Fuel is leaking down out of the carb,
After shutting it down when its hot pull the air cleaner, smell for raw gas etc,
Don't know about your brand of carb, but the Q-jets have a lead plug on the bottom that is prone to leaking over night.

 

Mine does the same thing with a Holley DP.

------------------
Rick Dorion
69 RS Conv,355,Autogear M22,4.10's and I don't worry about stone chips ( yet ).

 

Both my Q-jet and Demon to that, but only if it sits for a week or longer. The Q-jets plugs have been epoxied too.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/

[This message has been edited by Silver69Camaro (edited 11-15-2002).]

 

I have the same trouble with my Holley 650 DP, its even worse if the weather is a bit on the cool side...I think I have to mess around with my choke more though.

 

I'm running a brand new Edelbrock 800 carb. So I guess there really isn't anything to do to fix this?

 

on my old 350 with a quadrajet did this, but when i put my 750 demon dp (no choke) on it it started perfect every time. and after i put my 406 in, its still the same, a quick single pump when cold and it starts right up, and just hit the key when its warm, no problem. i would think you should be able to achieve this w/ your car as well, with some fine tuning/adjusting.

 

Basically the fuel is just draining out of your fuel bowls down the line and into the tank. Just gravity, unless its leaking out the carb onto or into your intake you have nothing to worry about.

 

The fuel isn't likely to be siphoning back into the tank! It's leaking into the intake and down the cylinder walls into the pan. If you get enough fuel in the oil pan, you could blow the valve covers and the oil pan right off the motor. (seen this happen! Kewl! wasn't my car!) If you are lucky enough for this not to happen, you could dilute the oil enough to ruin the bearings and/or seize the oil pump. If this is a new carb and it's leaking, take it off and get another one under warranty! or get it fixed.
Jim

 

I dunno 'bout that...my Demon does it, my Qjet does it, my old Edelbrock 1406 did it, and my new 625CFM Carter did it. I think the fuel is evaporating out of the fuel bowls, personally. But this is after an extended period of time though...not just a couple of days.

------------------
Matt Jones
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/

 

If you look closely at the mechanics of a float/needle and seat set up. It's like a toilet tank. The fuel is sitting below the valve that allows fuel to flow into the bowl. There is no way for the fuel to get back up there. In a Holley or a Demon, it would have to siphon two tanks empty. Also, the fuel pump works like your heart. One way clapper valves prevent fuel from draining back on the pressure side of the pump. The only other possibility besides leaking would be percolation. There may be enough heat soak into the carb to boil the fuel out.
As mentioned in the earlier post, a Q jet has a problem with a lead bowel plug that can leak. But then again what does MarkM mean by "a long time". Your suggestion of fuel evaporation might be the case?
Jim

 

Something's fishy, Mark. If I let my car sit for days, or a couple weeks, all I have to do is to pump the pedal once, and it fires on first try. Always. How's your timing? If you don't have enough advance at initial, it could crank a bit before catching spark.

If you think it is losing fuel, wait a couple days and then open the air cleaner, poke you head in there, and manually push the throttle plates. Look for gas out of the accelerator pump. If you get some, the issue is not fuel leakage/evap.

 

i have seen problems like this fixed by putting in a fuel pump. perhaps the check valve goes bad or something, and allows the fuel to drain back.

------------------
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik

 

ihave a 1406 edlbrock also, AND a brand new fuel pump with a Mr Gasket glass in-line filter. you can actually watch the fuel level in the filter decrease over time. it IS draining out of the filter and fuel line back to the tank. absolutly! i have investigated this by disconnecting the line from the tank to the pump and putting a bowl under it. it happens, no big deal.

 

hey mark,

got a novel idea. get fuel injection.....lol...

but i have to agree with the evaporation/or leak down... have had the same proble. i think that it may evaprorate a bit from the vent tubes....ever take off a carb turn it over to drain it and watch the fuel come from the vent tubes?

i agree with Mean and CAm... if you stab the throttle and see the gas pump from teh accelerator, then there is still fuel in the bowl....

good chance that the fuel is possibly draining back to the tank and you have to crank it to get it back to the bowls... you could get an electric fuel pump and see if the gas gets there sooner...

