Engine slowly leans out and dies out at traffic lights

Hey guys. I have an issue.
When sitting at a traffic light yesterday I noticed my engine slowly dropping in rpms and then sputtering trying to die. I gave her a little gas and that fixed it for about 10 seconds and then it did the same thing. The AF ratio gauge showed it leaning out as the rpms dropped.
What does this sound like to you guys?

I'm running a summit 600 cfm carb and have no issues at all other than this.

Thanks guys.

Hi, What is idle RPMS? check idle mixture screws, float level, fuel filter, just basic stuff first. Could be worn out points in the distributor. Good luck

I'd go with the float level/needle valve check as suggested.

69stang_250":ujhggyi9 said:

Hey guys. I have an issue.
When sitting at a traffic light yesterday I noticed my engine slowly dropping in rpms and then sputtering trying to die. I gave her a little gas and that fixed it for about 10 seconds and then it did the same thing. The AF ratio gauge showed it leaning out as the rpms dropped.
What does this sound like to you guys?

I'm running a summit 600 cfm carb and have no issues at all other than this.

Thanks guys.

Click to expand...

interesting that seems to point to a lack of fuel volume at idle or else a vacuum leak. Good luck in the hunt.

So I got to messing with it, and it does it once the electric fans kick on, but only when the engine has been running for a while. idle is set at 1050 with 12.7 - 13.5 AF ratio, I have checked, double checked, and triple checked and have not found any vacuum leaks anywhere. The fuel level is dead center on both primary and secondary's. fuel pressure is 5.5.
I assuming that the engine can't run at 950 rpms with the cam I have installed? I don't know if that is the case, but have read that the 280/280 110* should idle between 1000-1100 rpms.
Is there anything I can do to get the engine to compensate for the load of the electric fans?

Hi, how are the fans wired in. They should be on a relay, with a heavy gauge wire, fused, near the battery. Good luck

69stang_250":29noytnm said:

So I got to messing with it, and it does it once the electric fans kick on, but only when the engine has been running for a while. idle is set at 1050 with 12.7 - 13.5 AF ratio, I have checked, double checked, and triple checked and have not found any vacuum leaks anywhere. The fuel level is dead center on both primary and secondary's. fuel pressure is 5.5.
I assuming that the engine can't run at 950 rpms with the cam I have installed? I don't know if that is the case, but have read that the 280/280 110* should idle between 1000-1100 rpms.
Is there anything I can do to get the engine to compensate for the load of the electric fans?

Click to expand...

Yes this would be a much different problem and its possible causes. X2 how are the fans wired? Assuming duel fans, Is there a temp control that stages when one fan kick on or do they both come on at once? You could use a AC throdle switch to raise engine RPM enough so that the electrical load dosent drag the engine down so much. But in my opion this maybe causing your Ignition System to not have enough power to operate correctly (Loseing Voltage) to keep it running at your idle speed when the fan or fans kick on. A good way to test that theory is to mount a Battery Voltage gauge to see if the voltage is dropping during those times when fan or fans are working. Lastly what size alternator are you using? Maybe it's a bit too small of capacity for your needed power requirements especially at your idle RPM when the fan load kicks in. Good luck

Ok, so I raised the idle speed up and it does drop in rpms enough to kill it now.
It is the duel ford contour fans with a flex a lite fan controller. There is a place to hook up an AC throttle switch.
I will look into one of those.
The Alternator is a 140 AMP with only about 60-80 AMPS drawn with everything equipped right now.
Who should I look at for that kick up switch?

Make sure the fan is hooked up to power via a relay then fused to the fans.
Check battery voltage when fans kick in. You may have to install a smaller alternator pulley.
Might pay to remove the alternator & have it bench tested for diode problems & also amps it produces at all rpms.
Also have your battery tested for proper output.
A lot of people are not aware there is a difference in battery construction depending where you live.
For example a battery purchased above the Mason Dixon line have thinner plates but more of them & the specific gravity is also higher for cold weather.
Batteries made for the south have less plates but are thicker in construction to with stand the heat. The specific gravity of the acid is also less.
Two things kill batteries, cold & heat. Not related to your condition, but just general info.

What is the initial ignition timing with the vacuum advance disconnected and a very low idle rpm?

The reason for asking is: the 280/280 cam requires a lot of initial timing.
If the initial timing is not enough then the load put on the alternator by the fans will load the engine enough to stall it when you come to a stop.

I would check fuel level in the carb right after it dies. You might have a pinhole leak in a fuel line sucking air.

So the issue is the electric fan. I have a throttle solenoid on order and should be here tomorrow so I can fix this issue.
I' send y'all some pic of the install.

Ahhh…electrics.

I wuz thinkin 'fuel' 2...

How is a throttle solenoid going to fix that issue? Sounds like you need a relay w/ battery source power switched to the fan using your current control/fan power wiring? The fan is robbing the ignition of power? I've heard of this happening.