JWray707 Posted January 19, 2018 Report Share Posted January 19, 2018 I recently replaced the intake/exhaust gasket on the L20 because I noticed a leak. So now the engine will start and run for about 2 min and then will Rev up rpms close to 2000 and shut off. Luckily I have the glass sight on the Hitachi carb so I can see that the fuel bowl will fill when I first turn the key...start it and it quickly just empties. When I turn the key again it won't refill. If I wait a while it will refill again but it seems to be intermittently. I pulled the fuel inlet and checked the needle valve and cleaned all the components but that didn't help. I can see through the sight glass that the needle valve seems to be functioning the way it should. Fuel pump is working fine. Just replaced the fuel filter. So...ideas? Clogged fuel line? I was seeing something about vapor lock (it was sitting awhile while I was replacing the gaskets.) Possible vacuum leak still on the int/ex mani? Any suggestions would be of great help. Thank you! Quote Link to comment
Crashtd420 Posted January 19, 2018 Report Share Posted January 19, 2018 My first though goes back to a problem I had.. How clean is your gas tank? I had a problem with things floating in my tank... the pieces would get stuck on the end of the pickup tube in the tank and cause the gas to stop flowing.... I would disconnect your fuel line going into the carb and see how consistent your fuel flow is, just because you hear the pump doesn't mean anything is flowing... Quote Link to comment
banzai510(hainz) Posted January 19, 2018 Report Share Posted January 19, 2018 put a new fuel filter . maybe the dirt is keeping the needle valve from open or close not right. My stock carb did this . as one cranks tap on that Banjo fitting where the gas line oes into the carb. I just put on a weber and never had that proplem again 2 Quote Link to comment
Roadster-ka Posted January 20, 2018 Report Share Posted January 20, 2018 There's a screen inside the banjo fitting. Was that checked? Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 My first though goes back to a problem I had.. How clean is your gas tank? I had a problem with things floating in my tank... the pieces would get stuck on the end of the pickup tube in the tank and cause the gas to stop flowing.... I would disconnect your fuel line going into the carb and see how consistent your fuel flow is, just because you hear the pump doesn't mean anything is flowing... Not sure the condition of the gas tank or how clean it is, but I suppose something could have gotten in there or broke loose when the truck was sitting with the manifolds off. I will check the fuel flow, but looking at the fuel filter it seems to be flowing fine. Seems like if anything it's getting clogged somewhere between the fuel filter and the carb if not the fuel inlet on the carb. Could still be from junk in the tank though. Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 put a new fuel filter . maybe the dirt is keeping the needle valve from open or close not right. My stock carb did this . as one cranks tap on that Banjo fitting where the gas line oes into the carb. I just put on a weber and never had that proplem again It's a brand new filter on there. I can see gas flowing through. I cleaned the needle valve and there was a little spot of dirt on there but I would think that would make it not want to close based on where it was. Can't do the weber (though I'd love to) still trying to pass smog... Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 There's a screen inside the banjo fitting. Was that checked? No screen on mine...hmm? Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 I am going to try to blow the lines clean with air and see if that helps anything. Like I said, it seems to be clogged or restricted somewhere between the fuel filter and the carb and the fuel bowl WILL fill to the proper level, it just won't maintain the proper level while the truck is running. Quote Link to comment
datzenmike Posted January 20, 2018 Report Share Posted January 20, 2018 Fuel pump is working fine. Just replaced the fuel filter. How do you know the fuel pump is fine???? If filter or line plugged the pump would not be " working fine". Pull the outlet from the pump off and aim onto a suitable container. Take the coil wire off and crank engine a few times. You should see strong surges of gas if the filter and line are free. It's the only way... Quote Link to comment
banzai510(hainz) Posted January 20, 2018 Report Share Posted January 20, 2018 like I said one you see the gas going down tap on the banjo fitting where gas goes in the carb. Be honest at idle the truck barely uses any gas. so you have time to watch things happen and tap on the Banjo. try open the gas cap. Now maybe the needle valve arm got bent . But Im just winging it now. as mike said take the hose that goes to the carb and point in safe direction and the gas should shoot out alot 1 Quote Link to comment
datzenmike Posted January 20, 2018 Report Share Posted January 20, 2018 If gas shoots out you've eliminated pump and everything behind it, filter, lines and gas tank. Move on to carb. Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 like I said one you see the gas going down tap on the banjo fitting where gas goes in the carb. Be honest at idle the truck barely uses any gas. so you have time to watch things happen and tap on the Banjo. try open the gas cap. Now maybe the needle valve arm got bent . But Im just winging it now. as mike said take the hose that goes to the carb and point in safe direction and the gas should shoot out alot Was tapping on the banjo the only way you got it to work? Don't want to have to do that every time this problem arises. Tapping it didn't work anyway. I tried running it with the gas cap off and still dying. Quote Link to comment
