Strong Gas Smell with Triple Webers

[240zip]

I added webers to my 2.8L equiped 240Z. I've noticed that my triple webers (42DCOE-8's) have a strong gas smell in the garage. The tank has a mixture of pump and race (108 octane) gas. I checked all hoses, the fuel pump, and fuel lines. Absolutely no leaks. I checked around the carbs. Again, no leaks. Do DCOE's simply have a stronger gas smell as compared to SU's? Does race gas result in the strong smell? The smell was bad enough that I moved the car to the detached garage.

 

Any pointers as to what could be causing this issue?

[kamikaZeS30]

I thought the gas smell was just part of the Datsun/other carbureted vehicle experience?

 

If it's like over-powering and burning your nose there might be a problem. My car had a heavy gas smell when it had Webers. Then again, you could have stuck/flooded floats, eventually the bowl will fill up and you'll get gasoline dripping out of the intake of the carburetor. It's pretty easy to fix, even with brass floats. You'd notice other issues while driving, though, if that was the case.

[240zip]

no issues driving at all ... it drives great, just the smell of gas is stronger than I'd like when parked in the garage. DCOE's were rebuilt and tested. Car is likely running a bit rich, but nothing that affects performance.

[Tony D]

What functional EVAPORATION MITIGATION SYSTEM do you have in place?

 

This is usually the 'emissions crap' most people take off when doing this kind of conversion---what did you do to preserve the integrity of yours? Do you have a closed-element air cleaner and properly functioning EVAP system on the car after the conversion?

 

If not, start there. They did have a proper EVAP system on triples from Nissan in the OEM Triple Application (the 165HP L24 never imported or marketed, and the Z432)...

 

But don't kid yourself, it's not a modern car with total captive emissions containment. There will be some odor. If it's up since you changed from SU's go back, look what you 'eliminated that you didn't think you needed and start retrofitting it to get back to equivalent SU emissions in the garage!

[kamikaZeS30]

To add to what Tony said, I've found that having a properly functioning PCV and properly connected charcoal canister actually made the carburetors easier to tune. I'm not a guru, though. I'd imagine that it has something to do with properly managing manifold vacuum?

Edited December 27, 2010 by kamikaZeS30

[240zip]

Tony, you bring up a good point ... nearly all the standard emission items have been removed. As a general rule, do cars with Weber DCOE's run any sort of EVAP system? You mentioned cases where other OEM DCOE's had EVAP systems, but I'm concerned that I left something out of this installation.

 

[kamikaZeS30]

Shouldn't there be a hose going from the crankcase to the intake manifold? Or is it installed and I'm just not seeing it?

[240zip]

yes, it's there, and I think it's connected to the PCV valve that goes into the Cannon intake. I'll look again, maybe it's loose or something. I can't imagine that we left that unhooked.

[ezzzzzzz]

Two things come to mind. First, the fuel bowls are vented into the air filter housing(s). Since yours are open element you could be getting the vapor smell from that. Secondly, Webers have a crappy choke enrichment system that tends to leak while sitting dormant. Pull the filter housings to see if there is fuel puddled in the bore of any carb. Just a thought.

[240zip]

After reading your post I wondered ... my DCOE's are sitting without a heatshield on top of unwrapped ceramic coated headers. Perhaps the carbs are simply heating up (heat soak) after a long run and then as you stated are venting out the open element.

[rayaapp2]

What functional EVAPORATION MITIGATION SYSTEM do you have in place?

 

This is usually the 'emissions crap' most people take off when doing this kind of conversion---what did you do to preserve the integrity of yours? Do you have a closed-element air cleaner and properly functioning EVAP system on the car after the conversion?

 

If not, start there. They did have a proper EVAP system on triples from Nissan in the OEM Triple Application (the 165HP L24 never imported or marketed, and the Z432)...

 

But don't kid yourself, it's not a modern car with total captive emissions containment. There will be some odor. If it's up since you changed from SU's go back, look what you 'eliminated that you didn't think you needed and start retrofitting it to get back to equivalent SU emissions in the garage!

 

 

Two things come to mind. First, the fuel bowls are vented into the air filter housing(s). Since yours are open element you could be getting the vapor smell from that. Secondly, Webers have a crappy choke enrichment system that tends to leak while sitting dormant. Pull the filter housings to see if there is fuel puddled in the bore of any carb. Just a thought.