HTH, JS

 

i know some circle track sanctioning bodies require a one way check valve in the fuel line. maybe get one of those?

------------------
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik

 

Thanks for all the advice. I'll see if the carb shoots fuel out the next time I try to start it.

 

Worn fuel pumps will allow drain back. But there should be plenty of fuel in the carb to start the engine. Mechanical fuel pumps, by law, must meet anti drain back and anti siphoning specs so that in the event of a roll over or an engine fire there will be minimal fuel flow. Electric fuel pump systems have what's called a roll over valve. If you can see your fuel filter draining back to the tank, check the filler cap. You may have a defective or damaged cap, or someone may have installed a newer style cap that is non venting and the fuel is being sucked back into the tank. If your cap is the right one then your pump is worn or faulty. This doesn't mean your pump won't work, just that the safety features aren't working the way they should. I leave my cars in storage up to six months and have never had empty fuel bowls. If yours are empty after just a few days, I would suggest that a)It's leaking b)It's leaking or c)It's leaking. Not trying to be funny here! but where else can it go? For this much fuel to evaporate would take a long time (months)or there is a lot of heat involved.
Jim

 

I have the same problem. I just got online to post the very question, but you beat me to it. I took off the stock quadrajet and lost the built in check valve that the Qjets have. I put on an Edelbrock 4011. It did the same thing with the Holley 750 that I had on it. I also have a new stock fuel pump putting out good PSI. I have the stock venting gas cap that works fine. I can sometimes hear the gas pouring back into the tank. Does anyone know it someone makes a filter with a built in check valve or an inline check that won't restrict gas flow? Thanks for the help!!

------------------
69 SS 396 ragtop Clone/M-20/331 12 bolt posi/Lemans Blue/White Hockey/ Black Rag/Black deluxe Interior
Ragtop Pics http://hobbystage.net/camaro/kenth/

 

I also thought of the check valve idea about a year ago, and found that it won't help. The pressure in the line will eventually get through the needle and seat, and won't solve the problem.
Jim McFarland also had the same experience with the check valve idea.
------------------
Matt Jones
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/

[This message has been edited by Silver69Camaro (edited 11-24-2002).]

 

What you are hearing is not gas pouring back into the tank. The fuel pick up In the (stock)tank Is submerged. Don't know what you are hearing. (Maybe water in the cooling system?)The amount of fuel to drain down would be 12 to 18" In a 3/8" or smaller line, maybe 3 or 4 ounces at most. The Q Jet didn't have a built In check valve. The float system is the same as the Edelbrock (Carter) and the Holley. There Is a possibility that fuel will siphon down from the level of the carb (not from In the Carb), but no further than the fuel level in the tank. Most early cars are configured so that the fuel tank is above the fuel pump. What I would suggest everyone who has this problem do, is when you shut the car off, disconnect the fuel line at the carb and in the morning or next day etc., Check to see if the carb has gas in it by moving the linkage and watching for fuel to squirt down the barrel/s. And diagnose from there. For those of you who insist that your gas is being siphoned from the carb, I suggest you get a good carb book and look at how this thing works (Float system). Holley makes a good one, and It will help a lot when It comes time to do a rebuild.
Hope this helps
Jim

[This message has been edited by GMJim (edited 11-24-2002).]

 

I can sit there and watch the gas drain back towards the fuel pump through the clear filter as it empties. My carb is empty when I pull the throttle arm, that's probably why it takes over a minute if constant cranking to start after it has been sitting a couple of days. I can prime it and it fires right up then dies. I can do this twice then the fuel pump has enough time to pump gas to the carb. I might try a 3/8" stainless steel ball check valve at the low point on the rear frame rail to see if this helps.

