Bucked Like a Horse!

[WardL]

I just flew half way around the country and drove a beautiful 550 HP 427R Cobra. I didn't buy it because it jerked around at 0-50 MPH. Clearly the Roush motor is a racing motor and I want a steet beast. Some of it could be me and my driving skills. But cruising along at 40 MPH was bucking from the engine. Is this normal? I did not buy the Cobra. Is this normal?

[RedBarchetta]

Originally Posted by WardL

...But cruising along at 40 MPH was bucking from the engine.

Sounds like to me (based on your description) that the transition between the idle/main circuit and power circuit was not set properly and the car may have been "hunting" for more fuel and/or hitting a lean spot. Was this car injected or carbed?

-Dean

[Tommy]

I'll also ask what RPM you were running when it bucked. Engines tuned for maximum power at high RPM often don't run smoothly at very low RPM. Ordinary cars are designed to run smoothly at low RPM to provide maximum MPG. Cobras usually aren't.

[86Sebring]

A racing motor might be "jerking" at low RPM's, but above 2000-2500 it should not be jerking anymore, it is supposed to scream.
If you drove in 5th gear at 45mph, that is what could have happened, a lower gear selection should have eliminated the jerking.

[madmaxx]

i would not worry about that. does it have the 427r? what year? the problem is the customer did not have the carburator upgraded to the one with the green dot. Roush knows of this issue. It was prevalent around 2007 time frame. I have no idea if they would warrant it now. I have a roush and it is the drivable v8 i ever had zero bucking etc at any rpm above 1K. That was after the carb, before it was like you describe

[Got the Bug]

My experience was exactly the same as madmaxx's. I'm surprised that the owner/dealer hasn't fixed the problem. The R motor is probably not as happy at really low rpms, but it should be smooth as silk at 50 mph.

If it's the right car at the right price, you might want to reconsider. If it's the right car, but the price is just ok, take a pass and keep looking for something that has been fully sorted out.

[flyboy1997]

Mad Max You are Sooooo right on that Green Dot, my 427 KCR SB is a cut up also & Jody ( another LS owner with Roush powered SB almost like mine ) believed in that Dot so much that he pulled off his car & shipped to me for a try. Sometimes I hate being trusted because I sure did not want to send it back! First time that I had tootled back roads & ENJOYED it & my motor just loved it. I have not purchased my own yet because I have so much money in a Custom Carb for My Motor that I just can not seem to find a sweet spot but bolt on the green dot & No Adjustments & go cruise in comfort?
Wendell

[Double Venom]

Tranny ratios, rear end ratio's and gearing WILL cause the bucking, absolutely. Like driving an OEM (anything with a standard tranny) using I.e.; third gear in 20 mph traffic jamb!

If you liked the car/price think it over again quick!!!!!!!!!!!!!

DV

[madmaxx]

Heck I feel sorry for the original owner, he bought and paid retail and has lived with this problem. Once again buy used. If you do not want to deal with Roush call erik at performance engineering I beleive he knows the fix and what jets to change. Only problem he may want it on his chassis dyno. I held Roush feet to the fire since it was under warranty and made erik send the carb back to Roush. They repaired and never had a problem.

[madmaxx]

I forgot to mention, welcome to Cobras. If the rest of the car, paint, body, color, fit and finish were right and this scares you, A COBRA IS NOT FOR YOU. There is always something that is going to need attention, yes they are junk, no excuse as some will try to justify it is a hand made car, blah blah blah. Unless you buy it from me or someone who is a mechanic and worked the bugs out for 12 months you have alot of bolts to checks etc.

It would seam to me if this PO did not work out the bucking or used the lame excuse this is a high performance car then what else did he settle for. High performance or not it should run smoothly.

With the deal Vintage motorsports is running for a new bdr with ford 427 you might want to go that route. You will probably have break in issues but I think they have they have it figured out.

No a BDR is not an SPF. SPF is better but I bet you are paying more than 44k for the one you are looking at, so when factoring in the different cost they are each worth what you pay for them.

[WardL]

Once again, great info. It is a carberated Roush 427R with 550 HP built in 2007! The bucking would occur at 2k RPM or higher. Really just any cruising speed less than 50 MPH it would just buck a little. It was smooth when accellerating, no problem. If you lugged the engine or ran the RPM up, but accellerating, no problem, it was smooth. I had a 1980 280 ZX that ran exactly the same. I think if I had a little less camshaft it would not be quite so rough. The updated carb is the best next step.

