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Altema
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Joined: June 20, 2010
Posts: 2903
Location: Lower Michigan
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 Posted: Thu Oct 25, 2012 10:49 pm Post subject: Anyone tried a fuel line pressure relief? |
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I have a problem with residual pressure from my fuel pump. Not so sure it's fuel in the pump percolating from heat soak, but that seems likely. I thought of using a "T" fitting on the feed to to the carb and a "T" on the fuel line TO the carb, with a solenoid valve in the circuit. Basically it would not affect fuel pressure while running, but would shunt pressure back to the supply line when off.
I currently have a valve on the line to the carb which I close after a hard drive. Later, I'll come back to the car and open the valve, and you can hear fuel squirting into the carb, and it usually dumps some into the intake. The shunt would eliminate the back pressure. Any thoughts on this?
Paul
PS: The problem usually only occurs after a long hard drive on warm days. |
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slalombuggy
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Joined: July 17, 2010
Posts: 9143
Location: Canada
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| Posted: Fri Oct 26, 2012 5:23 am Post subject: |
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Sounds viable. What about just making your fuel system a loop and running the carbs in series with a return line back to the tank?
brad |
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Dale M.
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Location: Just a tiny bit west of Yosemite Valley
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| Posted: Fri Oct 26, 2012 7:44 am Post subject: |
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| slalombuggy wrote: |
Sounds viable. What about just making your fuel system a loop and running the carbs in series with a return line back to the tank?
brad |
You are going to need some sort of flow control to maintain pressure while running and drop pressure off when off.... Either a solenoid valve or maybe just a orifice (restriction) in return line....
Dale
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Altema
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Joined: June 20, 2010
Posts: 2903
Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 9:31 am Post subject: |
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| slalombuggy wrote: |
Sounds viable. What about just making your fuel system a loop and running the carbs in series with a return line back to the tank?
brad |
Thought about that, but did not want to run new line all they way up front in a car I'm trying to keep stock looking, or at least be easily returned to stock looking. I think just shortening the loop to tie it in before the pump should be just as effective. The car only has a stock single carb right now that I was trying to maximize, and I think I'm at the limit now (easy 100mph), but now I'm curious about how much I can get out of duals. Does it ever end? Nope.  |
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slalombuggy
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Location: Canada
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| Posted: Fri Oct 26, 2012 9:32 am Post subject: |
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Run the pump line through the carbs in series, then to the pressure regulator (every one with an electric pump uses one right  ) Then have the return line off the regulator back to the tank
brad |
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Altema
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Joined: June 20, 2010
Posts: 2903
Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 9:40 am Post subject: |
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| Dale M. wrote: |
You are going to need some sort of flow control to maintain pressure while running and drop pressure off when off.... Either a solenoid valve or maybe just a orifice (restriction) in return line....
Dale |
That my friend, is a great idea!
I was thinking a control solenoid, but a simple return with a small orifice would barely affect fuel delivery, yet bleed off excess pressure from fuel percolation or whatever when you shut down. Ok, I'm gonna do it and report back. I have to find some quality brass T's, and maybe an old carb jet for the restriction. |
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nextgen
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Posts: 6022
Location: CONGERS, N.Y.
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| Posted: Fri Oct 26, 2012 12:02 pm Post subject: |
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Guys what are you doing, back to square #1 - a guy has a arrow in his head, do you give him an asprin or figure out he has an arrow in his head.
Sure what you guys are saying are great ideas but what is causing it? I have seen that with heat but it has to be really hot. Altima, you live in cool climate as I do, is your engine running hot? Float issue maybe. Bad pump, not likely but???? Isolate the carb from the manifold with a phonolic spacer for a heat issue. Is all your sealing tin in place. Are your heater ducts tight and you are not losing cooling air.
Am I wrong in what I am saying, or am I not getting what he is asking??
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[email protected]
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| Posted: Fri Oct 26, 2012 12:29 pm Post subject: |
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a return style regulator will work, instead of a deadhead one.
