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Username Post: Car missing under acceleration/load        (Topic#368344)
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-05-22 08:27 AM - Post#2840733    

I know another one of these threads but looking for some more clues.

So I far this is what I have done and most of the issues that I was having have been resolved.

Car was originally dying/stalling coming off of idle to throttle...like leaving a stop or even from a roll when transitioning off no pedal to part throttle. This issue was after rebuilding the Rochester 4Jet/GC carb.

I think what ultimately resolved it was after researching this site and 348-409 I found some info pertaining to the idle adjustment screws not being adjusted properly. I found that the screws were 2 1/2 turns out. I turned them back in and reset the idle and screws to 1.5 turns out. Now the hesitation/stall is gone...runs great except for one now missing under load.

When I uncovered the car after sitting for 30 years, I did not replace the entire distributor, but did replace the:
points, condenser, rotor, cap, wires, and plugs.

I hooked up a mity vac to the vacuum advance on the distributor, and with the engine running and a timing a light, I applied vacuum with the hand pump and observed the timing. Not sure how much vacuum it takes to make the advance work, but it took around 26" of vacuum for the timing to increase, and it only increased about 3* at idle. Went from 6* to 9* once I applied vacuum to the advance. Might be correct considering it was only idling?

I set the dwell to 27, and the timing is the 1/2 way mark at 5*, I found that if it is at 6* it is pinging, I set it to 5* (1/2 way mark on the pointer) and it is better but I still heard a little ping for a second or too. So I might set the timing at 4*...car is a 409 Auto BTW.

When I gas it kicks down but as starts to pull/accelerates it acts like it could be starved for fuel, but I'm still convinced it is just missing as once it picks up through the rpm range it starts to get better. Other than that the car starts, comes off idle, and cruises well unless mid/upper throttle is given under load. I hadn't just replaced the plug wires I would be convinced it was a bad wire arcing.

I was wondering if the advance is working and or if the weights in the dizzy are not moving freely enough...if that would cause the issue it's having?

I was also wondering if a fuel pump could cause a similar issue? However I don't see any leaks around the pump, and I can see plenty of fuel in the filter bowl and clear plastic filter going to the fuel pump when the car is running.

Thoughts?



2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


Edited by Shinobi68 on 05-05-22 08:30 AM. Reason for edit: No reason given.

 


Tony1963 
Frequent Contributor
Posts: 1286

Loc: Orlando Florida
Reg: 07-09-18
05-05-22 08:47 AM - Post#2840734    
    In response to Shinobi68

Once the throttle moves to above idle, the idle mixture screw does not control the mixture. The other passage ways feed fuel.

Cutting out under load is either lack of fuel or the ignition system failing. I'd be checking for fuel first.



 
55Brodie 
Contributor
Posts: 393

Age: 70
Loc: Little River, SC
Reg: 12-26-15
05-05-22 08:53 AM - Post#2840735    
    In response to Shinobi68

Dwell should be 30° and timing should be 6° BTDC.



 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-05-22 09:54 AM - Post#2840739    
    In response to 55Brodie

The range states 28-30 on the tune up spec sheet for a '64 409 340 hp, new points .019, used .016-point gap. Since I used new points, I initially set at .019, with the dwell set at 30 and new points it was advancing the timing too much at 6*, so I took the dwell back down to the bottom of the dwell angle range and re-timed it as the dwell effects the timing...thus why having to time after setting dwell. I noticed some other 409 Auto owners were setting to 27-28* at 4-6* timing. Every car is a little different. All I know is that if I set the dwell to 30 and the timing to 6* it's ping city under load. So I'm using the older method to adjust timing, which is raise timing until it pings and then back off, but reverse which is too retard the timing until it doesn't ping.

I guess I will need to get a new fuel pump or find a fuel pump pressure tester.

I'm also considering a Pertronix dizzy that uses the stock cap and coil. Have to research what people's opinions are on those.

Thanks

2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


Edited by Shinobi68 on 05-05-22 09:55 AM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5352
Mel Foye
Reg: 09-29-00
05-05-22 12:12 PM - Post#2840744    
    In response to Shinobi68

It is your dist and settings. I suspect weights are dirty and not lubed. Pretty sure your vac unit is bad so replace. Agree that 30 degree of dwell is right on. I would go initial 12 - 14 b4tdc, cent be 22-24 and I like the little cushion of 34 and all in by 2,800-3,000. Vac advance about 8 -14 degrees at idle.
This should get you in the ballpark.
With a light load the idle circuit can still be impacting the A/F mixture at 30-40 mph.



It Was On Fire When I Laid Down.


 
Shepherd 
Valued Contributor
Posts: 2554

Loc: Lake George, NY
Reg: 11-11-15
05-05-22 12:47 PM - Post#2840746    
    In response to Mel Foye

Mel, again on the money.



 
turbo38s10 
"11th Year" Gold Supporting Member
Posts: 2004
turbo38s10
Loc: Agawam,MA
Reg: 09-17-09
05-05-22 01:21 PM - Post#2840748    
    In response to Shepherd

i'VE USED THE PERTRONIX AND HAD REALLY GOOD EXPERIENCE WITH IT. jUST REMEMBER TO USE THE HIGH OUTPUT COIL WITH IT. tHE STOCK COIL WILL NOT WORK WELL. wITH THAT SAID i AGREE WITH ABOVE SAYS YOUR VACUUM ADNAVE ISN'T WORKING AND YOUR SPRING AND PLATES MIGHT BE STOCK OR DRAGGING. i LIKE NOT HAVING TO MESS WITH THE POINT ANY MORE.



 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-05-22 03:53 PM - Post#2840758    
    In response to Mel Foye

Thanks, I kept questioning myself on the weights and how long they have been sitting in the dizzy. Do you recommend getting a new distributor? Or should I just order a new vacuum advance and weights/springs..assuming they are just drop in?

I think the distributor (shaft) is probably the original one too.


2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


 
Trailbum 
Member #727 Longest Supporting Member "22nd. Year"
Posts: 2122
Trailbum
Age: 63
Loc: Woodland Park, CO
Reg: 11-06-00
05-06-22 04:27 PM - Post#2840793    
    In response to Shinobi68

Those distributors are pretty easy to overhaul. Mine hadn't been out of the car in 50 years!!
I picked up this distributor kit from Ebay, plus installed a new vacuum advance when I reassembled it!! Works great now!!
https://www.ebay.com/itm/254718157518?_trk parms=am...

"They say men should get in touch with their feminine side.... Well, if I HAD a feminine side.. believe me, I'd be TOUCHING IT!!!"


 
bobb 
Super Senior Member
Posts: 5999

Loc: paradise
Reg: 09-05-03
05-07-22 10:02 AM - Post#2840831    
    In response to Shinobi68

do not use dwell to change timing. i believe 30 is a better choice but not sure. do not get stuck on timing numbers and marks. the marks could be off. set it where it runs best and keep notes. vacuum advance will not affect performance, just cruise speed timing. so you need to know cruise speed vacuum to get the right vacuum can. centrifugal advance on a stock distribitr normaly have springs that are too stiff for a performance application. i would compression test to make sure there is no ghost to chase. and as noted the idle mixture screws may have an affect too.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


Edited by bobb on 05-07-22 10:05 AM. Reason for edit: No reason given.

 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-10-22 12:53 PM - Post#2840976    
    In response to Mel Foye

  • Mel Foye Said:
It is your dist and settings. I suspect weights are dirty and not lubed. Pretty sure your vac unit is bad so replace. Agree that 30 degree of dwell is right on. I would go initial 12 - 14 b4tdc, cent be 22-24 and I like the little cushion of 34 and all in by 2,800-3,000. Vac advance about 8 -14 degrees at idle.
This should get you in the ballpark.
With a light load the idle circuit can still be impacting the A/F mixture at 30-40 mph.



I looked at the distributor and cleaned up the parts, should I replace the springs too? Do they get weak? I found a vacuum advance to replace the old one.

One thing I noticed on the Rochester 4GC is that the front vacuum line is called spark advance, which I'm assuming is "ported vacuum". What's different about this is that there is vacuum on it at idle. On my Fords the ported vacuum has no vacuum at idle and then when you give it the gas it registers vacuum.

I hooked up a vacuum gauge to the spark advance on the Rochester 4GC and it has vacuum at idle. When I disconnect the vacuum and set timing to 6* BTDC or ever 3* it pings after I hook back up the vacuum advance and test drive. Also when I hook back up the spark advance to the vacuum advance after setting initial timing, when I recheck the timing it is 12* at idle with vacuum advance connected. So there is vacuum on the spark advance hole all the time...vs. other ported vacuums that don't have any vacuum on them at idle.

I'm going to order a new vacuum advance as you suggested. Just wanted to point out some other observations. Other than that the car runs and idles great...no smoke....just pings when I start to pull though the mid rpm range...and then I lift once I hear any pinging so I don't damage the motor or blow a head gasket.

2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


 
Shepherd 
Valued Contributor
Posts: 2554

Loc: Lake George, NY
Reg: 11-11-15
05-10-22 02:21 PM - Post#2840983    
    In response to Shinobi68

On acceleration using manifold vacuum there is no vacuum advance being activated as a rule, look at your mechanical advance timing as mentioned, at the rpm it rattles, may be over advanced. Try it with the vac advance disconnected also.




 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-10-22 02:26 PM - Post#2840984    
    In response to Shepherd

so set the timing to 6* and plug off the vacuum connection?

2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


 
Shepherd 
Valued Contributor
Posts: 2554

Loc: Lake George, NY
Reg: 11-11-15
05-10-22 03:00 PM - Post#2840987    
    In response to Shinobi68

Yes, see if it pings under load. You need a set back timing lite or a degreed damper to check the mechanical advance at a given rpm.



