Thread: SB Chevy backfiring on startup

Tweet

Thanks Max,

Thanks for the informative reply, I am sure that will help a lot of people sort out this kind of problem. As you say little things add up to make one big problem!

I do have a breather in the other valve cover and there is the additional engine breather on the 327 as well.

I am buying a new carb tomorrow as I think that must be the root source of
the fuel in the crankcase. Obviously the piston ring blow-by will have to wait, but hopefully I can avoid a repeat of this incident.

Thanks everyone for all of your help, much appreciated, we all learn so much from your input.

It didn't look too bad on the stick but I just drained the oil ready for the new tomorrow and it looks really "burnt" it looks like it has done 50,000 miles, whereas in reality it has done less that 400. It was top quality stuff too.

After the "explosion", I seem to have lost at least 2 quarts and the oil is black like dark gravy. There was a lot of acrid smoke when it happened, could the petrol mixed in the oil cause the oil to burn off and cause the remainder to go like this?

I can't think what else could have happened to it?

I have started her up a few times today with new carb and oil and new wire carriers etc. I have set the carb and she is running fine again, though it does feel "leaner".

I have heard from a reliable source that if the mechanical fuel pump diaphragm splits it can cause similar symptoms to this? I think I will fit a new pump as well, just in case.

Here in England it cost me a total of £350 ($700) for the bits, so it does pay to get onto those little jobs you suspect need doing nice and early.

The fuel pump has a weep hole in the bottom to vent fuel in case of a diaphram rupture. Although there is no down side to replacing an old fuel pump, if the weep hole is dry the pump is probably fine.

That's not always correct: I have had a slpit diaphragm in my fuel pump and all it did was two things:
It didn't pump fuel to the carb anymore and
It spilt huge quantities of gas onto the road when I was parked slightly down hill
I guess if it goes in a different direction it will spill into the crankcase, which has an oil return hole on the bottom of it. The fuel pump pushrod is oiled off the lifter gallery (I think) and the oil returns through a little hole in the base of the hole you screw the fuel pump to. Through that gas can get into the crankcase very fast in large quantities. Normally it should go out the weep hole.
But as always: security measures always only help when everything is fine. As soon as a part is broken, the security measures often go haywire, too.
New fuel pump is cheap and might help out on this one.

Anything new yet?
Max