distributor tuning

40cpe

40cpe

Well-known member
I have a mechanical/vacuum advance distributor/Edelbrock 600 in my 272. It is a new rebuilt (Cardone, I think). With the vacuum connected, it breaks up badly at about 4000rpm. I disconnected the vacuum and set the initial on 15, which shows to give about 35 degrees total but it is only all in about 4000. It seems to rev pretty well like that. With vacuum connected and driving normally, I don't hear any pinging. Without vacuum I'm sure I don't have adequate advance at normal cruise (1600-2500 rpm) so I'm wondering how to get proper advance at lower cruise and still be able to rev it up occasionally. I'm sure the points are cheap off-shore, given the distributor's heritage. The condenser gave up at about 50 miles, so the points might be close behind. I've been through this advance balance on a 302 and a Chevy dist in my flathead but I'm in uncharted territory with this y-block. Any tricks you might share will be appreciated.
 
It sounds to me like the breaker plate is rotating too much and causing the timing to go off the chart so the engine is cutting out. I think you can correct it by increasing the tension on the primary breaker plate return spring (very slightly). Since the problem begins to occur at 4000 RPM, I think it is pretty close, just needs a tiny little bit more tension. I think you will need to adjust on a trial and error basis since it is not the factory dizzy for a Y-block, but you should have it dialed in right in a couple of try's.
 
I've had new points that really didn't follow the cam at low rpm. The worst set would stay open at 2500 rpm. Think of "point float" at low rpm. The reason we used to use dual point distributors. Try another set of points. How that interacts with the vacuum advance is beyond me. But points are cheap. Most of us run 10-12 degrees initial, and 35 or so at 2500-3000 on our y blocks. You can run a lot more vacumn advance under light load. If you don't find an answer here, try yblocksforever.
 
I don't see how you can have "point float" at low RPM unless the point spring tension is way too loose. "Point float" normally occurs due to distrib cam spinning around so fast that the points don't have time to close (high RPM).
On the other hand, I don't think of 2500 as low rpm. I can go down the road at a pretty good speed with engine at 2500 rpm. Still, that should not be fast enough for "point float" IMO.
 
An old trick to cure "point float", take apart the old point set and use the spring on the new set. Double springs may be hard on the rubbing block, make sure the grease gets on each cam lobe.
 
I have seen distributors, that when the vacuum advance comes on and rotates the plate where the points are mounted, the point gap changes enough to make the engine run bad. Maybe sloppy where the plate pivots ?
Just a thought.

Sal
 
Mine just had such a poor fit on the pivot point they would hang up. They weren't "floating" so much as sticking. That's why I put quote marks around it. But the effect was the same. That motor regularly saw 5000 rpm and 5 lbs boost. Not with that set of points. Offshore crap.
 
miker98038 said:
Mine just had such a poor fit on the pivot point they would hang up. Offshore crap.
Click to expand...

Ohhhh. I ordered four sets of points from Concours several years ago, still using my first set of new points from them. They are okay. Hope the rest of them are good too. Was hoping it was enough to last me till I'm dead.
 
Daves55Sedan said:
I don't see how you can have "point float" at low RPM unless the point spring tension is way too loose. "Point float" normally occurs due to distrib cam spinning around so fast that the points don't have time to close (high RPM).
On the other hand, I don't think of 2500 as low rpm. I can go down the road at a pretty good speed with engine at 2500 rpm. Still, that should not be fast enough for "point float" IMO.
Click to expand...

I didn't think so --but I had a model A dist on the machine "as is" and it had a rpm band that reacted like point float----a little dab of dist cam lube and it went away----the problam was in the 1200 rpm area, yet once through that band the points operated clean up to 5000 rpm, after lubing the cam 0-5000 was fine

Best to put on dist machine, but you can check dwell and operate the vacuum advance----the advance plate can be changing dwell too much
 
I've changed points, condenser, and the advance can. I've been through the wiring and advance plate and find nothing wrong. The dwell does drop about 4 degrees when the vacuum advance is kicked in with the vacuum tool. I can see the spark breaking up on the timing light strobe when it starts running badly. I've taken it to 5000 rpm without the vacuum and runs fine. It looks like points would float every time if they were the problem. The vacuum can adds about 25 degrees, I'm thinking of trying to limit the amount of advance the can delivers. I have one of the adjustable cans but it just makes the advance require more vacuum to advance and more to take it all the way. Max advance is the same.
 
40cpe said:
The vacuum can adds about 25 degrees, I'm thinking of trying to limit the amount of advance the can delivers.
Click to expand...

Okay, so if you go back up to my 05/27 reply to this post, I think we are talking about the exact same thing. You do want to limit the advance. It can be done by turning the little post that holds the primary breaker plate return spring so that it increases the tension on the breaker plate.
Also, I have seen the exact same distributors with different spring thicknesses and number of coils wound on the spring. So another option would be to go to a little bit heavier spring, but you will still need to adjust the advance curve to get the engine to perform optimally over the broad spectrum of RPM's. Right?
 
40cpe said:
..... The dwell does drop about 4 degrees when the vacuum advance is kicked in ......
Click to expand...
This seems wrong to me. When the advance mechanism moves the dwell should stay the same.
I think scicala may have come up with it...
scicala said:
I have seen distributors, that when the vacuum advance comes on and rotates the plate where the points are mounted, the point gap changes enough to make the engine run bad. Maybe sloppy where the plate pivots ?
Just a thought.
Sal
Click to expand...
 
Daves55Sedan said:
It can be done by turning the little post that holds the primary breaker plate return spring so that it increases the tension on the breaker plate.
Click to expand...

I don't find a spring on the breaker plate. Are you talking about a Loadamatic?

dmsfrr said:
This seems wrong to me. When the advance
mechanism moves the dwell should stay the same.
I think scicala may have come up with it...
Click to expand...

I check that out. Thanks for the ideas.
 
40cpe said:
I don't find a spring on the breaker plate. Are you talking about a Loadamatic?

I check that out. Thanks for the ideas.
Click to expand...
Can you post a couple close up photos of the top insides of the distributor? with the rotor out. Someone might be able to spot something.

.
 
Last edited:
40cpe said:
I don't find a spring on the breaker plate. Are you talking about a Loadamatic?
Click to expand...

OOOps, sorry, still living in the stone age here, yes I am talking about a loadomatic. I never even seen anything else, so can't help you with whatever mechanism other types of breaker plates have for advance curve adjustment. But there's got to be something there.
 
I have a Chevy distributor in my flathead and there are charts listing the different vacuum cans by total advance and rate of advance. I can't find anything like that for the Ford distributors.

Maybe the problem is unique to my distributor. I haven't found anyone with that problem in my searches.
 
I checked the points plate, it is tight. The vacuum can is the only thing that controls the position of the point plate. Here are the pictures of the distributor under the cap.
 

Attachments

  • '55dist1.jpg
    '55dist1.jpg
    49.3 KB · Views: 23
  • '55dist2.jpg
    '55dist2.jpg
    45.4 KB · Views: 20
You must log in or register to reply here.
Back
Top