Running Rough Suddenly - Solved

[Justice777]

10/21/17 Solved. See my last post.

'78 carburated, new to me.
Was running fine / smooth while out for a drive when I had to slow and possibly stop for a car in front of me waiting for oncoming traffic to pass so he could turn. I pushed in clutch and my car stalled. I got around other car put in 2nd gear, let out clutch and it started right away, but now car won't idle and is sputtering, missing... Still driveable but not running right as I can feel it miss / sputter a bit when accelerating / under load (still accelerates good) and more noticeable sputtering under light load / maintaining speed and even more noticeable when decelerating.
In garage there is no change when on or off brake and I checked what few vacuum lines there are. Visually inspected plugs (light ash and look ok), ign. wires (no chaffing and look sound), cap, rotor, and single points (a little wear on contacts) which I scuffed lightly w/ 600grit paper (made no difference w/ rough running). Looked at cap closely under high lighting and my cheater glasses on and couldn't detect any cracks.
I replaced metal canister fuel filter w a clear plastic one (so I could see fuel), and saw no contaminants. First drive in beginning of this month I filled fuel tank w/ 91 octane and drove maybe 2 hrs total before this recent issue.
When I replaced fuel filter I watched it fill via elect fuel pump, w/ out engine running. I was expecting to see it fill completely but it only filled 2/3 - 3/4 - maybe due to it's orientation which is maybe around 60 degrees off vertical.??
Should this fill completely regardless of orientation?
I have ordered new cap, rotor, condenser, points, wires and plugs.
Made a short video so you all could hear it - bumped it to around 800 - 1000 rpm w/ the manual throttle lever / knob so it would run (yea, very holey muffler):
https://www.youtube.com/watch?v=YQ_ZINP ... jreload=10
Anything else come to mind?

[cjl7516]

The same exact thing has happened to me and I can't figure it out either. Help!

[TX82FIAT]

I think the fuel filter is fine as described but I would not rule out a pressure issue and would test your fuel pressure. Sounds like you have done some basic trouble shooting with the ignition. I would ground the spark plug on the wire to the block and look at the spark for each plug to see of you possibly have a gapping issue or a weak (yellow/orange) spark or even a bad spark plug. Outside of those two items, I would start to look at air to see if you need to adjust the carb or if there is some other restriction.

[Justice777]

I think the fuel filter is fine as described but I would not rule out a pressure issue and would test your fuel pressure. Sounds like you have done some basic trouble shooting with the ignition. I would ground the spark plug on the wire to the block and look at the spark for each plug to see of you possibly have a gapping issue or a weak (yellow/orange) spark or even a bad spark plug. Outside of those two items, I would start to look at air to see if you need to adjust the carb or if there is some other restriction.

Just tried to start w/ out tune-up kit installed. Here is image of clear fuel filter w/ fuel pump ON:
This can't be right, correct? What fuel pressure should I be reading?

P.O. did replace tank, lines, and added elect fuel pump in trunk although I was told the car hasn't been driven more than 2500 miles since 2006 or so.
I did find exact replacement here:
http://www.autozone.com/performance/fue ... 732036_0_0
I'll start by pulling the little filter on it and make sure it is passing fluid / not clogged before I replace it.

[kilrwail]

Those two vacuum nipples (if that's what they are) under the fuel filter, should be capped. I don't recognize the position of the filter - it must be more rearward than mine.The level of fuel in the filter is normal. Have you adjusted the idle mixture screw ? A good starting point is two full turns out from tight. If it's too rich (i.e. loose) it will stumble and fart when you try to accelerate. Mine is set at 1-3/4 turns out from tight and it's perfect. For a carb'd engine, the fuel pressure should be 3-5 psi.

[Justice777]

Those nipples are on the unused mech. fuel pump. They were not capped when running fine, also why I am reluctant to make any carb. adjustments at this point as it was running fine also. Thank you for that tip though. Not sure how the level in fuel filter can be normal as fuel isn't even high enough to reach filter's outlet with the elect fuel pump on.
I see specs for new fuel pump - Mr. Gasket #42S is 2 - 3.5 psi and 42 gph. Blowing through the metal filter that comes with it, I don't detect any, or very much restriction. For $40 I may as well just replace it.

[kilrwail]

Adjusting the carb won't hurt anything and , who knows, it might help I have two of those transparent filters on my Porsche and they never fill up, with pressure regulated to 4 psi. Somehow the fuel gets through fine.

