Check Valve in Fuel Pump

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   I have a '68 AMX 343ci with Carter AFB 4 barrel (thermal Choke), Mechanical OEM Fuel Pump, and Auto Transmission. Car runs great once started and warmed up but after sitting for a while I have to crank it for around 5 - 10 seconds, 3 times or more, to get it to fire up and run. Then I have to wait for it to warm up before shifting to Drive or Reverse or it will stall. . Pretty sure the problem is the gas flowing out of the carb, and or Fuel pump, back to the gas tank.
Looking for a cure. Where is there a check valve in the Fuel line.is it in the Fuel Pump and if so can it be replaced, or is it the Carb? Also, the Carter AFB isn't setting fast Idle once running. I know this needs to be adjusted. Idle is set at 650 RPM when warm per spec.

Thanks,
Doug

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Doug in New Freedom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Aug/02/2014 Location: NEW FREEDOM, PA Status: Offline Points: 149	Post Options Post Reply Quote Doug in New Freedom Report Post Thanks(0) Quote Reply Topic: Check Valve in Fuel Pump Posted: Jul/05/2017 at 2:33pm
	I have a '68 AMX 343ci with Carter AFB 4 barrel (thermal Choke), Mechanical OEM Fuel Pump, and Auto Transmission. Car runs great once started and warmed up but after sitting for a while I have to crank it for around 5 - 10 seconds, 3 times or more, to get it to fire up and run. Then I have to wait for it to warm up before shifting to Drive or Reverse or it will stall. . Pretty sure the problem is the gas flowing out of the carb, and or Fuel pump, back to the gas tank. Looking for a cure. Where is there a check valve in the Fuel line.is it in the Fuel Pump and if so can it be replaced, or is it the Carb? Also, the Carter AFB isn't setting fast Idle once running. I know this needs to be adjusted. Idle is set at 650 RPM when warm per spec. Thanks, Doug
	Doug in New Freedom 68 AMX 69 CHEVY C1O PICKUP 74 PORSCHE 914 84 K5 BLAZER

6768rogues Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/03/2007 Location: United States Status: Offline Points: 6234	Post Options Post Reply Quote 6768rogues Report Post Thanks(0) Quote Reply Posted: Jul/05/2017 at 4:35pm
	I think new gas with ethanol evaporates more quickly than old gas, so that could be a factor, too. In a sealed fuel injection system it makes no difference. Gas in the fuel bowl should not flow back.
	Content intended for mature audiences. If you experience nausea or diarrhea, stop reading and seek medical attention. Located usually near Rochester, NY and sometimes central FL.

maximus7001 Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jun/27/2011 Location: Winnipeg,Canada Status: Offline Points: 1086	Post Options Post Reply Quote maximus7001 Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 4:56am
	I am thinking it is leaking out the bottom of the carb into the intake until the bowl is dry. Never had that exact carb apart before but have encountered it on other carbs like the bbd and qjets. Concord always did it after a few days. Edited by maximus7001 - Jul/27/2017 at 9:31am
	1968 Javelin SST 1997 GMC Safari AWD 2001 Daewoo Nubira SX (Winnipeg only model) 1997 Honda Accord EX (Canadian Model) Winnipeg, home of the Jets.

vinny Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jan/05/2012 Location: Calgary Status: Offline Points: 2837	Post Options Post Reply Quote vinny Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 5:25am
	Usually the mechanical fuel pumps and their double check valves are what stops the fuel from running back to the tank. I think both check valves would be leaking for fuel to run back. After my car has been up to operating temperature and then shut off for a few minutes it takes a bit to start it. I've heard others complain of the same thing. Evaporating fuel? I've never had an electric choke that I can recall but I think they are set the same way as the thermal exhaust type. When it is cold the plate should be closed which also raises the idle once the throttle is pressed by allowing the stop to re-position itself. After my car has been sitting for a week or more it also takes some cranking to get it going. A squirt down the carb first fixes that. Maybe just a normal phenomenon with the old carb systems? Edited by vinny - Jul/06/2017 at 5:31am

farna Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19675	Post Options Post Reply Quote farna Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 6:42am
	When sitting for a week the problem likely is evaporating fuel. A day or two shouldn't be that bad. Pour a bit of gas in a cup and see how long it takes to evaporate out in the open. Sealed in a carb should take longer. Maybe use a jar and punch 2-3 small holes in the lid to simulate in a carb bowl.
	Frank Swygert

