suddenly it started revving up then revving down unless I goosed it to keep it running

20

Asked by Jun 21, 2011 at 08:31 PM about the 1970 Volkswagen Beetle

Question type: Maintenance & Repair

It had been runnig very well. I had finely tuned the idle six months ago, But I have been driving it on a very rough gravel road a lot. The other day it began to act up. It would want to die but I could hit the gas but then it revved way up and then started to die. I could keep it going by using the gas each time  it revved down.
the  carb was loose on the manifold and I fixed that but it did not change anything
Yjee carb had come oose in the bolt on the manifpld - towad the endigne. Fixred that but no change. What could this be?

3 Answers

425

maybe the accelerator cable stretched. try replacing it and adjusting it.

20

I had thought of that but my neighbor said he did not think so. But I am not sure, it certainly does seem to have something to do with that cable or at least the pivot bar that turns when the gas pedal is pressed. But how would it make the engine go faster? I was wondering if maybe something is wrong with the cable like maybe it is caught on something. I did squirt silicone lubricant into the cable hole and it made it move easier. Here is exactly what has happened. The car was running really good - really good. I recently moved out of the city but when I was there all the traffic and bad drivers got me to really pushing it to get ahead of bad drivers, make lights, etc. I know that sounds like I was the bad driver but I never did anything to affect other drivers. Then I moved out of the city. For a while there was dirt in the tank and it was conking out at speed on the highway but I had a mechanic fix that by draining the tank, installing new filters front and rear and clearing out the gas line. That was over a year ago and the car was running really great. I used an article by some pros to adjust the idle maybe 8 months ago and it realy hummed at speed and at idle. But I have been using a part gravel part potholed old blacktop road lately and it has shaken the proor beast to the max. So bad the stud in the carb (the one to the front of the car) that holds the carb to the intake manifold stripped out and the other bolt (there are only two) loosened up. It was when the car first started revving up really high and then slowing down and dying out. When that started I was on that bad road and nursed it back home to have a look and the carb actually fell of in my hand! So I fixed that by putting a new stud in and tightening the other,. But that did nothing to stop that fast-then-slow phenom. I thought it was the choke maybe because the pin that many call the idle adjustment but it is not, not was flipping up --- scratch that ----- the cam with the steps in it that the pin contacts was rotating so the pin was at the highest step. It would not return or rotate so the pin and the throttle arm could drop to the lowest flat step. So there is something in that perhaps but I cannot find what. I tried rotating the choke assembly but it did nothing so I rotated it back to where it was. Besides that ring or collar around the choke was tight so how could that have been the cause that just happened in an instant? I am really baffled. But back to your suggestion, how much of a job is it to replace that cable? I have never messed with that. Actually it is not a cable, its just a stiff wire isn't it? (1970 Beetle) There is no reliable VW mechanic anywhere around within 40 miles so I am stuck. BTW are you a sailor? I've had some fun sailing long ago. Started up a sailing school, rental, and rides concession on the Santa Monica Pier in 1975, hmmm, that was just 5 years after my Beetle was born! Thanks mucho Anthony for your reply. t

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1,515

instead of replacing a throttle cable "just to see" if that's the problem, try disconnecting the cable at the carb. if your idle is still up-down, it's not the cable! just for reference, the cable is easy to replace. disconnect from carb, disconnect from pedal assembly. pull out from pedal side. feed new cable in from pedal side (make sure you grease it when you put it in) and reattach to carb. biggest problem is when the cable comes out of the pan (under car by transaxle) is feeding the cable into the bowden tube and thru engine tin. now to my suggestions. is the choke opening up fully when the engine is warm? if not, do you have power to the choke? if no power, check wire from choke to coil, if yes then choke element probably bad. wire choke fully open and see what happens. first startup you may have to hold a little throttle until car warms up. you said the carb "fell off in my hand". when you fixed this, did you change your carb/intake gasket?

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