Datsun 240z L28 stroker – adjusting the carburetor fuel float level (Hitachi SU round top)


Hi guys. Built On Purpose. This week
we’re adjusting fuel floats. [music] If your new to the channel the channel is about
DIY level modifications. If that’s an interest to you it might be worth you
subscribing. Also Build On Purpose can be found on Facebook, Instagram and we are
now on Twitter. So in the previous video I swapped out the SM needles and put the
SB needles in. If you missed that you can click on the card. As an outcome of that
the the a the AFR’s across all the ranges were very close to where they
needed to be with all offset by a little amount. When I did have the SM
needles in a band-aid fix I did do was raise the fuel float to lift the fuel
level higher in the nozzle to richen the mixture. That was to try…it worked a
little bit. It made, adjusted it by about 0.05 of an AFR across the range. So
coincidentally the SP needles seem to be better point by 0.5 to 1.0 AFR are too high. So
I’m hoping that if we adjust the fuel floats back down to the factory spec
that we will be very close to to where we need to be. because the SB needles they look like
they’re fairly good they’re just all offset a little bit rich. So the air fuel
filters off. I got that off because it’s not necessary if you just want to set it
up by measurement but what I want I want to do is I’m use my float sync tool
which sits on the front of the fuel bowl just to do a verification. I’ve got this
out because I love using these tools. So I did do a video with my
favourite tools as well for SU tuning. I’ll flashing another card up for
that as well. It’s important note we are working with fuel here so safety is
key just be careful. This has been sitting for a while so it’s unlikely
that much fuel splash out but always just be careful. We don’t want any
garage fires or any…any injury occurring. What I will do is I’ll
disconnect the fuel hoses first cause you could leave them on and turn it around and
work at a lower level but I think setting these things you need to get up
at a good eye height to be able to do it so I’ll take all the fuel hoses off and
then all them get these fuel floats out. [music] So these are the fuel floats.
I do have a bit of fuel in here I’ll have to drain. So I use cork gaskets which came
with the Zed therapy kit. That’s it there so you can see the float so again these
are the round top SUs used for the early model 240z.
so the floats do vary a bit. You can see the jet in there. There’s a
little little tab in there that touches on the the jet that it alters the flow.
Also be careful the pin that holds the fulcrum pin that holds the the fuel
floating is not held in, ah, its held in by the case like the actual body so it can
fall out at any time so be very careful. Um but what we do to adjust that tab is
we adjust the, these bits here. You can, sorry, what you can do to
adjust that tab as you adjust you can you adjust the fuel float by slightly
bending these things and it’s important to remember that when you do this you
need this to be as orientated as correctly as possible in the fuel bowl
for that height. Don’t just go bending it down because then that won’t sit square
sit correctly in the bowl and might jam and if it jams it will
hold the jet open or not function properly. Most height references are
reference to the ungaskitted face of this housing here. So carefully take this
off. I have heard…someone did..I can’t remember where I read… someone recommended silicon the gasket
to the top of the fuel bowl which seems like a good idea to me and because they
get very brittle and easy to tear. Particularly I got these from the states .If
you tear one it’s gonna take a while to get a new one. So I wish I had done that
in the first instance. So there’s two ways you…well there’s two ways you can
confirm whether the jet operates. You can either I blow through air pressure,
just a lower air pressure, as opposed to just going by eye. So a simple… [compressed air sound] [spluttering from taste of fuel] I don’t know if you could hear that
but you could hear it stop operation. As I said earlier I’ve got mine set so the
the float actually operates at a higher level
lifting the fuel up in the nozzle enriching it. So what I have is this this
is just a depth gauge I made it’s made out of a 11 by 31 trimming molding for a
house construction. General rule of thumb is you want to make sure that when
you stick that in there the fuel float is flat and it’s starting to touch this
nozzle here. But should get your… for these…for these kind of jets. If you
have different jets like, I think there’s gross jets, if they’re available still and you
put those in they operate differently so it’s always good to check rather just go