Midnight Rambler Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/17/2011 Location: SoCT Status: Offline Points: 1670	Post Options Post Reply Quote Midnight Rambler Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 7:38am
	It was the fuel pump on mine..... ;)
	'66 American 440 Convertible 290/M-40/AMC 20 3.15/PS/PB '04 Jeep Wrangler X Rocky Mountain Edition 4.0 5sp

Lucas660 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/16/2012 Location: Vic, Australia Status: Offline Points: 1344	Post Options Post Reply Quote Lucas660 Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 7:55am
	Pacerman mentioned a auxiliary electric fuel pump to prime the system in a recent post. Probably one of the best ideas ever to overcome these symptoms.

Doug in New Freedom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Aug/02/2014 Location: NEW FREEDOM, PA Status: Offline Points: 149	Post Options Post Reply Quote Doug in New Freedom Report Post Thanks(0) Quote Reply Posted: Jul/06/2017 at 9:01am
	Thanks guys for the responses, all good and gives me direction to source it all out. The Carb is a recent professionally rebuilt like new Carter AFB, and prior to this carb I replaced the original Carter with a new manual choke Edelbrock Performer. They all had to a degree the same hard start problems. So, could be evaporation or gas flow back to tank, or both. I thought about a hidden electric fuel pump but to stay with originality decided against it, plus if found during judging it would be a major deduction in pure stock class. One other thing I just remembered was I had a Glass fuel filter feeding the Edelbrock carb and noticed the gas would disappear in the glass filter after a couple days. We're going to the Shop next week to get everything checked out. Carb and Fuel Pump are the targets. Also, we're going to re-adjust the Carb to obtain fast Idle on cold start and dial in the Choke adjustment going from cold start to warmed up. If needed we'll re-adjust the normal idle (650rpm) up to where I can put it in gear after starting with out stalling if the fast idle when set doesn't fix it. Good to know this appears to be a normal minor problem with many of our Old Cars. I'll let ya'll know how it turns out. Thanks again, Doug
	Doug in New Freedom 68 AMX 69 CHEVY C1O PICKUP 74 PORSCHE 914 84 K5 BLAZER

Doug in New Freedom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Aug/02/2014 Location: NEW FREEDOM, PA Status: Offline Points: 149	Post Options Post Reply Quote Doug in New Freedom Report Post Thanks(0) Quote Reply Posted: Jul/08/2017 at 2:44pm
	Just got 'er back from the Shop...........Running perfectly now! So, Scot at Spicer Motors checked the carb and says the bowl is holding gas, no leakage but he also mentioned what we've been talking about, ethanol evaporating in the carb. He Adjusted the Choke, fixed and set the Fast Idle, which was not working and bumped the Idle up using an Electronic Test with car in gear to 555-560 rpms. Then he made slight adjustments to the Needle Valves. The Carb retains fuel but runs very low before the pump re-fills the bowl. He said the Fuel pump is the probable cause and the carb accelerator pump is showing signs of wear. When I started it today and drove it home it started instantly and runs better then ever before. I'll need to restart it in a couple days to see how the cold start goes after sitting for a while. We'll change the fuel pump, which is suspected of having leaking check valves, after the end of the Show Season in the late fall.
	Doug in New Freedom 68 AMX 69 CHEVY C1O PICKUP 74 PORSCHE 914 84 K5 BLAZER

rockAMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/16/2011 Location: Lethbridge AB Status: Offline Points: 983	Post Options Post Reply Quote rockAMX Report Post Thanks(0) Quote Reply Posted: Jul/10/2017 at 11:39am
	Also check that the gas tank vent tube is not plugged.
	DWR 1968 AMX