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W1K1
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Location: Southern AB
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| Posted: Fri Oct 26, 2012 2:49 pm Post subject: |
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I found having a mechanical gauge in line was absorbing the excess pressure at shutdown on mine.
When I took it off I had the same problem as Altema with the stock dual carbs on my type3 and mechanical fuel pump.
The pump was shimmed with extra gaskets to keep the pressure to 3 psi, but heat soak after shut down would cause it to push past the floats and flood the carbs without the gauge in line.
I have since gone to an electric pump with my 36 dells and don't have any problems anymore.
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Altema
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Joined: June 20, 2010
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Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 2:52 pm Post subject: |
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Well, it works! I went to a few different stores and found one that carried real brass fittings. Went through my jet collection and found a 125 jet, turned the flange end down so it would fit the hose properly, screwed it into the brass tee, then installed the tee before the carb and the return line straight down to the supply line. Took it for a drive and checked for leaks (dry), then after it got warm I took a WOT run to freeway speeds (yes, ON the freeway). No leanouts or starvation problems (running an A/F gauge), so it seems the pump supplies enough volume to not be affected by the little bleed line. Thanks for the idea Dale 
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Altema
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Joined: June 20, 2010
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Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 3:04 pm Post subject: |
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| nextgen wrote: |
| Am I wrong in what I am saying, or am I not getting what he is asking?? |
That may be part of the problem. I'm just looking for a simple solution for a common problem. And it is a common problem. Most people don't notice it, or just ignore it when they have to crank a few extra seconds on a restart. In most cases, you just get a little extra fuel in the bottom of the intake runner, but in some cases it can be enough to trickle down the manifold ends. I went through the trouble of finding out why, and looked for a solution. The VW's we had growing up had the same issue at times, and all seven of them were stone stock. For the record, my engine runs cool despite thermostat and flaps. Oil temp is usually around 160 degrees, and I have to run the car up to 100mph to get the 6 quarts much past that. The engine case temperature in everyone's fave spot (the dipstick!) is usually 170 to 220 on the typical engine, and that heat soaks into the fuel pump just because it right there on top. I might be wrong, but fuel vaporizes below that range (I'll let an expert chime in here). It's not a big problem, but it does waste fuel, and I just wanted a fix
TTYL,
Paul |
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Dale M.
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Joined: April 12, 2006
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Location: Just a tiny bit west of Yosemite Valley
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| Posted: Fri Oct 26, 2012 4:36 pm Post subject: |
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| Altema wrote: |
| Well, it works! I went to a few different stores and found one that carried real brass fittings. Went through my jet collection and found a 125 jet, turned the flange end down so it would fit the hose properly, screwed it into the brass tee, then installed the tee before the carb and the return line straight down to the supply line. Took it for a drive and checked for leaks (dry), then after it got warm I took a WOT run to freeway speeds (yes, ON the freeway). No leanouts or starvation problems (running an A/F gauge), so it seems the pump supplies enough volume to not be affected by the little bleed line. Thanks for the idea Dale |
Umm.... Don't thank me yet..... Put some time on ( days-weeks-months) and if it still functions like you desire, then thank me...
Dale
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Altema
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Joined: June 20, 2010
Posts: 2903
Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 6:02 pm Post subject: |
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| Dale M. wrote: |
| Umm.... Don't thank me yet..... Put some time on ( days-weeks-months) |
Yeah, guess it makes no sense to say "so far so good", when you haven't gone very far. At least we know having the bleeder orifice in there does not cause fuel starvation. And that the t's don't leak. Oh, one side benefit I can note: The fuel pump is unusually cool. It's normally around 110 to 115 degrees F when I first shut down, then warms up from heat soak. Tonight after a 20 mile freeway drive, the fuel pump was 85 degrees. 
