Dwell and timing set. Crisp take off and power! BUT rattles on acceleration.

nice. my adjustable vac adv should be arriving tomorrow.

 

Ok, I got the accel kit. It has black springs (short) silver and gold. I put the black ones on. I also got an adjustable vac advance from accel. So, its installed but I have not connected it yet to vacuum.


I made a mark on the balancer 1.75" to the right of the factory mark.


My vac advance is unplugged.

My dwell is set to 30 deg
My total plus initial is 32 deg all comes in at 3200 rpm.
The initial is off the tab. maybe 16 or so.

I took it out and drove it down my street. Very responsive. It does rattle though on a hard run until the rpms get to a certain point. It doesnt rattle at first, it doesnt rattle at higher rpm, but in the middle it rattles until it gets to a certain rpm and then it stops.


Should I back off the total timng to 30?

What should I do with the vac advance? Should I hook it up? Its on the lowest setting now. Should I try the other springs? Stiffer or weaker?

please advise

Gary

 

Ok, now about the vacuum. I got a new gage and checked it at idle (1000rpm) in park. 22" when I increase the rpm it goes up to 25". At idel (1000rpm) in park, it stays between 21 to 22 but quivers a bit but stays between 21 to 22. This is connected to the transmission kick down port on the intake.

So, back to the issue. I cant make the car idle lower than 1000 rpm. Is it possible the throttle shafts are leaking? Ill spray some gumout in there while its running and see if it speeds up. I know those shafts arent that tight to begin with though.

 

i sprayed carb cleaner around the shafts and no change in sound, no speeding up no slowing down no stumble. I sprayed it into the airhorn too though with no noticeable difference. Is it possible the throttle blades are not aligned or closing properly? I rebuilt the carb but never touched the shafts or blades. I held it up to the light and saw light but i assumed it was normal. The book said somem light is ok. What to do> Maybe I should take the carb back off and try to al ign the shafts.

What is a good spray to spray around looking for vacuum leaks?

standing by please advise over

Gary

 

larry, if i pull slightly on the throttle to close the blades when they are already in the closed position the engine slows down some. This would support what you just said. Is it possible someone rebuilt the carb before me and messed with the blades? they couldnt become misaligned naturally could they?

Those screws are staked, can they be removed withoutbreaking them? I remember taking some off before but I dont remember how i did it. Id hate to snap off a screw.

Maybe all it is is misaligned blades. If i had a drill press I would rebush the whole ting.

 

Larry, I changed to the gold springs and now Ive got 30 deg total timing at 2400 rpm, it stays there until I get to 4000 and then it reads 32 deg.

When I drive it without vac advance it pings a bit. But I know its not going higher than 32. When I hook up the vac adv i check it with the light and total timing is up around 40. I take it for a ride and it slightly pings.

I never mashed the pedal to the floor but when i reve it up to 4000 in the garage with vac adv hooked up, total timng was over 40 deg. without it at 4000 it was 32.

 

with this accel spring kit the black ones are strongest, gold medium , silver light.
Ive got gold ones on now, i tried the silver but it pinged more than the other and came in 30 deg at 1800 and 32 deg at 2400. too much.



so i backed the total timing off by 2 deg
The gold ones come in at 28 deg at 2400 and 30 deg at 3200.

and have the vac adv set to the least amount of advance and i cant hear any ping when i floor it. so now ill increase the vac advance until i hear ping and then back it off a turn. Does that sound reasonable?

The vacuum issue, Im going to get those bushings and find someone with a drill press. Ill get some extra 3 38 screws in case I break them off. Ill align the trhottle plates and make sure the shafts dont leak. That should fix my high idle problem, if it doesnt ill know what isnt the problem. ONce thats done i can dial in the idle and idle mixture for max vacuum and smoothness. Then it should be tuned as best as it can be tuned.

 

what does it mean "all in"

example


with the silver springs I have 30 deg total timing at 1200, no vac. it stays at 30deg until I get to 2500 then it creeps up to 34.

So is do I count my total timng being in at 1200 or 2500?

 

Looks like your mostly there..

Too much advance at a particular rpm is the cause of your part throttle ping.

Yes, it won't be as responsive at part throttle, but that's the compromise that has to be made. It should not be much different.

Now you have to slow the advance curve down slightly, to eliminate the ping. Do this with heavier springs on the mechanical advance mechanism, and as Larry said, make sure the weights are clean and well lubed.

You can mix and match springs, to find that sweet spot. (you can use a black and a gold spring).

Beware of the fact that you must have all the mechanical advance out of the distributor, and it back on base timing, at about 200 rpm above your idle speed in gear. If you in the advance curve at idle, it makes it just about impossible to get a good transition from park to drive.. You should see an rpm drop of about 100 rpm or so, when everything is set up properly, with a stock motor and converter.

While the old "all in at 2500" works for vitrually all modified engines, the closer you get to stock, the more important the curve is. You might not be able to achieve your full advance until a higher rpm.. like 3000 or 3500..

And having it "all out" in park at say 800 rpm. is the other side of the coin here.

On the vacuum advance, I would suggest limiting the total advance (base, mechanical, and vacuum) to around 45 degrees, for best mileage. As you no doubt read in the instructions for the adjustable mechanical advance, you set the total vacuum advance with the limit plate for the arm, and then use the adjustable screw on the diaphram to control at what vacuum level the advance comes in. This setting is critical, as part throttle ping can also come from the vacuum advance coming in at too high a vacuum.

I would dial in the mechanical first, with the vacuum disconnected, and then go back and work with the vacuum until you have no ping at any operating condition.

Good luck, and good tuning.. looks like you have learned a lot with this project..

JW

PS> If you have 22" of vacuum, I wouldn't be looking for any vacuum leaks.. that's about all they ever make, at idle.

 

Larry is it normal for it to come in rapidly and linearly like that and then 1100 rpms later, suddenly it goes up another 3 or 4 deg? I mean is that caused by the design of the shape of the weights?

If the emory fixes it then all the timing will be in at 1200 which is too early.



The weights are seem real loose. Ive had them off many times. There is no dirt on them. Emory meaning like what grit? 320? 600? I have some 1200. ..

and Jason, yea I tried that> right now I have a black spring and a gold spring on. does it matter which one they are on?d

 

at idle without any vac, i am at 12 deg. With the heavy springs I am still at 12 deg at idle. when I bring up the rpms, the 30 deg mark moves up smoothly to the 0 mark on the balancer at 1200 rpms when I get to 2500 rpms it moves up to the 32-33 and doesnt go any higher. I will use the emory and some grease on the weights to make sure they arent sticking.

I have backed it down now to 27 deg total and when it gets to 2500 its at 30 deg. There is no knock now at full acceleration from the stop sign. good seat of the pants feel. the best so far but i think there is more there. My vac is at 5 deg. I may start dialing that in until it knocks and back it off a turn.

Larry have you ever seen that phenomenon before with the timing jumping up 1200 rpms after everything seemed in?