vacuum gauge to solve idle issue

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4spdragtop

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This seems to be the year issues with the cuda. Recently developed a stumble idle issue. Surging rpm at idle, also wont idle below 1000 rpm.
Have to shift to neutral at a stop and feather the fuel.
My initial timing is around 11* btc BUT thats about 900-1000 rpm.

I checked for vacuum leaks with propane and small rubber hose and couldnt find any(no rpm Iincrease)
I also have a mighty vac and checked vac adv unit, it held vacuum so I assume good.

I have a vac gauge and was going to use it to help diagnose issue(s).
I can't remember which port on carb to conconnect to??
Im not sure whether its vacuum leak, fuel issue or timing issue.
273 4 bl eddy 1405 LD4B, 904 trans.

Thanks all
 
If you want to watch full manifold vacuum at idle it would be the port on the right front of the carb.
It's easy to tell which is which by putting your finger on the port at idle as the right side port sucks all the time and the left side only sucks when the throttle is opened.

If it were my car I would pull the idle mixture screws and blow some air in them and see how it does after that.
Surging is usually a side effect of a lean condition, so the idle circuit might have some crap in it.
Just count how many turns the needles takes to bottom out, so you can put them back where they were when you put them back in.
 
Drivers side port correct?
Pass side is for distributor.

Yup.
Either side could be for the distributor though, depending if one is using ported or non ported vacuum advance.
If the distributor is connected to the left port (passenger side) you are running ported vacuum.
If on the drivers side port it would be using non ported, or full manifold vacuum.
 
New plugs 100 miles ago. New PCV
It runs great driving, 1000 rpm seems to be its threshold for some reason.
MP elec ign.
I set idle mix screws at 1 1/4 turns out.
 
Carb is eddy 1405 but we added the eddy elec choke kit. Im wondering if choke needs adjusting? It appears like its working.

When I checked initial timing it was pretty steady, not bouncing all over but again that was around 1000 rpm.
 
The choke adjustment would only matter when the engine is cold, and wouldn't/shouldn't affect the idle or RPM's when warmed up.
You can run ported or non ported, but they require timing adjustments to change between the two.
FBO (4secondsflat.com) recommends full manifold vacuum with their products.

Ported only advances the timing when the throttle is opened, and manifold pulls the timing is as soon as the engine starts.
Both drop the timing back at higher throttle openings.
 
Do not know what engine you have but your timing seems low.Timing has to be correct before
you can set anything else
 
Steve...there's a small vacuum port that runs into that new electric choke you installed to provide choke pull-off duties....there's a gasket there that sometimes gets lost...and that will create a vacuum leak, causing the symptoms you describe.
 
No time to work on it today. Our granddaughter turned 2 so it was party time!
I will try to get to it this week.
Engine is 273 4bl. Timing was set before but could use tweaking.
Cant set initial dead nuts unless I can get it to idle.

Thanks all!

20161002_180653.jpg
 
Thanks Dar! We got to have all 3 grandbabies with us today, so triple awesome.

TB I have MP elec ign kit, and has been good so far??
I assumed that MP wants it hooked to Ported vacuum (pass side)
Within a second or 2 of dialing the idle below 1000 it stalls out?
Carb issue?
Spring or something come off in distributor?
As I mentioned above 1000 rpm, it runs pretty good.
Dar I will chk that choke gasket. I checked for vacuum leaks with small propane tank and rubber hose with no rpm increase. I will try carb cleaner next
Other kidlet pics

20161002_144704.jpg


20161002_145209.jpg
 
Comp cams CL20-246-4 solid lifter cam. Been in it for 4 years with no problems.
Tomorrow after work I plan on removing idle mix screws and blowing them out. I will also take distributor out and inspect.
Gasket @ choke housing for leaks
 
Im not schooled on carbs, Im hoping a quick blast solves the issue. Gotta get it to idle first than can adjust timing. Theres less than a month of driving left before its off to hibernation
 
Comp cams CL20-246-4 solid lifter cam. Been in it for 4 years with no problems.
Tomorrow after work I plan on removing idle mix screws and blowing them out. I will also take distributor out and inspect.
Gasket @ choke housing for leaks


Steve ...I was referring to the choke housing to carb body gasket for the leaks....just confirming.

El_Choke05.jpg
 
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I would turn the initial timing up to about 16 and see if it idles before doing anything else
 
Steve I'll tell you what works pretty well for me on the idle screw ports is to shoot a little WD40 in each hole and then blow some compressed air through them.
It has solved idle mixture problems for me multiple times over the years.
When I got Stephanie's 72 Swinger all back together it popped and sputtered and died at idle so I opened up the carb to find a bunch for fuel line rust particles in it.
I rinsed it all out, but the air with WD40 was what cleared up the idle problems.
The WD just adds some substance to what gets blown through the ports inside the carb and carries junk out way better than just straight air.
 
11° is way low.
I had a similar issue with wandering idle. Sprayed carb cleaner all over the place and could not find the leak. Finally smoke tested it and it turned out to be the throttle shaft on my Holley...FWIW...Keep looking for that leak.
 
Well got home and fired up the cuda. Neighbours weren't too happy but it was only 930, late but not drastic lol. Fired up and immediately went to 2000 rpm. let it warm up sprayed carb cleaner around base looking for vac leak. Couldnt find one. Dialed in idle screws while.running to stall engine but wouldnt stall out lol
Removed idle screws sprayed with wd40 and carb cleaner amd a quick blast of air. Snugged screws in then out 1 1/2 turns.
Fired right up, lowered idle to around 850 and runs good.
A quick set of timing to 15* and then out for a rip.
Still need to tweak but WAY better. Its drivable lol
Thanks all!
 
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