Thinking of an air-fuel meter to tune carb - any experience?

[patrickt]

Lippy, what is that makes you think your carb is not set right?

[lippy]

Originally Posted by patrickt

Lippy, what is that makes you think your carb is not set right?

(1) Runs on after stopping sometimes. Not that bad, but it does go for 1s or so. Could just be bad gas or ignition, but I retarded the timing from 36 to 34 (full). Problem still present. (2) It was stumbling when I gave it throttle. I changed the acceleration pump nozzles to 37s and I think that did the trick. (3) Plugs fouled. My first coil was out of spec and I replaced it, and hope that did the trick.

This is a pricey engine and I want to make sure it's operating within range for a carb'd car. With a sideband, I can verify and optimize.

Also, the fuel was percolating when I stopped. I added a 0.25" phenolic spacer and I *think* that fixed the percolation.

[patrickt]

Fair enough. I'm sure Brent picked a nice carb for your set up, and it is tuneable so that the engine will run perfectly. Here's a tip though, a brand new build will have the potential for more crap to get in to the carb than a build with a few years and a few thousand miles under its belt. Little flecks from the hoses, the lines, goo from here and there, it all makes its way in to the carb and filters don't always stop it. I don't know how many holes the emulsion tubes coming down for the main circuit has in your carb, but it doesn't take much to hamper one of them. A little dried varnish, a little fleck of hose/dirt/whathaveyou in and around the holes/tubes/passageways and it will throw off the performance. Then you find yourself trying to compensate for that shortcoming by tweaking other parts of the circuits. So, just make sure the insides of your metering blocks are clean enough to eat off of. Seriously, it really is a BFD with a fresh build, today's ethanol fuels, and you should try and get a chlorinated carb cleaner. They're outlawed in your state (California), I believe, so the best you're going to get is going to be something acetone based, which is better than nothing. But if you find yourself in a cheap, crappy dollar store, look for a no-name carb cleaner that has dichloromethane (methylene chloride) or another VOC that has chlorine as a component -- maybe you'll get lucky. Dang, you would think that in a state where you can just buy Panama Red at the corner dime store you'd be able to buy a chlorinated carb cleaner as well. I use a separate little miniature polyimide tubing, that is thin enough to fit through the high speed (main) bleeds, to blast everything out. The tube that comes with your cleaner is usually too fat to fit in there and will just blast it back in to your eyes -- but that's better than nothing. If your AF meter gives you wacky readings, the first thing to suspect is crap in the carb.

[DanEC]

Originally Posted by lippy

(1) Runs on after stopping sometimes.

Sometimes run on can simply be brought on by a high idle. What are you idling at?

Also, since I understand this engine to be pretty stout - are you familiar with the issue of where the throttle blade should sit at idle with respect to the idle slots in the bore? If the trottle blade rests at the upper part or above the idle fuel slots at idle, you lose tuning control of your idle fuel mixture and consequently tend to open the throttle up more with the idle screw to keep it running. If your idle is not responsive to adjustments in the idle screws this could be a part of the problem. When shutting the engine off, fuel can continue to be pulled from the idle slots and promote run on until the engine comes to a complete stop. On most Holley's it's pretty easy to compensate for because there is a set screw on the secondary throttle blades. The secondary throttle blades can be opened slightly to allow more air through them at idle - allowing the main idle adjustment to be backed off and the primary throttle blade to rest in the center of the idle slots where it needs to be. Actually I would anticipate Brent would check this when breaking in and dynoing the engine but if you have set the idle up a little higher in the car, it may have gotten outside where it needs to be.

Sorry if I'm telling you a bunch of stuff you have already looked at or considered.