 

 

After reading your post I wondered ... my DCOE's are sitting without a heatshield on top of unwrapped ceramic coated headers. Perhaps the carbs are simply heating up (heat soak) after a long run and then as you stated are venting out the open element.

 

I have Highlighted these quotes for you. The key word is "Closed" and yours K&N's are open or exposed to the engine bay. The gas can simply vent to atmosphere with minimal restriction from the float bowl.

 

Mikuni side drafts have an accelerator pump located on the bottom of the carb. Ive never had a set of side draft Webers in my hands to compare with, but if you have yours down there as well, I would think about installing a heat shield. If your pump diaphragms are cooked from all that heat they will eventually leak. Leak = gas smell. Next time you go to start the car. let it run for 30 secs and shut it off. Goose the throttle a couple of times and then run your hand under the center of each carb and see if it comes out wet and smelling of gas. If not get a heat shield under there and continue to search for your vapor issue.

 

"it's not a modern car with total captive emissions containment.". Ive actually tested both my 260Z and 240Z evap systems. I have replaced all the 35-40 year old rubber hoses in both cars related to these systems though. Both of these cars tested to a .020" leak which is the standard for a brand new vehicle in Ca. 1999 model year and older are required to have no more than a .040" leak in the evap system(yes I tested with the whole evap system including the gas cap!). The stock system exceeds the old standard and is at par with current vehicle standards. The only way in which it allows vapors to vent to atmosphere is the the jet nozzles on the stock SU's are loaded at all times and the float bowl vents that are located on the inside of the closed element air cleaner where as an injector would be closed. That's pretty darn sealed up in stock form. I believe 99% of the "my Datsun smells like gas" complaints are from faulty/unmaintained systems. The only smells I get are HC's coming out my exhaust pipe and through my hatch's missing seal during decel in gear... that can sometimes burn my eyes... its significantly worse with the window rolled down. lol

Its not totally sealed, but I dont get raw gas smells with stock SU's. A similar system can and should be implemented for the webers or mikuni side draft carbs. I will be addressing this same issue with a set of Mikuni/Solex side drafts soon as well. I guess the point is if you get it setup like stock, strong fuel vapors will not be an issue in my opinion.

[BluDestiny]

Do you have a return line?

[DrSideways]

After reading your post I wondered ... my DCOE's are sitting without a heatshield on top of unwrapped ceramic coated headers. Perhaps the carbs are simply heating up (heat soak) after a long run and then as you stated are venting out the open element.

 

Winner, winner.... chicken dinner?

 

Alan

[Tony D]

I have to agree with Ray 1000% on this, after doing my hoses and fuel system on my turbo car, I could maintain not a couple inches of water in the system, but a couple of PSIG! Absolutely no leakage. I would say the 0.020" leak he is registering is the diverter valve allowing crankcase accumulation to leak past the crankshaft seals---which on a PROPERLY MAINTAINED SYSTEM should be the ONLY leak path for the vapors! Retrofit a double or triple lip seal in their place and even that can be improved. My PSIG check was with the diverter valve plugged to test total fuel system integrity, doing it like this if I dent my gas tank, I can (and have!) literally blown the tank back straight with up to 5-10psig in the filler hole! The system IS tight. The only place for it to 'leak out' is the front and rear seals.

 

One of the startling differences was when I went from 44PHH's to TURBOCHARGED Blow-Through PHH's... No more gasoline smell after shutdown. Captive emissions in the surge tank.

 

The 240Z uses crankcase accumulation of gas vapors, and without a closed element air cleaner, proper heat shielding, and a functioning PCV system (what good does crankcase accumulation of vapors do if you just let them vent out through the valve cover 'filter'?)

 

If you can dig up some of Carl Beck's photos of the original 165HP L24 with triple 40 PHH's you will see an air cleaner very similar to the Z432. Also very similar to the Toyota 2T-G or 18R-G. None of these cars gave off objectionable vapors in OEM configuraiton. As a matter of fact, I had several GT Toyotas with the DOHC Engines and Mikuini Carbs (latest model was a 1980 Carina GT) which had no more 'gasoline vapors' than a comparable 280ZX which had EFI. The next year they went to EFI on the GT engines and the carbs were gone...but there was no noticable emissions increase in the garage that I could tell.

 

These systems are not that difficult to understand, it just takes some time to learn about them and then understand what they were doing. Likely nobody will want to make an OEM looking filter box, but that really helps. As does a heat shield. Toyota carbs (Mikuini PHH's) actually had some vapor dashpots to allow the vapors to go to a carbon cannister after 1974, same as the 260Z.

