Not getting full throttle?

[Porsche-poor]

Ok I am at a loss. Full pedal results in only about half throttle back at the engine, there is still lots of throw left. All the Rods look to be at full length and all movement of rods is free. There is however a slight catch in the throttle body bell crank that one can feel while rotating it by hand. What am I missing?

Thanks.

[ChkbookMechanic]

could it be the throttle cable itself is in need of tightening?

[Porsche-poor]

79SC its all rods right? Or am I just not looking at it right?

[mca]

Don't you shorten the rods to get full throttle? They are adjustable.

[DaddyGlenn]

all rods. you will need to shorten the rods in different places. It will take a bit of trial and error to get it right.

[Grady Clay]

David,

Porsche delivered the 911 with full throttle.
The rods don’t suddenly (or even slowly) get longer.


It has something wrong:

Again check the throttle cushion. Take it out and inspect it.

Inspect your floorboard for correct installation.

Inspect the accelerator pedal hinge for damage.

Inspect all the bell-crank bushings (at pedal assembly, transmission, engine) for radial play (they should have some axial play).

Don’t adjust anything until you find the problem.

Once fixed, make sure the accelerator pedal stop limits the travel to full throttlr and not at the engine.

Best,
Grady

[Porsche-poor]

Grady Clay,

The car has a new pedal, new brass pedal bushing, and an ABS floor board. I'll have the get out the old one and see if the stops are different. Can the floor board be installed wrong? I could only get it to go in one way and it lines up right with the upper mounts and the stud on hte floor. It probably is the throttle cushsion, that looks to be a bear to get out of the car.

[Porsche-poor]

Ok I went out and looked at the floor board, connected at all three points. Disconnected the forward rod at the tranny feels like free rotation at the tranny mount, no turning of the forward rod that does not include the boot around the cushion as in its turning the whole thing. Disconnected the upper last ball joint at the end of hte throttle linkage, here there is a catch about half way thru the rotation, all lower pivot points move with ease. Inspection of the throttle stop, there is none the gas pedal has a plastic "stop" that is 90 degrees to the pedal that contacts the carpet and floor board. I guess its time to oder a cushion or two (one extra) and just replace it.

[Flat6pac]

Make sure the nylon bushings in the bell swivels on the trans and on top of the engine are not disintergrated so there is positive acceleration across the changes of linkage.
Bruce

[Porsche-poor]

Bushings and cushion on order. Needed one for spare parts anyway.

[Porsche-poor]

Parts are here. That cushion rattles like a kids toy is it supposed to be like that already?

[Superman]

Most of the SC's I have seen have had at least one missing bushing at the plate that sits on top of the motor. If you follow the short rod connected to the throttle itself....follow that rod downward, it ends at a plate that is bolted to the top of the engine, just about directly above the base of the #3 cylinder. It connects to a shaft in that plate that is about three inches long. The shaft swivels. At the other end of the shaft, you will find the end of the rod that is coming upward from the transmission. The shaft sits in two small white plastic bushings. Most all the SC's I have seen have had at least one of these bushings missing. Replacing those bushings and adjusting the linkage rods typically gives about 30% additional throttle travel!

[Grady Clay]

David,

If you connect two throttle pieces (or two little bolts) to each end of the cushion, is there axial play?
How much?

I think the rubber has come off one end or the other of the metal.

Congratulations.

Now you must make sure that at full throttle (faster, faster, faster force) that the cushion isn’t under tension from full throttle limited at the engine.

Best,
Grady

[dshepp806]

I luv this sheeeit!..

Thanks, Grady.

Best,

Doyle

[Porsche-poor]

I was talking about the new one that rattles. I'll get under the car this weekend and pull the old one out.

[wdfifteen]

Originally Posted by Porsche-poor

I was talking about the new one that rattles. I'll get under the car this weekend and pull the old one out.

I;m curious about the throttle cushion too. Mine has about 1/4 inch of axial play. How much is too much? I'm not sure how this thing is supposed to work.

[Porsche-poor]

I have not had the tie yet to get under the car. I'll post when I do.

[wdfifteen]

Originally Posted by Porsche-poor

I have not had the tie yet to get under the car. I'll post when I do.

Thanks, I think I figured it out. It's a length of rubber with steel discs bonded to each end. The discs have deep "nuts" welded to them so the rod from the gas pedal and the extension rod that goes to the bellcrank can be screwed in. The whole thing is enclosed in a metal can that catches the steel discs if the rubber should become separated, so that you aren't left with no throttle at all.
This came up while I was under the car replacing the bellcrank bushings. What a miserable job.
T he extension shaft broke while I was removing the ball socket. It was broken about halfway through right at the locknut, and by messing with it, I finished it off. Anyone have a good one to sell? Pelican doesn't have them in stock. PCNA doesn't either. I'm thinking of getting a piece of threaded rod.
Getting the bellcrank off past the trailing arm was an adventure. It BARELY comes off with the left rear wheel jacked up as far as it will go and a liiittlle bending pressure applied to the stud.
The OD of the bronze bellcrank bushings from Pelican were too big by about .002 in. and I had to machine them down to get them to press into the bellcrank with reasonable pressure.
It's in now, but the car idles at 2000 rpm because the extension rod is about a 2.5 centimeters too short. Great way to spend a rainy Sunday.

[Porsche-poor]

First attempt no joy. I am going to have to find the tme to take off the transmission mount to get at it. It does seem solid. When I got the boot off of it and disconnected from the pivot point on the tranny there is no play in it from front of car to back.
Thoughts?

[Grady Clay]

here is more:

Originally Posted by Grady Clay

M491Cabriolet,

Here are some threads about accelerator cushions:

Not getting full throttle?

Linkage "stop" for MFI?

Long term & Commonly Neglected Maintenance

Lack of power when pressing gas pedal

Accelerator Cushion Installation

Are you really getting full throtle?

Throttle Cable Snapped....on my '68 911L....i think

Best,
Grady

Originally Posted by Grady Clay

Guys,

Check this thread:
”Accelerator Cushion”

If you have to shorten the linkage in the tunnel, you may have a broken Accelerator Cushion. The replacement part (starting about ’73) has a steel shell around it. When the rubber fails, the steel shell still allows about 2/3 throttle. The steel shell nicely hides the broken rubber part.

One cause of a broken accelerator cushion is the stop on the floor board is adjusted too far down. The wooden floor board can also fail.

When you have someone push hard on the accelerator pedal, you should still be able to move the linkage slightly more at the carburetors, MFI pump and throttle bodies or CIS/DME throttle. If it is on the stop at the engine you will break the accelerator cushion.

If you find the plastic bushings failed at one bell-crank, they are probably close at the others. There is one at the pedal assembly, one at the transmission and one sorta above the #3 cylinder. The hinge in the accelerator pedal can also fail.

Be aware that the later CIS and DME have a safety pin in the throttle linkage ball socket. You must remove that pin before the socket will come off the ball.

Best,
Grady