Where does the gas go? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jrork · 12-14-2002, 01:23 PM

Hi Everybody,
I have a 86 CC, 1-ton with a 454 that after setting for a few days, needs to be cranked over quite (40 sec.) awhile before gas will get up into the carb so it will start.
Does the fuel system have a check valve that keeps the gas from siphoning back to the fuel tank? This did the same thing with another carb so I know it's not that. The engine doesn't run hot so I don't think it's boiling off. Where does it go??

Thanks everybody.......John

*mike reeh* · 12-14-2002, 02:03 PM

good question. yes the mechanical fuel pump should hold fuel up in the line to the carb, but even my new delco pump will sometimes bleed off. It seems to be 50/50 and right now I have a big clear fram fuel filter before the carb so I do know when it does and doesnt. sometimes it will hold pressure for days and other times not even for a couple hours. Im not sure what to think. But more importantly I think your carb must be leaking because it should start and run on whats in the float bowl, at least long enough to get the fuel system primed... what do you think?

mike

Jrork · 12-14-2002, 03:41 PM

I don't think the carb is leaking since it's done this since I've owned it an thats darn near 9 years.
I replaced the stock Q-jet a couple years ago with a Edelbrock and there was no change with this symptom but since that wasn't what I was trying to accomplish with the switch, it didn't bug me at the time.
Now I would like to get my hands around this.

Thanks for the reply.....John

*mike reeh* · 12-14-2002, 04:55 PM

for what its worth, my 77 K25 will start instantly after setting for days and days. the qjet that I rebuilt (and was already epoxied) holds fuel real well.. Does your choke work? Granted sometimes it will die shortly after starting but waiting for fuel from the pump is never a problem. Id goto kragens and get a new delco pump, about $20 or so and throw that puppy on there. for 20 bucks, and an hour or two for installation-- thats some cheap insurance. you really cant go wrong..

something to consider, if it just cranks and cranks, maybe let the truck sit for a while, and then instead of starting it, pull the carb off and see if there is a puddle or anything inside the intake.. and operate the accel pump a bunch of times to see if its running dry.. I suppose evaporation is a possibility but it seems unlikely that it would dry itself out..

oh well keep us posted

mike

Jrork · 12-15-2002, 01:52 PM

With the Q-jet I use to have and the Edelbrock that's on it now both are bone dry when work the accelerator pump. It normally takes 30 sec of cranking to get fuel up to the carb to where it will fire. Once it fires it runs awesome and after I have ran it, it will start first crank everytime until I let it set for a few days then it's back to the same old thing.

*Piston* · 12-15-2002, 02:27 PM

Common problem on the Q-jets. The main jet fuel wells have caps on the bottem of the main body, these caps leak over time and will drain the float bowl overnight. Eventually it will get bad enough to cause a problem only after sitting for a few hours.
You wont be able to see this leak externaly. If your familiar with Q-Jets and know how to check the float level externaly, you can check for seepage from these plugs by checking before and after float settings. When rebuilding the carb (if you do it yourself) use JBWeld to seal the caps.

There is also a drainback or antisiphon valve located in the end of the fuel filter which will siphon fuel from the float bowl if missing or damaged. This is more common on vehicles with fuel tanks considerably lower than the carb.

12-14-2002, 01:23 PM	#1
Jrork Registered User Join Date: Dec 2002 Location: Seabeck, Washington Posts: 3	Where does the gas go? Hi Everybody, I have a 86 CC, 1-ton with a 454 that after setting for a few days, needs to be cranked over quite (40 sec.) awhile before gas will get up into the carb so it will start. Does the fuel system have a check valve that keeps the gas from siphoning back to the fuel tank? This did the same thing with another carb so I know it's not that. The engine doesn't run hot so I don't think it's boiling off. Where does it go?? Thanks everybody.......John __________________ 86, CrewCab, Dually-1ton, 454

12-14-2002, 03:41 PM	#3
Jrork Registered User Join Date: Dec 2002 Location: Seabeck, Washington Posts: 3	I don't think the carb is leaking since it's done this since I've owned it an thats darn near 9 years. I replaced the stock Q-jet a couple years ago with a Edelbrock and there was no change with this symptom but since that wasn't what I was trying to accomplish with the switch, it didn't bug me at the time. Now I would like to get my hands around this. Thanks for the reply.....John __________________ 86, CrewCab, Dually-1ton, 454

12-15-2002, 01:52 PM	#5
Jrork Registered User Join Date: Dec 2002 Location: Seabeck, Washington Posts: 3	With the Q-jet I use to have and the Edelbrock that's on it now both are bone dry when work the accelerator pump. It normally takes 30 sec of cranking to get fuel up to the carb to where it will fire. Once it fires it runs awesome and after I have ran it, it will start first crank everytime until I let it set for a few days then it's back to the same old thing. __________________ 86, CrewCab, Dually-1ton, 454

12-14-2002, 02:03 PM	#2
mike reeh 5 day ban, learn to behave. Join Date: Nov 2002 Location: san diego, ca Posts: 683	good question. yes the mechanical fuel pump should hold fuel up in the line to the carb, but even my new delco pump will sometimes bleed off. It seems to be 50/50 and right now I have a big clear fram fuel filter before the carb so I do know when it does and doesnt. sometimes it will hold pressure for days and other times not even for a couple hours. Im not sure what to think. But more importantly I think your carb must be leaking because it should start and run on whats in the float bowl, at least long enough to get the fuel system primed... what do you think? mike

12-14-2002, 04:55 PM	#4
mike reeh 5 day ban, learn to behave. Join Date: Nov 2002 Location: san diego, ca Posts: 683	for what its worth, my 77 K25 will start instantly after setting for days and days. the qjet that I rebuilt (and was already epoxied) holds fuel real well.. Does your choke work? Granted sometimes it will die shortly after starting but waiting for fuel from the pump is never a problem. Id goto kragens and get a new delco pump, about $20 or so and throw that puppy on there. for 20 bucks, and an hour or two for installation-- thats some cheap insurance. you really cant go wrong.. something to consider, if it just cranks and cranks, maybe let the truck sit for a while, and then instead of starting it, pull the carb off and see if there is a puddle or anything inside the intake.. and operate the accel pump a bunch of times to see if its running dry.. I suppose evaporation is a possibility but it seems unlikely that it would dry itself out.. oh well keep us posted mike

12-15-2002, 02:27 PM	#6
Piston Account Suspended Join Date: Oct 2002 Location: Olathe, KS Posts: 2,300	Common problem on the Q-jets. The main jet fuel wells have caps on the bottem of the main body, these caps leak over time and will drain the float bowl overnight. Eventually it will get bad enough to cause a problem only after sitting for a few hours. You wont be able to see this leak externaly. If your familiar with Q-Jets and know how to check the float level externaly, you can check for seepage from these plugs by checking before and after float settings. When rebuilding the carb (if you do it yourself) use JBWeld to seal the caps. There is also a drainback or antisiphon valve located in the end of the fuel filter which will siphon fuel from the float bowl if missing or damaged. This is more common on vehicles with fuel tanks considerably lower than the carb.



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