When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi guys. 69 350 Quad. If it sits for a few days I have to crank it like crazy to get fuel in the bowl. It doesn't hot soak. No smell of fuel when shut off. I'm thinking internal leak that's very slow. Another friend mentioned pinhole in fuel line between tank and body? Any thoughts would be appreciated.
Pull the top and put a fuel pump in it. You may need a new gasket, but if you're careful with a razor blade you may get lucky and shave it off without breaking it. It also could be a stopped up fuel filter or stuck needle valve. I would start by pulling the steel line from the carb to the fuel pump at the carb. Crank a few times to see if your getting fuel 1st. If not, fuel pump. Work your way up from there. Good luck with her.
Last edited by tru-blue 442; October 14th, 2015 at 01:41 PM.
Reason: Add info and a pic.
Pull the top and put a fuel pump in it. You may need a new gasket, but if you're careful with a razor blade you may get lucky and shave it off without breaking it.
I actually Frankensteined 3 carbs. Original throttle plates and another carbs centre jetting housing and a third carb was robbed of the top plate. I have built many q-jets with good results. Performance is great but the fuel pump could be bad. I just can't figure fuel going back past needle and seat as some guys have mentioned this siphoning phenomenon. Thanks
Oh, it happens and I don't get it either. Some of my best Quadrajets have been Frankensteins. Another thought, if you don't get fuel at the mechanical pump, you may try compressed air on the main line back from the pump to the tank. I always remove the cap too. And then there can always be pin holes in the line, depending on how rusty they're looking too. Ahh the joys of knuckle busting.
Last edited by tru-blue 442; October 14th, 2015 at 01:50 PM.
Try running the engine to fill the bowl and then pinch off the rubber hoses at the pump. If it stays full the problem is pump/supply related. If it empties look at the carburetor, it may be leaking at the plugs on the bottom of the fuel bowl.
Try running the engine to fill the bowl and then pinch off the rubber hoses at the pump. If it stays full the problem is pump/supply related. If it empties look at the carburetor, it may be leaking at the plugs on the bottom of the fuel bowl.
Great simple idea. I can deffinatley isolate it that way. Thanks
Can the OP clarify "a few days"? I have what I consider a properly running quadrajet on a car, and the car starts instantaneously when previously started that day, about 1 second of cranking when started the previous day, about 2 to 3 when it's been a couple days, but any more than a week causes the fuel to evaporate out or siphon or whatever and takes 7 seconds to start. I may pinch the line at some point like said above.
The plug design was changed in 1968. Did it totally solve the problem? Could a 1968 or later design leak after more than forty years of service? Probably yes, two different design repair kits for leaking well plugs are made, pre 1968 and 1968 and later. If repair kits are made for 1968 and later some of those probably leaked.
Additionally the OP stated that the carb in question was made from several carbs. The year/design of the components are unknown.
If repair kits are made for 1968 and later some of those probably leaked.
There are lots of unnecessary "fixes" sold to make a buck off the unsuspecting or uneducated public. The fact that the well plug issue continues to be retold is an indication that people don't always get the facts when making a decision.
In over four decades and well over three dozen GM vehicles with Qjets, I have NEVER experienced a leaking well plug with the spun-in aluminum plugs used on 1968-up carbs. Is it POSSIBLE? Yeah, sure. Is it LIKELY? Not even remotely. I'd look at all the other possible caused long before I'd worry about the well plugs.
Most likely problems are (1) evaporation of the gas in the float bowl over time, (2) incorrectly set float that has lowered the fuel level in the bowl, exacerbating this problem (often caused by a "heavy" plastic float that has been attacked by ethanol in the gas), and (3) incorrect or incorrectly installed fuel filter that doesn't have the check valve in place or oriented properly.
... AND, as mentioned in the first post, the very common pinholes in the steel line / cracks in the hoses (especially the usually-original hoses from tank to body).
Fuel WILL evaporate out of the carburetor - gasoline is volatile and the float bowl is open.
The fuel pump should fill the float bowl completely in no more than three strokes (and that's being generous), but if air entrance into the suction line breaks the pump's prime, then it can take many, many strokes to do the same job.
... AND, as mentioned in the first post, the very common pinholes in the steel line / cracks in the hoses (especially the usually-original hoses from tank to body).
Fuel WILL evaporate out of the carburetor - gasoline is volatile and the float bowl is open.
The fuel pump should fill the float bowl completely in no more than three strokes (and that's being generous), but if air entrance into the suction line breaks the pump's prime, then it can take many, many strokes to do the same job.
- Eric
It's also possible that the check valves in the pump have deteriorated and don't seal properly, allowing fuel to drain back into the suction line rather than being pumped into the carb. This can also significantly increase the time to refill the float bowl when cranking. Ethanol in today's fuel will do that to older pumps.
It's also possible that the check valves in the pump have deteriorated and don't seal properly, allowing fuel to drain back into the suction line rather than being pumped into the carb. This can also significantly increase the time to refill the float bowl when cranking. Ethanol in today's fuel will do that to older pumps.
Absolutely.
The only thing that CAN'T happen is for the gasoline that is actually in the float bowl to be siphoned or suctioned back out of it through the fuel lines - one needs only to look at the float bowl to see that this is impossible.
