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OK I'm being a little ignorant. I recently removed my Sniper EFI and put a Holley 855cfm carb on my 540. My question is about the idle rpm fluctuating so much.
I say I'm being ignorant because it's actually been a really long time since I've had a conventional carburetor so maybe I've forgotten how they act.
When I first start the engine after it's sat for days/weeks, after it warms up enough for the choke to kick off entirely, the idle is lower. Like around 700-800rpm. It acts like it wants to die. I have adjusted the idle rpm so that this rpm at this engine temperature is at a minimum. The coolant temp is around 150F at this point.
Later, after the engine is fully warmed up, the idle ends up around 1200rpm. That's after I've driven the car for a few minutes. The idle will end up at ~1100-1200rpm. That seems too fast.
I have adjusted the idle fuel mixture.
I have adjusted the idle rpm as low as I can without it dying when it's just kicked off the choke.
The carburetor runs great otherwise. Drivability, tip-in, WOT, all of that is good.
I did not change intake manifold when I removed the Sniper. With the Sniper, the vacuum levels were normal/as expected. I saw no indication of a problem with vacuum. If there was a vacuum leak, I didn't see it.
So, is this normal? Or, do I have a vacuum leak in this carburetor?
I bought the carburetor off ebay. It's a service counter replacement carb for the L88 carburetor. It's a 3418-1. The seller claimed to be an ASE mechanic. He rebuilt the carb.
If I decide the carb has a vacuum leak (maybe around the throttle shafts?), I will probably just go buy one of the brand new Holley carbs. I like the one that's specified for the ZZ572. That's an 850cfm DP with electric choke.
Try going through the electric choke set up procedure again. Exactly by the book. I was surprised how much the exact procedure helped in nailing the set up.
Try going through the electric choke set up procedure again. Exactly by the book. I was surprised how much the exact procedure helped in nailing the set up.
My issue is after I kick off the choke.
Are you saying that the choke should stay engaged longer?
My choke fully disengages around 150F water temp. That seems about right to me.
I'm running an aftermarket divorced electric coil for the choke. I have a Holley Strip Dominator intake manifold. There's no way to use the factory thermocoil.
I am not familiar with the Holley 3418, however, it appears to have a high idle cam and vacuum dash pot pull off like the 3367 Holley on R66.
I would unhook the choke rod and wire the choke open along with wiring or weighting the cam down to prevent it from moving around due to vibration. Then warm the engine to NOT, tune it to your desired idle rpm, and test drive it to see if you still experience the change in idle. If you do, it is in the carburetor circuits, not the choke.
The choke on the 3367 on R66 is extremely difficult to get properly set since I installed the L79 intake. I also experience occasional high idle after the engine is at NOT and have to kick the throttle to get it to return to hot idle. The plastic cam is forced up to get choke high idle, but there doesn't seem to be a mechanism to pull it down to prevent vibration or friction from allowing it to sticking or bounce back up. I thought of adding a weight or spring on the cam to assist it in returning to the hot idle position - I have yet to do it as I guess I am too lazy.
Ron Holley 3367 high idle cam configuration.
Long story short, I decided the carb is the problem. I got a deal for it on ebay. It was an impulse buy. In hindsight, "you get what you pay for" is probably the concept in play here. That's my theory anyway.
Do I KNOW the intake manifold isn't leaking? No, I don't know that. I do believe that the intake isn't leaking.
And, the "problems" started with this carb install. This carb had other silly problems along the way, too. Leaking where it shouldn't, etc.
So, I ordered a brand spanking new carburetor: https://sdparts.com/i-24504689-chevr...y-850-cfm.html
I bought it from Summit, not Scoggins-Dickey: https://www.summitracing.com/parts/nal-19420446
But, I think the pics are maybe a little better on the SDPC website.
This is the carburetor I wanted to buy anyway, before I impulsively bought the rebuilt 3418-1 when it popped up at a bargain price.
Hopefully, I'm right and this carburetor will help get the engine to start and run like it should.
If it behaves the same way as the 3418-1, then I guess I just burned up $1,000.
Carb problem or not?
