Fuel vapor odor
06-21-2006, 09:35 PM
#1
Cruising
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Fuel vapor odor
Long time lurker, first post. Appreciate anyone's thoughts.
I have a 1974 L-82 which I've owned for past 11 years. I finally got
sick of the carb's performance and decided to replace it (rather then rebuild it) since the one which came with the car had been replaced with an incorrect carb at some point. I found and purchased the proper numbered carb off Ebay. Other then requiring a rebuild kit, it has worked perfectly since I tore it apart, rebuilt it (thanks for Doug Roe's book and Lar's papers) and installed it about 3 weeks ago.
The only problem since installation has been a faint lingering fuel vapor odor after using the car. I mainly drive it only on the weekend's so say I drive it on Sat, then even on Monday morning there will be a faint fuel odor in the air.
There are no leaks when the car is running. The car has a charcoal canister for storing fuel vapor. It was reattached to the carb when reinstalled.
Any ideas where to search for the cause of the odor?
I have a 1974 L-82 which I've owned for past 11 years. I finally got
sick of the carb's performance and decided to replace it (rather then rebuild it) since the one which came with the car had been replaced with an incorrect carb at some point. I found and purchased the proper numbered carb off Ebay. Other then requiring a rebuild kit, it has worked perfectly since I tore it apart, rebuilt it (thanks for Doug Roe's book and Lar's papers) and installed it about 3 weeks ago.
The only problem since installation has been a faint lingering fuel vapor odor after using the car. I mainly drive it only on the weekend's so say I drive it on Sat, then even on Monday morning there will be a faint fuel odor in the air.
There are no leaks when the car is running. The car has a charcoal canister for storing fuel vapor. It was reattached to the carb when reinstalled.
Any ideas where to search for the cause of the odor?
06-21-2006, 11:17 PM
#2
Burning Brakes
Dont know if this is causing your problem, but I had a similar situation and after checking everything, I decided to chance to vapor canistrer. For me, it took away 95% of the problem.
06-21-2006, 11:19 PM
#3
Just another Corvette guy
That's where I'd start.
Welcome to the forum
Where do you hail from?
Greg
06-22-2006, 01:59 AM
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A few things to check:
It may be fuel evaporation out of the bowl ( or leaking well plugs on the bottom of the carb dripping fuel into the manifold , if it's a Q-jet , don't remember what carb a '74 L-82 originally had ) that is being aggravated by higher summer temps. Before you go to start the car next time , pull the air cleaner off and give the throttle a couple of good strokes to set the choke while you look down the primary bores for good strong pump shots of fuel. This would also be indicated if your previous start-ups have required cranking the motor over and stabbing the gas a few times to get the fuel pump to fill the bowls before it will start. If the Q-jet plugs weren't epoxied during the previous rebuild , that is a worthwhile thing to do , if that's the carb you're running.
If it is an evaporation issue , other than the Q-jet advice given , I don't know what you can do about that , since it's a fuel and ambient air temperature interaction.
You might also want to check around the gas fill cap to see if there's a heavy odor coming from there , and check the feed line connections from the tank to fuel pump , and fuel pump to carb , for cracked hoses or seepage at the threaded fittings.
You won't be able to see all of the metal fuel feed tube that runs through the frame , but check that for rusted spots that may be seeping wherever it's visible , and you might want to sniff for heavy fuel odor along the right side frame rail as well. It's not unusual for time , vibration , and the elements to cause problems with the fuel feed line , and lines that develop a raw fuel leak can cause serious safety issues.
Other things that may help:
Check all the hoses that run to the charcoal canister. Many times a hose will seem good , but if you check it's connection at the canister , they'll be heat beat and hardened. There may be cracks on the underside of the hoses that you aren't seeing without removing the hose. This can also cause a loose connection because the end connection has been bulged out to a larger size. Also check the canister connector for cracks.
You should also check along the length of each hose for cracks as well. Just bend the hoses into an arc , and inspect for cracking or abrasions that have rubbed through. If the hoses aren't reasonably pliable , just replace them.
There's an air filter pad on the underside of the canister that is meant to be replaced when it has become caked and clogged with dirt. This is what helps the canister to purge the vapors back into the running engine by drawing some fresh air through the charcoal.
Finally , charcoal canisters are one of those items that people never think about servicing, and I don't know how many miles are on the odometer, but the chances are that it's the original canister that came with the car. ( On the plus side , these are also usually one of the items that puts joy in the hearts of the hard-core NCRS types
)
I'm pretty sure that you never replaced it , and you've owned the car for 11 years , right? And , that canister was 11 years newer when the previous owner sold the car , and he didn't replace it either. ( I realize that I'm taking a risk in saying you haven't, but hey , life's short , live on the edge every now and then ).
If the foregoing items don't solve the problem , it's probable that the charcoal has been saturated to it's limit , and needs to be replaced. They weren't intended to last forever , and the car is over 30 years old.
And if the above steps don't completely eliminate the problem , ( such as an evaporation issue may be causing , as first mentioned ) you might consider installing a small ventilation fan ( similar to the bathroom type ) as close to your car as possible to keep the vapors from building up in your garage.
Hope this can help you to solve the problem.
