Help - RPM Accelerates When Hot

YOI · #1 (**permalink**) 05-03-2004, 11:03 AM

I recently purchased a Superformance Cobra #521, it is powered by a Motorsport 460 with a Demon Carb. As of today, the car has 681 miles on it. When the car gets up in temperature, I have noticed to my alarm, that when I depress the clutch to shift, the RPM lingers and then climbs on its own. I am forced to put my foot under the accelerator and pull it back to correct the problem. Has anyone had any similar experiences? Does this sound like a throttle linkage problem or a fast idle cam? I am scheduled to take the car in to a Ford dealership next week. I am hoping to get some advice to take with me. Thank you.

MidOHasp · #2 (**permalink**) 05-03-2004, 11:12 AM

Well, if you are able to pull back on the gas pedal, and that alleviates th eproblem, I'd say you probably have a linkage issue. My SPF 1670 probably has somewhat different linkage since it is newer, so I can't help you on specifics, but... I'd say that's your problem.

Get it good and hot and stop the car and get out. Pop the hood and rev it up by hand w/ the linkage. If it sticks open, see if you can find the hang-up.

Just my $.02

RallySnake · #3 (**permalink**) 05-03-2004, 11:29 AM

Yoi,

I had a similar problem. It was caused by the air filter. I hammered a little dent in the spot where the upper part of the carburetor lever was rubbing and solved the problem. Unless, I forget and put the air filter on backwards!

You do have two throttle return springs, right?

Paul

YOI · #4 (**permalink**) 05-03-2004, 11:42 AM

Paul,
Yes, I have double springs. Do you attribute your hang up to metal expansion when hot?
Thank you, YOI

RallySnake · #5 (**permalink**) 05-03-2004, 05:59 PM

Yoi,

No, when the carb is cold, the choke kicks in and advances the throttle. As the choke warms and relaxes, the lever should fall back to a more closed position. In my case, it was hitting the inside of the air filter bottom plate and not closing all the way. The warmer it got, the faster it would idle.

The easiest test is to remove the air filter housing and see if it runs right. Don't put your face right over the carb while it's running, though!

Also, try spraying a little WD40 on the throttle shafts. Maybe they're sticking.

Paul

YOI · #6 (**permalink**) 05-04-2004, 03:30 PM

Thanks to you guys for the help. Hopefully, I will get this resolved next week!
YOI

BlueRooster · #7 (**permalink**) 05-04-2004, 06:09 PM

Your still having the problem huh? Did you unhook the carb from the linkage and make sure that all the linkage prior to the carb is free flowing? Once pre carb is not suspect move on to the carb, Rallysnakes suggestion is good, spray down the linkage with WD-40 and run the carb through its full travel. Can you reproduce this behavior in the garage? Have you run the car on the road again since this first cropped up?

Dane

YOI · #8 (**permalink**) 05-09-2004, 01:07 PM

Dane, I just got back from out of town business. Early this week I am going into the Ford Dealership where I have a good relationship and we are going to try to locate the problem. Thanks for the help. I'll let you know how it turns out. Also, I am going to start a new thread for a forward sway bar bracket and bushing. Any thoughts on where I can get one?
YOI

terry lee · #9 (**permalink**) 05-09-2004, 01:49 PM

YOI,
Many of us with SPF's have experienced this problem.
More than likely it is the throttle linkage. Unfasten each ball connection and grease the fittings. This should eliminate the problem. There could be some other problem, but this solution seems to work in most cases. Also check to make sure the assembly is not hanging up when it makes its bends. This has been discussed at some length on "SCOF" the SPF forum.
TL