Suddenly running rough

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Mako21

Mako21

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Hi guys. Around two years ago you all helped me get my first classic car, a 1976 dart, running great. It now has developed an issue I can’t quite fix.

I’ve lashed the valves to factory spec, replaced the ECU, cap/rotor/plugs, fuel filter and checked timing to 8 degrees. I rebuilt the carb two years ago. I blew on the fuel hose to check if the gas tank screen plugged. All ok. Fuel pressure ok too, it’s pumping hard.

It cruises fine and no bogs off acceleration, but as I come to a stop it will misfire and run rough. Also, when I make turns to the left it will stumble like it’s about to shut off. Also just now I realized if I shake the car side to side left and right really aggressively it runs really rough and then cleans up once I stop swaying it side to side. The idle is inconsistent. It’s driving me crazy because when I try to diagnose it idles great and then I drive it and it runs rough.

Any ideas? Any help appreciated.
 
Gonna be your carb. Needs a freshening up . Has the gas tank ever been replaced? From my experience anytime you get a bog or rough conditions when your turning it’s related to carb. Could be debris, could be float level . Check the accelerator pump . When turning- it bogs when you hit the gas to pick up speed again right? Or mostly when you let off the accelerator?
 
I’m working on it now since I’m off for the long weekend. I hooked up a vacuum gauge and it is reading steady at 21hg at idle, 800 rpms.

What I am noticing though now is the idle mixture screw I turned it all the way in seated and it does not kill the engine. Turning it out does conch and kill it and it get real rich smell. Also to get a baseline I set the timing down to 2 BTDC degrees and drove it and it idles better than where I had it originally at 8 degrees BTDC.
 
The bog happens while in the left turn and initially straightening up out of it, and then once fully established straight it cleans up and accelerates and cruises great.
 
Mako21 said:
The bog happens while in the left turn and initially straightening up out of it, and then once fully established straight it cleans up and accelerates and cruises great.
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Yea I’ll check the carb. Look for debris and recalibrate the float. 50 bux gets you a new carb kit .
 
$50 for a 1 bbl carb kit these days? Yikes. Last one I bought was like $18
 
Mako21 said:
The bog happens while in the left turn and initially straightening up out of it, and then once fully established straight it cleans up and accelerates and cruises great.
Click to expand...
Sounds like either float level/float sinking, or,.... I ran into a Duster w/a Slanty that did that, turned out to be water in the fuel. Put an in-line separator on it & fixed it.
Let us know what You find, peace!
Jim K6
 
Sounds like the float has become compromised and is absorbing gas.
 
Mako21 said:
checked timing to 8 degrees
Click to expand...

That's a little excessive, with '76 distributor and carburetor. Back it off to 5°.

Mako21 said:
I rebuilt the carb two years ago.
Click to expand...

Carbs often don't "stay rebuilt" as long as we would like; time for some more TLC to the carb. First, see if dirt or corrosion in some of the very small idle passages in your carb's idle circuit are causing the problem; start here. Then from there, dig deeper. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Make sure you use good-quality kits and parts; the ones you can buy through normal parts channels have been crummy for quite awhile, and getting crummier. A good kit from Jon Hardgrove at The Carburetor Shop, will cost more, be more complete, and give a better result.
 
Thanks, I pulled the carb today and it was pretty gummed up at the base. I also noticed the needle was a little worn at the base from rubbing on the floats. And I’m a little concerned about one of the six screws that hold the upper and lower halves just spins, it no longer seats itself and tightens so to seal the gasket and two halves together. Probably had a small vacuum leak right there. I never over tightened or torqued it so not sure what that’s about. So looks like I’ll have to helicoil or sleeve it. Wierd how that just let loose. I went ahead and ordered a kit from a retailer called Mikes CarburetorParts. I ordered an ethanol compatible ready kit, hopefully it works and was only a few bucks more than a regular kit. Our gas here has up to 10% ethanol added. I plan to also order a 1/2 phelonic spacer now too.
Thank you for all your help.
 
Mako21 said:
Thanks, I pulled the carb today and it was pretty gummed up at the base. I also noticed the needle was a little worn at the base from rubbing on the floats. And I’m a little concerned about one of the six screws that hold the upper and lower halves just spins, it no longer seats itself and tightens so to seal the gasket and two halves together. Probably had a small vacuum leak right there. I never over tightened or torqued it so not sure what that’s about. So looks like I’ll have to helicoil or sleeve it. Wierd how that just let loose. I went ahead and ordered a kit from a retailer called Mikes CarburetorParts. I ordered an ethanol compatible ready kit, hopefully it works and was only a few bucks more than a regular kit. Our gas here has up to 10% ethanol added. I plan to also order a 1/2 phelonic spacer now too.
Thank you for all your help.
Click to expand...
Probably needs a heli coil in that screw hole. The joint at the carburetor top cover wouldn't leak vacuum. It will leak fuel, because the top of the carburetor is the cover for the fuel bowl. Order the ethanol friendly kit. That's a very good idea. A better idea is to run ethanol free fuel if it's available in your area. Good luck with it!
 
Mako21 said:
ordered a kit from a retailer called Mikes CarburetorParts.
Click to expand...

That's the same kit as from the parts store, at a higher price. Maybe you'll get lucky and it'll be good enough for awhile. ¯\_(ツ)_/¯

There was an actual, real reason I provided a link for the good kits.

Mako21 said:
I ordered an ethanol compatible ready kit
Click to expand...

They all have been for many years; charging extra for it is a sales gimmick.

Mako21 said:
I plan to also order a 1/2 phelonic spacer
Click to expand...

Use the correct carb mounting arrangement, which is a 3/8"-thick (or 5/16", depending on who's measuring) combination insulator/gasket. Do not use thicker, because you'll screw up the choke, throttle, and transmission kickdown arrangements.
 
Thanks Dan, I appreciate the insight on the spacer. Will keep the carb rebuild kit for a future reference to purchase. Appreciate this whole group taking the time. Happy Sunday!
 
Mako21 said:
Thanks Dan, I appreciate the insight on the spacer. Will keep the carb rebuild kit for a future reference to purchase. Appreciate this whole group taking the time. Happy Sunday!
Click to expand...
That future reference will be pretty quick unless you use ethanol free fuel. Like Dan said, that's the same parts store kit you can buy at the Autozone and it's not ethanol friendly.
 
FWIW, my '76 started doing that as well. I figured I needed to rebuild the carb, and when I went to take it off, I found 2 of the 3 screws that held the body of the carb onto the base of the carb backed completely out, and the 3rd was halfway out, so I had a MASSIVE vacuum leak. I ended up rebuilding it anyway and throwing a new float into it, sourced from rockauto....ran great after that.
 

Yup a lot of those Holley 1945s vibrated themselves loose
I don't remember what was up with the original but when my brother had his 76 feather duster I wound up going to the junkyard and getting another one, and I ended up mix matching 3 of those carbs into 1 good unit and that car ran better than it ever had. Still pisses me off to this day because that was supposed to be my first car, dad bought it and drove it a few years and when I got my license my brother wrecked his 74 charger and needed a car like "now* for work.
(I had the bus to get me to school so to mom and dad that was suddenly"good enough " for me) . I didn't think so.
 
Hello, to close this out I finally received the kit a week later and rebuilt the carb after work today to kick off the weekend. The floats were full of fuel. Rebuilt it and had the car running perfectly a couple hours later. Thanks for the help!

IMG_8825.jpeg
 
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