qjet float issue w/overflow

my 750cfm carb is having trouble with overflowing the bowl. I've adjusted the float after pulling the carb via hanging it upside down and measuring the float per the roe book. it also states that the float should be adjusted down .020 for each lb of fuel pressure above 4-6lbs (pg 6). I measured my pressure off the electric pump at 8.5lbs, so i dropped the float by .060 (new float height of 15/32")

if i flip the ign on (not started, just ign hot) the pump starts up right away, if i leave the ign on without starting it the pump continues to run and it overflows the bowl.

the needle is fairly new, along with the seat. other than replacing the needle/seat any other ideas?

 

Any chance there's some debris between the needle & seat?

 

it looked clean when i took it out to adjust it, but it has to be leaking somehow in there. is there a kit/pn that has a needle with a rubberish tip to seal better?

 

You also need to run the brass float only, as the black Nitrophyl ones can fill with fuel and sink.

When checking the float level, it takes a bit of extra finger actiomn, as you have to push the needle/seat and down, while lifting the D shaft upwards to where the top gasket stops it. If this isn't done, the liquid level will end up higher than the float level setting would have left it.

I also agree, too much fuel pressure is also an issue.

 

Spinon fuel filters?

I went out and bought a napa 610-1051 fuel pump (made by balkamp), puts out 2.5-4.5 PSI @ 30 gph. looks like this (taken from aircraft site) :



any ideas on a source/pn for a somewhat inexpensive spinon fuel filter? I've got alot of really fine grit in the bowl that I think may be keeping the float/needle from really seating. I've got a napa 3033bp in-line filter (the cheap clear see thru plastic one) but I'm concerned that stuff will get by this since its just an "inexpensive looking" paper filter. no specs on the filter or the box to tell me what kind of stuff it filters out. I'd rather go spin on, assuming better quality, since the car gets driven primarily in dusty environments

 

BbyCbra,

The grit in the bowl had to come from somewhere. Is there rust or debris in the tank? I would check this out before going much further.

As LARRY70GS mentioned, 8.5 psi is too much fuel pressure for a Q-jet. On the street I would recommend 7 psi maximum, with 6 to 6.5 ideal. And do NOT use the brass float in a Q-jet. I also have my doubts about a 30gph pump keeping up with your engine.

As for filters, that cheap Napa filter is probably too much of a fuel flow restriction for your 455 anyway. You will be much better off with a high flow race filter although they are more expensive. Companies such as System 1, Holley, Fram, Mallory, Russell, and others offer very efficient yet high flowing filters with prices that range from about $40 to $120 in Summit or Jeg's.

Dean Oliver
www.holsfan.com/deano

 

Dean,

Grit is probably coming in thru the vented cap since the car gets driven in dusty dirty environments as a rule (its actually the motor in my jeep truck, not the tr6, it doesn;t see much above 3k rpm unless I'm cruising the freeway which isn;t often). the new pump has solved the overflow issue, now I need to get out there and readjust the float arm height. its too low so it stumbles coming up hills, that and the pump just runs and runs - its kinda loud is the early complaint.

any idea what that filter will flow in gph, and what particle size it will catch?

 

What's the problem with a brass float?

 

BbyCbra,

I don't have any idea about the Napa filters as far as flow capability or how fine of particles it can catch. I doubt Napa would have these specs either, but for your Jeep I doubt I would change filters. Napa usually makes some pretty good stuff for everyday use.

wildcat2,

The plus to running a brass float is that you can easily tell if it is leaking or not. You can either shake it and listen for gas, or preferrably, submerse it in hot water and watch for bubbles.

The brass float is probably okay for low fuel pressure systems, but for higher fuel pressure systems it simply does not control the fuel very well. I have had customers that have tried them and after one pass they come back and take them out. It's probably a combination of their small size and their buoyancy properties that won't allow them to control the needle and seat under higher fuel pressures as well as the nitrophyl floats. The brass Q-jet floats that I have seen have all been smaller than any of the nitrophyl floats. I'm sure some people run them with no problems, but I have not had good luck with them in higher fuel pressure race applications.

Dean Oliver
www.holsfan.com/deano

 

I ran 10psi on a 1/2 inch feed and 3/8 return with the holley black pump fram spin on fuel filter and a holley regulator brass float stock height no problems you want to mount an electric pump as close to the tank as possible it feeds the pump easier and knocks down some of the noise.

HTH

 

this pump is a loud SOB, clickey clack all the time, at least the other pump shut down abit when the pressure built up

 

so it turns out that the float that is/was in there before had a hole in the top where "somebody" had put the threaded aircleaner rod down the wrong vent and tried to screw it tight but ended up screwing it into the top side of the float. I had another float in a spare carb of the same # (37705) so I swapped the new one in. other than the contstant pump noise it seems alot better