Hot Rods Awful gas smell - help me troubleshoot

Hi all,

For more-thousand miles than I care to count, my stock 1985 350cid Chevy motor with its Edelbrock manifold, 600cfm Edelbrock carb, and 1999 vortex nice breathing exhaust manifolds, and mandrel bent tubing I built, smells like a bad snowblower. The final straw is, now that it’s temporarily being parked in an attached garage, if I back it in, just in the time it takes to do so (not long) the whole first floor smells like a garage that a very worn snowblower was started in. It makes my clothes smell.

The stock Hei distributor is timed by vacuum... set high vacuum and then retarded a tiny bit. The idle air/fuel is set the same way. I don’t have a fuel pressure regulator. The floats are set to the specs per Edelbrock. This literally takes (some of) the joy out of driving the car, so any help would be appreciated

Thanks

Drew


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You can't run more than 6 lbs. of fuel pressure with an Edelbrock carb. It will push fuel past your "metering rods". May want to double check your floats again after getting the correct fuel pump[ I think #1721?] or a regulator.

 

Just a wild shot .. but if you used gasoline laced with Ethanol
It goes bad real fast and damages any rubber components .. I typically buy Shell mid grade gas in my 2 strokes and Model A !!


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I will look into a regulator. Perhaps there is a stock part number from a 60’s-80’s car I can use to avoid paying the speedshop price.

I’ve always run ethanol free with the exception of the time I ran out of gas (gauge works, brain doesnt) and a friend brought gas. I’ll try the regular and report back. Thanks

Any other ideas welcome, too


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I found attractive looking simple Holley one for $33, but it regulates between one and four psi. Is four too low for an Edelbrock? My guess is no, but I can’t find any information out there about this… Only that 6.5 is the maximum


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Is the car running rich, or is it vapors from the fuel tank? My truck has EFI (pressurized to motor, and a return line) before I got the vent system figured out on it I had a nasty fuel smell in the cab. Now that its vented better the fuel smell is almost gone.

 

Good point that Gearhead Graphics made. On the other hand is this a gasoline smell or a too rich exhaust smell that you are smelling?
Do you only smell it in the garage or do you smell it all the time when driving?
Do you smell it more if the tank is near full than if it is down below half?
More around under the hood or at the back?

 

This is a burned gas smell, that is, a rich exhaust smell. Not a rod gasoline smell like an open gas can in the garage or anything like that

Based on Edelbrock instructions and previous knowledge tuning carbs, everything is set right… That’s what’s so frustrating.


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Excess fuel pressure does not push fuel past the metering rods.... It will push past the needle and seat. When it does, it will overfill the float bowls and out up thru the bowl vents.

Pull your plugs and see what they look like. If they are dark grey/black and wet looking it is running rich. Depending on what your vacuum is at an idle in gear, you may just need a different spring under the Pistons the metering rods attach to. Some times if the spring is a bit too stiff, the metering rods will flutter up and down at an idle causing the richness. A little lighter spring will allow the piston to hold the rods down in the lean position. Simple test is to loosen the cover screw and partly uncover the Pistons a little, just enough to see them. Have someone start it and drop it in gear. The piston should remain at the bottom. If it bounces up and down or comes up and stays up... You found your problem.

 

Eat less cabbage, beans, Mexican food, drink less beer, condition's should improve IMO

 

You will be fine with 4 psi regulator on your combination. I have a Holley low pressure one on mine, with 1406 carb and 351W.

 

Is the choke working and adjusted properly? Do the distributor mechanical and vacuum advances work properly? Is the vacuum advance connected to a full manifold or ported vacuum source? Are you making good manifold vacuum at idle? Is the carb dripping fuel from the main nozzles at idle?

Have you checked the fuel pressure with a gauge? Worry less about what the regulator looks like than if it works properly.

 

Or ask your wife politely to sleep in the other room.

 

Greybeard thanks I will look into that. Somewhere I do have the rods and springs kit. Algoma thanks I’ll buy it. $28.
Claymart the distributor is connected to the port in the passenger wide which makes vacuum only under certain conditions, while the one on the driver side (both on the front of the carb) makes vacuum all the time for the TH350. I remember researching this to be correct when I put it all together but open to suggestions!

Others; thanks for the humor



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Also: I found a Mr. Gasket one adjustable from 1-6psi for $28. Should be fine


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Since this isn't a completely stock combination of parts, it becomes one of those cases where what's "correct" is what works best in your situation. I can't make the call from here because to a large degree it's going to depend on the rest of your tune-up. It involves balancing a mix of things like initial timing, total timing, and the amount of mechanical and vacuum advance in the distributor.

But you might want to give this a try. Connect a vacuum gauge and start the engine. Then temporarily switch the vacuum advance hose from ported vacuum to full manifold vacuum. You may hear the idle pick up and see an increase in manifold vacuum. And you may also notice that the idle cleans up. Which might indicate that the engine needs more initial timing.

And at the worst, if you don't like the results, it's easy enough to switch it back over to ported vacuum.

