I have recently purchased a demon street Jr and been tiring to get it working on my set up and i am having a problem setting the floats because it will never stay the same. i set it idling and i put it about half way up in the clear, and i take it for a drive and it does good at first and then down the road after maybe a mile or so then it is almost impossible to keep it alive and i check the float bowls and the primaries are all the way down and cannot even see fuel in there anymore, and i let it idle and it slowly raises up to the level i set it at. i don’t really understand why it would do this, fuel pressure is set at 7 psi and gets good flow at all times threw the fuel line. I can also start the car up and the floats are good and just rev to 3 grand over and over and see the floats go down till i cannot see any fuel any more and wait 10 sec and it comes up slowly.

Thanks for your time.

 

It really sounds like you have a dieing or leaky fuel pump.
You could also have a restriction some where in the fuel system. Maybe fuel filter or regulator.
You might also check to see if the fuel inlet needle valve is clear of any debris.

Tell us about the complete fuel system...

Ron

 

stock fuel electric fuel pump that just got replaced like 2 moths ago, mallory regulator with a return. and 3/8 tubing going to carb. i checked for flow on my fuel pump and unhooked my line and with it free flowing it had a constant flow and shot out a good distance more than good enough to fill the float bowls when driving around . Also had my fuel pressure guage hooked up and during flooring/normal driving there was no fuel pressure drop.

 

Don't see any mention of a inline fuel filter. A absolute must.
Are the fuel lines getting too hot? This will cause pressure spikes and vapour locks.
Do not try to run a high pressure fuel pump on the street with a carb. Even with a regulator. Get a pump that puts out 6 to 7 psi
without a regulator.

 

sorry i did not mention a filter yes i do have one, and well i had fun today and took my carb completely apart and found out that the bowls are set at the very bottom and i went and set it up right according to the book, flip up side down and put it 1/4" from the top of the carb and then put it back together. I turned on the fuel pump (constant 6 psi) and fuel dumps everywhere and fills up my butterflies. i took it apart and found out that when i put the metering block up against it there was a plastic drain that went over the bowls and was not allowing them to go up all the way and make them get stuck and keep letting fuel in because i tested it and blew air threw it and it would keep coming up because the float bowls would never go high enough to shut them off because the plastic was in the way so i took it out, and tried to blow in it and it would not allow any air threw it and still filled the butterflies when i applied fuel to it so i am lost, but i did adjust the fuel floats down a LOT and well there almost back were i started i will see if i can get some pics of the setting it is at now when i open it up tomorrow, but right now it seems to be keeping steady around half way in the clear and no real problems now with it running out of gas in the sec. so i don’t really understand why its so off from what they say it should be set at. More info tomorrow i guess when i open it up once again and get some pics of were it is at.

 

The float arm may be bent. So that when the float is "up" the needle and seat is not closing.

Turn the bowl up-side down. set the float so it is level with the
bowl bottom ( top). Flip it back over now and check that the float drops. Try it like that. Jet extentions may not allow the float to drop properly. Non holley bowl ven baffles or tubes may not allow the float to raise all the way.
Pull the needle and seat assembly and clean it.

The needle and seat may be toast.

 

ok i will try that, been kinda busy and behind on my car a little i will get to that as soon as possible, the needel in the seat is good from what i can tell, when blow in it and flip the floats up side down it seals very good. thanks for the help i see what that does.