Hello everybody! I am a new member, just bought a long awaited 86 xtracab last week. I love it but have had some issues with it.
I am new to carburetors, but have worked on my vehicles in the past. Just last weekend I rebuilt the carb to fix a horrible idle (sounded like it was running on two cylinders). while at it, i cleaned the egr with oven cleaner, checked all vacuum lines and took a look at all the plugs, wires, cap and rotor. All seemed fine and after rebuild ran great!!
Today however, in 90 degree weather, the truck developed a bad off-idle stumble, once i got it going, the accelleration was terrible and it would backfire when I lifted.
This truck has a newish (20k miles on it) motor that runs quite strong (though loud!) other than this. I hate the thought of spending another weekend on trial and error. Any suggestions?

Thanks ahead of time!!!!

 

anybody?

 

Backfire... do you mean afterfire (out the tail pipe)? Backfiring is up through the intake, afterfire is out the exhaust.

If it's out the exhaust, I'd guess you're running rich at idle. It won't be as much of a problem when cooler as it would be when warmed up. Since you recently rebuilt the carb, possibly the float is set a little high or you're a tad rich on the mixture screw. Even having the choke not pulling off completely or the throttle not closing completely could cause an issue like what you describe.

Additionally, valve clearances may be an issue. If the exhaust valves were set a little tight they will heat up and can cause popping out the pipe.

Incorrect ignition timing can cause issues as well.

 

Thanks for your advice abecedarian.

I finally got some time to work on this today.

It was indeed afterfire. Tried first adjusting idle mixture to no avail. Noticed that the fuel level in sight glass was super high, so i pulled the top of the carb to find the needle/seat leaking air when I blew in the fuel inlet even when I forced the float up.

After replacing the needle and seat, the truck ran well (fuel level in sight glass right in the middle) enough to warm up for valve adjustment. The intake side was good except for one tight one, all the exhaust valves were so tight the gauge wouldn't fit! Checked timing (set it at 0) and everything seemed fine until out of nowhere the problem recurred. Sight glass full, terrible idle! Screwed around making sure vacuum lines were hooked up and correct and put it back together. Ran fine, however, i am starting to notice a routine here. When I start the truck, the sight glass level is dead on but as it idles it slowly rises until the line is invisible. Sometimes it fills all the way and starts running like crap, sometimes not.

What could be causing this if the valves are good, timing good, float level is good and the needle and seat are sealing well?

Thanks!