Stalls when coming to a stop (1 Viewer)

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Feb 28, 2022
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Location
Austin, TX
I'm reading in circles and hoping someone can suggest a few next steps. My 40 stalls when coming to a stop. Original F 155 with original Aisan carb. It drives great. Vacuum holds steady around 17 when idling. I hear the clicking of the idle solenoid with the turn of the key. Fuel is near the top of the sight glass so if anything I need to lower the float.
I do have a brake booster.
I think if I were to increase the idle speed using the idle adjust screw it wouldn't stall but that would leave my idling way too high.
Another old thread mentioned to sit the idle stop screw deeper to prevent the butterfly from snapping shut. Is the "idle stop" screw different from the idle speed screw?
I've tuned the carb using the lean/drop and using the steps in the manual - drives great both ways but continues to stall when stopping unless I keep a bit of throttle on it.
All thoughts and ideas welcome -- Thanks!
 
Year? Does it happen stopping, or on a down hill? You can pinch off booster and see if that makes a difference (in a parking lot or something, stopping power should be much reduced- like when you coast down hill with engine off in your driveway)

My idle solenoid (aka fuel cut solenoid FCS) worked intermittently. Put 12volts on it direct and confirm it works good. Assuming there is no ECC? that can effect the FCS

Fully inspect and clean everything you can when you adjust float, jets, plunger seals, all orofices. I used wood shims and calipers to measure clearance on the valve and float (not having recommended measuring thingy on hand).

Inadequate fuel pressure could be another culprit. Replace filter, inspect lines for leaks, replace or inspect/test fuel pump. How is your gas? New, clean, and clear?
 
Year? Does it happen stopping, or on a down hill? You can pinch off booster and see if that makes a difference (in a parking lot or something, stopping power should be much reduced- like when you coast down hill with engine off in your driveway)

My idle solenoid (aka fuel cut solenoid FCS) worked intermittently. Put 12volts on it direct and confirm it works good. Assuming there is no ECC? that can effect the FCS

Fully inspect and clean everything you can when you adjust float, jets, plunger seals, all orofices. I used wood shims and calipers to measure clearance on the valve and float (not having recommended measuring thingy on hand).

Inadequate fuel pressure could be another culprit. Replace filter, inspect lines for leaks, replace or inspect/test fuel pump. How is your gas? New, clean, and clear?

Only when stopping. The solenoid works each time - or at least clicks. I don't think there is an ECC (1973). New gas, However, I have a fuel filter where I can see the fuel - it's clean now but that was after back to back to back to back weeks of cleaning the filter b/c particles were coming through. That was several months back and it's been clear and running fine until about 3 weeks ago. Perhaps something did get through and is now clogging the idle circuit.

The idle circuit in carb is plugged

Is this circuit open/closed based off the solenoid? As a first check could I blow some cleaner and/or air through where the solenoid goes (idle circuit) and possibly the mixture while I'm doing in there - I may give this a go and see if that helps.
Thanks!
 
Good ?, paging Mark, Trollhole, Wngrog, could be the brake booster is causing a vacuum leak when pressed but I have never heard of that.
 
The idle circuit in carb is plugged
You nailed it @peesalot -- I blew a bit of carb cleaner through the idle circuit and idle mixture. Cleaned the connections and put it back together. It fired right up and ran great around the block a few times - no stalling. I do need to re-adjust the carb b/c I modified the idle mixture and I had jacked with the idle speed beforehand trying to keep it running, but I'm going to wait until daylight when it's warmer. I think I'm good ... probably due for a carb overhaul / rebuild at some point over the winter, but we'll see if this sets me straight.
THANKS!
 
fwiw - that debris came from somewhere, changing the fuel filter is somewhat of a bandaide, when you get a look you will prolly find some sandy lookin stuff in bottom of bowl, hey its running, good.
 
Only when stopping. The solenoid works each time - or at least clicks. I don't think there is an ECC (1973). New gas, However, I have a fuel filter where I can see the fuel - it's clean now but that was after back to back to back to back weeks of cleaning the filter b/c particles were coming through. That was several months back and it's been clear and running fine until about 3 weeks ago. Perhaps something did get through and is now clogging the idle circuit.



Is this circuit open/closed based off the solenoid? As a first check could I blow some cleaner and/or air through where the solenoid goes (idle circuit) and possibly the mixture while I'm doing in there - I may give this a go and see if that helps.
Thanks!

Good to hear you figured it out. The FCS was not controlled by the emission computer until the 79 MY. There is an emission computer on the 73, it controls 3 VSVs depending on coolant temperature and vehicle speed. It does not control the fuel cut solenoid.
 

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