 

There's no reason triple have to be gassy and smelly. But if you are running an open element air cleaner and put it away hot...you WILL have vapors ad nauseaum! (Literally!)

Edited December 28, 2010 by Tony D

[rayaapp2]

...Likely nobody will want to make an OEM looking filter box, but that really helps. As does a heat shield...

 

I will be making one from scratch. Air craft body aluminum, pop rivets, and some liquid nails for the seams in the plenum box. Im planning on running it to the front where the filter will be. Im using the 432 box pictures that I have for a good reference. I need to source some quick latches from the junk yard and I should be good to start playing around with it. I also need to buy a set of real air horns. I have a set that bolt to my 40's, but they are obviously just bling and belong on some 44 or 45 carbs. Fingers crossed that it comes out functional and looks half descent.

Edited December 28, 2010 by rayaapp2

[Tony D]

Yeah, the 432 Box was nothing more than a box, with a duct to a cannister filter mounted near the radiator core support. The more volume it has, the more fumes work to pressurize it to the point of backflowing through the filter media!

 

We are talking inches of water column here!

[SHO-Z]

Here is what I fabed up. It is 4x4 Tube stock with a plate on each end. I have plates on each carb and the angle on the top and bottom bolts it all together. Install the air filter behind the grill and have cold air induction.

 

 

 

Also rayapp2 "The only smells I get are HC's coming out my exhaust pipe and through my hatch's missing seal during decel in gear... that can sometimes burn my eyes... its significantly worse with the window rolled down. lol"

 

If you have that much exhaust gas in your car you are really pushing the CO and that will kill you. Next project SEAL OFF THAT REAR END!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[rayaapp2]

Both seals on the hatch have been removed... because there was nothing left of them to seal. I need to order new ones. CO wasnt that bad on my car. There's plenty of moving air through the car that its not going to suffocate me. It gets strong smelling on decel with the window rolled down that creates a vacuum affect on the rear hatch seal. The low pressure in the car invites that exhaust in and passes by me on its way out the drivers side window. The effect isnt there with the windows rolled up or both windows down.

 

Like your plenum box. Its not dis-similar to what I had in mind. I have the aluminum around from the foils and belly pan I made up for my 260Z so I thought I would put it to use. Square stock works too.

[Tony D]

" It gets strong smelling on decel with the window rolled down that creates a vacuum affect on the rear hatch seal. The low pressure in the car invites that exhaust in and passes by me on its way out the drivers side window."

 

Another piece of "Emissions Related Crap" prevents or significantly reduces that (two things...uh, THREE things actually...

1) Idle Snubber Dashpot. This keeps the throttle plates closing the last several degrees VERRRRY slowly. This provides residual O2 into the combustion chamber to give a little combustion.

2) The Throttle Vacuum Pull-Off. This is the thing that when you snap the throttles closed over 3000 rpms makes the throttle close slowly over 3 seconds over the last say 1/4 throttle movement range. MAIN contributor to O2 in the exhaust so you don't get the massive spike in drop-throttle HC's due to shutting off all the O2 available for combustion.

3) AIR Pump / System. This simply pumps the O2 straight into the exhaust to post-combust the HC's in the head and exaust manifold. With an AIR pump attached to my 71 with headers and SU's I piped clean to catalyzed 83 standards.

 

ALL the above 'Emissions Crap Devices' will extract MAYBE a total of 2HP from the engine. If you don't use the AIR Pump, there is NO PENALTY WHATSOEVER but a DRASTIC reduction in HC emissions.

 

The Toyota 2TG and 18RG engines used both the throttle pull off and snubber dahspot for HC reduction. For their AIR system they used a 'Gulp Valve' arrangement which did not extract ANY horsepower, and would be easily adaptable to these cars with triples. In fact, my 1977 Toyota Celica GT with an 18RG-R running dual mikuini PHH's ALSO had a CATALYST on it, and we emissions calibrated to a tailpipe standard STRICTER than CALIFORNIA CELICAS with the SOHC 22R (or 20R, I forget which...damnable industrial refrigeration engine...)

 

There is absolutely no reason 'performance' needs to mean 'polluter', unfortunately very few people take the time to intellectually analyze their actions and simply cut, strip, and discard from rote that which they don't understand or take the time to understand. Years of 'experts' telling them 'emissions crap steals performance' and getting hung on a 2 or 5HP loss compared to a non-compliant car just steers them down a path which ends up being bad for everyone involved.

