401 Ignition Timing

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Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

401 Ignition Timing

Post by MReese Wagoneer »

So with the new 401

I have it idling at about 500 with vacuum line disconnected timing set at 10 deg
20 “ vacuum
I connect the vacuum line idle jumps up to about 700-800
Timing is about 25 deg
I’m inclined to think the distributor is bad as in not keeping consistent timing it jumps a bit

Main question is 25 deg normal at that 500 to 700 jump

Talk to me !!!


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New 83 Wagoneer Brougham
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letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: 401 Ignition Timing

Post by letank »

which source for vacuum are you using? if manifold, yes it will jump! if ported then your throttle plate is opened
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

401 Ignition Timing

Post by MReese Wagoneer »

Distributor is Ported from passenger side of the carb
Vacuum reading is manifold


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New 83 Wagoneer Brougham
old 99 Grand Cherokee Limited
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letank
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Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: 401 Ignition Timing

Post by letank »

MReese Wagoneer wrote: Sun Sep 13, 2020 7:55 pm Distributor is Ported from passenger side of the carb
may be the thermal control vacuum switch on top of the intake manifold -If you have one!-, that shift vacuum from manifold to ported vacuum has failed and you are defaulted to manifold vacuum. Plumb directly to either source and see how your timing is changing, or use a vacuum gauge to check the readings
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

401 Ignition Timing

Post by MReese Wagoneer »

letank wrote:
MReese Wagoneer wrote: Sun Sep 13, 2020 7:55 pm Distributor is Ported from passenger side of the carb
may be the thermal control vacuum switch on top of the intake manifold -If you have one!-, that shift vacuum from manifold to ported vacuum has failed and you are defaulted to manifold vacuum. Plumb directly to either source and see how your timing is changing, or use a vacuum gauge to check the readings
Nope straight from carb to dist.


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New 83 Wagoneer Brougham
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letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: 401 Ignition Timing

Post by letank »

MReese Wagoneer wrote: Tue Sep 15, 2020 6:43 am
letank wrote:
MReese Wagoneer wrote: Sun Sep 13, 2020 7:55 pm Distributor is Ported from passenger side of the carb
may be the thermal control vacuum switch on top of the intake manifold -If you have one!-, that shift vacuum from manifold to ported vacuum has failed and you are defaulted to manifold vacuum. Plumb directly to either source and see how your timing is changing, or use a vacuum gauge to check the readings
Nope straight from carb to dist.


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In that case the port is letting off vacuum at idle, the throttle plate might be a tad opened, I forgot which carburetor you have on that engine?
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

Re: 401 Ignition Timing

Post by MReese Wagoneer »

Edelbrock 1403


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New 83 Wagoneer Brougham
old 99 Grand Cherokee Limited
http://www.mandgoilandlube.com

Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

Re: 401 Ignition Timing

Post by MReese Wagoneer »

So in Facebook group, i have determined I need to check and fix too much vacuum on the ported port on carb, possible idle/butterfly plates open too far, i should have that much timing in it at that low/idle RPM
give it a few more degrees initial timing
Check vacuum advance on dist.
reset idle speed, timing
check full timing should be mid 30's
I will update, working on it tomorrow
tonight is wife's b-day dinner , cant miss that
:fsj:
New 83 Wagoneer Brougham
old 99 Grand Cherokee Limited
http://www.mandgoilandlube.com

letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: 401 Ignition Timing

Post by letank »

wild guess: too rich or too lean was my first idea... I would recheck all the specs for the main jet size then a search led me to the idle jet size ... as mentioned below:

https://www.tapatalk.com/groups/racingf ... t1513.html

You need to check the size of the idle jets. They are the pinch at the bottom end of the small tube hanging from the booster. It is common to find these carbs with two different size idle jets.

Another problem common to these carbs is the idle air bleed on top of the cluster is bashed partly closed, sometimes substantially so. It looks to me as if the machine tooling which inserts the main air bleed tube (brass tube pinched at the top pressed into top of cluster) tried to push it into the wrong hole.

Sometimes, the main air bleed tube orifices are different size.

Sometimes one (or both) primary emulsion tube gets pressed into the booster casting a little too far and the 'kill bleed' is blocked or partly blocked. In these carbs the kill bleed is drilled in the aluminum casting at an upward angle just above the inserted brass emulsion tube. The KB is probably .029" or .031", the smaller is preferred, but they both should be the same size.

Naturally, the float level and needle and seat size must be identical on each side.
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Topic author
MReese Wagoneer
Posts: 164
Joined: Wed Apr 10, 2019 8:14 am
Location: St Louis, MO

Re: 401 Ignition Timing

Post by MReese Wagoneer »

After a carb cleaning it seems to be running ton better
Image
Image


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New 83 Wagoneer Brougham
old 99 Grand Cherokee Limited
http://www.mandgoilandlube.com
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