C3 Vette Registry - The Best Resource on the Net for C3 Vettes! C3 Vette
Forums -> C3 Fuel, Emission Control, and Exhaust Systems
Not Logged In! Login or Register!  Users Online: 20 / Help 
Features  Find C3 Parts on ebay in only 2 or 3 clicks!  | Add YOUR C3 to the Registry

Supporting Vendors
Volunteer Vette Products
Mid America Motorworks
CorvetteClothing.com
Bair's Corvettes
VetteBookStore.com

C3 of the Month
None Current
Enter Yours Today!
Online C3 Show
13
C3s are Registered

Vanity Plates
MY SHARK
Big Fish
Featured Links

Buy Now
Corvette Masterpieces: Dream Cars You'd Love to Own (Hardcover)
Corvette Masterpieces: Dream Cars You'd Love to Own (Hardcover)


How To Rebuild Corvette Rolling Chassis 1963-1982
How To Rebuild Corvette Rolling Chassis 1963-1982


Collector's Originality Guide Corvette 1968-1982 (Paperback)
Collector's Originality Guide Corvette 1968-1982 (Paperback)


Corvette 50th Anniversary
Corvette 50th Anniversary



| Hide Signatures and Profile Pics

 New Topic New Topic Post Reply Reply New Poll New Poll Search     Search Page [1]  
9/14/14 10:35am - Original Message: 'Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Here is where I really need some help:

The car has been running fine for years through regular maintenance.
This is a 1971 LS5 (454) with a Q-jet. Bought it 12 years ago and never had this problem. I drove the car last weekend and didn't notice anything unusual.

The engine would fire up but won't hold idle. Stops immediately. To keep it running, I would have to keep it in the 2000 rpm range or more. Plus it doesn't run smootlhy and is kind of reluctant to rev in the 3500 rpm zone. Like if I had a couple of sparkplugs disconnected (I checked, they are not).
I questioned the fuel supply and looked at the fuel filter. Dirty. Time to replace it which I did. No change, still the same problem although there is no doubt I am getting plenty of fuel there).
When the engine quit, the carburetor "coughs", throwing a small cloud of gas in the air (one time, the cloud caught fire).

Any suggestion on where I should look at is welcome.


|UPDATED|9/14/2014 8:35:25 AM (AZT)|/UPDATED|
 Reply Reply  Quote Reply w/Quote
 
Support C3VR!
Suport our advertisers
9/14/14 1:01pm - Reply: 'Re: Engine fires up but won't keep running'
Adams' Apple Lifetime Member
Lifetime Member
Moderator
- Send Private Message


Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
Check for a vacuum leak...it would be a fairly large leak for it to not idle. It would cause it to run rough like that, as well as spit back thru the carb.
Does it have any black smoke from the tailpipes?
Do you smell raw/excessive fuel?
It's possible the float is stuck in the carb, and the engine is flooding with too much fuel. Tapping on the fuel inlet on the carb will usually un-stick a float, depending on what might be causing it to hang.
Also possible the points are burnt, or out of adjustment. Cap/rotor problems.
So many thing could cause it. Just gotta start with the basics. Vacuum leak? Too much fuel? Spark issue?
Eliminate one at a time. Thumbs Up

____________________________________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
 Reply Reply  Quote Reply w/Quote
9/14/14 3:53pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Joel, I did check the distributor: Cap, rotor and ignition points look fine and clean (except for a little bit of red dust in the cap and the rotor. No grease, no carbon trace. I also checked the ignition coil: I get 6V at the (+) and at the center connector tha goes to the distributor. 6V is kind of a surprise but I get the same in and out. The vacuum: Where should I start to check a leack? I do not understand the role of the vacuum in the carburation. Obviously there is as I got an excess of gasoline driping on the ground just aft of the front left wheel. I believe it came from the canister. The vacuum system usually needs several minutes to build up vacuum enough to lift the headlights. I wish I could keep the engine running long enough to see that. Not sure where to start from to find a leak (I didn't here any particular noise of this kind). Christian

____________________________________
 Reply Reply  Quote Reply w/Quote
9/14/14 5:47pm - Reply: 'Re: Engine fires up but won't keep running'
F4Gary Gold Member
Gold Member
- Send Private Message


Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 869
Disconnect the vacuum line at the white filter and plug it.  Then see how it idles.