 

Yeah, retaining some of this stuff will be work... But if your eyes don't water when you drop-throttle decel... If you don't have ANY HP penalty (using a gulp valve instead of the AIR pump)... Is it worth it?

 

And to be sure, converting those Triple Carbs to EFI with some screw in injector bungs and gutting them for use as nostalgic throttle bodies would solve that drop throttle eye watering issue as well. Every ECU has a decel-injector fuel cut subroutine, and when you have NO fuel in there you can't pump HC's out to make your eyes water! It's one of the biggest things you notice when you go to EFI from Carbs. The places where you got misty-eyed suddenly aren't so fume-acious as before!

 

I digress...

[rayaapp2]

" It gets strong smelling on decel with the window rolled down that creates a vacuum affect on the rear hatch seal. The low pressure in the car invites that exhaust in and passes by me on its way out the drivers side window."

 

Another piece of "Emissions Related Crap" prevents or significantly reduces that (two things...uh, THREE things actually...

1) Idle Snubber Dashpot. This keeps the throttle plates closing the last several degrees VERRRRY slowly. This provides residual O2 into the combustion chamber to give a little combustion.

2) The Throttle Vacuum Pull-Off. This is the thing that when you snap the throttles closed over 3000 rpms makes the throttle close slowly over 3 seconds over the last say 1/4 throttle movement range. MAIN contributor to O2 in the exhaust so you don't get the massive spike in drop-throttle HC's due to shutting off all the O2 available for combustion.

3) AIR Pump / System. This simply pumps the O2 straight into the exhaust to post-combust the HC's in the head and exaust manifold. With an AIR pump attached to my 71 with headers and SU's I piped clean to catalyzed 83 standards.

 

ALL the above 'Emissions Crap Devices' will extract MAYBE a total of 2HP from the engine. If you don't use the AIR Pump, there is NO PENALTY WHATSOEVER but a DRASTIC reduction in HC emissions.

 

The Toyota 2TG and 18RG engines used both the throttle pull off and snubber dahspot for HC reduction. For their AIR system they used a 'Gulp Valve' arrangement which did not extract ANY horsepower, and would be easily adaptable to these cars with triples. In fact, my 1977 Toyota Celica GT with an 18RG-R running dual mikuini PHH's ALSO had a CATALYST on it, and we emissions calibrated to a tailpipe standard STRICTER than CALIFORNIA CELICAS with the SOHC 22R (or 20R, I forget which...damnable industrial refrigeration engine...)

 

There is absolutely no reason 'performance' needs to mean 'polluter', unfortunately very few people take the time to intellectually analyze their actions and simply cut, strip, and discard from rote that which they don't understand or take the time to understand. Years of 'experts' telling them 'emissions crap steals performance' and getting hung on a 2 or 5HP loss compared to a non-compliant car just steers them down a path which ends up being bad for everyone involved.

 

Yeah, retaining some of this stuff will be work... But if your eyes don't water when you drop-throttle decel... If you don't have ANY HP penalty (using a gulp valve instead of the AIR pump)... Is it worth it?

 

And to be sure, converting those Triple Carbs to EFI with some screw in injector bungs and gutting them for use as nostalgic throttle bodies would solve that drop throttle eye watering issue as well. Every ECU has a decel-injector fuel cut subroutine, and when you have NO fuel in there you can't pump HC's out to make your eyes water! It's one of the biggest things you notice when you go to EFI from Carbs. The places where you got misty-eyed suddenly aren't so fume-acious as before!

 

I digress...

 

Trying not to totally thread jack here, but:

 

Tony, do you remember the thread I made about identifying the triple manifold and you asked why I wanted to be able to connect to each port? I had more reasons than I stated there for wanting a disconnect-able balance tube. Until yesterday I have been without an AB valve and my vacuum throttle pull-off assembly is not adjusted correctly. This is a major reason for my cars stinky decel(mostly the AB valve). I plan on connecting the AB valve to the plenum tube with the triples as well as the PCV valve. There was a post made by Derek about the custom itb horns he has on his car were he made a balance tube with the IAC and such on the block. Id like to do something much like that only in tube form. Seems like an easy solution for connecting up all the emissions stuff that keep the car from loading up the exhaust with fuel and back firing/smelling bad.