The herky jerky

Binding cable, or they have the linkage setup incorrectly

The engine is just way too big for the car. do they make dual weber 4400's?

In all seriousness I had the same problem. Could not figure it out but rebuilding the carburetor's fixed it. Sounds like the same problem anyway. Barely touch the accelerator and the car would bolt and with no change to the accelerator pedal would decelerate a second or two later. Like it got plenty of gas then nothing. It was absolutely maddening to say the least.

Thanks Rusty, sounds like a similar problem however I noticed no deceleration unless I let up on the accelerator pedal.  I was told the Webers were rebuilt in the last few thousand miles.

Different problem then... Well an extremely light flywheel would cause the engine to respond that way - especially if it has very high compression.

It may be a fairly high performance motor and in that case you would have to use a little finesse while shifting.

Sounds like a 600hp Camaro I once had. That was a fun fun car.

...adding something else here... you know with a big motor like that and stock gearing, without engaging the clutch, in 1st gear the car would definitely feel like you were in 4WD Low and respond very lurchy and jerky. If that's the case you have to finesse the clutch a little!

Finesse?...you already correctly made note of my finesse on the keyboard....

OK, it sounds like the accelerator "Bowden" tube may not have been installed.

There should be a metal tube going through the fan shroud, carrying the accelerator cable from the linkage arm through the fan shroud.  On the BACK side of the fan shroud that tube inserts into a flexible rubber/vinyl tube, the other end of which inserts onto the accelerator cable metal tube coming from the pedal cluster - that tube emerges from the tunnel right next to the clutch cable tube, just ahead of the rear torsion tube.  

When properly installed, there should be a long, gentle bend in the tube, similar to the bend in the clutch cable Bowden tube.

The purpose of these tubes is to compensate for the movement of the engine as power is applied and removed - when that happens, the engine rocks around the crankshaft axis.  As it does so, it requires more and less cable length.  the Bowden tubes keep all that relative.

Check to see if that tube is in place.  If not, it's a really easy install and should make a world of difference.

Thanks Gordon, that's makes some sense!

Trans/motor mount?

Gordon, what would you suggest for a 911 shroud?

Yeah, Bill...A shot forward motor mount might contribute to that symptom, too.  

Good catch.

I have zero experience with a 911 shroud, sorry.

Bill, are you looking for a linkage for your 911 shroud?

I'm having the exact same problem!!  My engine builder suggested bad front mount. But I put the car in gear and rocked it without seeing the motor even slightly move. If you figure it out let us know.

Fpcopo, check you dialog box for a message

I had had the same throttle drop and herky jerky response from the throttle a few months back. It was a front mount and could not be seen until I loosened the body to mount side of the mount (slotted side) before I could see it.

The way the mount was bonded to the metal halves allowed it to be supported by the rubber lip on the mount as its dished. I've enclosed a picture and I also installed a new mount but was still unhappy with throttle action so I attached springs to help the throttle return action.

The irony here is that I installed a new mount when I rebuilt the car and this mount might have had 100 miles on it before it quit. Our parts sources are getting worse and I think in the end I"ll probably beef up the the whole engine tranny support system as Gordan has recently done.

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I'm sure this will wear the throttle cable faster but I'll carry a spare like a lot of the people do here.

Gordon, my bowden cable is a little short. If I rev the engine by pushing the linkage on the engine the cable will drop off the tube going thru the shroud and jam the throttle open. I think you are right there is no bend in my bowden allowing slack for engine movement. Are there different lengths available or should I make a longer steel tube thru the shroud?  Thanks.

I only remember 2 offered:  Before 1966 and after 1966.  After 1966 they were longer by a bit.  

I think it would be a LOT easier to make up a new tube through the fan shroud by using a suitable length and diameter of steel brake line for a truck.  I always use a rubber grommet where it goes through the fan shroud metal - keeps it from rattling and hold it in place.  I think mine is 1/4" ID tubing but I'm not sure.  I seem to remember mine going through the fan shroud, then through the rear engine tin and then into the throttle flex tube.  It would be nice if someone had one kicking around and could measure the length for you as a reference.

Remember that as you increase the bend in the flex tube the overall cable length will have to increase so you may need to get a new, standard Beetle throttle cable and cut it to the new needed length.

I would give the flex tube about 1" - 1-1/4" bend in the middle at idle/rest (I find no reference for bend amount in my service manuals).  Measure across the length of the tube with a straight edge, the same way you measure the clutch tube flex.

Good luck!  Gn

I like the flywheel theory.

Great! Thanks

Gordon, throttle cable Bowden tube is what I was asking. I may have to fab a tube through the firewall.

The herky jerky is fixed!  I made a new 5/16" steel line that passes thru the fan shroud.  It is 1" longer than the one that came with the engine.  Now the bowden cable has a nice sag to it so there is enough play when the motor mounts flex.  The herky jerk in low gear is completely gone and the car seems a little easier to match speeds when shifting in the other gears also.  I am lucky that my throttle cable was a little long where it went thru the ferrell on the throttle arm so I didn't have to replace the cable.  Thanks to all you guys that gave advice.

That's cool!

Always great when some advice actually helps someone.

gn

A semi rigid plastic tube can work in there too. I used one for a couple of years with my 1915 and then again when I installed the Soob just to get around an intake manifold obstacle.

Would grease on that cable or the inside of the metal tube be a good idea ?

I would venture to say it couldn't hurt as it would decrease metal to metal friction, yet on the same token it may attract and hold some grit and grime if not sealed tightly...so since I'm a newbie to all this take it for what it's worth concerning Speedsters

You may be able to use a small diameter spiral wire/cable wrap sold at Home Depot.....

Its white UHMW (poor man'sTeflon) and works well in this application.....  Did it on my Spyder and another car....

There was a guy a while back selling a shroud throttle kit.  It consisted of a tube that went through the shroud with a small roller at one end.

I thought it was a good idea, but have no idea if it actually made the throttle response smoother.