[Mcronk]

Carb I am working on is a 69 original quadrajet for 400. Rebuilt several years ago using one of Cliffs kits and suggestions. Carb performs very well but has had a peculiar issue that I had a work around for till now. When I first installed it several years ago on my 67 GTO it started right up and idled nicely. Within about a minute or two the engine just quit. Sounded like it ran out of fuel. I cranked several times but it would not start and I could not smell fuel. I had a electric pusher pump on the car from drag racing days so I turned it on and confirmed I was getting fuel in carb. Car fired right up and ran fine. Once it warmed up Icould turn pusher pump off and car would run fine. After a while it would stall while idling at a light and I would have to turn the pump on to keep it running. I don't drive the car a lot and this was my work around till I had time to work on carb. Recently I purchased a 68 GTO with a carb that surged badly and would not idle. I went through some troubleshooting and everything pointed back to the carb. So I took the carb of my 67 GTO and put it on the 68. It started and idled much better but again after a couple of minutes it would run out of gas. I was able to drive the car a little and the car ran great till it ran out of gas. I would have to crank a lot (no pusher pump on this car) to get it started and it would run for a little over a minute then stall. So I took the air horn off to observe and measure float setting. I could crank till bowl was full and float would rise to within spec. However after about a minute or so I would see the float drop to about half it's travel and stop (engine not running and not cranking). Without fuel in the bowl the float will rise and fall like it should.

So do I have two cars with weak fuel pumps? The 67 has a pump that has been on it since 1992. The 68 I don't know how old it is but did not run out of fuel with the carb it came with. Or is there something going on with the carb.

[torqhead]

Long shot but try it without the gas cap on the tank and obviously without pusher pump.

[shaker455]

Mark,
I would suggest putting a fuel pressure gauge inline to see your pressure in that condition.
Today's gas destroys old rubber parts so a new fuel pump may be in your near future.
Also, the sock in the tank could have seen better days.
Jeff

[Navy Horn 16]

Originally Posted by torqhead

Long shot but try it without the gas cap on the tank and obviously without pusher pump.

That's not as long a shot as you think. I had a similar issue with a fuel cap not properly venting. Still, it sounds like fuel pump issues are the problem. If you are going to go through the trouble of having an electric pump, I'd say just get a good one and get the mechanical pump off the motor.

I had great luck with Holley pumps, though they are loud... Not as loud as open headers, but loud.

[steve25]

Electric pumps need to have a real good gravity feed and if the sock on the fuel tank pickup is restricted by dirt & crap or today's type fuel going bad, or a combination of all 3 then there's possibly the root cause!

I have also seen poorly crimped on or dirty electrical connectors that could not provide the full needed current to run the pump up to its normal rpm, and as the pump heats up its current needs will go up also.

[Tom Vaught]

The only advantage of a mechanical fuel pump is that if the "Holley Blue Pump" for example dies then you can still drive home on the mechanical pump. Redundant Fuel systems.

Agree on buying a GOOD fuel pump if you go away from the Mechanical Fuel Pump.

Tom V.

[johnta1]

Do you have a separate line to the electric pump or does it run through the electric pump to the carb when it's off?

I would also agree with the cap or look for a blocked vent somewhere.

[Mcronk]

Thanks everyone for the suggestions. A little more information on the fuel pump that seems to fix the problem.

It is one of the small body Carter preset pumps that is self regulated. Not a Holley pump. I used one for years on this car (since 1995). On full throttle it would nose over right at 2nd to high shift (Turbo 400). Adding the pump in line and running a 3/8 fuel line between tank and mechanical pump solved the problem. I use the Carter pump as a "pusher" to the mechanical pump. It is mounted down below tank pick up on inside of frame rail. Car is basically very stock . The 67 GTO has ran flawlessly for several years as long as I leave the Carter electric pump on.

If I had not tried this carb on the 68 GTO, and experienced the exact same problem of running out of fuel at idle, I would definitely think the mechanical fuel pump on the 67 is bad. However the problem followed the carburetor to the 68 GTO, unless both cars have marginal or bad mechanical pumps. The carb that was on the 68 GTO that I replaced was hard starting, bad idle, and would surge a lot while driving but did not run out of fuel. The carb I swapped on from 67 GTO started up much more easily, idled nicely, and for the short drive time I got before it died, ran very smoothly. It is possible both cars could have weak or bad pumps due to ethanol but it still makes me think something is not right in the carb.

I have air horn off and measured float level and watched it as I cranked engine to fill the bowl. When I stop cranking, and bowl is full, after about a minute the bowl level drops to about half full. Is this normal when engine is off and no flow from fuel pump?

