Rough running Roush 427R

[Goopie 18]

I have a Roush 427 R, Holley 770CFM carb, MSD ignition. Car starts right up but idles rough and seems to miss a speed. Very erratic at low and High RPMs. I have replaced the MSD box, new plugs, new rotor/cap, new coil, new fuel filter/mechanical fuel pump. Twin filters in Holley are spotless. Fresh fuel. Timing OK. Ignition wire continuity good. Magnetic pickup in coil reads proper OHMS. I'm stumped.

[A/S65]

Have you checked for vaccum leaks around intake and carb base? Also I didnt catch if you replaced or checked the plug wires. When you pulled the plugs did any of them appear to be burning signifacantly different than the others?

[jhv48]

Make sure your electric choke is fully opening. Let's start simple first. What do the plugs look like? Float level ok? You have already ruled out most of the usual suspects. If you can swap out the carb, it would either rule it in or out of the equation. I like the vacuum leak test too. A tiny piece of dirt in a jet could easily cause this problem.

[ERA Chas]

Do the suggested tests but remove those stone carb filters and put a big Fram upstream in the fuel system near the tank.

[JBCOBRA]

All great suggestions here. Must be something simple.
Dirt in carb needle
burned plug wire(s)
...I accidentally broke the carbon tip off my distributor cap while replacing it. That made a similar symptom.
ground wire from distributor.

[madmaxx]

Check connections to coil, not just the wire but the actual terminal, mine broke in half. Check timing is distributor loose? Try to rotate with your hand.

[Gaz64]

Compression test please before you chase your tail too much.

[VintageUpgrades]

What is the engine number? Possibly one of the defective Holley carbs from 05-06?

[Goopie 18]

engine #291

[TButtrick]

Did you replace all those items because it was running rough or did it start running rough after you replaced the items you mentioned?

Did you check base and total timing with vacuum removed from dizzy? (if applicable)

Is the coil you replaced the proper primary resistance for your ignition? 1.5Kohm or .700Kohm?

[Goopie 18]

Valuable responses. I started replacing parts after rough running. Didn't know if problem was fuel or spark related. My holley was built in 2005 (this was a recalled carb due to flaking of alloy walls inside carb. I'm going to open up the carb and inspect/clean it.

[patrickt]

Have you blasted out the air bleeds? I've written about that on here at least a dozen times. It takes less than five minutes and, if that's the problem, it will be a night and day experience. See: Holley Carb Woes - DCDoug Pay Attention (Long Post) and This is new: stumbling/missing at idle/cruise speed for starters....

[WildBill1965]

Had the same thing, chased all of the normal things and ended up being the intake gasket. Replaced it with the correct gasket. Roush and other MFG's were using the wrong gaskets in the beginning. Leaking from the bottom side of the manifold 2 cylinders affected. Pull carb and stick a mirror down the runners, shine light down runner and see if any are discolored in area of gasket, mine was dark around cylinders affected. Good luck!
B i l l

[Got the Bug]

Originally Posted by WildBill1965

Had the same thing, chased all of the normal things and ended up being the intake gasket. Replaced it with the correct gasket. Roush and other MFG's were using the wrong gaskets in the beginning. Leaking from the bottom side of the manifold 2 cylinders affected. Pull carb and stick a mirror down the runners, shine light down runner and see if any are discolored in area of gasket, mine was dark around cylinders affected. Good luck!
B i l l

Here's a thread with some pics of the Fel Pro gaskets that failed on my Roush 402 several years ago. Same kind of symptoms, until the the intake gasket failed big time.

Mustang ranch- roush authorized dealer

[WildBill1965]

Doug that is pretty much the same story and look except mine was on the bottom and sucking oil, never used any until then. Gasket fixed all of that!

B i l l

[TButtrick]

Did you read the plugs yet?

[Goopie 18]

Following Patrick's advice, I cleaned the air holes on my Holley and the problem is solved. If I had done this first, lots of time and $ would have been saved. Thanks to all (especially Patrick). I also opened the carb (2005) and thankfully did not have the flaking that many have experienced.

[patrickt]

Originally Posted by Goopie 18

Following Patrick's advice, I cleaned the air holes on my Holley and the problem is solved. If I had done this first, lots of time and $ would have been saved. Thanks to all (especially Patrick).

OK, you might now consider sending both RodKnock and ERAChas PMs referring to me as "God's Gift to Motorsports" and telling them that they should be nicer to me on all of their posts.

[D111]

I checked mine for the heck of it even though It Wasn't really running rough. Used a can of spray air and it would not blow through after spraying cleaner The canned air blew through nicely.



Thanks

[D111]

Would it be that the idle mixture screws would now need Readjusting?

It seems after clearing the air bleeders the car will not idle as low and smooth.
As I said in previous post the car was idling and running fairly well I just wanted to see if those Air bleeds were clogged and they did seem so.