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Distributor

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=100695
Printed Date: Mar/18/2024 at 11:37pm
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Topic: Distributor
Posted By: V8Mart
Subject: Distributor
Date Posted: Jun/25/2019 at 1:57pm
I am new to the world of AMC and would appreciate some advice on the distributor on my 73, 304 Hornet. When I take off the cap and rotate the shaft by hand it seems to ride up as if trying to unmesh the gears, this does not seem normal to me, am I right?I see no evidence of it riding up when engine running as rotor and cap show no damage . I also believe I may have a problem with the vac advance unit, possibly leaking diaphragm or seized mechanism since the car has been stood for many years...in order to compensate in some way, I notice the previous owner set the timing to around 15 degrees....when I set back to 5, the engine  stumbles on initial throttle opening but runs ok otherwise. Am I looking at getting a new distributor or is it possible to repair what I have?...it looks like the advance unit is not easily detachable from the distributor body. Also, is there a way of adjusting the acc pump mechanism on the 2bbl carb...just in case this is causing my problem.



Replies:
Posted By: BassBoat
Date Posted: Jun/25/2019 at 2:20pm
Normal to run poorly at factory setting of 5 deg.  this was done for emissions, NOT driveability.  The other part of the equation is the mechanical advance should have been limited to get the right total advance at rpm.  for example, 36 to 38 degrees is probably where you would want it to be.  With 5 initial and another 15 distributor = 30 engine degrees you would be at a nice safe total of 35.  Advancing the idle to 15, the distributor should be limited to 10 distributor = 20 engine degrees to get the same 35 total.  In my experience you will find 20 initial and 40 total to give the best performance.  Text book performance advance curve would be 12 initial and 36 total.  The advance in the distributor is limited by a pin in a slot.  You can modify the slot or put a bushing over the pin to limit travel.  don't be afraid to experiment.



Posted By: PHAT69AMX
Date Posted: Jun/25/2019 at 3:53pm
There is Endplay in the Distributor as stock and it is ok for stock, maybe as much as 0.150". 
The helical cut of the drive gears pulls the Distributor Shaft down under load
and also pushes the camshaft into the bloc, along with other things...
Is it an AMC Delco Points Type Distributor?  What are the stamped numbers on it?
If so the Vacuum Advance Canister is held in place by 2 Screws
and suitable replacement Vacuum Advance Canisters are still available.
Would think your existing Distributor is entirely and somewhat easily serviceable.
Unsure about the 2-Barrel Accel Pump adjustment, what Model Carb ?  Pictures help.
Link to an existing thread here containing considerable AMC Delco Distributor information.
It used to be a "sticky" here, but fell from grace...

http://theamcforum.com/forum/distributor-1967-to-1974-application-info_topic32011_page1.html?KW=Distributor" rel="nofollow - http://theamcforum.com/forum/distributor-1967-to-1974-application-info_topic32011_page1.html?KW=Distributor


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: ccowx
Date Posted: Jun/25/2019 at 5:09pm
What you need is a B-1 type vac advance diaphragm for a Delco Remy distributor. It is the same distributor as in just about any GM V8 from the mid 60's to the early 70's, at least. The vac canister is available from Amark or American parts depot etc. You can likely get it cheaper from Amazon or Jegs or similar. As for your timing, try around 7-10 btdc and see where it starts to detonate, then back off about 2 degrees. The advance curve is fairly slow and conservative, so it may pick up off the line without going too far advanced. If not, shorten the curve as mentioned above.

All easy cheap fixes!

