Lost vacuum?

[LARGEONE]

Hey carb guys...you did such an amazing job solving the overflowing 40 carb issue, that I thought I'd see if you have some more insight for mine?!!!

Old Gal (1967 40, with early 70's carb) had been driving and idling perfectly until this weekend. I usually drive her about every couple of weeks and this weekend went for a drive and she would not idle. It's like the idle circuit just got turned off (clogged), or there is no vacuum at idle? Those are my two guesses but I can't see where I would have lost idle (starter fluid spray around manifold and carb/base changes nothing), and messing with the idle circuit didn't change anything either. If I pull 1/4 choke, I can run her around town without issue, but as soon as I remove any choke, she DIES ALMOST IMMEDIATELY.

Am I on track with the Vac loss or Idle circuit clog? Fixes?

Thoughts? Anyone available in the next week(s) to help me diagnose?

 

[subzali]

okie carb rebuild

Seriously though I have had floaties show up in my fuel bowl before - pulled the drain plugs to drain the fuel, got the floaties out, and all was well.

Did your idle screw setting move at all? Or screw fall out? That's also happened to me before.

You are cable actuated?

 

[LARGEONE]

I sure hope I don't have to full rebuild again!!! I think I only have about 500 miles on it since the full rebuild

I assume the idle screw you speak of is the one toward the base and not the low throttle. I did not mess with the throttle stop at all, but I did unscrew the idle screw and screw it back to the exact position. I had not moved from my setting when it was running great.

Yes, throttle cable and choke cable.

The only thing I can see that looks different from when I rebuilt is that the rubber boot is already dried out and trashed on the throttle pivot lever. Hard to believe it only lasted this long.

 

[LARGEONE]

How would I go about ensuring the idle circuit is clear without removing carb?

 

[Cruisertrash]

A quick thing to try before you drain the float bowl or remove the carb: hook up a vac gauge. Get it choked out enough to run and see what you have, and if it's low you know you have an air leak versus a fuel blockage. Tighten the four nuts holding the carb down while you're at it - that got me once. Check any other hoses or fittings in the manifold, too - the ends of vac lines can get cracked or enlarged over time leading to a vac leak. Spraying carb cleaner or brake cleaner around hasn't even done a great job finding leaks for me and the carb can have just a hair gap at the base plate or at those hoses.

But if none of that works, see above: drain float bowl, maybe pull the jets, blow compressed air through passages, etc. How does the fuel filter look?

 

[LARGEONE]

I’ll have to get the vacuum gauge out later this week and see what I’m getting. It just won’t idle at all without a bit of choke. Odd that it just started suddenly.

Thanks for post!

 

[fjc man]

Is this carb “new” enough to have the idle circuit shut off solenoid? If so, could also be the culprit.

 

[simps80]

Okie rebuild Matt refers to is revving rpm then rapid shut down of intake to carb

Like putting a piece of cardboard or similar over the intake to the carb as the engine comes down quickly from acceleration

A dramatic quick “vacuum” increase within particularly the upper half of the carb can clear stuck passages is the theory
An “okie rebuild” or “redneck rebuild” or “Arkansas rebuild” etc etc etc

I have seen it work but only on shit that hasn’t run in a while

 

[LARGEONE]

Thanks for edumacating me, Mike.

I’m just a little bummed as the weather is improving and I enjoy getting out in her. I do still have the second carb cleaned and sitting in pieces on my bench. But I’ll have to source some more jets as they were a different length in that carb?

Also don’t really feel like digging into it fully again! Maybe I’ll check Vac and try removing carb and blowing out?

 

[LARGEONE]

Further question about the solenoid on the early 70s engine? If this solenoid was not functioning correctly, would the engine run at all, even choked?

 

[Rzeppa]

Further question about the solenoid on the early 70s engine? If this solenoid was not functioning correctly, would the engine run at all, even choked?

Gong through this thread, I am surprised no one brought up your idle cut solenoid operation. Given the symptom, that would be the very first thing I would check. Whenever the ignition key is in the "on" position (also while cranking) the idle cut solenoid should be energized and open. If it is not open, you will experience the exact symptom described in the first post above.

The quick and dirty test is to have an assistant turn the ignition key while you have your head under the hood with your ear as close as possible to hear the click of the idle cut solenoid operating. No click means it isn't operating. Could be as simple as a loose connection or broken wire.

FYI, since the idle fuel cut solenoid is always open while the key is in the on position, it adds to the fuel flow at all throttle settings.

 

[LARGEONE]

Thank you Jeff! That’s what I was remembering as well. I believe someone initially asked if these early carbs had a solenoid. It’s what got me thinking about it. But I couldn’t remember if the engine could run at all with the solenoid not working. I’ll check that first as those are the exact symptoms. Maybe a squirrel got in there?!!

 

[LARGEONE]

Ok…not declaring victory yet, but OG2 maybe an idling queen again?

This evening I had a chance to mess with her for a bit…so first, I checked the idle solenoid (Thank you @fjc man man and @Rzeppa). Definite audible click when key turned on. Check!

Next I ran her with a bit of choke and got her warmed up Fully. I reduced the choke just to the point of dying and tried to adjust the idle circuit with no effect. Put it back where I found it.

Then, I added a little bit of throttle with the low end throttle adj screw. This allowed me to remove all choke and barely get it to idle (not on idle circuit). I hooked a vacuum gauge to the manifold and got around 13 with engine idling at correct rpm, and around 10-11 in with engine barely putting along. I think this is a bit low for the manifold, but it seems to be very close to what I was getting when I first set this carb and it was idling fine. I tightened the carb base nuts a tiny bit and called it good for vac check.

So, with all of these items checked, I remembered that I am from KY. So what does a KY redneck do? He does the “redneck rebuild” or whatever @subzali and @simps80 called it? I’ll just call it the “suck and burn method”! I revved her up while spraying some carb cleaner in the manifolds, then kept revving and threw a block off plate over the top of the engine. Did this a couple of times without letting her die and she seemed to perk up a little. I slowly backed off the throttle adj screw until I had zero throttle help and she continued to chug. Didn’t idle great, but she would stay running with no throttle help! I added just a touch of low throttle to just even out her chug, which was basically right where she was at setup.

Took her for a drive and she ran great! No dying at idle and No Choke!

happy

Thanks to those who commented and juiced my approach!

 

[LARGEONE]

Ok…after driving the 40 all over today, I am declaring victory on the idle issue. I’m even considering dropping idle RPMs down a little further, as it is running really great on the fresh gas added today.

Next up…cutting front shackle pins out and replacing all bushings with poly greasable. Maybe do a little more welding on the passenger rusted rocker panel?