My car seems to have developed a stumble when I nail it. I't may have been there for awhile
since I don't run it hard often. I have a 670 street avenger and recently I found out that they come out of the box with those "stone type filters" at each bowl. Mine never had them and I decided while changing some fuel line to install them. It seems like I noticed the stumble afterwards but I'm not positive. Are those things restrictive enough to cause this type of problem?
I'm frankly not very good with tuning Holley carbs and I have trouble determining too much fuel or too much air. What I can tell you..Total timing is dead on 36 degrees thanks the new MSD ignition. graemlins/thumbsup.gif Fuel pressure is set at 6psi, jets are out of the box 65 front 68 rear.
383, Performer RPM heads, Chevy Hot Cam. The car runs fine other than the stumble. Any suggestions..Thanks a bunch.

The filters won't cause that.

I'd try a pump cam kit.

I just had a massive stumble on mine and I was just sure it was carburetor related. Turns out my alternator wasnt charging and my spark wasnt to hot. It drove fine, but stumbled like when the secondaries open to early.

If its a very slight stumble, try adding .001 or so to the pump arm clearance, may fix it right up.

Or taking .001" out and see which way it needs to go. That's something a new squirter can cure. Marty's trick is cool, as it will let you know which it needs to go, more or less fuel.

Wow 65 ands 68's are stock.I mean to tell you that is small.

Does it surge at all?

Or does it stumble, recover, and then give smooth power to the shift point?

Hey guys thanks for the replies. The "stumble" is not an off idle stumble but I believe its as the secondaries are opening. How would you decide between too much air or too much fuel? It seems like it falls on its face then runs out normally. I realize the jets seem pretty small compared to what I see most of you guys running but it didn't seem to be a problem in the past. I have the yellow spring in the secondaries and have not changed that. I hadn't considered an electrical problem but I guess thats something to look into since I had a little fire recently and had to make some wiring repairs..Thats a story for another time. Lets just say gasoline sure has a way of finding a spark. :( I hadn't been that excited in a while... Visions of bubbling red paint keep running in my head :eek: The next day I was at SAM's buying a couple of extinquishers for the garage and promised myself to quit tinkering when I'm tired. Anyway keep the suggestions coming, if it don't have an injector I'm short on experience...

I would try the next lightest spring, sounds like a lean bog to me.

And if that doesn't help, get a vacuum reading at the stumble. Get your power valve rated at that vacuum, or 1/2" above. And trust me, even if the engine idles at 11" and you run a 10.5" power valve, it WILL NOT flow fuel at idle if the idle is properly set.

Also, assume these 'fancy' vaccum carbs also have a secondary butterfly adjustment. ensure that the transfer slot ( a small cut out of the venturi wall)is JUST peeking through when viewed from the bottom of the carb. It'll become obvious the first time you see it. This will ensure fuel starts flowing IMMEIDATELY when the butterflys open and draw air through the venturi.

When you dial it in right, man , there ins't anything better than a Holley carb, or maybe two, or a brace of three! Have fun graemlins/beers.gif

And yeah next step is to check coil voltage at 1800 rpm, and you better have near 14V.