____________________________________
 Reply Reply  Quote Reply w/Quote
9/14/14 6:30pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Just did it. No change. Still running rough and not holding idle.

____________________________________
 Reply Reply  Quote Reply w/Quote
9/14/14 9:15pm - Reply: 'Re: Engine fires up but won't keep running'
Adams' Apple Lifetime Member
Lifetime Member
Moderator
- Send Private Message


Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
Christian said:... an excess of gasoline dripping on the ground just aft of the front left wheel. I believe it came from the canister.


This points to the carb flooding. It sounds like fuel is overflowing into the vent tube on the front of the carb, and running down into the canister. See if you can pinch off the fuel line going TO the fuel pump, effectively shutting off the fuel supply to the carb. Start it up, and once running again, it will use the excess fuel, and then run ok for a few minutes, until it runs out of fuel. Sometimes doing this will also flush out any debris that might be stuck in the needle/seat of the carb, if that is what is causing the flooding. Thumbs Up


____________________________________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
 Reply Reply  Quote Reply w/Quote
9/15/14 9:44am - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Thank you Joel,

I am travelling for work this week, but I will perform this test as soon as I get back. I'll let you know. Thanks again for your advices.


____________________________________
 Reply Reply  Quote Reply w/Quote
9/15/14 11:40am - Reply: 'Re: Engine fires up but won't keep running'
Adams' Apple Lifetime Member
Lifetime Member
Moderator
- Send Private Message


Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
 Hope it's something simple. Thumbs Up

Years ago, when I was taking the '74 to it's 1st NCRS Judging in Waco, we were to meet up with some other folks on the road. I was driving the car down(for driving points), and trailering it back home.We got to the meeting spot, and I realized I had forgotten to bring the lug nuts for the steel rims, which I was going to change to from the aluminuminum rims once we got there. I hop in the car and haul butt back to the house for the lug nuts. As I exited the hiway, the car wouldn't stay running...it was flooding out big-time. I made it to the house, got the nuts, and limped back to the meeting spot. Once there, I had to take the top off the carb, took the float out, and had someone crank the engine(with the coil wire off), and flushed some crap out of the needle/seat. Took about 10 minutes....car has run fine ever since. Was running fine before, too...just something made it past the filters, and lodged in the needle/seat. Ya never know when it could happen, but you can bet it will usually be at the worst possible time...Angry

LOL

____________________________________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
 Reply Reply  Quote Reply w/Quote
9/20/14 1:56pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Adams' Apple said:
Christian said:... an excess of gasoline dripping on the ground just aft of the front left wheel. I believe it came from the canister.


... pinch off the fuel line going TO the fuel pump, effectively shutting off the fuel supply to the carb. Start it up, and once running again, it will use the excess fuel, and then run ok for a few minutes, until it runs out of fuel. 


Joel,

Following your advice, I clamped the fuel line and, indeed, I got the engine running and idling fine. Happy as I was, I removed the clamp with the intention to go for a test ride. The time to turn around and get my wallet, the engine stalled. I am back to square one with the engine running rough and not idling anymore.
I understand the carburetor is definitely the problem and is good for a rebuild. Am I correct?
I tried to take the top off. I am struggling with the pump rod linkage: How to disconnect this one without damaging anything?





|UPDATED|9/20/2014 11:56:06 AM (AZT)|/UPDATED|


____________________________________
 Reply Reply  Quote Reply w/Quote
9/20/14 1:55pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Now I am even more puzzled!!!!!

I had a doubt: I was surprised the engine could idle for so long just on the fuel left in the carburetor when the fuel line is clamped. I was wondering whether I had clamped the correct line (the one TO the pump, not the one back to the tank). To make sure, I did the test again, with both lines clamped. I started the engine and it ran out of fuel after a few seconds. I removed the clamp on the line I hadn't clamp the first time and restarted the engine I kept it idling for a couple minutes. Obviously, this must be the line TO the pump. Then, with the engine still idling, I removed the other clamp, which I believe now was on the return line. After one minute or so, the engine started to idle rough and finally stalled. 

