imariver

#3 & 5 exhaust valves on my 73, L-48. Why are they different colors?
There are three other exhaust valves that look white and three other ones that look black.
Valves not adjusted right?





Steve

73racevette

Likely differences in AF ratio per cylinder. Could be a leak in the valve seat, but doubtful. Probably the difference in AF that the intake manifold is presenting to each cylinder. It is probably fine and unless you are looking to spend a ton of cash equalizing things, I would run it as is.

CanadaGrant

A white exhaust valve along with piston top is a good sign of a small head gasket leak and the white coating is a result of burning antifreeze. Have you checked your coolant level? Burning antifreeze leaves a white residue like that as long as the cylinder is still firing.

Easy Mike

Why post twice?
https://www.corvetteforum.com/forums...s-picture.html

BKarol

Because some people think they were funny in the other post rather than answering his question.

68post

That's a very big discrepancy btw the two ports/valves ! I wouldn't think of an AF ratio difference being the culprit , likely it's sucking air into the white valve side .

Bob K

I agree with CanadaGrant.

Bob K.

7T1vette

What intake manifold is on the engine? Interesting that 4 cylinders are "fat" and the others are "lean"....

imariver

Alan 71

Hi imar,
We could certainly be more civil with each other!
People have questions....and they deserve answers.
Regards,
Alan

imariver

The engine is the original numbers matching L-48, never been out of the car and the odometer shows 129 K miles. It still has it's original intake and all rotating parts are original too.

However, in Feb. 2016, I replaced the (original) heads with a set of 041 heads. Since that time, I have never had a coolant issue, no leaks external or internal. The fluid level in the overflow jug, has always remained the same.

imariver

I don't often post on these boards, but when I do, I'm seeking advice and information from those that have more knowledge and experience than me and the last thing I need, (or want) is to be confronted. After all, the advice posted, benefits everyone.

imariver

Interesting, I did replace the Q-Jet last winter with a new Holly. So that brings up my next question . . . Of the two valves in the pic, which one looks "normal"? (as opposed to the other) Or I guess I should ask, which one looks to be the most normal?

Thanks

v2racing

What did the plugs look like. Did they show the same variance in color?

Mike

HeadsU.P.

Somewhere on the internet is a drawing of an SBC intake manifold showing which cylinders are fed from the top chamber side of the intake plenum and which are fed from the bottom chamber. This would be on a dual plane of course.

I bet that the secondary jets are either not functioning well due to a low float level, plugged secondary metering block or the secondary throttle plates are closed shut at idle. Did you play with the secondary adjustment screw under the Holley by chance?

calwldlife

the white reminds me of shell gasoline
every time i ran shell, i had white soot on my plugs.
not uncommon that some manifolds
on some engines have a rich and lean side.
different jets are not unheard of.
the white looks cleaner.
the valve stroke is clear.
both valves are on the edge.
a little too dark on one and a little too white on the other.
if the white was around the head of the valve only,
I would say ok.
tough call.
check the valve seals and guide wear.

Les

Steve, I saw you recently did a few dyno pulls. Was everything OK at that time or was there some indication of problems, such as a miss or A/F ratio being off? Is that perhaps why you're poking around or is this more of a random inspection? The white being on the valve only has me mystified. Everything around it and in the next door port looks normal in color to me.

doorgunner

Wondering: Is the valve seating?

CanadaGrant

This isn't like you are sucking in a bunch of coolant and blowing it out the exhaust. It's just a small leak, as in drops. There is no way you can run a carb through a common intake and end up with side by side cylinder exhaust like in your pic. The only thing that turns an exhaust valve white, and it will be the piston top too, is a small glycol leak. It's not even beige or close to the normal exhaust valve beside it. It's white and only one thing does that. You said everything is stock but you changed the heads. Look there.

CanadaGrant

If the valve wasn't seating it would be black with fuel and oil. I did see the gap and wondered WT but I think it's only because of the white against the black in the pic.