Guest tony78_280z Posted June 9, 2004 Share Posted June 9, 2004 Right now I have the fuel return line capped off in the engine comp. My tank fills with pressure that is only relieved when I remove the gas cap, with quite a hiss. I've got a carbed 350 in my 280z (once was FI) and have no use for the return line. What should I do with the return line? Is the presure build up in my tank a bad thing? or is it ignorable? Should I drill a small hole in my cap as a friend has urged? Thanks -T Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted June 10, 2004 Share Posted June 10, 2004 MALLORY Competition-Race 3 Port Ajd. regulator with return line and carb. vacuum reference point at idle at 6psi. The return line increases the life span of an electric fuel pump. LARRY Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted June 10, 2004 Share Posted June 10, 2004 Larry has the right idea, using a regulator with a return port... it will also keep your fuel to the carb a little cooler for slightly better power, and with mechanical pumps it pretty much does away with vapor locking. Larry, please expand upon the function of the vacuum reference line on your regulator. Other than possibly acting as a tank vent (which Tony needs in one form or another) why does the regulator give a hoot about engine vacuum? Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted June 10, 2004 Share Posted June 10, 2004 A.G. ...... The vacuum reference on the fuel pressure regulator decreases the pressure on the top of the diaphragm of the regulator. This reduces fuel pressure at high vacuum conditions such as at idle and at cruising. When the engine load is increased the pressure on the diaphragm increases also resulting in a slight rise in fuel pressure.The vacuum reference also compensates for the compliance of the regulator which is the difference in output pressure with a varying flow. Case in point is, when starting my car with the key turned to activate the electric fuel pump, the fuel pressure guage reads 9psi. With the starter engaged and at idle , the fuel pressure guage drops to 6psi, because the high vacuum is recognized because of this set-up. LARRY Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted June 11, 2004 Share Posted June 11, 2004 Thanks Larry... as usual, things are a bit more complex than I would have assumed. Compliance in a fuel regulator is a concept I'd not heard of previously; I figured that the regulator regulated as set, and if the pump, fuel line, and windows in the carb's needle valves were big enough to feed the carb at WOT, all would be well. Sounds like Tony will still need to vent his tank somehow. I've drilled a gas cap to act as a vent on a low performance pickup... don't now how good an idea that would be on a Z. If the cap is close enough to gas tank fuel level, a hard corner might make the drilled hole spew. Quote Link to comment Share on other sites More sharing options...
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