Chris


Posted By: V8Mart
Date Posted: Jun/26/2019 at 11:49am
Ill make a start by advancing the timing back up and see how it goes. From what I recall the shaft lifts way more than 0.1" when I twist it. I noticed the mech advance springs looked a little loose/worn  too...its all a bit tired I think. Not sure what type of dist, though it uses points,cant find any screws to retain vac advance unit.....will have to look closer  ,  and the carb was a new replacement by PO, looks a bit like a motorcraft 2bbl but no obvious markings on it


Posted By: ccowx
Date Posted: Jun/26/2019 at 12:56pm
The two screws that hold in the vac advance are under the cap. End play on the distributor is important, but only so much. As mentioned, the rotation and gears will suck it down to being seated on the oil pump shaft anyway. Shims are easy to buy to tighten that up. Otherwise the unit is fairly bulletproof. The advance springs are no big deal because you will likely replace them anyway, as part of tuning the distributor. Mr. Gasket, Accel and others all make advance tuning kits for that distributor, which include springs and weights and in some cases bushings for the advance.

Overall, the Delco distributor is pretty solid and easy to fix. I can not think of any other points type unit that it could be, so likely it is still the stock Delco one.

Chris

PS: It sounds like you have a timing light, so you can get a rough idea of how the advance is working by revving it up and watching the timing advance. Unless it is reaching full advance before 3000 rpms or so, the springs in the dissy are within usable range.  


Posted By: PHAT69AMX
Date Posted: Jun/26/2019 at 7:18pm
Quite a bit of AMC Delco Points Type Distributor info and pictures here in this thread:
( edit: doh!  sorry, failed to realize the below link had already been posted )

http://theamcforum.com/forum/distributor-1967-to-1974-application-info_topic32011_page1.html?KW=distributor" rel="nofollow - http://theamcforum.com/forum/distributor-1967-to-1974-application-info_topic32011_page1.html?KW=distributor


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: V8Mart
Date Posted: Jun/27/2019 at 6:34am
thanks guys, plenty to keep me busy once I finish repairing the body


Posted By: FSJunkie
Date Posted: Jun/28/2019 at 4:02am
It should idle smooth and respond cleanly to throttle opening with a 5 degree initial timing setting. Advancing the timing beyond that often covers up some other problem in the engine tune, usually faulty carburetion. I prefer fixing the actual problem to slapping a band-aid over it.

1972 AMC timing specs were actually pretty close to ideal.

My 1972 360 idles very smooth and responds instantly to the throttle from idle with enough torque to break both tires on a 4000 pound Wagoneer. It's timing is set to OE spec. I found that worked best after ten years of experimenting with other settings. Turns out AMC knew what they were doing.

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1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited


Posted By: V8Mart
Date Posted: Jun/28/2019 at 5:11am
I dont seem to be getting any initial advance when throttle opened from idle . I removed the vac unit,sucked on it (??)  seems to work ok all seems free, from what I can tell, I am not getting much vacuum from the take off on the carb,(tried both take offs by the mixture screws, no difference)  feels weak when I put a strip of paper against it and work throttle...certainly not enough to activate the unit, I get advance once the mech adv kicks in....I will check around for any vac leaks, the blanked off take offs are a little suspect, I would expect it to idle badly with a vac leak but its fine, when I disconnect the vac advance pie there is no difference in idle.


Posted By: Lucas660
Date Posted: Jun/28/2019 at 8:52am
The port above the butterfly will have little to no effect at idle. Because the butterfly is restricting the vacuum signal. You should get vacuum there at cruise. There is varying opinions of whether to connect to "ported" vacuum or manifold vacuum. I would follow what the tsm recommends.


Posted By: V8Mart
Date Posted: Jun/28/2019 at 12:28pm
both ports are below the butterfly...just....level with the mixture screws



Posted By: ChillyB
Date Posted: Jun/28/2019 at 10:21pm
End play will allow the rotor to raise up, and that is where it will ride adter engine is spinning.   The only problem is the mech advance cam raises up out of level with the weights.  I'll speculate that your weights show tip wear at the tops but the bottoms have sharp burr.  I shimmed mine and replaced the weights. 


Posted By: ChillyB
Date Posted: Jun/28/2019 at 10:22pm
Also, the Mr Gasket recurve weight kit for those distributors may be out of production.  Mine (Jeep) uses short beak weights.  Ordered NOS kit from ebay  


Posted By: FSJunkie
Date Posted: Jun/29/2019 at 2:09am
It shouldn't idle poorly or stumble off idle even with no vacuum advance what so ever. Half of my AMC engines have no vacuum advance below 35 miles per hour because the TCS solenoid blocks the vacuum to the distributor until that speed. None of them idle bad or stumble.