Heres a sure fire way to tell if you have a leaking fuel bowl...Do what ever it is you need to do to induce the problem(sit for a day or a week no longer). Before attempting to start the engine pull the air cleaner lid and look down the primaries while actuating the throttle. If you dont see any gas squirting out of the squirters you likely have a leaking fuel bowl. By a leak I dont necessarily mean from the plugs. You can have other problems causing a leak such as a crack. To further troubleshoot pull the air horn and visually verify its dry if you must have further confirmation. Then pull and disassemble the carb down to its 3 major components, T.Plate, Bowl and horn. Clean and dry the bowl then hit it with brake cleaner inside and out and dry that off. Fill the bowl with some gas or clean parts cleaning solvent. Now look for leaks. They will show up fairly quickly. JB Weld can fix leaks successfully. Larger defects or defects in inaccessible areas will require bowl or whole carb replacement. If you do see plenty of gas squirting out from the squirters then lack of fuel is not your problem. In this case I would look at the choke setting or possible ignition problems. Whats the choke do when you set it cold? It should completely close then pull off as soon as it sees a vacuum signal from the pull off diaphragm, about 1/16th"
Heres a sure fire way to tell if you have a leaking fuel bowl...Do what ever it is you need to do to induce the problem(sit for a day or a week no longer). Before attempting to start the engine pull the air cleaner lid and look down the primaries while actuating the throttle. If you dont see any gas squirting out of the squirters you likely have a leaking fuel bowl.
How does this test differentiate a leaking fuel bowl from evaporating fuel?
I guess that's still a "leak", just through the vent.
Frankly, I've had more evaporation problems in the last few years, possibly due to increased ethanol?
If the fuel evaporates out of the bowl, the float will drop, and open the needle valve, thus exposing the gasoline under it to air. Obviously the surface area of the gasoline in the fuel bowl, some few inches squared, is bigger than the ~.125 in^2 of the needle seat hole, but can some gas evaporate out of the fuel line down to the pump?
Assuming the answer to the above is no, or negligible, how long should it take a quadrajet with an empty fuel bowl, but full gas line to the needle to start? I would think a matter of a couple seconds. I think if it takes a long time, like 7 or 10 seconds, the fuel bowl is empty, but it may be empty down to the pump, at least, due to gaskets and check ***** like said above.
How does this test differentiate a leaking fuel bowl from evaporating fuel?
I guess that's still a "leak", just through the vent.
Frankly, I've had more evaporation problems in the last few years, possibly due to increased ethanol?
Joe, Note the disclaimer of "sitting no longer than a week". Should not exhibit significant evap in that short time, but a leak will rear its head in that amount of time. Not sure on the E10 or E15 crap as I run ethanol free in all old equipment.
I have a very similar problem so I was wondering how long would it take for gas to naturally evaporate from the bowl?. Thought I would ask before messing with an otherwise good running carb. Never had this on vehicles with Q-jets in my younger days, but then again never had the luxury of a weekend driver back then. Seems like we have alcohol in the gas now on top of inactivity, plus I have Texas heat and an open element air cleaner.
If the car sits for about a week, I find it easiest to crank the motor for a few secs to move some fuel, then press the gas pedal to set the choke and it starts normally.
By the way, have the exact same problem on a boat with a 5.0l Chevy 2bbl.....
I have this problem in my G series carb. It will squirt, figure some fuel is left in pump well, but takes a lot of crank time before it will idle. Admitting that I have an old pump and original steel lines and will be looking at that next. But I still blame it on ethanol evaporation dropping the level in the bowls when it sits, and my old parts make it more of an ordeal to get it to start and idle.
My carb typically is dry after the car sits in the garage all summer, waiting for the temperature to drop below 100 so it can come out of hiding. I have resorted to spraying some starting fluid into the carb bore in order to get the engine to fire easily on the first try.
FYI, this is what Phoenix was like on the way home from work yesterday:
I've had more evaporation problems in the last few years, possibly due to increased ethanol?
Possibly, but remember that ethanol is at most 10% of the gasoline. Even if it all evaporated away, 90% of the liquid volume would still be there. The ethanol does not cause the gasoline to evaporate more quickly.
Fun, I normally use straight gas to prime my 442 instead of ether. I think it's easier on the engine. I popped a small hole in the cap of a 20 oz coke bottle to make a squeezer.
Some people, like Mr. Witt, know how to fill the fuel bowl via the vent, but I have yet to figure out which hole it is to pour it into.
I purchased a few years ago a small bottle of some kind of all purpose oil. Did not care what the oil was as I wanted the bottle. It is a mostly clear plastic bottle it has a spout about 2 inches long and has a hose that pulls out of the spout. I can fill the carb through the vent tube without spilling all over. This bottle holds 4 oz by the label. I use a small funnel to fill it and the carb will take about 3/4 of the bottle so I usually fill it about that far. If I remember correctly I bought it at a Napa store and it was on the counter as one of those items they have that you never think of. I use this everytime I prime a carb for a start up and everytime I need to fill a carb due to evaporation or leakage.
Koda I will post a few pictures you can see where to fill a qjet with it.
Dump the gas down the primaries, bout a 1/4 cup. I never use starting fluid I don't like shattered pistons. Your car should start easily after a week of sitting. Again whats the choke doing? Lets start simple with the troubleshooting and not gravitate towards catastrophic failure yet.
Mine will sit for a month with minimal evaporation. I also only use NON-ethanol. Mine will hard start when it sits only because I dont set the choke until I see oil pressure. Once the choke closes it takes right off. If it sits for a week it will start with out setting the choke say 5-6 revolutions of the engine but again I'm going for oil pressure first so I'm not concerned. Before I fixed the carb it was a hard starter because the bowl was dry. I resorted to the 1/4 cup of gas down the carb to save the starter.
October 14th, 2015, 01:22 PM
