Really bad idle

[84prspctr]

I scanned the site and can’t really find anything the same as the issue I’m having, truck has been running great for months never let me down, now it is idling like crap. The carburetor has only been on there a couple months and was brand new. I have two fuel filters so I don’t think something got in there. It runs great above 1200 rpm or so, runs great down the highway no power loss. After a long 3500 rpm pull on the highway I pulled into the driveway and it was idling like crap, idling really low like there was a big load on the engine. Now it is dying at stop lights and has no power under 1000 rpm. It is also vibrating really bad. I raised the idle up and it’s still doing it. I cleaned the plugs and it’s still doing it. I checked the timing and it’s still at 13 degrees and is not jumping around. I sprayed for vacuum leaks and can’t find any. I tried adjusting the idle mixture and it’s still doing it. When I screw in the right side mixture screw all the way the engine won’t try to die, which is wierd and if I screw in the passenger side mixture screw it will. I took the mixture screw out and sprayed carb cleaner down that jet and it’s still not changing anything. When rev it a little past idle there’s a weird clicking popping noise coming from around the carburetor distributor area. Any ideas where to look next?

 

[84prspctr]

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The best way I can describe what the idle sounds like out the exhaust is it sounds like a 4 cylinder car.

 

[84prspctr]

I took the cap and rotor off and gave them a good cleaning. It’s still not running good. It’s almost making a slapping sound out the exhaust too

 

[DoubleDingo]

That fuel filter looks dirty. And now you have to readjust your mixture correctly. Turning the screws with your fingers is not the preferred method, a screwdriver is, so you can set each side the same and count the turns of each screw.

 

[KnuckleBuster]

Starting point: Check the cylinder balance by grounding each spark plug wire. Make a note of any cylinder that has little or no RPM drop as compared to the others. The easiest way to do this is to install a short piece (2" will suffice) of vacuum hose on each distributor cap terminal, then plug the spark plug wire onto the hose. Start engine and allow it to idle. Touch a test lamp to each piece of hose. Once you've determined which cylinders are weak you'll know where to look for problems.

 

[84prspctr]

Found the issue, pulled the needle out sprayed carb cleaner in there followed by compressed air. Put it back in and it runs great so I re tuned it with a vacuum gauge. The filter looks dirty because there’s grime and oil around the outside, it’s really clean inside. I’m putting a new filter coming out of the tank and changing out the one going to the carb though just to be safe

 

[DoubleDingo]

Glad you found the problem and posted back.

 

[PrairieDrifter]

My next suggestion woulda been to pull the valve covers and look for a bent pushrod or a rocker arm issue.

 

[SquareRoot]

My next suggestion woulda been to pull the valve covers and look for a bent pushrod or a rocker arm issue.

From his other thread" It smells like it’s running a little rich at idle, but over idle it doesn’t seem like it’s running rich at all. Has a slight miss when not fully warmed up at around 1000 rpm but goes away at anything above that. Engine revs up to 7k rpm no problem. I’m going to try to find a number on that vacuum advance and replace it".

I think you're on to something Mason!

 

[PrairieDrifter]

From his other thread" It smells like it’s running a little rich at idle, but over idle it doesn’t seem like it’s running rich at all. Has a slight miss when not fully warmed up at around 1000 rpm but goes away at anything above that. Engine revs up to 7k rpm no problem. I’m going to try to find a number on that vacuum advance and replace it".

I think you're on to something Mason!

Engine revs to 7k?!? Is it built? lolol

 

[84prspctr]

From his other thread" It smells like it’s running a little rich at idle, but over idle it doesn’t seem like it’s running rich at all. Has a slight miss when not fully warmed up at around 1000 rpm but goes away at anything above that. Engine revs up to 7k rpm no problem. I’m going to try to find a number on that vacuum advance and replace it".

I think you're on to something Mason!

When I changed the valve cover gaskets I cranked the engine over and watched each valve open and close. They all looked to be moving the same amount.