Why would the engine run and idle smooth with the return line clamped and not with return line open to the tank?
Does it point to the fuel pump now? (Last weekend, I had disconnected the fuel line from the carburetor and plugged it on a bottle: The fuel was gushing abundantly in the bottle when cranking the engine).

Does it make sense to anyone?


|UPDATED|9/20/2014 11:55:21 AM (AZT)|/UPDATED|


____________________________________
 Reply Reply  Quote Reply w/Quote
9/20/14 3:27pm - Reply: 'Re: Engine fires up but won't keep running'
Adams' Apple Lifetime Member
Lifetime Member
Moderator
- Send Private Message


Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
 Two things could be happening, from your description. The fuel pump may be able to provide decent volume, but what about pressure?It's possible that when clamping off the return line, you raised the pressure enough to keep the bowl full. The problem MAY be a stuck float still....if it is hanging, the extra pressure from the return line being clamped off could force the fuel on thru. The problem could also be the fuel pump itself.
Do you have a way to check the fuel pressure?

To get the accelerator linkage lever off the carb top, there is a TINY roll pin that goes thru it....take a small punch, or nail, and press the roll pin inward, toward the carb body. This will allow you to remove the linkage, and the top of the carb. When re-assembling it, you can use a small screwdriver to pry the roll pin back into the linkage lever.

____________________________________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
 Reply Reply  Quote Reply w/Quote
9/20/14 5:15pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Adams' Apple said:  
Do you have a way to check the fuel pressure?

No, I don't. How would you do that?

Adams' Apple said:  
To get the accelerator linkage lever off the carb top, there is a TINY roll pin that goes thru it....take a small punch, or nail, and press the roll pin inward, toward the carb body.

Thanks. I saw it, but I didn't dare to remove it because I was not sure I can insert it back in place, correctly.

____________________________________
 Reply Reply  Quote Reply w/Quote
9/21/14 10:29am - Reply: 'Re: Engine fires up but won't keep running'
Adams' Apple Lifetime Member
Lifetime Member
Moderator
- Send Private Message


Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19454
You would need a fuel pressure gauge,and connect it after the fuel pump. You could remove the fuel line going into the carb, and connect it there. You'll be looking for at least 6psi under heavy throttle.

The roll pin, when pushed IN, will not go anywhere...it will bottom out against the carb choke housing...so it will not fall out, and get lost.





____________________________________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
 Reply Reply  Quote Reply w/Quote
9/23/14 4:56pm - Reply: 'Re: Engine fires up but won't keep running'
Christian
Standard Member
- Send Private Message


Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 154
Thank you very much for the tip.

____________________________________
 Reply Reply  Quote Reply w/Quote
 New Topic New Topic Post Reply Reply New Poll New Poll Search     Search Page [1]  
 Forums -> C3 Fuel, Emission Control, and Exhaust Systems
(Moderator: Adam Wartell, Norsky, Adams' Apple, kstyer)
 

 
Official C3 Vette Registry Community:
Home | Forums | Email | Who's Online | Clubs | Events | Member Stats

Other Official C3 Vette Registry Areas:
Members | Research | Shop | My Account | About C3VR
 

Corvette is a registered trademark of the General Motors Corporation(GM) & Chevrolet Motor Division. Vette Registries, LLC is responsible for all site content (except for member submitted content or where otherwise noted) and does not claim or imply that Chevrolet or GM is responsible for Official C3 Vette Registry content. Vette Registries, LLC is independent from GM and is not affiliated with, sponsored or supported by GM.  Copyright/trademark/sales mark infringements are not intended, or implied and are in fact used to support GM, Chevrolet and Corvette

Official C3 Vette Registry content is Copyright 2001-2017, Vette Registries, LLC. Content may not be reused without written consent. All Rights Reserved. NS

Corvette (Vette) Model Years on this site: 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 30