Hi guys,

Was wondering if someone had any insight on my problem. I’ve got a 1968 F100 with a 302 and a C4 Automatic. I bought it about a year and a half ago and apparently the motor was rebuilt and has about 5000 miles on it. I’m struggling with white smoke coming from my exhaust and a strong fuel smell.
I did a compression test (dry only) 109-119 on each. I did a combustion leak test (no problems at all didn’t change colour). I just plugged in a Vacuum gauge on 2 different ports on my Holley carb, one was reading super low so I did it on the other one at the lower left underneath the front float and these are my results (I couldn’t even see much change when turning the screws an 1/8 at the time cause it was shaking so much):

Idling in Park:



In Drive:



Smoke from exhaust (fully warmed up water on ground cause I hadn’t started it in about 2 months let it idle for 10 mins before the clip was recorded.):



In the video it’s set to 2 turns out.


When I was setting my mixture screws the smoke was pretty consistent (when it forced the idle up it smoked a bit more).


Im at the point where I think I just need to find a good mechanic.


302 with a C4 Automatic

Holley Carb (I think it’s a 750)

Any advice before I throw in the towel? Much appreciated.


Thanks,
-Crazz

 

It sounds kind of cool but - if I closed my eyes I thought it was a boat .

 

One possibilty: Check the vacuum modulator valve on the transmission. If the diaphragm inside it ruptures, the engine will be drawing a direct vacuum on the transmission and it'll siphon the transmission fluid out of the transmission, into the combustion chambers and burn the transmission fluid along with the fuel. The result is a nice white cloud of smoke out the exhaust pipe.

 

I actually have been leaking small amounts of transmission fluid from my pan. The gasket is so disgustingly bad that if I press it even a tiny bit with my hand it drops some fluid. But I'll take a look at the modulator valve. Thanks!

 

 

 

Holly carbs have POWER Valve diaphram problems especially with pump gas alcohol/Gasoline, worn valve stem &or guides, valve seals, worn piston rings, fuel leaking from carb into engine thins oil & causes smoking, oil will have gasoline odor, trans shift modulator should hold vacuum or it will suck trans fluid into intake manifold causing smoke especially on high vacuum deceleration,
hope this helps

 

also - if you have a mechanical fuel pump driven by camshaft, it can have a deteriated pump diaphram causing fuel to leak into engine oil. Smell the engine oil - smell of gasoline in oil & thin oil will cause white smoke & engine damage will eventually result.

 

Any idea on the specs of the camshaft? Sounds like it's got some overlap in it.

A 750 is much too large for a 302, unless you're running a tunnel ram and racing it wide open all day.


Using too large a carb can result in being unable to tune it properly, since the engine doesn't move enough air to properly activate the venturies and different fueling circuits. (Or something like that)
You'd be better off with a 500Cfm carb. Depending on usage, possibly a 600.


Bouncing vacuum gauge like that could indicate a sticking valve, or one that's stuck, or one that for some reason isn't lifting or closing like the others are. Maybe a failed lifter, mismatched pushrod, mismatched/collapsed/broken valve spring. The list goes on. So I would be looking at the valvetrain. (Speaking from experience chasing "ghost" problems)

 

I'll start small from the trans modulator and keep going from there. I did do an oil change because my choke didn't have power for about 50 miles or so and I didn't realize it got ripped off. Whoever had it set up before did a poor job and my oil went black pretty quickly. 3.5 qts came out, put 5 in drove about 100 more miles since. I'll smell the oil and see how thin it is. It does have a mechanical fuel pump.

Unfortunately I don't know, its my first vehicle I'm working on, I feel like I should start diving in at this point, gotta learn through experience. I'll take the manifold and the heads off and start looking. Yeah other guys told me the 750 was quite overkill. The owner before the guy I bought it from wanted it to be a 'racing truck' but gave up half way through and I believe he just slapped on the c6 and sold it.

I'm almost 100% its this: https://www.holley.com/products/fuel...parts/0-80508S

Pic of my Carb - https://i.imgur.com/BrGaEp9.jpg

 

Both the 302 and the C6 have been swapped into your truck, the Holley 4V isn't original either.

1969 was the first year the 302 was available in F100's. C6 not available with 302 until 1978.

So, it's possible that your 1968 F100 has a 302/C6 combo from a 1978/79 F100/150.

The original carb (if your '68 F100 had a 360 or 390 V8 originally) was the Auto-Lite 2100 series 2V

 

You can start with just pulling the valve covers and watching the rockers as the engine runs. See if one is acting differently than the rest.

 

Let us know what you find.

 

 

the smoke video shows evaporation quickly like steam, oil burning smoke lingers and fades away slowly with a blue tint & smells oily. Water passage at intake manifold may seep into intake runner causing steam cloud smoke.
Vacuum gauge looks like the timing is retarded, advance the timing, slow idle down to get throttle plate/butterfly closed to adjust air bleed idle mixture screws, re check timing with timing light. repeat if necessary.
Just a few sugestions.
may you do well, good luck