[Greg Reid]

A leakdown test will tell you a lot more than a compression test and you can get the tester for well under $100.
A compression test will tell you how much pressure the piston it building. The leakdown test tells you how much compression the cylinder is holding...and if it's not holding it, where it's going...Out the exhaust valve, the intake valve, past the rings, to an adjacent cylinder or into the water jacket.

I fought the stinky exhaust problem for several years. An acrid, eye watering smell that I could smell on my clothes later.
After four used carbs with identical results I came to the same conclusion as PontGuy...There's something wrong and it's not the carb.
I did a Leakdown test and found I had some fairly significant blowby into the crankcase.
My engine is in the shop now. My machinist not only found that I needed valve guides but the last shop that worked on the engine installed 30 over pistons and the cylinders were bored 40 over.
Surprisingly, the engine ran very well and if not for the fuel smell, I would have just run it like it was.
Not saying you have that problem but just to give you more evididence that it could be internal to the engine.

[PontGuy]

I'm taking the day off today- working hard to get my engine ready to start so living/breathing old Pontiacs right now. Installed my new Pypes x-over exhaust system over the weekend. What a PITA. I'm getting too old to be crawling under and back out of a car a couple hundred times in two days!

Yeah at the back of my mind there is a distinct possibility that something bad has happened to this engine but hoping not. I've been thinking wiped cam lobes or sunk/burned valves, but haven't considered blow-by since there aren't that many miles since the bottom end build. The compression test numbers made me feel better, but they certainly haven't eliminated the possibility. And we don't have numbers for two of the cylinders.

Mike more questions-

The bottom end of the engine was rebuilt quite a while back but has very low miles on it, way less than 50,000, right?

Does it runs smooth, with no obvious miss or stumbles?

With the Rhodes lifters the valvetrain should be a bit noisy- is it?

Has the smell been there from the beginning, ever since the engine was installed?

If you run it up without the breather you don't see a plume of oily air coming out of the vent tube from the valve cover, do you?

Walt

[madtexan]

Guys, thanks for the help. Here is the best I can answer right now:

Originally Posted by PontGuy

Bad fuel pump - causing low fuel pressure at lower RPM (seen this before) Not sure but it was installed new when I did the rebuild 15 yrs ago... <1000 miles
Ignition timing wrong - frozen mech advance, slipped balancer, something like that I'm going to get out the timing light tonight
Cam timing way off - would have to have been installed incorrectly I specifically remember lining up the dots and isn't there only one place to install the keys on the shafts?
Crushed exhaust pipe - easy to check Not the problem
Carb problem, I think we covered that.. but is the choke opening properly? Choke works great. Opens all the way when manifold gets warm.

Walt

Originally Posted by Greg Reid

A leakdown test will tell you a lot more than a compression test and you can get the tester for well under $100. Where do I get one?
A compression test will tell you how much pressure the piston it building. The leakdown test tells you how much compression the cylinder is holding...and if it's not holding it, where it's going...Out the exhaust valve, the intake valve, past the rings, to an adjacent cylinder or into the water jacket.

I fought the stinky exhaust problem for several years. An acrid, eye watering smell that I could smell on my clothes later. That's the smell and lingering effect
After four used carbs with identical results I came to the same conclusion as PontGuy...There's something wrong and it's not the carb.
I did a Leakdown test and found I had some fairly significant blowby into the crankcase.
My engine is in the shop now. My machinist not only found that I needed valve guides but the last shop that worked on the engine installed 30 over pistons and the cylinders were bored 40 over. Wouldn't the compression be really low with this problem?
Surprisingly, the engine ran very well and if not for the fuel smell, I would have just run it like it was.
Not saying you have that problem but just to give you more evididence that it could be internal to the engine.

I'm hoping that's not the case here

Originally Posted by PontGuy

Mike more questions-

The bottom end of the engine was rebuilt quite a while back but has very low miles on it, way less than 50,000, right? Yes it was less than 1000 miles ago but 15 yrs. I start it every few months and add fuel stabilizer. Change the oil every year too. Mobile 1 only

Does it runs smooth, with no obvious miss or stumbles? Runs pretty smooth.

With the Rhodes lifters the valvetrain should be a bit noisy- is it?I think it is but with tube headers, it's hard to tell

Has the smell been there from the beginning, ever since the engine was installed? I think so but not sure. It use to stay outside before it was painted

If you run it up without the breather you don't see a plume of oily air coming out of the vent tube from the valve cover, do you? I think the crankcase air is pretty clean but i'll check again. It's not an oil burning smell though. More like ROTTEN EGGS

Walt

[Greg Reid]

A leakdown test will tell you a lot more than a compression test and you can get the tester for well under $100. Where do I get one?

I got mine from somewhere online. Do a google search and you'll find lots of sources but more importantly, you'll find lots of info on using one and how to utilize the information it gives you. There's even a couple of plans for making one from spare parts and a couple of pressure gauges.
One thing I didn't mention is that you do need a compressor. Even a small one would probably work ok.

Wouldn't the compression be really low with this problem?

Seemed ok to me but I can't remember now what it was. We're only talking about 10 thousanths of an inch spread out over the entire diameter of the piston..and since it was equally distributed over all the cylinders, there was virtually no difference from cylinder to cylinder...and that's mostly what you're looking for in a compression test.
Plus, the engine ran strong. No problem laying rubber from a slow roll. No noticeable miss and decent vacuum.

With the leakdown tester, I could clearly hear air coming out of the carb. Which reminds me...Someone earlier mentioned oil vapors coming out of the valve cover tube. Looking back, I had a significant amount of that occuring but because of the raw fuel smelling exhaust, I couldn't get away from thinking it was a carb problem. I just didn't think they were related.
I guess the reality is, the fumes are probably a mixture of oil and gas. I definitely had a light colored smoke at the exhaust, not the typical black smoke indicating a rich condition.
All these things I ignored because I never recall smelling that acrid raw fuel smell with a car before that was simply burning oil

[PontGuy]

A compression tester is a good tool to get an idea what the valvetrain is doing but I don't think it is good for determining ring fit problems. The problem is that when the engine is running it develops pressures that are much, much higher than just the cranking compression, and this can blow by the rings even if the cranking compression looks OK. I never tried a leakdown tester, but it sounds like that would work.

Blow-by is pretty obvious, though, because the combustion gases go right into the crankcase and the only way out is the PCV valve, vents, etc. So you will get a plume of oily air from these, especially under load. In the early days I a had a bunch of old worn out cars that did this. I had a 65 Corvair that would literally blow the dipstick out of the tube (and yes it was very stinky!)

If the compression rings don't fit good but the oil control rings are OK then you can actually have a car with excessive blow-by that runs well and doesn't use much oil. But usually you will see at least some oil usage as well.

Walt