Smoke From Exhaust Manifold

[Thunderlane]

Hello,

 

I recently did an oil change (5 quarts), replaced the fuel pump (external electric in-line) and set the mixtures on my SU carburetors to the recommended starting point for tuning (3 turns out). It had been several months since my engine was run for any period of time.

 

However, I took the car out for a celebratory test drive (to celebrate getting the car running on the wiring I did) and I was getting A LOT of white smoke off of the exhaust manifold. It had never done this before, and I'm wondering what this could be.

 

If anyone can get back to me, it'd be greatly appreciated.

 

Thanks!

[skirkland1980]

Is your exhaust manifold wrapped? Wraps tend to hold moisture. I've also had valve cover bolts loosen over time.

[Thunderlane]

No, it isn't wrapped and I made sure the valve cover bolts were snugged down, sine I initially thought it was excess oil leaking out and burning. I've ordered a new gasket to replace the questionable one. I'll be sure to clean both the exhaust and intake manifolds before re installing them and I'll also make sure the new gasket is sealing properly.

 

But besides a bad gasket, what could be the cause of this?

Edited September 30, 2014 by Thunderlane

[NewZed]

How long did the smoke last?  What did it smell like?  If you went out and drove it now would it do the same?  How can you see smoke from the exhaust manifold if you're driving and the hood is closed?  By "exhaust manifold" do you really mean exhaust pipe (the hole in the back)?  Did you do any other work besides the fuel pump and oil change?

 

You're either making something big out of not much, or you broke something when you were working on it.

[Thunderlane]

... Wow, so many assumptions that I'm clueless. I don't know if I should respond or talk to the moderators abotu whether it is acceptable to assume someone is an idiot here...

 

No, I mean the exhaust manifold. I can see it while I drive because the car has no hood. It starts almost immediately, and only increases in volume once the car has warmed up. It has a slightly sweet, sickly smell, much like exhaust fumes. And, no, I don't mean the bloody tailpipe.

 

And the car is under complete overhaul, as I stated in the previous thread I put up that you also posted in. But the only work was to the fuel pump and oil change. I have never tampered with the exhaust manifold.

 

And just a slight side note, I'm not an imbecile, and I certainly wouldn't have purchased a 40 year old project car if I didn't know an exhaust manifold from an exhaust tip, or as you feel it necessary to explain: "the hole in the back".

[gira]

Just a couple of guesses.

 

Could it be overfilled with oil?

 

Could you have enrichened the mixture so much that now it has found a previous leak at the exhaust manifold gasket?

 

Can you feel air or see the source of the smoke while looking under the hood and gassing the throttle?

 

Greg Ira

[johnc]

You need a thicker skin. If the smoke is white and has a sweet smell it is most likely coolant. Check the thermostat housing and the coolant tube between the two intake manifolds.

[NewZed]

You put 5 quarts in, on a 4 3/4 quart spec.  And finding the source of "smoke" is a very basic skill for a competent mechanic. 

 

Check those hose clamps.  

[seattlejester]

Relax dude, you didn't give us any info so assumptions can easily be made, NewZed is just trying to clear things up. Not sure why you are up in arms about it, you came asking for help.

 

Take a deep breath. And read on.

 

The exhaust out the tail pipe shouldn't smell sweet per say. By sweet it's closer to almost a caramel or melting sugar type of smell, usually associated with coolant. If your exhaust fumes smell sweet then you might have alternative problems. Although you may not have played with the cooling system, it is possible for the hoses to have have deteriorated. Checking the condition of the hoses and the clamps is a good place to start.

 

If you can replicate the same situation while idling, can you observe if it is coming from the front, the side, the back? 

 

What kind of fuel pump did you replace it with? Are you running a regulator? Did you set the carbs after zeroing them out? Have an AFR gauge? 

 

If you did everything and checked for obvious leaks and it isn't something easy or silly, it is possible that you leaned out your carbs and that they are in turn making the exhaust temps really hot and burning off old crud from your manifold. Refer to tuning guides to tune the carbs and see how many turns off you are from your starting point.

[Thunderlane]

Okay, y'all, sorry about that, I was stressed after a double shift at work.

 

Anyways, I just replaced it with an OEM equivalent 4psi fuel pump from NAPA, with a cheesy dial-type regulator pushing it down to 2.5psi.

