Please Help! Ran perfect BEFORE I did work

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Nov 18, 2009 | 09:32 AM

#21

midlifemuscle

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Joined: Jan 2008

Posts: 99

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From: Chesapeake Virginia

Quote:

Originally Posted by weimer20

So WHY did you mess around with the carb and everything else? All that did was introduce a whole mess of other possibilities!

I suggest you find and read the paper that Lars did on timing and put your learning cap on before you go any further. You can keep shopping here for ideas or you can apply some logic and troubleshooting ability to solve the problem. Good luck and I hope you resolve the issue.

Used his timing sticky for my timing. Did the other stuff to rule out coincedental issues. Bottom line is that I did those things correctly because it runs the same now as before. I've used up my logic and ability - that's why I'm hitting you guys up for help!

Nov 18, 2009 | 10:25 AM

#22

mysixtynine

Burning Brakes

Joined: Dec 2008

Posts: 971

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From: Middlesex NJ

You know.... 13 inches of vacuum at idle at the manifold on a relatively stock engine seems to be too little to me? Almost indicative of a major vacuum leak.

My 509 with with a pretty big cam pulls 15 at idle.

I'm thinking you should be more like 18. Does anyone else think 13 at idle is too low for this motor.

Nov 18, 2009 | 10:58 AM

#23

ajrothm

Le Mans Master

Joined: May 2006

Posts: 9,993

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From: League City Tx

I think you still have a carb problem myself. Do you have anyone near by that can loan you a carb just for testing? Its one of two things, either the timing isn't coming in soon enough or the carb is jacked. Since you said the accelerator pump is working well, maybe the primary jets are just too small...but normally that would cause a lean condition through out the powerband, not just off idle. I would look into the accelerator pump circuit again...might need a bigger cam on the accelerator pump.

Nov 18, 2009 | 11:10 AM

#24

Matt Gruber

Race Director

Joined: Oct 2000

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From: central FL, near the beach.

Quote:

Originally Posted by Matt Gruber

that causes a bog. 4

do a quick test at 16 base.
just prove it fixes it, don't drive any distance.
(then alter the stop later)

did u try 16 base timing?

Nov 18, 2009 | 11:55 AM

#25

Matt Gruber

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Joined: Oct 2000

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From: central FL, near the beach.

Quote:

Originally Posted by Matt Gruber

did u try 16 base timing?

u can't add headers and expect to run a stock tune.

Nov 18, 2009 | 02:56 PM

#26

mandingo214

Racer

Joined: Jan 2006

Posts: 323

Likes: 4

From: McKinney Texas

Quote:

Originally Posted by midlifemuscle

I completely agree with your logic that the initial work I did caused the problem

The distributor is set for about 16 degrees of centrifical advance (no vacuum advance). At idle, I'm running about 24 degrees which would indicate that I'm getting about 4 degrees of advance at 700 rpm. Sounds right to me - your thoughts?

I think I understand what you are saying: You have total timing of 36 degrees at 3000rpm, 16 degrees of which is mechanical. At idle when there will not be any mechanical advance, your timing light is showing 24 degrees of advance. So 36 minus 16 is 20, but since you have 24 you are saying you have dialed in another 4? It does not work that way, if that is what you are saying.

Now that I am clear that you do not have a vacuum advance, it appears to me that you have 24 degrees of advance at 700rpm based on distributor position, and 12 degrees of total mechanical advance coming in at 3000rpms to give you the 36 total advance.

24 is too much at idle, but if you back it down you will not have enough total advance.

Though the car will not run as well at midrange rpms, try what Matt Gruber says, just to see if it fixes the stumble.

It is strange that it ran fine with these settings before.....are you pretty confident you got the distributor set back to TDC?

One other item: The guy I bought my '74 from had the 6 and 2 spark plug wires switched. It ran OK, but had a "little bit" of a miss. Could be something that easy.

Nov 20, 2009 | 05:40 PM

#27

midlifemuscle

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Joined: Jan 2008

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From: Chesapeake Virginia

Got it there today without much change. Still not pinging - should I keep going?

Nov 20, 2009 | 08:15 PM

#28

thoyer

Melting Slicks

Joined: Sep 2005

Posts: 2,712

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From: Warminster PA

Does it happen just under load or can you duplicate the problem by "blipping" the throttle? If it happens while parked then it should be a bit easier to troubleshoot since you don't have to drive it to see if you fixed the problem.

Try advancing your timing a bit while blipping the throttle and see if the hesitation is less. Watch though, because advancing the timing will increase the idle and may mask the issue.

The vacuum does seem a tad on the low side. Get a vacuum gauge and use it to set the idle mixture screws. Adjust the screws for max vacuum while getting a good idle. Make sure the throttle is closed enough so you are running on the idle circuit.

I don't know much about the avenger carb, but most Holleys have a cam on the throttle shaft that works the accelerator pump. You may try experimenting with that cam

Bottom line, I would verify that the timing is set correctly first, get the initial timing set properly, you can worry about the "all in" part later and adjust that with the weights.

Check for vacuum leaks and adjust mixture with gauge.

Then go after the carb.

Maybe try a different distributor with vacuum advance, I was never a big fan of a mechanical advance only dist for a street car.

Good luck.
Tom