I need Help ! 6 pack

[D575]

I need help. this is what I have, car had a small vac. leak at the manifold
so I changed the pan and sealed it up real good, at the same time I blocked off the heat riser. it's a six pack car . it runs like a raped ape. except when I do a long downshift to a stop. then the idle goes away and wants to die. a quick blip of the gas and it's idling again. any ideas ? float level is good . mixture is good, great color on the plugs. would too low a power valve cause this ? when I had it apart I checked the power valve and it was good. I had 8 inches of vacuum . now it's 11. I believe it's a 4.5 PV I'm going crazy trying to figure this out..

 

[63BlackMax]

Sounds like you may have a distributor with advance springs that are too light and will not return the weights back to the stop (Home Position) once they have advanced out all the way. Your downshifting is creating a situation where they close back all the way and you lose your initial timing and the engine wants to die.

If you check your timing and have a dial back to zero timing light you can check you initial timing setting at idle. (disconnect your vacuum advance hose and plug it so you don't cause a vacuum leak) when setting your initial timing. Then run your ungine up in steps adding 500RPM per step. Log all timing advance readings and RPM and create a graph line of your advance curve. Take it up to 3000 rpm. when you get there blip the throttle lightly and see if your get anymore advance. Let it settle back to idle and record the timing reading again. See if it changes and has less than your 1st check. Sometimes if you just blip the throttle you can get the advance springs to close all the way and your idle speed will drop drastically causing the engine to almost die.

If this happens you need to take a look at your advance springs advance weights and see what's going on there. I've seen it too many times where this issue is related to distributor mods made trying to get the advance "all in" as quickly as possible to improve accelleration, and not being done properly, causing a situation much like you are describing.

If not, then I'd check the fuel / Float levels etc.


Good Luck

63BlackMax

 

[63BlackMax]

Sounds like you have too light weight of Distributer advance springs. They will not return the Advance weight back to the Home (Stop) after acceleration. Whatever you are doing by downshifting is causing the advance weights to return to the stop /home position and your are losing your Idle timing to the point the engine wants to die.

Check or have someone who is familiar with distributors check and see if that is the cause of your problem. You can use a Dial Back to Zero timing light and do it yourself, just remember to disconnect the vacuum advance line and plug it when setting your timing as you don't want that to interfere with your reading / settings.

I've seen it too many times when someone puts light weight advance springs in a distributor to improve performance by getting the advance "All In" as quickly as possible, and doesn't set the distributor up properly, so they get advance at idle and the weights won't return to Home /Stop position until you Blip the throttle hard enough and quickly enough that the weights pull back all the way and your engine will barely idle or dies.

Worth looking into this to sse if it is the problem.

Good Luck,

63BlackMax

 

[D575]

Sounds like you have too light weight of Distributer advance springs. They will not return the Advance weight back to the Home (Stop) after acceleration. Whatever you are doing by downshifting is causing the advance weights to return to the stop /home position and your are losing your Idle timing to the point the engine wants to die.

Check or have someone who is familiar with distributors check and see if that is the cause of your problem. You can use a Dial Back to Zero timing light and do it yourself, just remember to disconnect the vacuum advance line and plug it when setting your timing as you don't want that to interfere with your reading / settings.

I've seen it too many times when someone puts light weight advance springs in a distributor to improve performance by getting the advance "All In" as quickly as possible, and doesn't set the distributor up properly, so they get advance at idle and the weights won't return to Home /Stop position until you Blip the throttle hard enough and quickly enough that the weights pull back all the way and your engine will barely idle or dies.

Worth looking into this to sse if it is the problem.

Good Luck,

63BlackMax

I'll check, It's weird that it just started out of the blue, thanks for your input..

 

[lewtot184]

float level is too low on the end carbs or the idle mix is too lean.

 

[D575]

float level is too low on the end carbs or the idle mix is too lean.

could be too lean. I was trying to get the plugs to burn cleaner... it's raining now, I can't go out and check it.. :angryfire:

 

[lewtot184]

could be too lean. I was trying to get the plugs to burn cleaner... it's raining now, I can't go out and check it.. :angryfire:

if you look carefully at the float bowls on the end carbs you'll notice the site plug is lower than on the center carb. what holley did was take a secondary float bowl from a 4bbl carb, turn it around backwards and mount it on the end carbs. the lower float setting for the 4bbl carb keeps fuel from sloshing thru the boosters at hard stops. a hard stop with the lower float level on the end carbs lets fuel rush away from the main metering orifices in the metering plates exposing them to air rather than fuel. this results in a momentary lean condition and stall. bad part is the fuel levels can't be raised to the level of the center carb because the metering plates don't like the higher fuel level. what i always done was bring the level in the end carbs up to the bottom of the site hole plus about 1/8 turn; other wise a slight trickle out. make sure the mixture screws in the end carbs are about 3/4 out.

 

[D575]

if you look carefully at the float bowls on the end carbs you'll notice the site plug is lower than on the center carb. what holley did was take a secondary float bowl from a 4bbl carb, turn it around backwards and mount it on the end carbs. the lower float setting for the 4bbl carb keeps fuel from sloshing thru the boosters at hard stops. a hard stop with the lower float level on the end carbs lets fuel rush away from the main metering orifices in the metering plates exposing them to air rather than fuel. this results in a momentary lean condition and stall. bad part is the fuel levels can't be raised to the level of the center carb because the metering plates don't like the higher fuel level. what i always done was bring the level in the end carbs up to the bottom of the site hole plus about 1/8 turn; other wise a slight trickle out. make sure the mixture screws in the end carbs are about 3/4 out.

Nice !,, good to know

 

[Meep-Meep]

Do you have the idle solenoid? That long arm on the center carb throttle lever has a screw that contacts an idle solenoid and it's purpose is to prevent dieseling. In my experience those repo solenoids are not very consistent in keeping an idle. Try setting idle with carb stop screw and see of problem goes away.

 

[D575]

Do you have the idle solenoid? That long arm on the center carb throttle lever has a screw that contacts an idle solenoid and it's purpose is to prevent dieseling. In my experience those repo solenoids are not very consistent in keeping an idle. Try setting idle with carb stop screw and see of problem goes away.

I do have an Idle solenoid, but I'm not using it. you are right, very inconsistent and if you let off the throttle too fast it would just drop right off..

 

[D575]

if you look carefully at the float bowls on the end carbs you'll notice the site plug is lower than on the center carb. what holley did was take a secondary float bowl from a 4bbl carb, turn it around backwards and mount it on the end carbs. the lower float setting for the 4bbl carb keeps fuel from sloshing thru the boosters at hard stops. a hard stop with the lower float level on the end carbs lets fuel rush away from the main metering orifices in the metering plates exposing them to air rather than fuel. this results in a momentary lean condition and stall. bad part is the fuel levels can't be raised to the level of the center carb because the metering plates don't like the higher fuel level. what i always done was bring the level in the end carbs up to the bottom of the site hole plus about 1/8 turn; other wise a slight trickle out. make sure the mixture screws in the end carbs are about 3/4 out.

You were right, I raised the float level on the end carbs and it went right away. Thank you so much. I owe you a Beer. ccasion14: