Idle issues

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k3522

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Recently purchased a 1969 Dart Custom in great condition from a very honest person. He did great work. It has a 360 with a cam and AVS carb with manual choke. The good is from take off to any speed it runs great.The only drive issue is slight surging at low RPMs in drive at 55 mph.

The problem is idle at 1000 rpms is troublesome and when idling at this speed putting in to drive or reverse can stall it. The new TTI header have some discoloration which may indicate lean or rich, but it run great. WHAT DO I DO TO SOLVE IDLE.
Retard timing, decrease vacum advance, lean idle screws, buy a new carb?
 
If you "do" have a large cam, maybe you could find out if the torque convertor was ever changed before as well to match-up with your size of cam. If still stock convertor, you may want to swap to a higher stall. This will/should allow you to idle without stalling the engine. Anyone agree..or not agree.
 
on the converter? Yes if the cam has too much overlap then a looser converter is needed, ie if you motor is loping at idle when you drop into gear it should not change the motor RPM for that same car a foot brake may let the motor spin up to 3,000 rpm before the converter pervents the motor from spinning faster.
 
In most cases a bigger cam requires more intial advance, especially if the motor still has the stock low compression. Try advancing the intial timing to 12-15 degrees before top dead center.
 
My cam could be a step too high. The prior owner changed the converter to a 2300-2500 stall and rebuilt the 904 tranny recently. I think the higher convert was put in to help the idle and help matchthe cam and since he had it out he rebuilt the tranny again. The motor was rebuilt 1500 miles ago and runs great. I hate to drop the cam.

Could I lean the idle or back off the timing to help with idle? When I put it in gear it drops from 1100 rpms to about 700. The new TTI ceramic coated headers have some slight blueing which may indicate it is running a little rich, but the plugs look good.
 
k3522 said:
Recently purchased a 1969 Dart Custom in great condition from a very honest person. He did great work. It has a 360 with a cam and AVS carb with manual choke. The good is from take off to any speed it runs great.The only drive issue is slight surging at low RPMs in drive at 55 mph.

The problem is idle at 1000 rpms is troublesome and when idling at this speed putting in to drive or reverse can stall it. The new TTI header have some discoloration which may indicate lean or rich, but it run great. WHAT DO I DO TO SOLVE IDLE.
Retard timing, decrease vacum advance, lean idle screws, buy a new carb?
Click to expand...
My cam could be a step too high. The prior owner changed the converter to a 2300-2500 stall and rebuilt the 904 tranny recently. I think the higher convert was put in to help the idle and help matchthe cam and since he had it out he rebuilt the tranny again. The motor was rebuilt 1500 miles ago and runs great. I hate to drop the cam.

Could I lean the idle or back off the timing to help with idle? When I put it in gear it drops from 1100 rpms to about 700. The new TTI ceramic coated headers have some slight blueing which may indicate it is running a little rich, but the plugs look good.
 
I would advance the timing not retard it. see my orignal note. Advancing the timing should allow you to back down the idle speed.

Also, if the PO had put the mopar performance performance advance kit in the distributor it is likely starting to advance at 1000 rpm. You need to check that it's not advancing until the rpm are up to 12-1300 rpm. If it is you will have all sorts of trouble getting it to idle and go into gear. Because; you drop it into gear the rpm's drop causing the timing to back off which causes the rpm to drop more, hence the stalling.

The steps to follow are;

1. turn the idle down to 800 or so and using a timing light verify that you get no mechanical advance until 12-1300 rpm. NOTE: vacuum advance should be disconnected. If you are getting advance then you will need to rework the curve in the distributor.
2. If you pass 1 then using a vacuum guage start advancing the initial timing in 2 degree increments watching for peak vacuum. NOTE: turn the idle back down to you starting point. If you start getting past 15 degrees BTDC then you need to stop the engine an make sure that it still starts OK without fighting back agains the starter. Also, past 15 degrees you will need to worry about total advance. Unless you have access to a dyno to tune to no more than 35 degrees total is the rule of thumb. More than a couple degrees past this will require reworking the distributor to limit timing.
3. plug in the vacuum advance, you should see no change in the timing at idle.

When a cam is changed the initial timing requirements the engine needs change too. This is the process for determining what the car wants for initial timing.
 
I have always been told for performance on a engine, I mean one that is taken to the track every once in awhile and may see cruise night. You should only set total timing. This is not for the daily driver,and gas mileage. this is the only way to get a honest timing reading. Start the car let it get to operating temp, the adjust the idler screw till you reach 2000 rpms. IT should reach total timing at this piont. with the timing light on press the throttle lever. See if it advances anymore. IF it dose not now you can set your total timing to 35*. then return the car back to normal idle. This should be the all out best spot for performance. :thumblef:
 
35 degrees is a good ballpark number and 2000 rpm is to low for most engines that are driven on the street, 2500-3000 is a better number for a street driven vehicle. You need a dyno to fine tune when the timing is all in and total timing to obtain max power.

However, just setting the total timing with out getting the intial timing dialed in can result in idle and off idle driveability problems. Initial timing you can dial in with a vacuum gauge.
 
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