Another carb idle mess

[richie49]

   My quadrajet is off a 1976 cadillac. The engine is a 500 basic stock except the cam. The cam is a high duratian 296 in 296ex 554 lift with a lsa of 108 set on a 104 center line. Lots of overlap. Of course  my best bet is to replace it with a cam with a  higher lsa like a 112 ,113 ,or even a 114. But Id like to try this out now and replace it in the summer.
 Right now  it is acting strange and I'd like to see if someone can point me to where to look.  Now the problem.I got the idle tubes from Cliff sometime back,I'm slow too many things going on.The engine would start fairly easy but didnt like under 850 rpm in gear. ran rather rough. And that was after I put in a 2500 stall converter.I pulled it back off and enlarged the tubes and down restrictions. Now it starts the same fairly easy.set the idle at 900 rpm and goes into gear with a decent idle. But the longer in gear at idle it goes down to 800,then 700 all the way to 500 still in gear.put it in park and the idle stays at 500 for a few seconds and then kinda snaps back up to 900. It also seems to have a slight hesitation when you try to rev it up. What all you think I need to look at? Oh yes the carb is a 117056230

     Richard richie49

[Kenth]

I would check distributor centrifugal advance for approx. 1200 rpm start. Too weak springs may cause wandering idle.
And, fuel inlet system for leaks, i would use a new float set at 13/32", a new .135" inlet valve and no more than 7 psi fuel pressure.
For calibration recipe based on intake manifold vacuum signal i recommend getting Cliffs book.

[richie49]

Well the thing is the carb wasn't doing this problem before I took it apart for cleaning. While apart I enlarged the Idle tube one size up and the restrictions next size and set the float to 9/32 . Before I changed the tubes and restrictions it wouldn't idle below 800 to 850 in gear.now it will idle down to 500.  The only thing I would think is the float level is being affected. The timing isn't moving  between idle in park or idle in gear
      Richard richie49

[Cliff Ruggles]

If the timing is rock solid at idle I'd look at a leak at the needle or under the fuel inlet seat.  A tiny leak may not show up as a problem until the engine idles for a while when the leak rate becomes greater that the fuel consumed at idle speed.

I actually see this a LOT these days, leaks under the fuel inlet seat or right at the needle on the seat.  High fuel pressure is another culprit we're seeing more and more as fuel pumps are almost all off-shore parts these days.  Difficult to diagnose and makes idle tuning impossible......Cliff

[richie49]

 Thanks Cliff
     That's one problem that could be happening because I did pull the float and needle out to check the carb and make sure the  various hole were't plugged.
 I guess it's time to look again.
        Richard richie49

[Cliff Ruggles]

Might want to leave the clip off the needle as well.  they are a little "wide" and if used often need a little tweaking to work correctly.

The clip is NOT needed, it only serves to lift the needle off the seat when the carb dries up to keep it from sticking.

This new fuel doesn't seem to create those issues like fuel we had 20-30 years ago that turned to a big sticky mess if you left it in anything for any length of time.

I haven't had a clip on the needle in my own carb for decades and zero issues.......

[richie49]

  It was fussie when I put it back on. One thing now a days is putting those dang needles back down in the jets.Never used to be a problem ,but not as steady as I was .   Oh well back to the drawing board.
      Richard richie49

[Cliff Ruggles]

Agreed, the later carbs where the splash guard has to go in first can be a PITA to get the rods into the jets on occasion.

We ALWAYS include a new plastic retainer for the power piston in all of our kits to make sure the piston doesn't jump out and the rods and hanger arms get bent during assembly.

Your be surprised at how many folks contact me wanting to buy just the retainer after going cheap and buying the junk Ebay $17.99 kit with free shipping.  I mention to them that the cheap POS blue seal isn't going to make the grade either, but they don't believe me.

Then weeks or months later I'll see an order come in from the same customer buying one of my kits....I have a very good memory for these things!........Cliff