600cfm Holley cutting out suddeny

[MrSony]

So the 600cfm Holley I have on my 429 in my tbird has been professionally rebuilt by my dad's coworker who happens to build 1100hp motors on the side and has an early 90s buick regal (modified of course) that runs some serious times in the 1/4. Anyway, as of about two or three days ago it'll just cut out for a split second and return to normal. It's as if someone is playing an audio clip and pressing the mute button every three seconds. Throttle respons is still excellent (unless it's cold then it'll just flat out stall if I punch it) and WOT is great. Sometimes there isn't any fuel in the glass filter before the carb. Could it be a clogged fuel filter under the car? There was a problem starting the car when I left work last night, cranked and cranked until it finally roared to life and then drove and started fine. What gives? I'm thinking that under body filter may be the culprit. What say you guys? It's probably the OEM filter too.

 

[pontiacgp]

could be the fuel pump is on it's way out......if your glass filter looks like this please get rid of it, they have been the cause of car fires..

 

[565bbchevy]

I could be the fuel pump is not working properly and possibly there is another filter that is before the pump or in tank "sock" that is causing a restriction.
Also to me a 600 cfm carb seems small for that size engine.

 

[MrSony]

Well, I guess I better swap out for a plastic filter then? Also the only filter's I can even find on the internet for this car or a "Full size Ford" of that era are the ones that screw into those crappy ford OEM carbs so I don't think there is a filter mounted to the frame, but I never really looked for one. And for a big ol engine that has unknown insides and came factory with a 600cfm, I think a 600cfm holley is fine enough especially since this engine never really ever sees the high side of 4500rpm. Cruising car. Plus it was already on the car when I got it.

 

[MrSony]

It only seems to cut out and sputter, also loss of power until im essentially WOT for about 10 seconds. The fuel pump is not an expensive nor an intensive part to replace so I might as well do that. It on;y does it for an hour or so when it's cold and after it's warmed up for about an hour it is mostly fine. It just recently started doing this. It's very irritating. This big ol 360hp big block is wheezing and sputtering like a grandpa.

 

[pontiacgp]

http://forums.holley.com/entry.php?428-How-To-Cure-Carburetor-Stumble

 

[MrSony]

But the thing its, it doesn't stumble at least not from a stop. It's only at speed it cuts in and out like it's running out of gas almost. But I have half a tank (yes the gauge is accurate). I threw half a can of seafoam and 9 gallons of gas in the tank to see if that would do anything yesterday. I guess I gotta burn through that batch first before I do anything drastic. I am however going to purchase an inline fuel pressure gauge. Thinking of the Mr. Gasket one with the fuel block and hose clamps in the kit for like 50$. Should it be like 6-10 psi or something with that mechanical pump? I think it might be the stock unit.

 

[MrSony]

OK, so I got the fuel pressure gauge (I had to bring in a picture and part number because none of the idiots knew what "Mr. Gasket fuel pressure gauge with the fuel block and hose clamps" meant), and it holds steady at 7PSI before the filter, and the filter is clean. The car does NOT have an underbody filter, just the one at the carb. I will change that glass one out for a plastic one soon. So, the fuel pump and filter are not the problem. To restate what it's doing, under acceleration it cuts in and out rapidly as if the throttle blades are opening and closing in less than a second. While cruising at any speed with just enough throttle to maintain speed (very litte) its perfectly fine. But if I give it ANY gas at all, it starts doing it again. It only started happening about a week ago, and it seems that a cylinder has a miss on the passenger side, but that may be caused by an exhaust leak (pipes aren't fully connected. I'd fix it myself if I could. I am NOT paying 200+ dollars for 30 bucks in parts and an hours labor so I guess that will have to stay for a month or two longer until I sell my Regal to get cash to redo the motor. Anyway, back to the carb. It is getting very annoying and I am starting to get concerned with how much it's doing it. And it only does it sometimes. Any suggestions? I was thinking of picking up a vacuum gauge to try and diagnose it. Would that be good?

 

[MrSony]

So, I got the exhaust fixed. Those choads tried to charge me 300 bucks for a 3.17$ job that took 10 minutes. Well, the car is a LOT quieter now, kind of miss the loudness. The carb is still stumbling, but only when cold. If I drive around for a few hours, WELL after it reaches operating temperature, it will calm down and haul *ss like it used too. I have not taken the carb apart yet, the fuel pump is in good shape, pulls 7psi on the gauge at all rpm (only revved it to 4k, but that's good enough for me). I previously adjusted the carb when the exhaust was badly leaking so it could be in need of adjustment again. I should also look at the plugs. Like I said I'm going to pick up a vacuum gauge to help me, something like this: http://shop.advanceautoparts.com/p/...leIdSearch=26504&searchTerm=cp7803&showTitle= I hope this carb isn't junk.

 

[MrSony]

And it just SUDDENLY started doing it a week o two ago. before that, with the exhaust leak it was fine. It then started to spit sputter and cut in and out rapidly upon acceleration when cold, and takes a few hours of driving to clear up. And fuel filter is spotless. ***EDIT: Fixing the exhaust leak made no difference******