I think that distributor needs a proper rebuild. Points distributors wear out and get messed up by mechanics over the years and miles until they no longer work properly. Most points distributors are getting pretty sloppy in their dwell and timing stability by 125,000 miles. Pertronix conversion is an expensive but easy way to make a worn out points distributor run properly again rather than rebuild it.

A plugged or exceptionally lean idle or transfer system in the carburetor is not out of the question.



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1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited


Posted By: V8Mart
Date Posted: Jun/29/2019 at 5:59am
latest update....set initial timing back to 5, connected vac advance pipe to a spare port on the intake instead of carb, timing advanced to 20 at idle instantly , stumble reduced but not eliminated completely, stumbles when throttle is floored and sometimes results in a backfire through carb......too much advance perhaps?


Posted By: ChillyB
Date Posted: Jun/29/2019 at 7:28am
Sounds like it needs an accelerator pump.  If that doesnt solve it replace power valve.  


Posted By: V8Mart
Date Posted: Jun/30/2019 at 11:24am
Im thinking a distributor rebuild kit is needed, wheres a good source ?


Posted By: BassBoat
Date Posted: Jul/03/2019 at 5:40pm
My advice to increase the initial timing assumed that it would be set without vacuum advance.  Not uncommon to have 20-25 advance at idle with vacuum added.  Vacuum will be lower when you crack the throttle so you still may not have enough advance.  But I agree 100% a bad accelerator will result in a stumble when the throttle is moved even a little.  Good luck.



Posted By: purple72Gremlin
Date Posted: Jul/05/2019 at 1:13pm
How many miles on this 304? If its got over 70k, you can bet the timing chain will have slack.
And if the chain is worn, the 5 degrees will be too retarded. The factory settings is for emissions. I would not be afraid to advance it to anywhere from 8-12 degrees.....
But if you are going to leave it stock.....fix the advance and the acc pump in the carburetor. 
If you want better performance...then you can do a bit more. But be careful if you go past 14 degrees...some engines will crank hard with too much initial....  Im with Bassboat.


Posted By: purple72Gremlin
Date Posted: Jul/05/2019 at 2:02pm
Originally posted by V8Mart V8Mart wrote:

latest update....set initial timing back to 5, connected vac advance pipe to a spare port on the intake instead of carb, timing advanced to 20 at idle instantly , stumble reduced but not eliminated completely, stumbles when throttle is floored and sometimes results in a backfire through carb......too much advance perhaps?
If it backfired.....by by the power valve. But then it probably was gone anyway.  And sometimes you cant just buy the power valve alone for the motorcraft carburetor.....


Posted By: ChillyB
Date Posted: Jul/05/2019 at 5:45pm
Originally posted by purple72Gremlin purple72Gremlin wrote:

Originally posted by V8Mart V8Mart wrote:

latest update....set initial timing back to 5, connected vac advance pipe to a spare port on the intake instead of carb, timing advanced to 20 at idle instantly , stumble reduced but not eliminated completely, stumbles when throttle is floored and sometimes results in a backfire through carb......too much advance perhaps?
If it backfired.....by by the power valve. But then it probably was gone anyway.  And sometimes you cant just buy the power valve alone for the motorcraft carburetor.....

I'd think a stumble just as the throttle is applied is more likely acellerator pump than power valve?  But both are possible, and agree that a backfire can easily pop a MC2100 valve.  If carb hasnt been rebuilt in recent memory then do that.  Acellerator pump rubber gets stiff and develops pin holes.  Power valves are vulnerable to backfire.   


