71 F100 takes off like a rocket

[RWVNRAL]

New to the board. I've benefited from many of the postings here and have been able to make some definite improvements on my truck as a result. Many thanks. Now I have something I cannot find an answer to.

1971 Ford F-100 with 302 V8 and what I believe is an automatic/cruisomatic?? C4 tranny. Bought this truck about a year ago. Runs pretty well, but it's got a number of issues related to previous owners. I am not certain, for instance, that I have either the original engine or the original tranny. My shop guys tell me that the ignition system has been toyed with...and it's obvious from the looks of it that the engine has been stripped of its emissions components (which is why I doubt it's the original engine). The carb is an autolite 2100.

I don't dare let anyone drive it. Whenever the truck is at a stop, and when I am ready to begin moving forward again, it will sometimes take off on it's own with just a very slight depression on the accelerator. This happens most often when the truck is on a slight incline, or it senses that there is a load. It always happens when the incline is steep. It's exceptionally dangerous because once this surging/take-off occurs, the only option one has is either to rip the truck out of gear, slam on the brakes, or turn off the engine. On several occasions, I have nearly lost control of the truck. This surging/take-off phenomenon will run a cycle of approximately 3 to 4 seconds. Then the situation corrects and normal acceleration resumes. However, during a very violent episode, the truck will throw itself out of drive into second gear.

I have posted this as a drivetrain question. Perhaps its a carb issue? I imagine it's a combination of both, but thought I'd start here first. Any ideas?

[cep62]

Well seeing as nobody else has piped up ,I'll start by asking if you have a throttle cable or the rod style linkage?
If you have a broken motor mount and the rod style throttle linkage ,it can cause an engine to accelerate on it's own.

[RWVNRAL]

I'll start by asking if you have a throttle cable or the rod style linkage?

It's the rod style. Haven't checked the motor mounts....but I haven't gotten any other indications that there is a problem there. What's the best way to inspect the mounts?

[basketcase0302]

What's the best way to inspect the mounts?

Easier done with two guys, (one on the gas/truck in gear/at a stop-while your watching the engine to see if it's lifting off the perches). I'm also guessing like above-carburetion. 2BBL or 4BBL carb? Do you have another one you can throw on it to see what it would do?

[michael69]

I agree it sounds like bad motor mounts. Have someone watch engine while you hold brakes and give it gas while in gear to see if motor raises up off frame stands. Or use a floor jack and jack motor up and see if it separates from engine mounts.

[michael69]

Basketcase bet me to it.

[BobbyFord]

Damn, my truck does that, too...

[michael69]

Bobby yours does it like I wish mine would.

[70 ranger]

I broke the motor mount in my 65 mustang when I was a kid, and reading your post that was what it sounded like to me! A 289 has way more power in it when your not expecting it!

[RWVNRAL]

Or use a floor jack and jack motor up and see if it separates from engine mounts.

I think I'll use the floor jack option....I don't want to take the chance that this truck slips it's skin and drives itself over someone. I recently had it's brakes checked by a local shop, and, when I got back to the shop to learn the quote for the brake job, I was informed that none of the mechanics would back it out of the bay. Apparently, it had exhibited its aggressive acceleration while pulling it into the bay. The guys were all looking at me askance...as if I had intended to do them bodily harm by way of my possessed truck. So, this is a serious problem. I'm all in favor of torque.....I'd just like to be in control of the truck's power----rather than it being in control of me! There's something wrong with a truck that will throw itself into a full-bore gape towards wherever.

[nolan in blaine]

my 70 used to do that too. broken motor mount on the passenger side. 302 C4... same thing

[thebannister8]

my 67 mustang did that...it was a broken motor mount

[Donnie]

If your motor mounts are suspect, you can check these yourself, just open the hood & watch & listen as you torque it up a bit..do it in both foreward & reverse. If your mts are good, then I would suspect the linkage control rods, bell crank & springs etc.....Did you say that it does this in both foreward & reverse?...Donnie