View original topic: "Gravity/air pressure" flooding those at altitude? Page: 1, 2  Next
Fredrok Sat Jul 26, 2014 8:17 am

So I've filled up twice since owning our bus. Both times, the garage would smell of raw gas until we drove it again (assuming burning some volume) and then it's ok. Since my old Jeep would leak a bit around the sending unit a bit when full and I saw no visible leakage, I had assumed this may be the same and put it on my "to do" list. (which would mean don't fill it all the way)

After this second time, I went out to start and the engine abruptly stopped turning over after a second. I got out and turned it over by hand and after some slight resistance, it was rotating....mmm. Tried starting again, it cranked up and I pulled it out of the garage to warm up before driving. Heading back to the garage and inside on the floor are 2 pools of gas, looks like just under left side of engine and tailpipe area. Mmmmm, hydrolock would be the answer to why is stopped spinning.

1600cc SP (1776), 30PICT1, no cut off solenoid, runs great otherwise (fresh oil change now)

My assumption and looking to hear from others far more experienced in this system and/or at altitude is:
1) Float needle is just weak enough that at full tank volume, the weight is just enough to gravity feed and push past the needle/seat and continue flooding with engine off, filling cylinders.
2) Both times, I filled up at 6,000ft and live at 7,400ft. If the tank is not venting (new cap gasket also) the pressure inside would be greater than ambient and push fuel out the path of least resistance. (but if it seals that tight, fuel wouldn't normally flow out anyway??)
3) Combination of both?

I've had the Blazecut system on order with the cut off solenoid anyway to complete "fire proofing" the bus which would solve the issue, but I'd still be interested in knowing why it's occurring in the first place.

I'm pulling the carb off soon to tap the fuel nipple with a threaded barb so will be looking at the float needle then but maybe some one has run into the same and can expedite my sleuthing.

Thank you for any input.

Eric&Barb Sat Jul 26, 2014 10:55 am

Check that your gas cap is venting properly. Remove a few time in a quite place and listen for air whoosh in or out. Not only can this pour fuel into the engine and damage it, but can cause the fuel tank to get a vaccum and crack the tank from flexing.

Eric&Barb Sat Jul 26, 2014 11:33 am

When you fill the tank all the way up best to do so just before taking a 30 mile or more trip. That will help keep from over flowing the tank cap, especially if you park on a crowned road.

Fredrok Sat Jul 26, 2014 4:13 pm

Thank you. When this happened, first thing I did after noticing the gas pool was pull the cap and listen but nothing. Of course by that time, the pressure may have equalized anyway. I'm guessing overall that the pressure either from gravity or air pressure delta is enough to overcome the needle and seat in which case the solenoid I have coming would remedy, but still.....

BarryL Sat Jul 26, 2014 7:01 pm

First guess is non venting gas cap.

Second guess is float not floating and/or needle not seating. You should be able to fill up and park your bus full and level with no problem.

Fredrok Sat Jul 26, 2014 10:12 pm

Thanks Barry. Are there year cut offs with vented and non vented caps?
Even though I'm going to pull it to do other work soon, for now I'm going to assume the needle/seat and float are good since I only have this issue at fill up. I'll check that it's the correct cap and actually working tomorrow.

Dunno, but I'm off to OACDP to look for an exploded view for the fuel system and do some homework.

Fredrok Sun Jul 27, 2014 7:36 am

Cap vents so there goes the easy solution....

BarryL Sun Jul 27, 2014 8:59 am

Fredrok wrote: I'm going to assume the needle/seat and float are good since I only have this issue at fill up.

Easy way to check needle over-ride is, fill up, run it, shut off, take off elbow and look down the throat of the carb with a bright light and mirror.

If it's trickling then your fuel pump has too high a pressure, needle is leaking (or float sunk), or cap is not venting and engine heat builds pressure in the tank.

Fredrok Sun Jul 27, 2014 3:00 pm

Thanks Barry, I'll run through the checklist next time I fill it up. It's just damn bizarre it only does it then.


BarryL Mon Jul 28, 2014 12:08 pm

Fredrok wrote: ... I'm guessing overall that the pressure either from gravity...

