Hello again, I am starting to think that I am experiencing vapor lock problems on 1971. Can some of you please provide me tips on how i can prevent? Thanks again

 

Do you know what "vapor lock" is..? See my comments about it here:

https://www.corvetteforum.com/forums...apor-lock.html

If you actually have vapor lock issues, you need to install a small, electric fuel boost pump at the fuel tank to keep the fuel in the line between the tank and the mechanical fuel pump under pressure in order to prevent fuel vaporization in the suction line. This will prevent the vapor lock. This is why fuel injected modern cars have the fuel pump in the tank, thus keeping the entire fuel line under pressure. This eliminates vapor lock issues in modern cars.

Lars

 

Thanks for the information and the link to the old thread!

 

You have soooo many threads around the forum, In a few of them you state this just stared happening, What makes you think that vapor lock just started happening, if that is the problem?
Pin hole in the rubber lines by the tank?
Leak in exhaust just happening to blow on the fuel line?
What did you replace or fix just before it started happening?

 

thank you. My problem started maybe 6 months ago year and a couple times I thought it was fixed. The car starts, idles and drives good when cold but after a 15 minute drive often it will miss, stall, and not want to start back up. Something drastically and suddenly happens that shuts the car down when it gets hot. Then a few hours later the car will start fine when cold.

nothing was changed prior to car messing up and since problem began I have changed coil, fuel filter, air filter, condenser, points, rotor, power booster valve, and timed / dwelled lots. Still not sure problem but vapor lock sorta makes sense as I learn more.

thanks for suggestions and I will check them out.

 

thanks lars, yes I am am learning more about vapor lock in my research. It sorta sounds like that may be my problem. Car starts and drives good when cold but drastically shuts down and does not want to start when hot.. thanks again for all your help.

 

When it doesn't want to start, pull the air cleaner off and look down the carb primary venturies - pump the throttle. Do you see fuel being discharged from the accelerator pump nozzles? If there is fuel discharge, you do not have vapor lock or a carb problem. If there is no fuel discharge, you could have a fuel delivery problem caused by vapor lock. Your next step is to install a fuel pressure gauge into your fuel line at the carb inlet and run the hose for the gauge up so you can tape the pressure gauge to the outside of your windshield where you can see it while driving. Very easy to do - I've posted threads here on how to "T" in a pressure gauge in this fashion. When the problem occurs, does the fuel pressure drop to zero? If you have fuel pressure when the problem occurs, you have an ignition problem. If pressure is "0", you have a fuel delivery problem, which could be caused by vapor lock. It can also be caused by restrictions in the fuel supply line and by a faulty fuel pump.

 

thank you Lars, and you have gone way overboard helping me so much. You’re great and please do not spend so much time on my posts. Also so much thanks to everyone that has helped me, I cannot express how much your efforts and support is appreciated. Corvette forum is awesome!

I’ll try to look at my carb gas flow during bad running cycle after limping back home. Most of the time car stalls and get super grumpy in middle of road with traffic near. Thanks everybody!

 

I know you changed the ignition coil, but the issue you’re having is very typical of a coil going bad.
There have been several forum members who have replaced their coils and the new replacement coil is bad out of the box.
It’s not uncommon.
Coils are cheap.
I would buy a good quality coil, replace the new one and see if it cures the problem.
It might save you a few headaches.

 

thank you. Car will idle great now and drive well usually for 15 minutes or so and then starts missing, stalling, and not wanting to start. Coil was replaced about 3 months ago and is ac delco u505 I think. I tried to install farthest away from manifold because heat. Can heat make coil breakdown and be intermittent?

ill try another coil and wire in a couple weeks if i have not figured it out. What brand of coil would you suggest? Thanks again.

 

Coils should have an air gap underneath (~1/4"+) to insulate it from the manifold heat. Yes heat, in general, is not good for any electronics.

I went through a couple old and new coils (NAPA) until I discovered NGK makes a coil for our engines: NGK U1173 (49030)
(Be aware most of my local auto parts stores list this same coil at almost $80, but it lists for $28 on NGK's and .)

 

Thanks so much. Doesn’t the coil need to have internal resistor? Both of the previous coils had internal resistor.


QUOTE=67:72;1608302622]Coils should have an air gap underneath (~1/4"+) to insulate it from the manifold heat. Yes heat, in general, is not good for any electronics.

I went through a couple old and new coils (NAPA) until I discovered NGK makes a coil for our engines: NGK U1173 (49030)
(Be aware most of my local auto parts stores list this same coil at almost $80, but it lists for $28 on NGK's and .)[/QUOTE]

 

It depends on what you have for the car's ignition system: factory for '71 was a resistance wire in the harness which the NGK coil accommodates. The NGK site has a year/model/parts search engine and this is what it returned for a '71 w/SB or BB. (I believe the systems like MSD do not need the resistor wire like the factory points design.)

