Thread: New 496 wont run??

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Ok so I did go and get a spark tester and with it installed and just turning the distributor I had it light up. I got in contact with the engine company to find out my plug gaps and timing again. They told me the plug gaps should be .35, the new ones I got were not that gap they were much smaller. So I gapped them all to .35. They also told me the timing should be 12 initial and 36 total.

So with all the plugs out I put a little bit of oil down all the cylinders in case of wash down, I then pulled bank 1's valve cover off and watched the intake valve one cylinder one open and close and then set the crank pully on 0 degree's. Looked at my rotor and it was pretty much pointing to number one cylinder. I marked the housing for the rotor location and put the cap on and put number one at the mark on the dist. I cranked the motor over a few times to let the oil in the cylinders move around, put all the plugs back in, and exchanged the oil.

I pulled the carb off and went through it I set both primary and secondary throttle plates so you can just barely start to see the idle circuit groove. I exchanged the power valve from a 6.5 to a 3.5 even though everything I read told me that that will not effect idle. I set the idle mixture screws to only 1/2 turn out from stop to start. I re-installed everything and I am going to flush the fuel system and ensure I have fresh fuel in it and attempt to start it this weekend. If you guys can think of anything I might have missed please let me know.

Originally Posted by Camaro350

I exchanged the power valve from a 6.5 to a 3.5 even though everything I read told me that that will not effect idle.

This is true normally, because the power enrichment circuit operates via venturi vacuum (fuel is introduced above throttle blades through the boosters). However there are a couple of exceptions;

1). If the power valves diaphragm is damaged, it can leak and pull fuel in through the vacuum passages.
2). The idle stop on the carb is set too high combined with low vacuum, the low vacuum opens the the valve with the throttle blades opened enough to introduce the fuel through the boosters. Usually this condition also activates the transition circuit adding even more fuel.

Skipping past this, if the throttle relationship and low vacuum are a contributing problem changing to a lower value PV will not help it (may make it worse). While tuning the PV circuit is essential and contributes greatly to performance, I would not lower the value until I had it running correctly.

Unfortunately, guessing at this is not the answer.

I'm going to ask a few questions that may have been asked already but I did not see when scanning back through your thread (apologies if it has been asked), so at the risk of redundancy;

1). Is this a NEW or used carburetor?
2). While it is running at its lowest idle speed, have you looked down into the boosters to affirm NO fuel is coming out of them.

At idle you should NOT see any fuel coming through the boosters. If you are unsure what the boosters are, just ask we'll explain, no need to be embarrassed.

At IDLE, you should NOT see any fuel entering the motor, as the idle circuit's entrance is below the throttle blades (transition circuit as well for that matter). So, if you see fuel entering the motor at idle, you have another problem.

If this is a used or rebuilt (even from the manufacturer) there could be an error in assembly causing fuel to enter the motor from a source it should not be coming from. Often, it is a simple as a misaligned or incorrect metering block or gasket.

If this is a new carb, and you see fuel entering through the boosters at idle. Contact the manufacturer for directions on what they want to do to correct it for you.

Good luck!