 

I ran the engine for a decent amount of time this morning to make sure it was repeatable. The smoke is coming directly from the exhaust manifold, exclusively from that side of the engine and once it reaches a certain amount, it stabilizes regardless of engine speed.

 

I was advised by my local Z club that SU carbs should have a starting point for tuning of 18 flats out on the adjustment nuts. I did lean them out slightly from here, by going 3 flats leaner on each carb.

 

On a different note, I discovered that the engine was missing one of the studs for the exhaust manifold, so that's just one more thing to do.

[seattlejester]

Hey it happens, just trust us, no one is out to get you, we just need some more cards to play sometimes.

 

Main thing we want to make sure is safety, so as annoying as it is, check the fuel line for any leaks or cracks, depending on where the regulator and pump were installed it could be making its way around. Check the valve cover for any possible oil leaks, any chance you spilled while filling the engine? Trace amounts of oil smoke real well.

 

If you use a 4 psi pump, and the standard fuel rail, you may not need the regulator unless you find the bowls are draining at higher rpm.

 

Gaskets to check, which seems you are already planning: valve cover gasket, intake/exhaust gasket. I actually have a spare fel-pro valve cover gasket if you need one.

 

Do you have access to a wideband o2 and an AFR gauge? That would tell us if you are lean or not. There are some video guides to get to the right ball park including the lifting of the piston method etc. I know I had to play with my adjustment quite a bit from the standard starting place. By flats I'm guessing you have the 6 sided adjustment screw? I would set the idle and sync them up and fatten them up until the car tries to stumble and start around there and lean it out a tad and see if the smoke continues. Your fuel economy might not be great, but if that fixes the problem then that means you were just running too lean. Lean mixtures run real hot which can be real bad.

 

Cooling system is working alright? Water temp holding, radiator fan moving etc?

 

Just to make sure manifold is not wrapped, painted, coated, etc correct?

 

Pre post edit:

Found the video that I like, very good explanations and what to expect without the pricier tools.

Whole thing is worth watching but he gets into the tuning aspect around 4-5 minutes in, keep in mind ours are slightly different, principles are very much the same though.

[Xnke]

MG SU's and Datsun SU's are not exactly the same. Close, but not exactly the same and so MG tuning guides will be a little "off".

 

Turn the nuts all the way in, then two and a half full turns out. The nuts are knurled and have big and small "dot" marks. Use the stock needles and make sure they are in sync at idle and at 1500RPM, and that you do not have air leaks. Air leaks in the carb body are very common.

 

Use a stock replacement mechanical pump, and a stock fuel rail...you will not need a regulator and it will provide proper fueling. It's that easy. Often times electric low-pressure pumps and regulators don't work out well on these cars...be it because of wrong/poor/sloppy installs or that it just doesn't work out well, I don't know...but many posts here that deal with SU carbs and not-stock fuel rails or fuel pumps are resolved with "stock parts".

 

As far as smoke on the manifold, white smoke is generally going to be coolant. it may actually be burning glycol in the chamber or steam rising off an external leak. Oil/grease/fuel generally will be blue/black smoke, so you can probably rule those out.

 

Take the radiator cap off and make sure you're not loosing coolant. Run the cold engine with the cap off, see if it bubbles from cold...if so, likely BHG.

Edited October 2, 2014 by Xnke

[Tony D]

... Wow, so many assumptions that I'm clueless. I don't know if I should respond or talk to the moderators abotu whether it is acceptable to assume someone is an idiot here...

I'll save you some time: it is. The assumption is usually proven false, or true based on the comments following. The persons so offended usually dig their own graves in terms of reinforcing their own inexperience, or idiocy as the case warrants.

 

Did you read the forum rules and understand the philosophy about the site in regards to basic maintenance questions?

 

From what you put in the OP the first, obvious thing that jumps to mind is you got oil all over the thing and it's burning off... Maybe coolant. Common sense says if a cast iron object is giving off smoke, there's something on it that's burning off... What that is, would need to be determined, and the source eliminated.

 

Then again taking the car for the standard 30 minute road test might reveal that the "smoking" has stopped... If it hasn't then the obvious conclusion is something is leaking...and you look to see what it was.

 

Metals don't smoke when hot unless contaminated. If they do, find the contaminant source and stop it, and the smoking will stop.

 

Idling the engine will not necessarily remove all residues in a short time, or a long time... All depends on what the contaminant was, and the base constituent parts burn-off point.

Edited October 3, 2014 by Tony D