JWray707 Posted January 20, 2018 Author Report Share Posted January 20, 2018 If gas shoots out you've eliminated pump and everything behind it, filter, lines and gas tank. Move on to carb. Fuel is squirting out of the pump strongly and consistently. I sprayed compressed air through the gas line anyways, just to be sure it's clear. Gotta be something with the banjo/fuel inlet, eh? Here's the parts to it... Everything look to be there and complete? It seems to be getting clogged somewhere, but I've cleaned it well. Don't know what's going on, seems like a simple valve setup...probably a simple solution too. Quote Link to comment
datzenmike Posted January 21, 2018 Report Share Posted January 21, 2018 Follow the fuel line to the carb... there's the banjo fitting. It will be more apparent why it's called this after you remove it. Be careful... some are brass screen, newer ones are plastic. It slides onto the brass inlet fitting which holds the needle valve in the bottom end. The float pushes up on the bottom of the needle to close of gas flow. 1 Quote Link to comment
Roadster-ka Posted January 21, 2018 Report Share Posted January 21, 2018 The float could be sticking in the full position. There is a screen missing from the banjo assembly. 1 Quote Link to comment
JWray707 Posted January 21, 2018 Author Report Share Posted January 21, 2018 Floats not sticking...I can see the whole assembly and the float drops when bowl is empty and the needle valve drops aswell, maybe not enough though. Might just be something sticking or gummed up. I have an old carb that maybe I can swap some pieces off to see if that helps and maybe it has that screen too. Quote Link to comment
datzenmike Posted January 21, 2018 Report Share Posted January 21, 2018 Maybe just take it apart and clean it? Quote Link to comment
banzai510(hainz) Posted January 21, 2018 Report Share Posted January 21, 2018 has to be the needle valve Quote Link to comment
JWray707 Posted January 21, 2018 Author Report Share Posted January 21, 2018 Yep, pretty sure the needle valve is malfunctioning or sticking somehow. Soaking it in carb cleaner now. Thanks for the responses! 1 Quote Link to comment
Doctor510 Posted January 22, 2018 Report Share Posted January 22, 2018 Be care ful, if the needle has a "rubber" tip, it will swell up. If you take iy apart, DO NOT loose the little spring... Quote Link to comment
distributorguy Posted January 23, 2018 Report Share Posted January 23, 2018 Common fuel pump problem: and I admit I'm not familiar with the Datsun pump, but other cam driven pumps, they all have an internal check valve that prevents fuel from flowing back down the line through the pump. If that check valve is bad, it'll siphon the fuel back down to the tank level and you have to reprime the pump when you start the engine. It can even potentially pull fuel out of the bowl, with some carbs. A slight leak in a fuel line - small enough it may not even leak fuel - will allow the same thing to happen. Clamp every connection with good clamps and replace a steel line if you have one - its just brake line. Replace banjo fitting seals and check mating surface for warpage or burrs. The engine revving is usually a gross vacuum leak offense, like a fitting missing from the manifold or a hose hooked up in the wrong place. Quote Link to comment
datzenmike Posted January 24, 2018 Report Share Posted January 24, 2018 The L series carb (at least) can't siphon. The inlet is at the top of the float chamber and gas would have to jump up hill a 1/2" gap and more, even if the gas in the line was to somehow drain back into the tank. There is more than enough gas in the float chamber to start the engine and drive a block or more without the need to prime the carb. Fluid pumps can produce unbelievable pressures but no pump made can suck fluid vertically more that about 30 feet. Suction is limited by atmospheric pressure. If you are higher above sea level this height decreases and pumps have even more trouble drawing fuel from the tank. Quote Link to comment
JWray707 Posted January 25, 2018 Author Report Share Posted January 25, 2018 The pump is an aftermarket pump. I know it's pumping gas all the way to the fuel inlet on the carb cause I pulled the hose from the banjo fitting inlet and it's pumping gas all the way through the line. Fuel is being sucked into the manifold, not back through the line. The needle valve is definitely the issue...just can't figure out what's happening. Could possibly be a vacuum issue I guess, not allowing fuel to continue pumping through the valve due to vacuum pressure? I'll recheck all the manifold bolts...maybe a vacuum leak through there. Quote Link to comment
datzenmike Posted January 26, 2018 Report Share Posted January 26, 2018 There is no vacuum inside the float chamber. Gas only goes into and fills the carb, never the manifold.The needle valve opens as the float lowers as the gas is used up. Gas is pushed in. Usually a cleaning and make sure there is nothing stuck in it that will prevent it opening. A carb rebuild kit will usually have a replacement needle valve. There is a glass on the front of the carb float chamber. Gas should be seen at the half way dot on the glass. Have you taken the front off the carb? Maybe the float is stuck in the up or closed position???? Quote Link to comment
racerx Posted January 26, 2018 Report Share Posted January 26, 2018 If that's a 32.36 weber. Pierce manifold sells them. Mine went south many moons ago and was the needle valve. Quote Link to comment
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