If I had restriction in tank pick up or vent I would think that using the low pressure Carter pump would not overcome the problem? The 68 GTO would have to have same problem and it did not run out of gas with its original carb. On full throttle with the original carb the 68 pulled good so I don't think it has a restriction in tank pick up. One thing that seems consistent is both cars seem to run out of fuel with the 67 GTO carb when at low rpm such as idle. If under throttle they don't stall but when at idle or low cruise rpm they will. Does this sound like low pressure/flow from mechanical pump?

[1968GTO421]

Just a wild guess, but could you have one of those floats that have gone bad and sink? Some absorb gas then sink and later"dry out" and act fine. FWIW

[johnta1]

When I stop cranking, and bowl is full, after about a minute the bowl level drops to about half full.

The wells underneath the main body are probably leaking.
Usually a glob of sealer is put on them to keep them from leaking.

[Mcronk]

When I rebuilt this carb a couple of years ago I used one of Cliff's kits with the better parts for ethanol. The float definitely "floats". With air horn off I can crank engine and watch it rise to the proper height. After about a minute of just sitting I can see fuel level in bowl drop down to about half but float is still "on top" of fuel.

This carb had the main wells sealed back in 1995. At that time I had it done by a racing quadrajet shop "Carburetor Shop" in Ontario California. It was a Stage 1 build. Is it possible that it could be leaking now? Would the engine sound like it would be loading up and run rich with this leaking? With the electric pump on the car will idle smoothly for 30 minutes, not load up or exhibit any black smoke or smell bad. Would the main wells leaking cause it to run out of fuel while idling without electric pump on? Would fuel return back to mechanical pump/line when not under pressure i.e. car not running? With the air horn off the fuel bowl area is open could this allow fuel to drain back to pump/line? I noticed neither of the two carbs have the filter and spring in the fuel line inlet. I did put one in and it made no difference the fuel still went down about half way after sitting about a minute or more.

As engine starts to lose Rpm when idling i can crack the throttle open to try and keep it running. It just sucks in a lot of air and stalls. It does not try and respond at all. I would think if it was loading up due to wells leaking it would respond to the additional air and throttle blade opening.

Sorry for all the questions. It just seems odd the car runs great as long as the pusher pump is on. At first I thought it had to be a float/needle/seat problem or fuel pump but float measures in spec, bowl fills properly, and float drops as fuel level goes down.

Thanks for all the help. I will put air horn back on and try taking gas cap off.

[Sirrotica]

If the gasoline is running out of the float bowl that quickly, removing the carb from the intake and taking care to keep it level while holding it above your head and observing the well plugs ought to tell you if they are leaking.

Dabbing the bottom of the carb off with a dry rag should let you see where the gas is running out of.

I usually leave the air cleaner stud in and lift it with that, as it's in the middle of the carb, easier to keep it level by lifting it by the air cleaner stud.

One thing that is puzzling is that if the float bowl was leaking that badly, the engine would be extremely rich at idle. It would be hard to start after a five minute shutdown and restart too.

After removing the carb there would be evidence of raw gas in the intake manifold if it was dumping that quantity of fuel in that short of period.

That would be the first thing I'd be looking at, but I've never seen well plugs leak that profusely in many years of working on Q Jets.

[Mcronk]

We recently put the original turbo 400 and a stock type convertor back in the car. I had it idling for quite a while to check for transmission leaks and adjust fluid level. I shut the car off and on many times. All I have to do is reach in the window and turn the key and it instantly fires up as long as electric pusher pump is on. I recently did a long cruise, shut car off, let it sit a few minutes and it fires right back up with no hesitation or need for throttle. It does not seem like it is leaking into the engine.

When I pull it off car I will see if there is any fuel puddling in the intake or bottom of carb is wet.

Thanks.

[Tom Vaught]

My 64 GTO always had the same instant start on cranking when I ran the pusher pump
thru the factory mechanical fuel pump. .

Tom V.

[Joe's Garage]

Originally Posted by Sirrotica

One thing that is puzzling is that if the float bowl was leaking that badly, the engine would be extremely rich at idle. It would be hard to start after a five minute shutdown and restart too.

After removing the carb there would be evidence of raw gas in the intake manifold if it was dumping that quantity of fuel in that short of period.

That would be the first thing I'd be looking at, but I've never seen well plugs leak that profusely in many years of working on Q Jets.

We've had a couple where the valves in the mechanical fuel pump failed and they siphoned fuel back thru the fuel line and pump and into the tank when you shut it off.

New mechanical pumps fixed that.

Also, check for a cracked rubber line at the tank, the fuel pump or at the union where the front and rear fuel lines hook together (I think GTOs have them). It doesn't take much leakage to cause problems.

Good luck!