Posted By: V8Mart
Date Posted: Jul/06/2019 at 10:52am
I would like to remind all posters that my carb is virtually brand new...distributor looks very worn, cant find any suitable rebuild kits so will get a new or rebuilt distributor



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that is all


Posted By: purple72Gremlin
Date Posted: Jul/06/2019 at 10:58am
Originally posted by V8Mart V8Mart wrote:

I would like to remind all posters that my carb is virtually brand new...distributor looks very worn, cant find any suitable rebuild kits so will get a new or rebuilt distributor

Virtually new doesnt mean much.  If it backfired, you blew the power valve. And IIRC you can adjust the acc pump. By the way, how long did the carburetor sit on the shelf?  As it sits.......rubber and paper gets hard. 


Posted By: V8Mart
Date Posted: Jul/07/2019 at 1:25am
how do I know if power valve is bad, Had the carb apart to clean and all looks fine

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that is all


Posted By: mrblatzman
Date Posted: Jul/07/2019 at 7:54am
I have a good used distributor that I have had in storage for some time now...The number lists it as fitting a 1972 304 engine...Its dirty, complete with out cap, but should clean up and be fine...I ran across it while getting stuff ready for Saint Louis...I priced it at $35.00 if you or anyone else needs/can make use of it...I would install a new vacuum advance just as a routine thing...Bob in Fort Payne Alabama

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Thankyou....Bob


Posted By: ChillyB
Date Posted: Jul/08/2019 at 5:46am
Originally posted by V8Mart V8Mart wrote:

how do I know if power valve is bad, Had the carb apart to clean and all looks fine

Blown power valves continuously pass fuel.  You may see it running in the vacuum passages.  It'll be wet under the PV's circular steel cover.  Seems like you have a lean stumble during acelleration so I'm still suspecting the acellerator pump.   Could be an adjustment, or a leaking diaphragm, or a leaking/missing red rubber check valve.


Posted By: V8Mart
Date Posted: Jul/11/2019 at 9:46am
took power valve cover off and it was full of fuel. Removed power valve and found gasket very soggy and split close to vac port. Valve seems to seat and unseat ok , put new gasket on...vast improvement but still not perfect, still stumbles when mashed very hard from idle but does not die, a gentler approach with the throttle works fine .All looks ok with the acc pump valve and diaphragm, squirts fine, no cracks or splits 



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that is all


Posted By: BassBoat
Date Posted: Jul/11/2019 at 6:27pm
Holley carbs are fussy about the linkage adjustment for the accelerator pump.  You may already know the procedure, but if not familiar something you can check.  It kinda takes three hands to do it, but basically you hold the throttle wide open, then push on the pump arm (a small open end wrench is handy for this) to the max travel and then measure or set the clearance between the pump arm and the spring end of the arm that rides on the pump cam should be 0.015 inch.  When I read those instructions I admit it is confusing, and I have done it many times.  If the timing is advanced enough, and the pump linkage is set properly and you still have a stumble, you should try a larger shooter.



Posted By: PHAT69AMX
Date Posted: Jul/12/2019 at 3:29pm
Agree about the Holley Accelerator Pump and proper adjustment.
And if the Idle Speed screw is adjusted much, may have to readjust Accel Pump.
And watch out for the Accel Pump Arm that it DOES NOT ride on the
shaft mounted wound return spring instead of the plastic Accel Cam.
And the Metal Accel Pump Arms can get bent / tweaked out of original shape / contour.
Have also seen them "wore out" with a rough ditch worn into them on the cam end.
The black plastic Accel Pump Arms may seem kinda hoakey, but at least they can't get bent out of shape!


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Link to a http://www.youtube.com/watch?v=MySiKQsmWxU" rel="nofollow - Short YouTube Burnout Video



Posted By: ChillyB
Date Posted: Jul/13/2019 at 7:16am
So it was a stumble from a very rich condition that just got richer when you stomped on it.  Was exhaust making smoke and smelling of raw gas?  Plugs are probably dark, too?

Tough to diagnose via interweb.  I'd probably change plugs then read them after some driving.  You solved one over-fueling problem.  If someone tried to "tune out" a gasket leak maybe you are now lean.  Recommend reading new plugs and go from there.

I didnt read where you specified carb model.  One reply mentioned Holley but I didnt read where you stated carb make and model.  



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