(SOLVED!) Will not hold idle, stalls - need advice to debug

[worzella]

Hello all - 

 

A recent issue has me stumped and as I wade through the related forum posts, was 
hoping for any specific debug suggestions.

 

My '75 with 32/36 electric choke and also a rebuilt motor 3 yrs ago with 3000 miles
was flawless till about 2 weeks ago. She would start, idle, run like a charm.

Then about 2 weeks ago I started her in the storage unit where she sat for about 
2 weeks prior, warmed her up and moved her out in the lot. Worked on my 
other problem child car for about 4 hours and then went to start up BMW to take 
her home. 

 

Immediately when I started her, I sensed something amiss. She would not hold idle 
and unless I really juiced the gas pedal, she stalled. I nursed her home praying for green 
lights and revving in neutral at the reds. 

 

Next day at home I set choke, started up fine, idles at 1500 and as she fully 
warms up raises to about 2000.

 

When I kicked off choke, in the old days she would nicely purr at about 900,
not she sputters, misses and eventually just stalls after about 15s or so.

If I manually close the butterfly on the carb, the idle raises and it runs smoother, 
but letting butterfly back to its natural level, motor misses, stumbles and stalls.

 

If I rotate the idle screw to about 1500, she will not die but still not totally smooth.
As I lower the idle,  it gets to the point where it misses and stall happens.

 

Now some details about what I have and have tried:

 

- Ran direct fresh fuel into pump from gas can, removing the tank and fuel 
  filer from the equation - no difference.

 

- Pump was new 3 years ago, a proper stubby model from Blunt
  Not sure of the inner workings, but is it worth putting on my original 
  pump. Nothing was wrong with it, just wanted new pump during restoration.

 

- New coil from 3 years ago - I have a new replacement I can try

 

- Plug wires new 3 years ago. All connected well and tight

 

- 32/26 carb new also with CD jet recipe - Sprayed ample amounts of carb cleaner
  while trying to get her running last weekend  

- New plugs also, but I have not pulled them to see what clues they might provide

 

- Rebuilt dizzy also, new rotor and cap and Pertronix
  Bit of up/down play in shaft but would expect this would 
  affect roaming idle, not cause total stall

 

- Strong battery

 

 - Valve adjust, timing set and carb dialed in about 6 months ago. Like I said
   the whole motor was flawless and smooth for these 6 months 

 

- Checked for vacuum leaks - New nipples on unused inputs as needed and plugged vac adv 
  port at carb temporarily

 

- Electric choke gets 14v while motor running and does its thing as the car warms up. 
  The linkage sets and releases as it should. 

 

So from my limited expertise, I don't think compression is an issue since newly rebuilt motor. 

I believe I have spark and timing since at elevated RPM, she runs. Carb seems to be sucking air 

so I believe air-flow is not an issue and finally, unless the pump or jets are malfunctioning I 

don't see how fuel starvation is the issue.

 

But is has to be one (or more) of these. The oddest clue to me is that this literally started 

like a light switch. No warning of anything degrading, etc. but most problems not that lucky to

have a nice warning. 

 

Anyway, any methodical debug steps you can provide would be greatly appreciated. 

 

Randy in Raleigh

 

Edited March 20, 2022 by worzella

[dang]

9 minutes ago, worzella said:

If I manually close the butterfly on the carb, the idle raises and it runs smoother, 
but letting butterfly back to its natural level, motor misses, stumbles and stalls.

I think this is the biggest clue.  Air/fuel mixture wrong at idle.  I'd follow up with your vacuum leak and jets/mixture theory.

[Mike Self]

You can be pretty well assured that the jets didn't change size themselves while the car was sitting, and it sounds like your choke is working property, as the problems don't start until the engine is warm and the choke turns itself off.  

 

First thing I would suspect is a bit of trash in an idle jet.  The "idle" circuit actually supplies most of the engine's gas until you reach about 2000-2500 rpm, and those jet openings are very small, and it doesn't take much to plug one up.  Besides, that's an easy thing to check.  Presume you don't have an idle solenoid (anti-dieseling solenoid).  A failed one = no idle at all.  And I've had several fail...

