JG2020 Posted July 2, 2021 Share Posted July 2, 2021 I noticed on a couple of very hot days gas leaking from the top of the tank. I had this issue before when filling all the way and replaced the breather gasket on the top of the tank. I have not checked this again to see if that's the issue or maybe it's coming from the fuel take sender. More concerning is I got on the highway and the truck started bogging down like I was running out of gas. Press the pedal to floor and it would just start to die. Then it would pickup speed again and then start to die again. My fuel gauge is broken and I thought for sure I was out of gas. It started running fine but I stopped at a gas station just to check and put in only 5 gallons to fill it. This was about a 40 mile drive each way. It happened once or twice more on the way to the Dr. and back. I took it out the other day for about 25 minute drive and same thing. Acts like it has no fuel. Then it kicks back in and is fine. Any ideas? I thought I read the carb nuts might loosen on the 300? I have not checked yet as I have been away. I did a quick check after my last drive and did not see any vacuum hoses loose or anything obvious. Thanks! Josh Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 2, 2021 Share Posted July 2, 2021 I think you may have a problem with the rollover valve. It sits in the top of the tank and if its grommet is cracked or shrunk it can leak when you get the tank completely full. And if it is stuck partially shut, or if the vent hose is partially clogged, then you could be pulling a vacuum on the tank as you drive, which will prevent the fuel pump from keeping the carb full of gas. But I'm not quite sure why it would start working again, unless by bogging down that releases the vacuum? Is this the front or rear tank? The top of the front tank can usually be reached from under the truck, although getting a good look at the valve and its grommet might be difficult. Perhaps with a camera? And check the vent hose that is connected to it. The hose must not be blocked. Link to comment Share on other sites More sharing options...
Frank Wyatt Posted July 2, 2021 Share Posted July 2, 2021 I think you may have a problem with the rollover valve. It sits in the top of the tank and if its grommet is cracked or shrunk it can leak when you get the tank completely full. And if it is stuck partially shut, or if the vent hose is partially clogged, then you could be pulling a vacuum on the tank as you drive, which will prevent the fuel pump from keeping the carb full of gas. But I'm not quite sure why it would start working again, unless by bogging down that releases the vacuum? Is this the front or rear tank? The top of the front tank can usually be reached from under the truck, although getting a good look at the valve and its grommet might be difficult. Perhaps with a camera? And check the vent hose that is connected to it. The hose must not be blocked. On the issue of losing power don't over-think things and do as my Grand-Dad always told me, check the simple things first. It's easier and almost always cheaper, like a clogged fuel filter. .i had the same issue and it was a clogged fuel filter, and it looked just fine but is was probably about 95% clogged. Link to comment Share on other sites More sharing options...
JG2020 Posted July 3, 2021 Author Share Posted July 3, 2021 On the issue of losing power don't over-think things and do as my Grand-Dad always told me, check the simple things first. It's easier and almost always cheaper, like a clogged fuel filter. .i had the same issue and it was a clogged fuel filter, and it looked just fine but is was probably about 95% clogged. Thanks all, I replaced the grommet and vent valve a few hundred miles ago because the truck was overflowing when I filled it up. That fixed that problem. .I will have to take a look and see if something happened to it. This leak happened while just sitting and the tank was about 2/3 full. It was really pouring out down the side of the tank onto the street. A steady stream. The fuel filter has about 500 miles on it but easy enough to change I guess. This is the side tank. I did buy one of those flexi cameras when I was troubleshooting the vent valve grommet so I can take a looksy. I need to really drop the tank down enough replace the fuel gauge sender also. Raining here today so I will report back tomorrow! Josh Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 3, 2021 Share Posted July 3, 2021 Thanks all, I replaced the grommet and vent valve a few hundred miles ago because the truck was overflowing when I filled it up. That fixed that problem. .I will have to take a look and see if something happened to it. This leak happened while just sitting and the tank was about 2/3 full. It was really pouring out down the side of the tank onto the street. A steady stream. The fuel filter has about 500 miles on it but easy enough to change I guess. This is the side tank. I did buy one of those flexi cameras when I was troubleshooting the vent valve grommet so I can take a looksy. I need to really drop the tank down enough replace the fuel gauge sender also. Raining here today so I will report back tomorrow! Josh If it truly was only 2/3 full and you had that kind of a leak then I'm at a loss as to what could do that. But gas expands quite a bit and I've had leaks with my trucks if I fill the tank up FULL and either drive it or sit it outside. Driving it seems to heat the tank from the exhaust and if it is the tank that is not being used it can overflow. But I wouldn't expect a tank that was only 2/3 full to have that problem. When you are looking for things, check out the vent hose. One of mine was off and it was leaking there as the outlet of the rollover valve is well below the filler neck. Link to comment Share on other sites More sharing options...