whack a measurement in, is just actually check the operation once you’ve
adjusted it. So I’ll go about adjusting this now. [music] So I got one adjusted it’s a bit of
buggerising around. Sometimes to makes EFI a little bit more
appealing. But, um, mucking around, if you can, I don’t know if you can hear
this but I’ll blow on it and I’ll lower it, bring the float up to where it’s gotta
be and you should be able to hear the the the air coming out of the jet and
gets closed off. [inhales] [faint hissing sound] Always check the operation and how
it’s going to be in the fuel bowl otherwise you’ll get skew result. But… [inhales] [faint hissing sound] That should be pretty close to where we need
to be. So I’ll bust out the other one. I’ll do the same on the other one and we’ll
install it and put the the float-snyc on the front and we’ll see if we’re
close. It is a bit of a trial and error and if you know if there’s some…you
might have to pull them off and have a couple of goes at it. Some people might
wonder why we these you screw threads and not bolts. Well that’s because
you’re dealing with soft alloys. If you had a bolt head there there’s
opportunity for you to do it up too tight and strip the thread and it’s also
worth noting that with the screws there is always, particularly on the
float bowls, there is always…gotta have under the screw a metal washer.
For the side where there’s the the tab that holds the the fuel line that’s
metal. Then from these these ones over here there’s also a metal washer. So
make sure you put…you know you don’t take them off and get them mixed up
because these ones don’t have a washer on them. That’s again because you’re
dealing with soft alloys it’s good to have a metal face against it otherwise
if you keep doing up the screw you might scratch out the the alloy so just a
keen little thing there to note. So just looking at these puppies the back one is
quite low it’s about nine millimeters and the front one what it’s about
thirteen and a half well so some neat little directions that come here with
the float-snyc. According to the standard it’s supposed to be 14 mil above the
level of the the top of the fuel blocks. So front ones better car
a smidgen or not at all and the back one you I need to do a bit of work on.
So I spent a bit of time adjusting these these floats. The back bowl took a bit of
effort to get because it seemed to have… I couldn’t get the float perfectly
vertical and it kept getting stuck in the bowl and filling up the fuel bowl
almost up to full because it must have lifted up a bit and get jammed and
didn’t close off the the the valve. So they’re both set now. I couldn’t…
I just went with the thirteen and a half on front and back. That’s not exactly
right but it’s a little bit less which means and I’m heading towards a leaner
condition which is what I’m after. so that’s all done. A bit of trial and error,
mucking around. The gaskets probably take a little bit of a
flogging so I hope they stay together. So that’s how I adjust the the fuel floats
in the Hitachis SUs. I hope someone had…was able to take something away from that.
A bit defeated by time. Despite my best efforts I’m not gonna get around to
doing a test drive and reviewing the data in this episode feature it. I’ll feature it the
next episode along. In the end I got both to sit around the 13 to 13 and a half
millimeters which I think’s okay. That’s not quite what the factory specs are but
what I am trying to do is get it leaner. so I guess when get around to doing a
bit of testing and data logging that’ll certainly determine whether it’s done
the right thing. So wrapping up. Summary if you’re doing this yourself
gotta I have patience and expect to go back a few times to get it right unless
you’re really good at it and just just to have patience. Don’t don’t rush it.
Need patience for this. So if you like that and there’ll be more videos like
that so might be worth consider subscribing also like this video and if
you got comments love to hear ’em. That’s it for me, catchya’s later! [music]

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4 thoughts on “Datsun 240z L28 stroker – adjusting the carburetor fuel float level (Hitachi SU round top)

  1. First rule of su , float height first. English su kits came with a washer kit to change the height of the seat
    I did my mixtures the old school leaded petrol days and checked spark plug color. in the middle of nowhere fun
    If i was you now ,i would have 2 OX sensors where the 3 pipes join to balance the carbys

  2. Can you share the name and brand of the tool you are using to measure the level of gasoline on the bowls? Thanks

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