[Justice777]

Thanks. I realized that if carb float bowl is full then float is up and effectively shuts of fuel inlet until float falls. I'm off to work and will re-visit this problem later. Thank you for your input.

[Justice777]

Changing out plugs, wires, cap, rotor, points and condenser made NO change in rough running.
Checked compression while changing plugs and have 160 to 135 psi range across all 4 cyls.
Changed out fuel pump.
Still doesn't want to idle and runs rough even up off idle. I noted position of 2 spring backed adj. screws on carb. and tried each 1/2 turn in both directions and did NOT note any change in rough running.
Could my car's running condition be caused by a weak connection in my problematic ignition switch wiring? I did re do some of the connections as advised and it at least starts reliably now. I also have a brand new 6 tab connector I can wire in tomorrow and see if that makes any diff. I don't think brown wire fix has been done but will check.
Any more advise?
Could this be carb. issue and should I consider rebuilding or replacing? Drove a couple laps on my paved rural roads and it still goes like hell, just not running smooth.
Thanks.

[Justice777]

I just thought to add that while cold starting and trying to keep running by feathering throttle, if i let rpms drop to say 500 and its struggling to stay running it will back fire a couple times and may stall if i fail to get revs up. When it backfires ill see what i assume is exhaust smoke coming from what seems like under carb. Is thiss possible w/ no vacuum leak?. I will do diligent vacuum leak check tomorrow.
Any thoughts and comments welxome.

[kilrwail]

Have you verified the points gap? If it's wrong, that can lead to all sorts of rough running problems. Ditto the timing.

Now, humour me. Turn the mixture adjustment screw all the way in until it stops. Then back it off 2 whole turns. How does it behave now? When you turned it half a turn in both directions, you could have been starting from a really bad initial setting. It should be 1-3/4 to 2 turns out from a full stop. I'm ignoring the fact that you said it was running fine before. With all the ignition work you've done, you've rearranged things a lot in the right direction. The carb should be the last thing that's adjusted once the ignition is right.

[Justice777]

Thanks Peter,
The idle mix screw was 1.5 turns out. I did as you suggested and turned it in to stop then out 2 turns. No diff in running condition.
Point gap was tight at .4mm (I read spec as .42mm to .48mm). Took me a while but finally got gap to .45mm. Still no diff in running cond.
I don't have a timing light yet so cannot check that at this time. I can go and buy one though.

Another clue, possibly - When first starting this morning - ambient temp around 45'F, I set choke by depressing throttle all the way to floor then let off, car started right up then died right away. 2nd start I feathered throttle a little, started right up, and while keeping running w. throttle I adjusted manual knob throttle to keep rpm at around 1000. Noticed engine running smooth - no skipping / sputtering / shaking. This was first time since this prob. started that it has run smooth. I left it running and popped air cleaner off and see choke is open. I snap open throttle linkage as I'm standing there to give it a quick rev and as soon as I did that, all of the sudden engine is again skipping / sputtering / shaking.

Is this an indication of anything that comes to mind?

[kilrwail]

Maybe your main jets are dirty/clogged? What you've described still sounds like a mixture issue, but you've eliminated the idle setting at least. Thanks for trying. Did the choke stay open when you bliipped the throttle? It should if the engine is warm.

The timing light will be helpful, to eliminate timing as a cause.

[Justice777]

Well, I figured it out. I'd love to say due to my troubleshooting prowess but more like accidental. On left side of carb is a metal canister w/ 2 wires connected to it. Apparently this is called an ICU Solenoid, AKA Idle Shutoff Solenoid assembly. When my wrist put pressure on the connector towards the firewall, the engine ran very smooth. I replaced connector, cleaned male tab coming out of the solenoid and no difference, except still, if I pushed it a little toward firewall engine smoothed out.
You were on the right track Peter. I looked down primary barrel and when rough running there was fuel spitting out of accelerator pump nozzle while at idle. Favor the elect tab coming out of solenoid towards firewall and that stopped and engine running smooth. For now (until I can replace this part) I have tie-wrapped the connector with just a little pressure toward firewall. Just got back from an hour ride and car performed flawless. Yay!!!
Thanks so much for your help!
Edit: quick search shows one here for $49:
http://www.spiderroadster.com/124carb75.htm

[kilrwail]

I'm glad to hear that you found the problem. My next suggestion would have been to inspect the wiring to the choke connection (ICU Solenoid), but I wouldn't have guessed that it had somehow become damaged. That should be an easy fix once you get the part.