If you sight from the inlet to the carb and transpose a line to the fuel tank at that height you will see there is some fuel above that line when your tank is full. It most likely is that amount of fuel that is causing the "it only does it after I fill up" syndrome.

The poppet valves in some fuel pumps will actually keep fuel from sneaking past when not running but it is not a built-in feature that you should count on.

Fredrok Mon Jul 28, 2014 1:39 pm

Barry, thank you. That makes all the sense in the world after looking at it. The fuel inlet to the carb is right at the top of the tank. I suppose the only sure way to remedy that is to install the inline cut off solenoid that I was going to do for fire reasons anyway?

BarryL Mon Jul 28, 2014 6:59 pm

Fredrok wrote: I suppose the only sure way to remedy that is to install the inline cut off solenoid that I was going to do for fire reasons anyway?

That would be considered a patch albeit safer for fire reasons. The only sure way is to make it operate stock such that the needle and seat close off the fuel.

Fredrok Mon Jul 28, 2014 7:20 pm

I agree 100% and I'll get a closer look at that when I pull the carb to complete the other work. I already have kit 111198567D on the way and includes a needle valve assembly, hoping it's not a saturated float. While it would effectively solve the issue, my question was a bit tongue in cheek regarding the only "sure" way to eliminate it (it's a brand new carb). ;)

Cheers, thanks for all of your insight.

Fredrok Mon Aug 04, 2014 8:21 am

Well, I pulled the carb, tapped the fuel inlet and installed a threaded nipple (needed to drill with 7/32 drill to get the tap to go deep enough). The needle/seat I pulled seems to work good when blowing air through it and closing. No wear on float tab and float is perfect. Unfortunately, replacing the needle with the one in the universal kit was going to happen:

I bent the tab on the float just a smidge and put it back together. THEN noticed the screws weren't seating all the way before they got tight. The through holes weren't tapped completely. Could have been the issue all along if the needle wasn't seating all the way.

At any rate, installed the fuel solenoid, added an aluminum filter before the solenoid and added all new fuel hose with fuel injection clamps on pressure side. FWIW, I measured the amperage of this solenoid that you get from JOGR and it's 1.2A for the initial hit and draw bleeds down to .9A. I'm a fan of relays also, but then you create more failure points as well. At that amperage, it works fine off of the extra tab on the 12V side of coil.

BarryL Tue Aug 05, 2014 2:34 pm

That is weird about the needle/seat. The one on the right is a nice design fwiw.

I'm not a fan of the barbs which stress the hose when using factory hose plus they propagate cuts/cracks in the hose. If it were on my fuel train I'd sand those flat and try to get it down to 6mm diameter.

Still, a sano set up.

Fredrok Wed Aug 06, 2014 7:14 am

The unit on the right is the one out of the carb that I reinstalled, Considering that the screws securing the top of the carb (and needle/seat) weren't even compressing the lock washers, I'm pretty satisfied with the theory that it was creating just enough distance between the float and not shutting off completely. Gasket was compressed "just enough" I guess.

I had those barbs in the garage and will likely change them later to the smooth type as I have more hose on order now anyway. I was 1" too short to complete the job and had to reorder (story of my life).

Thanks Barry! (what's sano?)

EverettB Wed Aug 06, 2014 8:30 am

Sano = clean.

More (I didn't know all of this so worth a read):

BarryL Wed Aug 06, 2014 8:32 am

Fredrok wrote: (what's sano?)

sano = sanitary

I'm allowed to use it in my speech pattern sparingly such that I fly under the criticism limbo-line.

Fredrok Wed Aug 06, 2014 4:36 pm

Haha, right on guys thanks!

Fredrok Wed Aug 13, 2014 3:26 pm

An FYI for anyone interested, this shut off solenoid got me 45 miles total before shitting the bed today leaving me sandwiched between the pavement and frame while I bypassed it.

I pulled it when I got home and tested directly to battery and instead of a "clunk" it had when new, it was just a "click". When it's "on" there's just barely a flow of air I'm able to push through now as opposed to an easy flow new.

No good deed goes unpunished.

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