------------------
69 SS 396 ragtop Clone/M-20/331 12 bolt posi/Lemans Blue/White Hockey/ Black Rag/Black deluxe Interior
Ragtop Pics http://hobbystage.net/camaro/kenth/

 

Gentleman

I took the liberty of sending a copy of Kent H's post about his fuel siphoning problem (without using his name) To Holley's Tech department. He described the problem that we've been batting around and I thought you might be more convinced If you heard It from the horses mouth. Here is the material I sent and the reply I got.
Jim


There is no way for that to happen. One just has to look at the inside of the bowl to discover that there is no tube or way for the fuel to be picked up from anywhere below the needle and seat. A more likely reason for this would be a metering block or power valve gasket that is not sealing correctly or a power valve that is blown. Any of these conditions would allow the fuel bowl to empty through the power valve reference hole in the baseplate.




Thanks,
Chris Reid
Tech Service Rep
Holley Performance Products
Phone: 270-781-9741
Fax: 270-781-9772
To find your closest dealer call 800-465-5391
website: www.holley.com
----- Original Message -----
From: reply@support.holley.com
To: chris@support.holley.com
Sent: Sunday, November 24, 2002 8:54 PM
Subject: Bowl siphoning [T20021125006AZ408984]

Sender : jngood@rogers.com
Tracking Number : T20021125006AZ408984
Pool : techmail
Sent to : techmail@support.holley.com
Date : 11/25/02 8:36 AM
Dear Holley Tech
Members of our forum are trying to diagnose a problem. This problem has been reported by more than one member.
The problem we are having is fuel being sucked out of the float bowl by way of the fuel feed line. I have been trying to explain to people who are insisting that their carb bowl is empty a short time after running their engines that the float assembly, just by It's construction will not allow this to happen. It Is my belief that the fuel is leaking or percolating out of the carb, not being sucked out.
The following is a quote by one of the forum members. Other people have insisted that this is taking place In their Holley equipped cars as well.


Your help in this problem Is greatly appreciated.
Thanks
Jim
Quote:
"I can sit there and watch the gas drain back towards the fuel pump through the clear filter as it empties. My carb is empty when I pull the throttle arm, that's probably why it takes over a minute if constant cranking to start after it has been sitting a couple of days. I can prime it and it fires right up then dies. I can do this twice then the fuel pump has enough time to pump gas to the carb. I might try a 3/8" stainless steel ball check valve at the low point on the rear frame rail to see if this helps."

 

I have the exact same problem 69 Camaro. I am running a summit electric fuel pump and a 770 St. Avenger. I have been through 4 regulators and 2 pumps, and I have also installed a check valve. The check valve help some but not enough after it sets 3 or four days, I can tell by the sound of the pump, that it is dry. over the winter I want to try and redo the lines from the tank to the pump. all I have to do to get started is to unhook the line at the regulator and Prime it. sometimes I can just barely blow on it, and it works. It just drains back enough for the pump to be dry, as soon as fuel hits the pump it works fine. I have tried loosening the gas cap and leaving it off altogether but neither worked. Maybe if I move the check valve to a different position I may solve my problem. Good luck guys, if I cure my problem in the near future I'll let you know.

------------------
69 RS Camaro (383,700r-4,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)
Check out my site and the For Sale Page http://rodsrides.freeservers.com

[This message has been edited by wildkatz (edited 11-26-2002).]

 

Where is the pump located? Above the fuel level or below? Close to the tank or far from the tank? Are the float bowls empty after 3 or 4 days?
Jim

[This message has been edited by GMJim (edited 11-26-2002).]

 

The pump is located in the rear end tunnel just under the passenger side rear seat, below the tank with about 1 1/2 foot of line from the pickup tube and I don't think the bowls are empty just no fuel in the pump.

------------------
69 RS Camaro (383,700r-4,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)
Check out my site and the For Sale Page http://rodsrides.freeservers.com