Last edited by Altema on Fri Oct 26, 2012 6:11 pm; edited 1 time in total |
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Altema
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Location: Lower Michigan
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| Posted: Fri Oct 26, 2012 6:07 pm Post subject: |
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| [email protected] wrote: |
| a return style regulator will work, instead of a deadhead one. |
Looking at the big picture, this is probably the best route to go. Would keep the fuel pressure consistent, and eliminate any excess pressure build up even after shutdown. |
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Altema
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Location: Lower Michigan
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| Posted: Sat Nov 03, 2012 11:16 pm Post subject: |
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Well, it's been a week and it seems to be working fine. And thanks to Nextgen for making me take a closer look at other things that could be a contribution to the problem. What I did find after looking some more, is that my float setting was a bit too high. It was 19mm from the top, but watching down the carb throat while the engine was running, there were ocassional sputters of raw fuel coming out! I dropped the float level 2mm and the excess fuel stopped. As a result, I had to retune and rejet the carb, moving from a 135 main to a 138.
Now the good news is that with the return line, there is no pressure build up and no fuel pushed past the float valve when sitting with both the low and high float settings. The intake stays dry and the car starts instantly, hot or cold. A lower float setting without the return line still allowed some fuel to be pushed past the float, so the lower setting alone would not have eliminated the problem. So, no more issues. There is one more benefit that I was not expecting: cooler fuel pump temperatures. Much cooler. Apparently, the little bit of fuel circulating through the restrictor (from pressure to suction) causes a thermal drop. Typical fuel pump temperature before the return line was 115 to 125 degrees F. Now the fuel pump temperatures are around 68 degrees F.
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Altema
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Location: Lower Michigan
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| Posted: Mon Dec 03, 2012 4:12 pm Post subject: |
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Ok Dale, it's been over a month... can I thank ya yet?
Seriously though, it has been working well, and I appreciate not having to open my decklid 5 or 6 times a day to flip the shutoff valve. Best part is I don't have to worry about the car dying when I forget to open the fuel valve, which usually happens right after I pull into traffic from our neighborhood! Fuel pump temperatures remain low as well. The only downside so far is not having the shutoff valve there when I change carb jets.
Paul |
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808OvalGreasemonkey
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| Posted: Mon Dec 03, 2012 5:16 pm Post subject: |
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On my electric pumped/carb'd motor I simpy installed a toggle switch to turn off the pumps about 1 minute before I kill the car,now my garage does'nt smell like a gas spill/leak. The residual pressure really makes a hard start and really bad gas smell. That is a cool solution you have found there.
I am running dual Kadrons with a mechanical pump on my bus and have no issues with residual pressure though....have you ever checked your pressure? It may be too high. |
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Altema
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Joined: June 20, 2010
Posts: 2903
Location: Lower Michigan
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| Posted: Mon Dec 03, 2012 5:57 pm Post subject: |
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| 808OvalGreasemonkey wrote: |
| have you ever checked your pressure? It may be too high. |
Hmm... I have not checked the actual pressure. The float adjustment was not excessive, so it seemed like excess running pressure was not an issue. Besides, my problems occured when the engine was not running. But you have me curious and I'll have to get an accurate reading now, lol.
So you turned the fuel pump off early, huh? That funny, because before this mod I would close the fuel valve and then drive into the garage for the same reason you cut the pump.
By the way, I think that even if I was not having the build up problem, I would do it again just because it makes the fuel pump run so much cooler. A 40 degree F drop is significant.
Paul |
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mightymouse
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| Posted: Tue Dec 04, 2012 10:12 am Post subject: |
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Theres this new thing.... called an electric fuel pump. You should try it some time.
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Altema
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Location: Lower Michigan
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| Posted: Tue Dec 04, 2012 11:33 am Post subject: |
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| mightymouse wrote: |
| Theres this new thing.... called an electric fuel pump. You should try it some time. |
Aww, you're no fun! I thought it would be more creative to solve the problem rather than abandon the mechanical pump. Besides, I've gotten PM's from people with electric pumps and similar problems.
Paul |
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