i think....

i replaced my fuel pump with the carter unit and holley regulator that are in the archives. i'm running a stock nikki. no rats nest. i bought the unit in anticipation of a weber carb in the future.

i went to start it the first time and everything was ok. the fuel pressure guage i have is crap. i'll be replacing that next. my question is, if the pump is left running with the engine not running, regardless of the pressure i have the regulator set to, fuel will begin entering the throttle. the primaries and secondarys are both dripping slowly.

so what exactly in the carb controls the pressure to the throttle and return lines? i know that there is a valve somewhere predesignated for a certain pressure. if that is not met, the fuel goes back to the tank via the return line.

i have verified that the regulator is working by pulling the line after it and setting the pressure extremely low. there was almost no flow. i know the pump is working correctly. that leaves the carb. i've read that some people have blocked the return line after this install. Why?

EDIT: i have also verified the return line is working. but fuel is still entering the engine.

any other info and thoughts would be appreciated.


Nick

 

There's no valve per se; there's a small bypass orifice in the fuel inlet that serves a similar function. This is why the max pressure spec for a stock Nikki is so low; there's little to prevent the pump from overwhelming float buoyancy if fuel pressure from the pump is too high, or if the fuel return becomes more restricted than it should be..

IIRC, Sterling recommends that even with his modified Nikki Fuel press shouldn't rise above 3.75 PSI.

 

the thing is, even with the pressure set extremely low, it would still spill in after a while. the easy and obvious solution is dont leave the pump running. but it wasnt an issue with the old fuel pump. and thats all that changed.

should i remove the one way valve from the return line?

 

the reason people block there return line is..by doing that you get a bit more fuel pressure. i did that once cause my fuel pump went out and i replaced it with a low pressure fuel pump..so i blocked the return to up the pressure a bit..it wasent enough but was good enough for me to get home on. i just couldent floor it or it would lean out and bog. not that i did..but you get the idea.

:AA:

 

another thread, sounds like my issue a bit as well. the diagnosis there was that the floats are stuck up. i'm going to check this as well the next chance i get. that would definitely cause an overflow and explain why even at very low pressures the fuel still drips into the throttle

 

What do the fuel levels in your sight glasses look like? Way high?

 

there should be a notch in the sight glass on the left and right..that's where your fuel level should be.

:AA:

 

thanks for the help. i'll check that the next chance i get. i'm in lubbock and the car is in dallas. so i will bump this thread when i get a chance to check the float bowls.

any other input or things to check would be appreciated.

thanks a ton for the info

Nick

 

If the bowl levels are correct then the next most likely cause is probably a stuck vent solenoid allowing pressure buildup in the bowls.

Plugged air bleeds can also cause this, but it'd be odd for both primaries and secondaries to plug up at the same time.

 

i doubt the jets/bleeds are clogged. i rebuilt the carb last december. will also check the avsv.

thanks,

Nick

 

Check with Sterling (our resident carb expert) www.sterlingmetalworks.com/bymc

Since it still does this with the pressure set very low, I would guess that the float needles are not seating correctly. This could be due to debris in the bottom of the float bowls, or a number of other things.

Is the restrictor in the return line installed correctly (not backwards)?

And I will be interested in hearing what the fuel level is in the float bowls as well. Good luck.




.

 

the guage i had was not readying correctly. it was reading low. so my guess is increased the pressure too much which overpowered the floats. something the old pump could not accomplish. when this happened they probably stuck or whatever.

i'm thinking the avsv is fine because like i said before, this wasnt an issue with the old pump. but i am still going to pull it out and test it.

the valve in the return line is working correctly. i disconnected the line at the firewall and it had fuel in it. turned the pump on and got flow just to be sure.

i'll keep you guys updated, thanks a ton for the info.

Nick

 

bumpity bump. home for easter so i can work on the car

the float levels seemed fine and i got the car started the first time. the pressure was set very low. i let it idle and had someone on the throttle as i watched the float levels. they seemed fine.

after it was warmed up i shut it off, left the pump running with the pressure still low, and the level began to rise slowly. so i've confirmed that is where the issue is. tomorrow and monday i will disassemble the airhorn and see whats up.

 

another bump to make sure this gets seen.

my AVSV isnt working. i connected it to power and got nothing. then tested for current and nothing. so, where can i get another one?

 

no one knows where to get an air vent solenoid valve?

on another note. the mesh screens in the fuel rails basically disintegrated. which is what was getting in the floats and preventing the needles from seating.

 

bumpity bump. one last time. new avsv and the fuel is still dripping in after a while. i'm completely out of ideas. the pressure regulator works, the float bowls are clean. i'm completely at a loss.

i think i'm gonna order a sterling nikki. the gremlin i have has beaten me

 

just rip the air vent solenoid out and plug up the external hole with JB weld

your pressure could still be too high, get a gauge and measure it, should be around the 3psi mark i think, check sterling's site

if the regulator can't go low enough, you can enlarge the return line restrictor (tiny orifice on the return line inside the carb) but this will be a lot of stuffing around to get the pressure right

 

One thing that throws some people off when adjusting the Holley FPR is that it works backwards to what would seem to be the right way. Backing the adjusting screw out, lowers fuel pressure. Turning the adjusting screw in, increases pressure.

I'm sure that you are already aware of this, but just thought I'd throw it out there rather than making any assumptions.

 

bumpity bump. car is still doing this. i'm giving up and getting a sterling nikki.

in the mean time. this is my current setup with the regulator. i ditched my broken cheapo mr.gasket gauge for a nice, liquid filled holley. the line going to the carb is capped in this pic.

when the line is capped, i get a reading on the gauge. however, in the short time i had the car running yesterday, there was no reading on the pressure gauge. is that normal? i dont think i plumbed it wrong. or is that a gauge issue?

 

I have seen the same issue with the guage reading zero even though I know
there is pressure there. It always reads correctly right after startup ( or near
correct ) but after running for awhile the guage appears to read zero but I can
see the fuel flowing and the car is running great.

My guage is a 0-15 like yours but its a Summit brand instead of Holley. Looks
almost identical. One thing to note is that pressure guages are not accurate at
the bottom and top 20% of whatever the range is normally. I didn't know this
until after I got my guage. What this means is that to dial in for 2.5 psi exactly is
almost impossible. You have to keep adjusting until its close with the 0-15 psi
guages.

What we need for low pressure carbs (Nikkis, Dells etc) is a 0-5 psi guage. I
think Re-Speed sells one.

 

thanks for the quick reply. i hunted for the re-speed gauge, which i thought was pineapple racing. since i couldnt find it, i got this one. that's good to know about the reading. it seems to read fairly accurate when its capped. so i'll keep that cap handy and use that to tune the pressure. glad to know its a normal thing. pressure shouldnt change that much once its set.

anywho, the new carb should fix the remaining issues then the car will be streetable. maybe.

 

lol, the Respeed gauge can be found at www.re-speed.com

And, like everything else they sell, it works great...

 

i'll bet. but re-speed slipped my mind and i convinced myself i saw it at pineapple. i just thought they must've stopped carrying it or something lol. oh well

 

spray out your fpr with some carb cleaner too.... new holley fpr's have a reputation of having little metal bur's in them that can block the pressure gauge and cause them to read incorrectly

re-speed's gauge has been said to be the most accurate gauge on the market as well.... GREAT GAUGE

 

oh crap. thanks didnt know that. that may be what broke the first gauge. and my carb...