 

Most road cars need manifold vacuum for the distributor. Just because we say "vacuum advance" it's not really advancing in the way it sounds. It's really a load compensation device that drops advance when the pedal is applied. If you stomp the gas at full advance it would likely buck or knock, so vacuum drops, timing backs off, as the engine accelerates and things meld into themselves vacuum rises, pulls in more timing along with the mechanical advance. Suddenly all is well and it's humming along. Under low load/no load scenarios that are usually at low engine RPM more advance is tolerated and it runs cleaner. "Spark Ported" curves are best for higher performance apps that can use or even need extra advance to maintain peak operating pressures at all times (horsepower). For instance, I ran 36 degrees at all times in my racer. I had a 21 degree spark retard box to start it. Couldn't do that on the street. Well, maybe, but it'd be miserable and expensive at what's $10/gal now ( ! ).

You asked the time and I built you a watch. But I did that so it might ring the bells we can't from this side of our screens. You know what you have and what might need changing to get it to behave. Maybe this review will help.

 

I appreciate all this, gents. I am going to jump at it on the next couple days


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I have seen the dial style (Mr. Gasket, Napa, etc.) leak gas and fall apart more than once. I'd go Holley here.

 

Oh! Thanks for that. Certainly wouldn’t want to deal with that! Had a fuel pump start to fall apart once. Scary stuff.

This is the spring we’re talking about, right? And I guess just try a step stiffer until the fluttering stops (if this is the problem, that is)?

I appreciate the help guys. Certainly would love the car more if I didn’t need a shower after every time I drove it


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Make sure the standard tune up stuff is good.

Sacrilege and blasphemous but a couple high flow universal catalytic converters will help quite a bit. 80 each and that "makes your clothes stink" stuff goes away.

 

Don't put a stiffer spring under the power valves. That controls the fuel mixture, richens it up as the vacuum drops. It is calibrated by spring strength. If you put a stiffer spring there, it will richen the mixture at cruise speeds.

The needle and seat (27) is what leaks by in these carbs.

 

I'd also check & advance the timing

 

I just solved this problem with my '53 with a mostly stock 1978 350. Switched to an electric fuel pump (for other reasons) and found a slight leak in my fuel line while I was replacing it. Timed it with a vacuum gauge. Car has never run better, and no smell while running or after shutdown. My vacuum advance was already on manifold vacuum, and my problem was never as bad as what you describe, but something worked!

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Thanks guys. I can count probably 20 LS/s10 2.3 creations in my local club running cats
And happy. I am not opposed. Would still like to get this right without them though as there are exponentially more cars around me all the time that are carbureted and don’t stink. I should reiterate that even with a proper air fuel setting, it does this during idle as well


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Hi drewl987,

"I should reiterate that even with a proper air fuel setting, ......"

Please elaborate, how are you determining the air/fuel setting is correct ?
At idle only ?

thanks.

Dan T

 

If you're trying to improve your idle, don't make any changes with these springs. These control the operation of the power pistons and metering rods which only come into play at part to wide open throttle. Ideally, they should have no effect on your idle.

Concentrate on the idle mixture, manifold vacuum at idle, initial timing, fuel pressure, etc. for right now.

At idle at operating temperature, are the secondary throttle blades completely closed? Are the primary throttle blades nearly closed? Do you see fuel dripping from the main nozzles at idle? How much vacuum does it have at idle in neutral?

 

The old manifold vs ported vacuum debate.
I save these 2 articles:
https://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

Briefly.....The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaustgas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

https://www.hotrod.com/articles/eve...now-about-vacuum-advance-and-ignition-timing/

Briefly....Plugging your vacuum advance into a direct source will allow it to engage at idle, which is good for a number of reasons. Much like cruise conditions, engines run leaner at idle than they do under load. Again, this means the mixture burns slower and needs an earlier spark to optimize the burn. Ensuring that the mixture has a complete burn before leaving through the exhaust port also helps the engine to run cooler at idle.

So, full manifold vacuum and turn your idle speed back to where you want it.

 

Big update on this. My 1985 350 smallblock has 8* PTDC for its timing specs.... That is with all the smog crap, a GM intake and a quadrajet. its said to be done with the vacuum advance disconnected and plugged, the car in drive, and the E Brake on.
Its important to note that I have an Edelbrock intake, Edelbrock carb, the stock HEI dizzy, and 1999 Tahoe manifolds.

I did that the manual for the 1985 truck my motor came from after finding my exact TDC. The car did not seem to run nearly as well at idle that way. I also re adjusted the Air Fuel per Edelbrock. The exhaust smells WAY less potent. Perhaps my nose is just done for the day but I swear its no more pungent than my 2002 daily driver (no CEL). It also idles WAY more smoothly in drive at a stop, like a red light. Here is the trade off. The car used to run like scalded dog through all three of the TH350's gears, now it falls on its face after a high RPM (wide open throttle) shift... I experienced this twice, the second time felt like completely dead for a fraction of second. Lastly, it appears that it wants to run hotter.... could be my imagination or the 90*f day we are having, but it creeped up a good ways past 200*f with a 185*f thermostat... I made a shroud I plan to install, but that wasnt (as bad of) a problem before.



I'd appreciate some expertise.... I am sure this would be easier if the motor was in its original configuration (smog crap). Thanks all

 

Retarded ignition timing will run hot and down on power.