Thread: New 496 wont run??
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04-15-2020 02:56 PM #33
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.
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.
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.
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?
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.
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 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!
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