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Re: Engine runs rough when the headlights are on (2/12)
 1/5/18 1:32pm
gtr1999
Limited Member
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CHESHIRE, CT - USA

Vette(s):
1969 350 4 spd drop top 1972 350 auto coupe


Joined: 5/2/2016
Posts: 61

Joe, could be from the headlight switch, can you hear a leak with the knob pulled out and the engine running? There should be a diagram of the complete system online so you can trace it out as well.
Wish I had a better answer for you. One note, the new switches sold today have a lot of issues with them. If you find you need a new switch I would look for a good used or NOS one.


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Re: Engine runs rough when the headlights are on (3/12)
 1/6/18 12:12pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 541

If an '81 still has the manual headlight control switch under the steering column, you might try that and see if the vacuum leak is still present. That would rule out the headlight switch, maybe.

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1973 L-82 4 spd

Re: Engine runs rough when the headlights are on (4/12)
 1/6/18 1:24pm
JoeHower
Former Member

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Long Beach, CA - USA

Vette(s):
1981, Grey, six-speed tremec


Joined: 2/26/2016
Posts: 11

Re: Engine runs rough when the headlights are on (5/12)
 1/6/18 1:24pm
JoeHower
Former Member

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Long Beach, CA - USA

Vette(s):
1981, Grey, six-speed tremec


Joined: 2/26/2016
Posts: 11

Re: Engine runs rough when the headlights are on (6/12)
 1/7/18 1:54am
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 541

You can also try using an unlit propane torch and play the nozzle around areas that you think the leak might be and see if the engine idle speed changes. If it does, you have found at least one of the leaks.

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1973 L-82 4 spd

Re: Engine runs rough when the headlights are on (7/12)
 1/7/18 3:06pm
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 1979

A shot of ether/starting fluid spray will do the same thing, have the same effect.
Re: Engine runs rough when the headlights are on (8/12)
 1/7/18 3:43pm
Vman73
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Gig Harbor, WA - USA

Vette(s):
1973 L82 4 Speed Coupe - Very original, well documented driver/survivor. 2016 Bend Regional NCRS Top Flight.


Joined: 10/2/2014
Posts: 405

If the engine runs fine with the lights out, I would also suspect the HL switch or the up/down control valves up front. +1 on using the override to possibly eliminate a bad switch. If the lights go up with the override switch pulled and the engine runs fine, its probably the switch. If the engine stumbles when the override switch is pulled then I would go to the control valves. They are a very common leak and may need to be replaced. Good luck and let us know what you find.

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John Sigmund
valkman57@sbcglobal.net
NCRS Member 61302
NW NCRS Chapter Member



Duct tape is the new Black !!
Re: Engine runs rough when the headlights are on (9/12)
 1/7/18 4:19pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 541

manchestershark said: A shot of ether/starting fluid spray will do the same thing, have the same effect.



Propane is a lot less messy especially when you're dealing under the dash or on plastic parts.

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1973 L-82 4 spd

Re: Engine runs rough when the headlights are on (10/12)
 1/7/18 4:21pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 541

Deleted duplicate post

|UPDATED|1/7/2018 1:21:11 PM (AZT)|/UPDATED|


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1973 L-82 4 spd

Re: Engine runs rough when the headlights are on (11/12)
 1/7/18 6:00pm
manchestersharkLifetime Member
Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 1979

Point well taken. Wasn't thinking of inside assessment, as much as under hood at other connections.
Re: Engine runs rough when the headlights are on (12/12)
 1/12/18 12:06pm
dwa175Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6


Joined: 7/19/2014
Posts: 189

I suggest something I used  a smoke  machine   blow smoke then look for smoke  easy to use 

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