It may be fuel evaporation out of the bowl ( or leaking well plugs on the bottom of the carb dripping fuel into the manifold , if it's a Q-jet , don't remember what carb a '74 L-82 originally had ) that is being aggravated by higher summer temps. Before you go to start the car next time , pull the air cleaner off and give the throttle a couple of good strokes to set the choke while you look down the primary bores for good strong pump shots of fuel. This would also be indicated if your previous start-ups have required cranking the motor over and stabbing the gas a few times to get the fuel pump to fill the bowls before it will start. If the Q-jet plugs weren't epoxied during the previous rebuild , that is a worthwhile thing to do , if that's the carb you're running.
If it is an evaporation issue , other than the Q-jet advice given , I don't know what you can do about that , since it's a fuel and ambient air temperature interaction.
You might also want to check around the gas fill cap to see if there's a heavy odor coming from there , and check the feed line connections from the tank to fuel pump , and fuel pump to carb , for cracked hoses or seepage at the threaded fittings.
You won't be able to see all of the metal fuel feed tube that runs through the frame , but check that for rusted spots that may be seeping wherever it's visible , and you might want to sniff for heavy fuel odor along the right side frame rail as well. It's not unusual for time , vibration , and the elements to cause problems with the fuel feed line , and lines that develop a raw fuel leak can cause serious safety issues.
Other things that may help:
Check all the hoses that run to the charcoal canister. Many times a hose will seem good , but if you check it's connection at the canister , they'll be heat beat and hardened. There may be cracks on the underside of the hoses that you aren't seeing without removing the hose. This can also cause a loose connection because the end connection has been bulged out to a larger size. Also check the canister connector for cracks.
You should also check along the length of each hose for cracks as well. Just bend the hoses into an arc , and inspect for cracking or abrasions that have rubbed through. If the hoses aren't reasonably pliable , just replace them.
There's an air filter pad on the underside of the canister that is meant to be replaced when it has become caked and clogged with dirt. This is what helps the canister to purge the vapors back into the running engine by drawing some fresh air through the charcoal.
Finally , charcoal canisters are one of those items that people never think about servicing, and I don't know how many miles are on the odometer, but the chances are that it's the original canister that came with the car. ( On the plus side , these are also usually one of the items that puts joy in the hearts of the hard-core NCRS types
)I'm pretty sure that you never replaced it , and you've owned the car for 11 years , right? And , that canister was 11 years newer when the previous owner sold the car , and he didn't replace it either. ( I realize that I'm taking a risk in saying you haven't, but hey , life's short , live on the edge every now and then ).
If the foregoing items don't solve the problem , it's probable that the charcoal has been saturated to it's limit , and needs to be replaced. They weren't intended to last forever , and the car is over 30 years old.
And if the above steps don't completely eliminate the problem , ( such as an evaporation issue may be causing , as first mentioned ) you might consider installing a small ventilation fan ( similar to the bathroom type ) as close to your car as possible to keep the vapors from building up in your garage.
Hope this can help you to solve the problem.
06-22-2006, 02:22 AM
#5
Burning Brakes
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All very good information. Another possibility is the vapor separator has failed. It's located back at the fuel tank. Here's another post that may help: http://forums.corvetteforum.com/show...ighlight=vapor
Steve
Steve
06-22-2006, 02:51 AM
#6
Melting Slicks
I have the same proplem at times...
When you replaced the carb, did you install a heat shield or heat absorbing spacer between the intake and the carb? was advised that this would help any fuel in the carb boiling away causing the smell....
I just havent got around to checking the other things yet......
06-22-2006, 07:34 AM
#7
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Thanks for all the tips.
I'l certainly start with checking out the canister, vapor seperator and all the hoses. As far as I know the canister is original . Car has just over 70k miles.
Greg, I'm in Westford MA. I updated my profile just now. Still need to get a picture up there.
I'l certainly start with checking out the canister, vapor seperator and all the hoses. As far as I know the canister is original . Car has just over 70k miles.
Greg, I'm in Westford MA. I updated my profile just now. Still need to get a picture up there.
06-22-2006, 09:32 AM
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One last question.
Assuming I need to replace either the entire canister or just its air filter, what is the easiest access to it?
From above or from below?
Assuming I need to replace either the entire canister or just its air filter, what is the easiest access to it?
From above or from below?
06-22-2006, 01:43 PM
#10
Le Mans Master
Originally Posted by 74L82
One last question.
Assuming I need to replace either the entire canister or just its air filter, what is the easiest access to it?
From above or from below?
Assuming I need to replace either the entire canister or just its air filter, what is the easiest access to it?
From above or from below?
See if you can isolate the source of the odor a little better. It could really speed up the process of finding the problem.
The canister is of course in the left side of the engine compartment below the master cylinder. The fuel separator on the other hand is in the left rear of the car mounted to the top of the gas tank. (Separator leaks are most pronounced right after a fill-up.)
There's also the rubber fuel lines that go to the fuel pump on the right side of the engine compartment. (Connect the steel lines from the tank to the fuel pump.) These hoses (should be 2) can get old and deteriorate causing them to weep at first. They are factory pre-formed to make the bend from the frame to the pump and folks often try to replace them with just a regular piece of hose. Not a good idea as they fail much quicker and often kink, restricting fuel flow to the pump.
Right rear - you have two rubber hoses that connect the gas tank to the steel lines that then travel to the engine compartment. One is the feed line to the engine and the second is a smaller return line back to the tank.
Good luck... GUSTO