[Mcronk]

Update:

Definitely think the issue is in the carb. I put it back together and engine started on second attempt at cranking. I set idle speed at about 950rpm (RA II, 041 cam, 4 speed car). The engine ran for about 6 minutes till I shut it off. Idled smoothly once it warmed a little (choke not hooked up).

So I decided to do a road test around the neighborhood. Car ran smooth and i was even able to lug engine down to about 1,500rpm in 4th gear and still smooth (has 4.33 gears). I past the point it stalled on me in previous road test and decided to go out of neighborhood to open road. Ran through the gears at a slightly aggressive throttle and car pulled as expected smoothly no bucking or surging. Headed home and as I was manuvering into garage and engine tried to stall. I reved engine a little and it cleaned up and idled fine. Let clutch out with no throttle and rpm dropped down to about 600 or so and engine stalled. Temp was at about 195 (we had 100 degree temps yesterday). So i got out looked in the primaries and worked the throttle to see if i was getting a good shot of fuel or if it just dribbled or nothing at all. I got a very good shot each time I worked the throttle. So I don't think it is running out of fuel. Now the engine is at 200 degrees from heat soak. I get in and crank but it does not start. Of course I just put a lot of fuel in the motor without it running with pump shot test. So I hold throttle down about 3/4 way and it starts and motor clears out and idles fine. Pulled in garage shut it off and let it heat soak for about 10 minutes. Went back out and car started normally and idled fine.

So I do not believe it is running out of fuel nor do I think it is leaking fuel into motor but will check for that when I remove carb. What does seem to happen is when rpms drop much below idle rpm at 900 it wants to stall when warmed up. Good news is I confirmed that the original carb on the 68 is bad as car ran great with the carb from the 67. However there is a "peculiarity" with the 67 carb and why it does not exhibit this behaviour when on the 67 with the electric pusher pump on.

One thing I noticed when putting air horn back on is that the power piston was sitting up high enough that the air horn was ever so slightly above the gasket. I tried several times to push power piston down so air horn was seated on gasket without bolting it down. My assembly instructions talked about being carefull with power piston and making sure it was held in place by gasket pin or spring clip on some models. I could easily apply slight pressure to the airhorn and it would set down flush on gasket. I need to go back and read up on theory of operation to remember how the power piston works. Just want to make sure i did not create this problem with improper assembly.

I will install this carb back on the 67 and continue looking into the issue. However now I need to decide what to do for a carb on the 68 RA II car. The engine is not the original but i do have a correct block, heads, exhaust manifolds, and intake. Distributor is a 68 unit but not RA II. I don't really want to spend the big bucks for a correct RA II carb since this will never be a numbers matching car and I plan on driving it locally and not a concourse restoration. I saw a correct 68 GTO 4 speed carb on ebay but know nothing about the company that is offering it. It is a Service Replacement and has had throttle shaft bushings installed and main wells epoxied. All parts are finished in mostly correct plating but it does not have the correct throttle bracket for idle stop solenoid. It does have the correct baseplate with the vacuum port on the passenger side. It is listed by The carburetorman and rebuilt by Custom Rebuilt Carburetors of NJ. Anybody know these people?

[Gary H]

Hey Mark! Congratulations on your new car. Re: the carb. Do you think you may have a fuel percolation problem? I just recently ran into a similar problem on a customers car I built an engine for. The car ran perfect but several times on hot days it would start running rough and shut off while sitting a long time idling at red light. I installed a 3/8" insulated spacer under the carb and insulated the fuel line between the pump and the carb. Never had a issue after that. Before the spacer I could actually hear the fuel boiling in the carb after taking the car for a drive getting it really hot, and then shutting the engine off.

[Mcronk]

Hi Gary! FYI i now am living in the Leesburg area a little closer to you than before.

This carb performs flawlessly on my 67 GTO that has a Carter electrical pusher pump (self requlated to 5 psi). Never has a problem no matter how hot it gets. But if i turn the pump off the car will stall like it is running out of fuel. Turn it back on and it starts and runs fine. Been like that for a couple of years. I swapped it on to the 68 car to determine that car had a bad carb. But the 68 just has the stock mechanical pump and car would stall. More testing has revealed it is not running out of fuel on the 68 but seems to want to stall at rpms below 750. This car does have 041 cam and the carb from 67 was rebuilt and rejetted per Cliff's recomendations for the 67 engine specs so it is not "perfectly" set up for a 041 cam.

I am going to put it back on 67 and do some more testing. Other than having to use the electrical pusher pump i have no trouble from this carb. I am going to check the fuel pump on 67. It has been on car since 1992! Good thing is i determined the carb on 68 is bad. So now i have to either rebuild or find a better one that is more "correct" for the car.