 

The other thing to check is the float.  Weber floats (both brass and plastic) have been known to develop leaks, and a low-floating float will cause a very rich--too rich--idle; thus stalling.  

 

Let us know whatcha find...

 

mike

[tech71]

43 minutes ago, Mike Self said:

The other thing to check is the float.  Weber floats (both brass and plastic) have been known to develop leaks, and a low-floating float will cause a very rich--too rich--idle; thus stalling.  

Yep. Raw, not atomized fuel can literally spill over into the carb venturi.

[AustrianVespaGuy]

I agree with @dang that if closing the choke flaps makes it run better, that's a big clue.  It also indicates you're probably running too lean, not too rich, as the flaps limit the volume of air whilst also creating more vacuum that then draws more fuel through the idle circuit, so the gummed up idle jet theory fits well, as does a low float level but that seems much less likely.  While this doesn't sound ignition related, it also can't hurt to throw your timing light on there to make sure your points didn't loosen up and 'wander' a bit!

[71bmr02]

My 71 did just about the same thing, i went thru the carb did some rejetting, then back to original jetting, adjusted valves, new fuel filter (which it likely needed) then changed plugs which appears to be the very thing it needed all along.  At least i did the spring tuneup thing so I'm ready for the vintage.  

[stone02]

another thing to check is to see that the idle solenoid,

if electric, is connected and getting voltage. I have seen 

the wire fall off and the circuit that it was on burn a fuse.

check that too.

stone

[Lorin]

I bet money your idle jet has a piece of trash in it. 

[Chris_B]

i have to agree that this is an idle circuit problem. If you have an idle solenoid and make sure the end is clean, and blow out hole with something: air, carb cleaner or the like, etc.

 

Otherwise, pull your idle jet and similarly blow it out.

[John76]

3 hours ago, Lorin said:

I bet money your idle jet has a piece of trash in it. 

Me too!  

This happened to me just "out of the blue" after running perfectly for years.

Don't have a clue as to where the obstruction came from, but I suspect old gas.

Easy to check. Blow it out with air or a thin broom bristle.

 

 

[worzella]

Woo hoo! Thanks so much everyone. Can't wait to investigate once the rain halts.

 

To answer a few points from the posts... no points, running Pertronix. No idle solenoid. And after reading the info in the posts I also agree the float issue does not seem as relevant since I appear to have a fuel starvation issue (lean) not a rich excess fuel issue. I watched a couple videos on 32/36 rebuilds last night and understand more about the structure and exactly where the two idle vales are. Seems easy-peasy to pull, inspect and clean. John76, your picture is an awesome example :)

 

Will report back the results this weekend. Go Badgers!!

 

Randy

[TobyB]

Check both the 'idle' transition jet AND the idle screw passageway.

The idle screw draws fuel through the transition jet, so a clog in either

can cause exactly your symptoms in exactly your circumstances.

 

hth

 

t

[worzella]

OMFG...excuse the French but had to add the 'F'!

 

You will not believe the solution to the problem!

 

We all were on the 'not enough fuel' idea with suggestions to check idle jets and mix passages...which is what I did today.

 

But as I was mucking about I bumped the carb and...the whole thing moved! Grabbed it and shook and sure enough the damn thing slid back and forth!

 

Turns out  4 nuts on carb base were totally loose..ergo..huge vac leak. I assume they were loose but I bumped carb when issue started and "broke seal". Hence air leak!!

 

Tightened nuts and BOOM! she idled like a charm. Just had her out and thrashed the shit out of her and all good!!

 

Can't explain the joy of fixing an issue that has been weighing on my mind. But ypu all know the feeling!

 

So problem was the carb riser and gaskets leftva short stud and Nylok nuts could not grab enough to to lock it down

 

Will get thin nuts and wave washers and thread lock...job done!!