[madmaxx]

Roush makes three 427. The S, the SR, The R. The SR seams to be the best of both worlds in excess of 500 hp but still drivable. The R likes to live at high rpm. I am confident 99% of the problem is in the carb. As him to pull the air cleaner and look at the front of the carb, there should be a green dot made by a paint marker. I bet he finds a different color. Knock $1k off for a new carb, call Roush and tell them you want this was serviced, I ams sure the cost will be less than $1k but you need to reimburse yourself for the troubleshooting

[mdross1]

It does sound like a carb issue,there are a lot of good carb people out there that can help dail this motor in.Have fun in your search.

[Roush #1]

Ward,

Just to add a bit to this mix .... my repair, from a blue dot to a green dot ....
did not involve a jet change, air bleed change, idle air bleed adjustment, or squirter change.

I checked all of these on the original blue dot and they were the same on the green dot replacement carburetor. What I am saying is the difference in the two carburetors on mine was not visible.

I am aware of one more Roush engine that was built about the same time that had very similar problems. I have heard there are more, but I do not know that for sure. Mine was number 444 and I think Maxx was somewhere about the same time.

Don't give up on the engine. It could be as simple as an air bleed adjustment.

I understand your frustration, but the 427R should not be "bucking like a horse" when it is properly tuned. Mine runs smoothly in any gear at 1,000 RPM and idles well at 800 RPM - and yours can as well.

Gearing has something to do with it and it should be more prone to buck at higher gear ratios (lower numbers), but when I am in 6th gear (.62:1 ratio) with 3.89:1 rear gears, not many Cobras are geared higher which normally causes the bucking.

Good luck!

Jody

[jhv48]

That bucking at cruise speed sounds like a lean condition in the transition between idle and main circuits.

Definitely a carb issue, and a simple one to boot.

[madmaxx]

My guess is any Roush 427 between 400 and 600. The numbers are stamped on the valve cover, and on the dyno sheet, and the roush plaq. Without a doubt my Roush has performed flawlessly from the day I got it, the installer addressed the carb issue before I got it. Oh did I mention Sunny, 65F and 40% humidity in Houston today. How that snow hitting you guys LOL LOL LOL LOL LOL LOL!!!!!

Originally Posted by Roush #1

Ward,

Just to add a bit to this mix .... my repair, from a blue dot to a green dot ....
did not involve a jet change, air bleed change, idle air bleed adjustment, or squirter change.

I checked all of these on the original blue dot and they were the same on the green dot replacement carburetor. What I am saying is the difference in the two carburetors on mine was not visible.

I am aware of one more Roush engine that was built about the same time that had very similar problems. I have heard there are more, but I do not know that for sure. Mine was number 444 and I think Maxx was somewhere about the same time.

Don't give up on the engine. It could be as simple as an air bleed adjustment.

I understand your frustration, but the 427R should not be "bucking like a horse" when it is properly tuned. Mine runs smoothly in any gear at 1,000 RPM and idles well at 800 RPM - and yours can as well.

Gearing has something to do with it and it should be more prone to buck at higher gear ratios (lower numbers), but when I am in 6th gear (.62:1 ratio) with 3.89:1 rear gears, not many Cobras are geared higher which normally causes the bucking.

Good luck!

Jody

[WardL]

This is the Roush 427R - 443! Oh, are they numbered sequentially independent of the street or race version? either way, thanks so much for the great suggestions! I'm going to inform the dealer of this thread, but pass on the car. I think I could get a great car but now I realize the car color is not for me. I saw a black one and almost passed out with desire. Sure helps you appreciate Club Cobra and its members! Thanks again.

[madmaxx]

The engines are all identicle except for the camshaft and I think the manifold. The blocks, pistons, cranks, etc are identicle. It is just the 427R likes high rpm so better suited for a track then stop and go. That being said, even the 427S is 99.999% more engine than most drivers can handle effectively.

Your right look at the body and color, those are very expensive to change.

[madmaxx]

Yes number sequentially and no doubt it is the carb, if Roush 1 had it at 443 and I had at 518 then it is smack dab in the middle.

[Larry Spillman]

If you have a light weight car with hugh power and you are in too high of a gear you will get neck snap as engine will surge and buck car around.if you keep it in a lower gear with light gas pedal it should calm down a lot also check tire pressure for correct traction/