Engine Revving Problem When Clutch Depressed

[chstephens5219]

Happy Father's Day to all fathers out there!

I have a problem I would appreciate any insights on how to solve. I just completed a 3.6L 993 conversion in my 1985 Carrera using the Instant G kit. No problems on the install and it started right up.

When I have the car in neutral, and depress the accelerator, it returns to idle just fine. I have checked and rechecked the throttle linkage and it appears to be adjusted correctly.

However when I try to drive the car, place it in first and slightly accelerate, then depress the clutch, the engine runs up to 4000 rpm. A pull back on the accelerator with my foot seems to return it to idle.

If this is a throttle cable adjustment, why does this only happen in gear vs. neutral. Is there something I am missing on the set-up?

Thanks in advance, Craig

[Flat6pac]

It sounds like you have something crossing. I can remember on the 914 I had that problem in the late 70s
Bruce

[BURN-BROS]

I would inspect for improperly routed cable or a broken tube in the tunnel. It sounds as iff the clutch cable, when depressed is moving and making contact with the accelerator cable or linkage. Check your pedal assembly as well for worn parts or simple lubrication of the moving parts.

[chstephens5219]

That makes good sense. I'll check the clutch cable routing/clearance.

Should the clutch cable be routed above or below the bell crank that holds the throttle cable?

Craig

[Henry Schmidt]

It is not uncommon for the clutch cable to actually rap around the accelerator cable when being replaced. This issue happens near the pedals not the trans.

The cables should run side by side not over and under.

[john walker's workshop]

the cable sheath comes down against the throttle bellcrank on the side of the transmission most likely. create some clearance there.

[cgarr]

It most likely around the tranny area but if its not take a look at the peddle cluster too, things get pretty tite up front in that area too.

[Walt Fricke]

I don't think movement of the Bouden (Bowden?) tube by the tranny throttle bell crank could do this. The lever arms on the crank are much longer relative to the center tube. Though if the flexible tube rubs the lever, and not just the tube, that could create reasonable friction?

I think the Bouden tube usually goes above the tranny bell crank.

I'd guess the problem is up front. But did you change any of this in order to plant your 3.6? Same tranny as before?

None of this explains why the same thing doesn't happen when in neutral, though.

[john walker's workshop]

when the bowden tube is tensioned, it can pull down onto the bellcrank and keep it from moving freely, if it's pretty close already. seen it many times. i don't just make these things up.

[cstreit]

Bouden tube is rubbing on the bell-crank almost assuredly....

[chstephens5219]

Thanks to everyone for your advice. It actually turned out to be 2 different yet contributing issues.

First, the clutch cable was rubbing the bellcrank. Once this was resolved I still had an idle issue and tracked that down to a vacuum leak at the base of the throttle body assembly. Repaired that and it now runs like a gem.

Craig

[Tom '74 911]

Hi Craig -

Glad to see you're up and running w/a new motor after our winter 3.6 fiasco w/our mutual "friend" in San Francisco. Good things come to those w/patience!

Enjoy,
Tom

[chstephens5219]

Hi Tom

Good to hear from you. And yes, I don't think either of us want to go through that experience again! Back to the track next week with the new power plant....

Craig

[miketoo]

If this is a throttle cable adjustment, why does this only happen in gear vs. neutral. Is there something I am missing on the set-up?

[chstephens5219]

The clutch cable runs through a tube that "flexes" when the clutch is depressed. The tube runs parallel and very near the throttle assembly located on the gearbox. If the tube is too near the throttle cable bell crank, it can make contact and in effect hold the throttle cable from returning to idle position.

Perhaps not the best design as there ideally would be a way to route the clutch further away from the throttle assembly on the gearbox.

Craig

[cay-ahe]

I'm not sure if you found the issue or not, but I had a similar issue and the pedal cluster was the problem for me. Mine would accelerate as I pushed the clutch in.

[Walt Fricke]

Craig

My '77 had a fabric strap with eylet ends or something of the sort which attached to the chassis (or maybe the tranny?) and held the Bouden tube up midway through its travel. I think its purpose must have been to keep it from interfering with the bell crank. And I suppose that later models had something similar.

Walt

[Flieger]

I still need the bushing for the clutch bowden tube at the differential side cover ring.