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Unexpected Engine Rev at Stop in Gear #1334226 Mon Nov 18 2019 05:48 PM
Joined: Aug 2019
Posts: 10
D
DES57 Offline OP
New Guy
Hey guys,
I have a ‘57 3200 with a rebuilt 350, topped with Carter AFB Competition Series 9635S, pushing a TH350 tranny. On occasion, it surprises me at a stop sign with an engine rev of probably 1000 rpm. A quick shift into neutral drops it back to normal. Does this sound like a vacuum problem or could it be transmission related?


Newbie Classic Owner, 1957 Chevy 3200
Rebuilt 350 pushing a rebuilt TH350
Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334389 Tue Nov 19 2019 11:28 PM
Joined: Nov 2005
Posts: 5,519
3
3B Offline
Master Gabster
Hy DES57, welcome, I can honestly say that never in all my years have I heard of such a symptom. I wouldn't put something like this past a confusilator controlled engine, but a carbureted one? You say when you shift the transmission into neutral the engine returns to idle, no load on the engine and the r.p.m. goes down??? Does this occur as you're coming to a stop or after you're actually stopped? I'll be very interested to follow this thread.

Re: Unexpected Engine Rev at Stop in Gear [Re: 3B] #1334411 Wed Nov 20 2019 01:33 AM
Joined: Aug 2019
Posts: 10
D
DES57 Offline OP
New Guy
It occurs while stopped for 10-20 seconds with my foot firmly placed on the brake and my hand on shifter, ready to throw it in neutral. I have a three mile drive to town at 45 mph so it’s typically warmed up. Just this week I discovered an open vacuum connection so I plugged that but haven’t had a chance to see if that made a difference. I have the door panels off to upholster them myself. This past spring I had a/c, ps, tilt column, parking brake, and exhaust installed. After four years, this is my first year to actually start driving it. Just building a daily driver. Any suggestions appreciated.


Newbie Classic Owner, 1957 Chevy 3200
Rebuilt 350 pushing a rebuilt TH350
Re: Unexpected Engine Rev at Stop in Gear [Re: 3B] #1334412 Wed Nov 20 2019 01:35 AM
Joined: Aug 2019
Posts: 10
D
DES57 Offline OP
New Guy
It occurs while stopped for 10-20 seconds with my foot firmly placed on the brake and my hand on shifter, ready to throw it in neutral. I have a three mile drive to town at 45 mph so it’s typically warmed up. Just this week I discovered an open vacuum connection so I plugged that but haven’t had a chance to see if that made a difference. I have the door panels off to upholster them myself. This past spring I had a/c, ps, tilt column, parking brake, and exhaust installed. After four years, this is my first year to actually start driving it. Just building a daily driver. Any suggestions appreciated.


Newbie Classic Owner, 1957 Chevy 3200
Rebuilt 350 pushing a rebuilt TH350
Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334414 Wed Nov 20 2019 01:41 AM
Joined: Dec 2015
Posts: 2,028
69Cuda Offline
Big Bolt Forum Moderator
power brakes? that could change the vacuum when you come to a stop, which could change idle a bit but I would not think that much. It may be that he vacuum leak you fixed will solve your problem. I would take it for another test drive and see!


Mike

1955 Chevy 6400 ex-flatbed (no bed now!)
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1958 Chevy 6400 flatbed W/dump
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1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
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Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334557 Thu Nov 21 2019 01:48 AM
Joined: Aug 2019
Posts: 10
D
DES57 Offline OP
New Guy
Update: Ran some errands today and it still revved up at the first traffic signal. My fixed vacuum leak didn’t change anything. I’m wondering if something from the transmission is affecting it. PO rebuilt engine and transmission. Also, no power brakes.

Last edited by DES57; Thu Nov 21 2019 03:21 AM.

Newbie Classic Owner, 1957 Chevy 3200
Rebuilt 350 pushing a rebuilt TH350
Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334584 Thu Nov 21 2019 04:41 AM
Joined: Mar 2010
Posts: 8,641
5
52Carl Offline
Master Gabster
Is there a vacuum line going to the transmission?

Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334589 Thu Nov 21 2019 05:02 AM
Joined: Feb 2004
Posts: 19,274
H
Hotrod Lincoln Offline
Boltergeist
Check your motor mounts. The engine could be shifting around enough at a stop to pull on the throttle linkage.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1334982 Sat Nov 23 2019 05:36 PM
Joined: Aug 2019
Posts: 10
D
DES57 Offline OP
New Guy
There is a vacuum hose from Carter 9635s carb to the TH350 transmission. Motor mounts appear tight and not cracked. Took another drive today and it did not lunge/surge. A little cooler out at only about 35 F. When I get time I’ll see if it will stay running with the warm idol dropped a tad. No tach, but I’m guessing it’s about 900 now.


Newbie Classic Owner, 1957 Chevy 3200
Rebuilt 350 pushing a rebuilt TH350
Re: Unexpected Engine Rev at Stop in Gear [Re: DES57] #1335048 Sun Nov 24 2019 03:48 AM
Joined: Mar 2010
Posts: 8,641
5
52Carl Offline
Master Gabster
Originally Posted by DES57
There is a vacuum hose from Carter 9635s carb to the TH350 transmission.

Check to see if the diaphragm to which the vacuum line is attached is not ruptured. You can use a Mitey-vac or your mouth on the hose. It should hold vacuum until next Tuesday if its good.

Last edited by 52Carl; Sun Nov 24 2019 03:48 AM.
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