JG2020 Posted July 4, 2021 Author Share Posted July 4, 2021 If it truly was only 2/3 full and you had that kind of a leak then I'm at a loss as to what could do that. But gas expands quite a bit and I've had leaks with my trucks if I fill the tank up FULL and either drive it or sit it outside. Driving it seems to heat the tank from the exhaust and if it is the tank that is not being used it can overflow. But I wouldn't expect a tank that was only 2/3 full to have that problem. When you are looking for things, check out the vent hose. One of mine was off and it was leaking there as the outlet of the rollover valve is well below the filler neck. Update! I was away for 9 days and when I went to start old Bessy up she would not have it. This truck has always started right up. Tried for 10 mins . Choke is operating normally. I ended up having to spray some gum out and after a couple tries got her running. The carb mounting bolts had about a turn and a half or so on each one so I tightened those. 2 vacuum caps on the tree were dry rotted and broke apart when I pulled on them . I replaced all the caps and also recut the brake booster house and clamped since the end was bloated and had some cracks. This morning the truck started right up and was purring like a kitten. It had been running a little rougher lately. Drove to the supermarket and got about a mile from and lost power. Was bucking all over the place. Not fun on a bridge ha ha. I made it into a parking lot and the truck was idling perfectly . Gave it gas in neutral and no bogging down. Choke was wide open. It happened a couple more times but I made it to the market. On the way back it happened once . Totally just bogged down like it had no fuel. Pumped it in neutral and it came back and made it home fine. It doesn’t seem like it’s related to giving it more or less gas pedal. I’ll be crawling under with the camera to see what I can see. Sorry for the long story! Link to comment Share on other sites More sharing options...
JG2020 Posted July 4, 2021 Author Share Posted July 4, 2021 Update! I was away for 9 days and when I went to start old Bessy up she would not have it. This truck has always started right up. Tried for 10 mins . Choke is operating normally. I ended up having to spray some gum out and after a couple tries got her running. The carb mounting bolts had about a turn and a half or so on each one so I tightened those. 2 vacuum caps on the tree were dry rotted and broke apart when I pulled on them . I replaced all the caps and also recut the brake booster house and clamped since the end was bloated and had some cracks. This morning the truck started right up and was purring like a kitten. It had been running a little rougher lately. Drove to the supermarket and got about a mile from and lost power. Was bucking all over the place. Not fun on a bridge ha ha. I made it into a parking lot and the truck was idling perfectly . Gave it gas in neutral and no bogging down. Choke was wide open. It happened a couple more times but I made it to the market. On the way back it happened once . Totally just bogged down like it had no fuel. Pumped it in neutral and it came back and made it home fine. It doesn’t seem like it’s related to giving it more or less gas pedal. I’ll be crawling under with the camera to see what I can see. Sorry for the long story! Happy 4th to all by the way! I took some pics. Found the fuel filler hose cracked some and not secured. Fixed that. I have a new one to replace with. The rollover vent valve I replaced with the new gasket attaches to this metal line in the photo. It was tucked into the frame up from and goes nowhere . Since my fuel gauge is not working ( goes 1/2 way when full and then drops to empty after about 20 miles I may as well drop the tank and replace all those bits . Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 4, 2021 Share Posted July 4, 2021 Happy 4th to all by the way! I took some pics. Found the fuel filler hose cracked some and not secured. Fixed that. I have a new one to replace with. The rollover vent valve I replaced with the new gasket attaches to this metal line in the photo. It was tucked into the frame up from and goes nowhere . Since my fuel gauge is not working ( goes 1/2 way when full and then drops to empty after about 20 miles I may as well drop the tank and replace all those bits . Also check your fuel lines. The rubber hoses from the tank to the hard line, and from the hard line to the fuel pump. And from the hard line to the switching valve and back to the hard line if you have dual tanks. The hoses can get so bad that they allow air in, which kills the pump's ability to move gas to the carb. I've had a truck die on me repeatedly until I replaced the hoses. Link to comment Share on other sites More sharing options...
JG2020 Posted July 4, 2021 Author Share Posted July 4, 2021 Also check your fuel lines. The rubber hoses from the tank to the hard line, and from the hard line to the fuel pump. And from the hard line to the switching valve and back to the hard line if you have dual tanks. The hoses can get so bad that they allow air in, which kills the pump's ability to move gas to the carb. I've had a truck die on me repeatedly until I replaced the hoses. Thanks Gary! I am going to order it all from LMC and get this done . Hopefully that fixes the issue. I’ll replace the fuel filter also for good measure even though it’s new . Link to comment Share on other sites More sharing options...
JG2020 Posted July 6, 2021 Author Share Posted July 6, 2021 Thanks Gary! I am going to order it all from LMC and get this done . Hopefully that fixes the issue. I’ll replace the fuel filter also for good measure even though it’s new . The metal line that goes all the way from the vent valve on top of the tank to nowhere at the front of the truck.... I assume this used to go to a long gone charcoal canister of some type? Can I just eliminate most of it and just leave a small vent tube? Thanks Link to comment Share on other sites More sharing options...
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