Ok so this is actually for a Yamaha 600cc motorcycle however same principles should apply...I think.

Noticed that the bike was smoking out the exhaust a little bit when I went to start it up. It looked white but it wasn't very dense. I figured it was the headgasket.

Decided to do a little more diagnostic work before I went out and bought new parts. First I did a compression test and it was a little low but every cylinder was right on par with each other.

So I went and got my trusty vacuum gauge and hooked it up. At idle, the needle is very eratic, bouncing all over the place from 0 to 25in HG. Revving the motor up to about 4k rpms steadies it out a little bit but still fluctuates rapidly between 8-10in HG. This would be diagnosed as worn valve guides correct?

As soon as I thought of that I looked the the smoke a little more and just maaaybe it has a blue tint to it now. Its hard to say. But if it were indeed the headgasket, wouldn't I have substantially lower compression on those affect cylinders? And on the vacuum gauge, wouldn't the needle fluctuate a huge amount rapidly at all engine speeds and not just at idle?

Lets say if the head cracked in a valve guide, would it be possible for coolant to get in there too?

Intake Leak? Vacuum leaks cause such symptoms. Wonder though, is Oil involved in the Intake (sucking oil into the cylinder?)

If it were just a vacuum leak the vacuum gauge would just read low wouldn't it?

I should also mention the exhaust does not smell like burning oil. I 'guess' it smells sweet, although I don't really go around huffing exhaust fumes so I can't be sure lol.

A bit of White at first startup may be condensation. Gas (HC) when burned (combined with oxygen or O2) forms CO2 (Carbon dioxide)and H2O (Water). with a cold exhaust, the steam of H2O cools enough to be seen.

The vacuum reading could be because multi-cylinder bikes use a carb for each cylinder, unlike cars. You will see a wild vacuum fluctuation.

I'm not sure, and the following is a personal opinion...

Bikes are between cars and airplanes. In a car, you can get away with a lot of mechanical issues. Just coast over to the side of the road when trouble strikes. In an airplane, you want ZERO mechanical issues. A bike is where you want as few as possible. Either get professional help or learn all you need to know about them before messing about. A Mopar site, while a great source of info, is not the place to fix a bike.

Try taking a vacuum reading at 178,000 rpm....and post the results.

You need to have a vacuum gage that balances all the cylinders for the reason mentioned.

a 4 gauge vac manifold to check a bike

when hooked to all 4 carbs and running the vac reading with not fluctuate as much

and you can sync all them together

pull the plugs and take a look

most likly valve seals

how does it run/ride??