 

Thank you very much

QUOTE=67:72;1608302823]It depends on what you have for the car's ignition system: factory for '71 was a resistance wire in the harness which the NGK coil accommodates. The NGK site has a year/model/parts search engine and this is what it returned for a '71 w/SB or BB. (I believe the systems like MSD do not need the resistor wire like the factory points design.)[/QUOTE]

 

With everybody and their mechanical fuel pumps and fuel lines mounted on the side of the engine, right in the HOT airflow from the radiator it is no wonder that engines "Vapor Lock".

On a very hot running engine I brought my fuel up from the rear of the car inside of a DEI Insulating tube and then the front 10 feet has a fireproof sleeve over the insulation. The routing was done to keep the fuel lines as far away from any source of heat from the tank to the throttle body. My fuel lines comes up over the bell-housing from behind the engine in an effort to keep the fuel COOL as it enters the throttle body. There are NO fuel lines near the radiator and every inch of fuel lines is insulated from the tank forward

As far as the choice of Ignition Coils out there some are better than others. First you need to know what kind of ignition system your Corvette has. A stock car that uses a ballast resistor needs a specific coil. A Factory T.I. Corvette needs a special # Coil that was designed to work just with the factory T.I. systems.

If you have a aftermarket CD box that might have requirements all of it's own. I have a MSD ignition system on my C3 and it uses the standard Blaster coils from MSD which can make up to 40K volts versus the 30k that a factory coil can make. In the past two years I have seen a rash of failures of Coils on my C3. MSD suggested that I mount a higher quality Ignition coil on the firewall (a more $$ coil) and not mount it on the intake with the air gap below it. Coils do not like high temperatures so I will be fire wall mounting my next ignition coil. That way there is less heat and vibration so the coil should last longer.

 

Earlier you posted you’re running the stock points and condenser.
I would try the NGK coil and insure it is for the correct ignition system and not an HEI or electronic.
I would also trace down your resistance wire leading to the coil (usually a pink wire) and check the resistance through the wire.
It does help to mount a coil away from the heat but many oem coils lasted years mounted in the oem position, on the intake with about a one inch gap.
Any more I purchase my parts factory direct so I know it is an original part and not a cheap Chinese knock off.
Keep us posted!

 

thank you, I’ll probably try Ngk coil after a couple tests that I’ll do when it runs bad to check spark and fuel spray in carb. Yesterday, I did trace coil wires far as I could without cutting everything apart and looks like a red and black wire go to coil positive. I think car does have resistance wire and the coil installed in car when I bought it 15 years ago does indicate to use external resistor. I was incorrect about that previously and thought coil had internal resistor in coil.

 

Also try and get some gas with no ethanol in it.

 

thank you and I am not sure if my problem is vapor lock and will more test next time I drive it and I’m sure the engine will mess up again. I drive the car only a couple miles away until I get this figured out.

it is odd how I have owned the car 15 years and driven it 15k miles and now I start to have vapor lock problems. Car starts good, will idle good at 600 rpm, and then usually drive for ten minutes, engine then typically misses, stalls, and does not want to start. Car will cool down for few hours, start, run goods and then the bad running cycle repeats.

ill do a couple tests next time I drive it and then runs bad to check gas spray in carb and spark coming from coil.

I do think car has resistor wire and will get coil that requires external resistor and will probably get the Ngk if I have not figured out problem.. car had standard plus coil when purchased car and then 3 months ago I changed to ac delco u505. Seems surprise that 2 coils go bad but who knows? Thanks ☺️ so much!


QUOTE=ctmccloskey;1608303215]With everybody and their mechanical fuel pumps and fuel lines mounted on the side of the engine, right in the HOT airflow from the radiator it is no wonder that engines "Vapor Lock".

On a very hot running engine I brought my fuel up from the rear of the car inside of a DEI Insulating tube and then the front 10 feet has a fireproof sleeve over the insulation. The routing was done to keep the fuel lines as far away from any source of heat from the tank to the throttle body. My fuel lines comes up over the bell-housing from behind the engine in an effort to keep the fuel COOL as it enters the throttle body. There are NO fuel lines near the radiator and every inch of fuel lines is insulated from the tank forward

As far as the choice of Ignition Coils out there some are better than others. First you need to know what kind of ignition system your Corvette has. A stock car that uses a ballast resistor needs a specific coil. A Factory T.I. Corvette needs a special # Coil that was designed to work just with the factory T.I. systems.

If you have a aftermarket CD box that might have requirements all of it's own. I have a MSD ignition system on my C3 and it uses the standard Blaster coils from MSD which can make up to 40K volts versus the 30k that a factory coil can make. In the past two years I have seen a rash of failures of Coils on my C3. MSD suggested that I mount a higher quality Ignition coil on the firewall (a more $$ coil) and not mount it on the intake with the air gap below it. Coils do not like high temperatures so I will be fire wall mounting my next ignition coil. That way there is less heat and vibration so the coil should last longer.[/QUOTE]

 

thanks have used non ethanol 93 octane the last 15 years