 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-10-22 08:30 PM - Post#2841004    
    In response to Shepherd

Ok found my grandfather's MAC Tools Dwell Machine in a cabinet in back of his garage, hooked it up and set the dwell to 30, re-timed the dizzy to 6* btc with the vacuum advance disconnected and plugged. Car drives way better but starts missing...but no pinging at all. I think we can confirm the vacuum advance (as mentioned by Mel) needs to be replaced. Points, Cap, Condenser, Rotor, Plugs, Coil, and Wires are all new. Idles at 750-800 rpms in park.

Thanks

2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


Edited by Shinobi68 on 05-10-22 09:01 PM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5352
Mel Foye
Reg: 09-29-00
05-15-22 08:31 PM - Post#2841242    
    In response to Shinobi68

Sorry guy but I got off track. Where are you now with the the car? My numbers maybe too aggressive on the car?
If not too late shoot for stock timing.
Two hours of search left me with ONLY these: 64 409/340 Plugs AC43N--.035, 28-32 dwell. 19 new 16 old points. 6 degree BTDC on 64 and 10 BTDC on 63 340 and 10 to 1 on 64 CR. I came up with ZERO info on mech adv. Also ZIP on vac adv.specs.
Maybe someone has an old magazine that has info.



It Was On Fire When I Laid Down.


 
Shinobi68 
Silver Supporting Member
Posts: 48
Shinobi68
Reg: 09-28-21
05-16-22 09:23 PM - Post#2841314    
    In response to Mel Foye

I used the Tune Up Specs from the Shop Manual linked to this site/above.

I set the dwell to 30*, plug gap to .035, timing with vac disconnected to 6* BTDC. I currently do not have the vacuum advance hooked up, but plan to hook it back up. The PG started slipping after sitting for 30 years the rubber seals must have gotten old and are losing pressure. I thought it was from me letting it idle in Park while adjusting the timing, but the tranny shop said that they didn't think that would do it. I did explain that it states not to idle in Park but to idle in Neutral if idling for prolonged time.

I drove the car 45 miles to the tranny shop, and it runs good but I couldn't lay into it to see if it would ping like it was with the tranny slipping on the upshift.

What I do find interesting is that the Spark Timing Port on the front/right (passenger) side of the Rochester 4GC always has vacuum. Most other carbs have no vacuum on the Spark/Port vacuum at idle, and when the rpms come up so does the vacuum advance for the low to mid rpms off idle or part throttle.

So for now I have the car timed at 6* BTDC with the spark port vacuum disconnected, and I set the dwell to 30* prior to adjusting the timing.

2021 Tesla Plaid
2020 (C8 traded in on Plaid)
2017 C7Z06 (850hp)
1991 Camaro Z28
1966 Mustang
1964 Impala SS 409


Edited by Shinobi68 on 05-16-22 09:24 PM. Reason for edit: No reason given.

 
japete92 
"8th Year" Silver Supporting Member
Posts: 2002
japete92
Loc: No. Virginia
Reg: 01-18-13
05-17-22 06:24 AM - Post#2841332    
    In response to Shinobi68

  • Shinobi68 Said:
I used the Tune Up Specs from the Shop Manual linked to this site/above.

I set the dwell to 30*, plug gap to .035, timing with vac disconnected to 6* BTDC. I currently do not have the vacuum advance hooked up, but plan to hook it back up. The PG started slipping after sitting for 30 years the rubber seals must have gotten old and are losing pressure. I thought it was from me letting it idle in Park while adjusting the timing, but the tranny shop said that they didn't think that would do it. I did explain that it states not to idle in Park but to idle in Neutral if idling for prolonged time.

I drove the car 45 miles to the tranny shop, and it runs good but I couldn't lay into it to see if it would ping like it was with the tranny slipping on the upshift.

What I do find interesting is that the Spark Timing Port on the front/right (passenger) side of the Rochester 4GC always has vacuum. Most other carbs have no vacuum on the Spark/Port vacuum at idle, and when the rpms come up so does the vacuum advance for the low to mid rpms off idle or part throttle.

So for now I have the car timed at 6* BTDC with the spark port vacuum disconnected, and I set the dwell to 30* prior to adjusting the timing.




You may find the info provide here helpful:

https://www.chevelles.com/threads/ignition-101.189...

When connecting the vacuum advance, make sure the 'port' is below the throttle plates. That will connect you to the 'full' manifold vacuum.

Pete




 
turbo38s10 
"11th Year" Gold Supporting Member
Posts: 2004
turbo38s10
Loc: Agawam,MA
Reg: 09-17-09
05-17-22 08:04 AM - Post#2841337    
    In response to japete92

I think later year they went to ported vacuum for emissions reasons. Ours should hbe in a full vaccuum
port as stated above.



 


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