Exhaust Stench
 

Thanks to many on the forum, my car is actually running and I want to get it road-worthy.

Shaker455 (Jeff) fixed my QJ and I'm kind of afraid to touch it because it starts and idles well which did not come easy... I can't drive it more than idling around the block so I don't know about the overall performance.

What I do know is the exhaust is stifling. It doesn't smell like gas, but I know Jeff added bypass air to richen up the idle and got it running on the idle circuit.

The engine is unknown, but likely to be worn out.... the distributor was rebuilt with new springs from SunTuned and the timing is stable at idle. I think I have it about 11 degrees at idle and I'm using ported vacuum.

I don't know if the stench is from tuning or from blow-by or from oil running down the valve stems. I don't see any smoke, so I'm hoping I have a tuning opportunity...

So where do I start?

Mike

I think I’d take some longer drives than just around your neighborhood to get the engine hot enough to burn off crankcase condensation. Get some actual highway miles on it and then reevaluate the situation before doing anything to it.

Finding out what the oil consumption actually is would be good so as to give you a better picture of the engine’s health. After some miles taking out the spark plugs for a look would also be helpful.

You might not see any smoke but somebody following you down the road watching your tailpipes might be able to tell you different.

Exh smell at idle that burns your eyes with todays pump fuel can be due to the idle mixture being lean.
You have given no info / details about your motor this carb is on, and doing such would be a real help in you getting useful answers.

Mike,
I replied to your email and here as well.
As B-Man suggested, drive and evaluate health of your engine and don't dig into the carb.
It has been set up for your old and current elevation.
Jeff

Shaker
 

It would be wise to take Shakers advise. He did my Q_jet and it is flawless.

Thank you Jeff! I have no intention of "digging into the carb" but if adjusting the idle screws could reduce the stench, I'd try it. As I recall, you had them set at 3.5 turns out so I can always get back to where they were.

Pulling it in and out of the garage to work on it is a near-gag experience right now.

I may adjust the choke and fast idle cam and see if that helps. The choke closes but not sure if it opens too soon. The fast idle is definitely not working... hopefully just an adjustment.

Thank you. Seems you are well aligned with Jeff on this.

Thank you. Lean idle mixture is unlikely - I know and trust Jeff's carb tuning, but don't have a clue if the stench could be caused by blow-by or burning oil.

Seems I really need to get a few miles and thermal cycles on the engine before trying to diagnose.

Thanks everyone!

Mike

Have you looked at your spark plugs? That's where I'd start

My .02 Leave it alone. I start mine up and it stinks too. Its setup with correct jetting, but mine is close to 600 hp with a 950 quickfuel on it. Different fuels do cause issues for me especially ethanol. Like was mentioned. Bring the engine up to temp and the smell usually goes away. Mine is just rich when first starting. Probably yours too. Engine needs fuel to run. It's a cold engine.

Have you adjusted the idle mixture?

Define stink.

None of the pump gas smells spectacular but if it's overwhelmingly stinky it could be too rich or too lean at idle. Every engine is different and your idle timing plays a huge roll as well.
Carb could be fine but your idle timing may not be sufficient.

What Steve said earlier is correct. Typically stinky exhaust can come from an excessive lean mixture. That's what I've seen more often than not.
You'll have to drive the car and put some miles on it to get a good idea where the tune is and how well drivability is and go from there.

My guess is a vacuum leak bad enough to overcome the rich carb settings.

A mismatched or damaged intake gasket could be an issue on a new build, or a leak at the carb base.

One trick I used in my pro days (70s) was to hold a shop rag over the carb horn and crush it somewhat to vary the density of the cloth. If the problem diminishes you're likely to see idle speed up and smooth out. Then you go looking for the source of your leak.

Thanks all.

The odor is just a very strong exhaust smell. Not like gas fumes. But strong enough to be repulsive. It takes 30 minutes to clear from the garage with the door open.

Jeff (Shaker455) fixed a vacuum leak in the APT adjustment on my carb, added bypass air, tuned it for my engine and altitude, and tested it with an A/F sensor. I haven't touched it and won't until I can drive it on the highway and get some hours on it. I'm very happy with the way the car idles and drives around the block.

So far, responses have focused on the carb mixtures. Given the carb has been tuned by a pro, I was looking for other ideas... and I have a few. I'm going to adjust the choke. The fast idle is not working. Hopefully that's just an adjustment. I will revisit the gasket but it's new and came from Cliff so I doubt there's a vacuum leak.

Effect of timing is a possibility and something I can revisit. Engine is 70 350, 11 heads (7.8 CR?), Summit 2800, 71 intake, QJ w/ divorced choke. TH350, 3.55 rear. Ported vacuum advance, mechanical advance attached.

I don't know condition of engine internals but guess it's worn. To everyone's point, I need to drive it and get some time on the engine. Meanwhile, I'll be happy it's running and keep focused on getting it road-worthy.

Mike

Along the lines of what was posted in #11, just warm up the motor fully( drive for 5 minutes) then with it idling close down the choke slowly.

If the idle speed picks up at some point in doing that then you are lean at idle or a vacuum leak is making you lean at idle.

If closing the choke down by even 1/4 it's range makes the motor run ruff then your idle is too rich, and that could be for many reasons.

Thanks Steve and einstein... that's simple and direct!

Have you tried manifold vacuum for the distributor?

Blow-by smells like oil.

A rich mixture will smell like gas, the emissions are unburnt hydrocarbons. Starting may require holding your foot to the floor while cranking to get enough air to fire.

A lean mixture send excessive amounts of NOx out the exhaust. It smells like insecticide and burns the eyes.

Pull a sparkplug under idle and at cruise (shift to neutral, cut the ignition and coast to a spot where you can pull a plug without idling the engine again.

Rich = black and sooty deposits, Normal = brown to tan tip, Lean = Very light tan to white/gray tip.

No, I have not tried manifold vacuum. Thanks for bringing this up as the carb is unlikely to be the cause for the stench.

As Cliff teaches, it's possible my CR is too low for the 2800 cam and I just need a lot more timing at idle....

I will revisit this thread:

https://forums.maxperformanceinc.com...errerid=160974

... and try advancing the idle timing until the engine pukes. I don't remember the exact vac can I ended up with but I think I picked one and/or set a limit to add 10 degrees.

Mike

Good input, thank you. Based on this, I'd guess blow-by or lean.

If it's blow-by, I understand a leak-down test might tell me that. The engine hasn't run on the road in almost 20 years and I've done enough to it to mess it up... flooding, coolant leak into crankcase, etc... so the advice to leave the carb alone until I can drive it is good.

Mike

Great observation. I never could come up with anything that described it so well. Smells toxic was the best I could do and not at all like all our favorite automotive odors of ethanol-free gas, oils and other lubricants.

Shiny, bigger vacuum leaks can be as simple as a large hose that cracked or deteriorated. Brake booster or PCV hoses are the 2 biggies. Unless there's a crack in your intake manifold or an extra open port somewhere.

The first years I owned my '68 I experienced the same problem. It's an acrid, foul odor that gets into your clothes. You can smell it on yourself even when you've left the garage.
Mine was likely from blowby. It was pretty loose and my machinist later told me that somebody had previously bored the block .040" and put .030" over pistons in.
If the car hasn't really been run in 20 years maybe the rings are stuck? Maybe a little MMO and get it on the road.