The other day I was out driving and and I noticed something weird after I took off from a stop sign. I took my foot off the gas but the car kept on going and didn't even drop any RPM's. In fact, it started going faster and I wan't even touching the gas. I had to STAND on the brakes a lot harder to get it stopped. There really wan't any engine braking either as the RPM's stayed pretty steady even as I came to a stop. I thought there was a pull on my throttle spring so I moved the mount till the spring had no tension on it. Took the car for a spin with the same results. I backed off the idle screw barely one turn and it stumbled and died when I dropped it in gear so the idle isn't the problem. I noticed when I start the car from the outside (I can reach through the roof and start it while grabbing the the throttle with the other.) If I pull back on the throttle then let it go, the idle is really high. I can take my hand and move it slightly forward (towards the radiator) and the idle calms down to normal. Unfortunately I can't do this from the driver's seat. I also looked down the carb while it was running and I didn't see any fuel dumping in there so I think the carb is pretty close. What else should I be looking for, I'm wasing gas and its no a lot of fun to drive right now.
Do you have a throttle cable or linkage, I had a throttle cable bind on me before and do something similar.
Beat me to it 54BOMB - maybe a kink or dirt in a cable? Check all connections between your gas pedal and carb and make sure they are good and free. If you have a cable maybe it is not running freely in the outer sheath?
What kind of carbs and linkages are you running? I have had my linkage bind at the carbs (I run 97s). I had to drill out the slider on the throttle are so that it could slide on the shaft better. Also try a bit of white grease on them. Usually what happens is it binds on the shaft. (see the pic) Look at it this way, at least you are sorting this at home, I had to figure it out by the side of the road! Good luck.
You should have tension on your throttle spring, it is used to close the throttle, are you sure you have it connected to close the throttle? If it is connected wrong it will pull the throttle open as you are saying your problem is.
Its just a single, off the shelf 500 Holley 2 bbl. I'm using the linkage that came with the Lokar kit.
I have it (the spring) mounted behind the carb with a bracket on my valve cover stud. I've never ran the mount/spring behind the carb before. My neighbor set it up like that in the midst of the pre-Autorama thrash. its worked fine (untill now) so I didn't think there was any problem with that setup. Now I'm wondering if the throttle shaft might be binding slightly because things are being pulled in opposite directions instead of in line as it would be with the spring out in front.
Bingo! You better have tension on the spring with the throttle plates closed. It should snap the throttle back when you blip it with your hand. Good throttle return springs have an inner and outer spring for safety in case one spring breaks.
I do have tension on the spring. I thought I may have undo tension that was holding the throttle open just a little. All I did was tap my mount a little forward to make sure it wasn't being pulled. I'll check it again today on my lunch break. I have two return springs as well. I used race circle track cars, seen way too many stuck throttles.
motor mounts?... If they go bad it allows the engine to move especially when accelerating from a dead stop. It's because the movement of the engine pulls on the throttle. Just changed some out on a car that was having the same issue.
beat me to it, check for a vacuum leak. That same deal happened to my non-HAMB friendly, fuel injected daily driver. There was a dry rotted vacuum line. I replaced it and order was restored.
Mount the spring in front of carb. Sounds to me like its pulling throttle OPEN. Needs to hold it closed. Frank
I had the exact same thing happen. It was spooky. Bad motor mounts were replaced and that cured the problem.
Re-read his post guys. No tension on throttle spring, because it is mounted backwards. Pulling wrong direction!!! Frank Chopper got it right.
My old Chrysler Hemi tried to get away from me once. A motor mount with torn rubber would let the engine lean over a bit, and push against the throttle linkage and give me almost full throttle even after I took my foot off the gas. Check if the engine rocks, or squirms around under changing conditions. frame brackets etc. Are there any other cables (trans etc) that may be sticking or influencing the throttle movement? Do you have any vacuum accessories or vent hoses that may be opening up that can simulate a throttle opening even if the throttle is not open very much? If you introduce an open vacuum leak (leaking booster?), it could imitate a throttle opening. If your carb is a bit rich, it might not have the usual leanout stumble that a vac leak will often give, and act just like the throttle opened up a bit. It can come and go. If you had a lean carb, a vac leak would make it lean out and stumble, but if the carb is running rich, it could cover over the lean stumble and a vac leak could act the same as opening the throttle. I hope I described that in an understandable way.
What? Undo tension holding it open? For that to be even possible then you clearly have the throttle return spring backwards. Wow -
Just beat me to it Bort, "undo tension holding the throttle open" is the wrong answer. Tension is supposed to close it not open it. I can't think of why the spring being in front of, or behind the carb would make any difference one way or the other. Wherever it is, it should be closing the throttle. The pivot point, or fulcrum of the linkage doesn't care where the spring is but it's quite important which side of the pivot you attach the spring. It should snap the throttle shut. Jn thinking about your problem and not being familiar with your carb is it possible that the plate with "stair-steps" on it, that the idle screw rests on, is binding, rusty, dirty or whatever and is not rotating back to the idle position?
Doh! Spring goes in FRONT of the throttle?? LOL..JK. On this same topic, I had a friends 53 Chevy doing the same thing and we tried everything. Turned out that due to vibration the sleeve around the throttle rod was vibration and the rod was walking up the inside of the sleeve. We hogged it out and greased the rod and the problem finally went away.
Maybe I worded it wrong, I was thinking something either the spring or a bind was holding the throttle open when I let off the gas. It ended up being the simplest of all cures. I went out to the car at lunch and tapped my mount back a few times and made the spring a little more taught. Fired it up, problem solved. That mount must have been able to move on the valve cover stud and relax the spring tension causing the throttle plates to not completely close. The throttle did snap back, just not that 1/32" or whatever it was that caused the plates to be slightly opened. Thank you guys for all the advice and tips to look for if something like this happens again.
Frank did you read his post, He has stated a few times that the spring has tension and is closing the butterflies. It is mounted to the rear, I have mounted mine to the rear and front before, doesn't matter as long as it pulls closed. Hasn't anyone heard of worn shaft bushing, or leaking seals before. Why does everyone pay so much to their strombergs and holley bases, shafts fitted and honed, if there wasn't a possibility of vacuum leak from worn shafts and bushings. Bent shaft will also prevent a butterfly from closing, shifted butterfly on the shaft, ... alot of factors can interfere with butterflies closing.
Make sure the choke is not working back wards. Had a car that as the car wormed up it would idle faster.
Is the fast idle cam on the choke moving out of the way as it should? Also I agree on the vacuum leaks. Are you running an adapter plate? sometimes they aren't flat enough. I have the same carb and put springs on both ends. The bottom pulling back, and the top pulling forward. I had problems with the idle speed creaping up on me, enough so it was trying to run after I shut it down. The added springs worked nicely.
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