as long as the idle speed is set correctly as noted in the previous step). This will make your timing stable and unchanging regardless of manifold vacuum at idle.

3. Last thing: You really need to test and set up your timing - it sounds like you may be running retarded if you're getting a large change in rpm between "park" and "drive." Make sure you're getting 36 degree total timing (with the vacuum advance hose disconnected), and make sure your centrifugal advance curve is operating fully and smoothly. 36 total timing should get you about 12-16 initial.

4. If you really need to run the vacuum advance off of manifold vacuum, you need to use a vacuum advance control unit that pulls its full advance range in at your minimum idle manifold vacuum level. I can give you the specs for a unit that will do this - the stock factory unit will not because it's intended to run off of ported vacuum.

 

Thanks Lars I have already printed your instruction and,will get the timing gun out today. I just got it from the dealer idling at 1500 in park. I noticed a tune up plate on the firewall calling for 1500 in park with the gas cap off and the distributor vacuum hose off and plugged, set a dwell of 30 with a 8 degree initial. Following this plate procedure it made no change in the idle rpm with the dist vacuum hose plugged /gas cap off plugged or not, I did not put a gun on her timing yet. The dwell was at 60 so I backed it to back it to around 32 and screwed the idle down to 1000 which was the slowest speed I could and keep her alive in reverse. The carb will respond to a idle change down to 800 and shift into drive dropping her to around 650 to 700 and she runs at that idle fairly smoothly but reverse she will die immediately, so 1000rpm was the lowest I could get and maintain a running car in reverse.

This solenoid plunger has 2 wires coming into the back of it and it appears this plastic back is a vacuum switch with 2 vacuum hoses attached, one hose leads over and attaches to the carb base plate in the front ,and the other hose goes from the plastic valve leading all the way around to the dist, that's why I thought this was a switching valve. I will also check it attachment points on the carb as you describe and get out my old vacuum gage and see what this valve is doing(vacuum wise) before the shift and after. The solenoid plunger seems to work as design as the plunger pushes out to move the throttle arm faster when cold.

I'll let you know after I get the timing gun on her if the dwell was at 60 no telling where the timing is going to be. I noticed by the threads I read most are at 12 to 18 initial and 36 total. I think I might wait for the book so I don't DRIVE YOU NICE PEOPLE crazy with question when I should be reading first then asking question SORRY I broke my own rule!!!!! it is slowly comming back to me(mental wise what going on hear) I am happy I still can find my dwell meter,vacuum gague ect............. I did have to blow off several years of dust off of them however LOL.

Thanks again you helped me more than you know.

 

The vacuum switch with the wires that you describe is a TCS (transmission controlled spark). If you "feed" ported vacuum to it the switch won't alter the timing between "drive" and "reverse."

 

Lars I can't THANK YOU enough. I took your advice (you hit it dead on with the retard timing)and started at the timing, idle screw and set the dwell last. I really don't know how she was even running. The dwell was at 60, I put the timing light on her and the light LAUGHED AT ME !!!!!!!! and I swear I heard a wisper say ARE YOU KIDDING ME, it was not even close to be on the timing number gauge, so far retarded it took almost a 1/4 dist turn to get her on the marks, I ended up at 12 or 14 degrees, it's so tight in their I could not see to good!!!!!! put the idle at 800 in park and ended up at 650 in gear, forward or reverse.

She runs and idles so smooth now I can't believe it's the same car, how the dealer mechanic got her so far off is a mystery to me!!!!

Thanks again "one happy owner" :steering: