Sup peeps.... I was getting my special ready for a cruise when i noticed that my carb was leaking gas from around its base plate area. This doesn't happen while the car is running. It happens right after i turn the car off. I figured it might be a gasket so i rebuilt the carb with all new gaskets, got it installed and back up and running but the issue with the gas leaking is still there. The car will run and stay running with out flooding nor will gas leak anywhere but as soon as i turn the car off, it starts to leak around the base plate. I can reduce the leaking a little if i unplug the vacuum hose. I can also stop the leak if i open up the bottom butterfly's but normally they stay closed when the car is off. Anyone have a idea on what could be going on here?
Re: Carborator leaking gas but its not flooding. I would take a guess that the fuel is boiling in the carb. after shut off. Heat riser closed/partially closed. Engine running hot internally/timing issue. Float level too high. Try lowering it 1/16th. At the top of my head at 6am that's all I've got for now. Tom T.
I tried lowering the float. It seems to be sealing good when the float rises. The car starts and runs smooth. No hesitation or stalling so far but i still get the gas leak when i turn the car off.
Heat riser? Is that the pipe that connects to the choke spring and allows the choke to open when it warms up?
No, the heat riser is between the exhaust manifold and the exhaust pipe. It has a butterfly type valve which restricts exhaust flow to aid in warming the engine faster. These often freeze up and cause problems, especially if it sticks closed. HTH
Under the carburetor there is a passage in the intake manifold directs the hot exhaust gas to provide heat or the carburetor
Okay; I've seen this happen with 2GC carbs that were set up completely wrong. What I mean by this is that the ignition, timing and the carb were set up in such a way that the car was running off the idle circuit and into the "cruise" circuit. When the carb runs in the off-idle or "cruising" band more fuel is being introduced through the mains and the idle circuit drains raw fuel off onto the butterflies after the motor is shut off. Obviously this is very dangerous. So, start from scratch, check point dwell, make sure it's set to specs, 29-31 degrees on most Buick engines. Check ignition timing, (Nailheads run between 2 1/2 to 5 degrees before top-dead-centre, the others generally about 5-12) make sure that it is set properly with the distributor vacuum off and plugged (a lot of backyard guys would ignore this step). This insures that there is no advance happening and the counter-weights in the distributor are "at rest". Make sure the distributor is being fed the correct vacuum, you'd be surprised how many people hook it up to ported when it calls for manifold vacuum or vice-versa. Once the ignition is set up properly, turn out the mixture screws about 1/2 a turn, and turn down the idle; then turn in the mixture screws until it just about dies, and then back out a 1/4 turn. Optimum would be to use a vacuum gauge and turn in (or out) the mixture screws until the highest vacuum is obtained. It seems that back in the day everyone who has ever owned an old car knew someone who supposedly knew how to "power-time" an engine; invariably most of these people had no idea of the theory of how a carb works and just got lucky. The most common thing was someone who "got rid of all that useless pollution crap" and hooked up the vacuum lines where ever they saw fit. The nice thing with an American engine is that they are over-engineered and can take a lot of abuse and just about run backwards if they have to. Try this with an old Mercedes and see how far you get, those things just hiccup and explode into flame if they are not perfectly set up. This can be time consuming, especially if there's an undetermined vacuum leak. The car might not even want to run or start, so be prepared to take some time. This is where those miserable steel plates off the heat-riser can be a real pain; sometimes they're the source of the leak. I've had to double-gasket these things many times, especially with worn out or rusted ones. Please note that a vacuum leak will probably cause many a tuner to go off-idle in order to maintain an idle, and then attribute the resulting bog (when stepping on the gas) to a worn out engine or a bad carb. Hope this helps, good luck.
The only way raw gasoline will leak out of the base plate is if it is flooding. I could see fuel boiling from excessive heat transfer, but I think it must be over powering the needle/seat when you shut it down. Have you tried replacing the needle/seat? Ethanol in gasoline wreaks havoc with fuel system parts.
Of course this should be checked out. Far be it for someone like me to question your comments, but here are the observations that I made when I came across this same problem. I thought the same thing as you did on the last pair of 2GCs I did, that it had to be bad parts. Both engines were SBCs, should be pretty easy to set up, right? Both carbs in these last cases were rebuilt "jobber" carbs like those that are sold at places like NAPA. They were fresh out of the box, because both complaints were with rough running and bad throttle performance which was assumed to be because the carbs were worn out. In both cases they were supposedly set up by "competent" mechanics at a local shop which will remain nameless. The reason they came to me is because I have a bit of a reputation for being able to tune older engines, I've been doing it successfully for 30 years. These new ones were of an undetermined age though, so I assumed like you did, that ethanol was wreaking havoc with the rubber parts. So I threw a new kit into them and got the same results, raw fuel leaked through the weep holes above the butterflies after the motor had been shut down. Float level and check balls were all properly in place and set up, needle and seat were new and tested; but in order to idle the car the idle was set much higher than normal. What was weird was that no matter how much I turned the mixture screws it seemed to make little or no difference to how the car ran, which implied that the engine was running off the idle circuit to begin with. The last one I did also had an electric solenoid that compensated on idle, it was cranked up quite a bit to knock the throttle ahead while idling in gear, and the moment the car was shut off the solenoid slammed "off", the butterflies closed, and then raw fuel leaked out the weep holes. Once I got the engine calmed down and running on the idle circuit there were no more leaks, and the throttle response was better. But in order to do this I had to completely reset all of the ignition components and timing was then reset by the book, as well as having to reroute some vacuum hoses that had been goofed. The primary one was the distributor, on this engine it called for ported vacuum and it was getting direct or manifold vacuum, you can see how that would change things a bit. I've found in my experience that this rerouting of vacuum is a very common mistake made usually when someone attempts change carbs or pulls off things that they feel impede the car's performance.
This is a very common problem with Quadrajets so it doesn't surprise me that it applies to the 2G carburetors. If the throttle blades are open too far, the very efficient primary side of the carburetor will run on the mains and not on the idle system of the carburetor. This renders the mixture screws unresponsive for obvious reasons. It's referred to as nozzle drip. What you refer to as weep holes are the idle discharge ports and transfer slots I suspect. It is normal for fuel to flow from them at idle and also off idle as well. In fact, I believe there is a certain amount of fuel that continues to flow from them throughout all throttle openings. To keep the engine on the idle system when it is idling requires the throttle blades be nearly closed at idle speeds. That requires more ignition timing, not less, so the vacuum advance hooked to manifold vacuum at idle should help not hurt as long as you back off the idle speed screw to close the throttle blades further. Increasing ignition advance at idle enables you to close the throttle and maintain the same idle speed. I still don't understand why gasoline would flow from the idle discharge and transfer slots once the engine is shut down unless it is boiling in the carburetor because the intake is so hot.
I have seen a Qjet drain itself out because the upper idle air bleed was clogged. The bleed acts as a syphon break when the car stops running. When its clogged or epoxied shut, the fuel can syphon from the bowl thru the idle tubes and channel and into the primary bore via the transfer slot. not too common or likely, but maybe it is something to consider.
That is one of the issues im having as well. I thought the mixture screws might be worn out. Would adding lead additive help reduce the havoc that Ethanol gas does to carbs? ---------- Post added at 03:41 AM ---------- Previous post was at 03:22 AM ---------- The only thing i changed on the carb were the gaskets. I thoroughly checked and cleaned that needle/seat and that thing is sealing like it should. If fuel is over powering the needle/seat, would that be a fuel pump issue? (like its giving to much pressure)?
See my post above; you've got the idle set too high and the engine is running on the mains. So the question then is why does the idle need to be set so high? Is there; a) a vacuum leak? Check the base of the carb; particularly around the butterflies and the base-plate. As discussed above, the heat-riser and the steel plate covering it may be leaking, and if the carb is old there could be vacuum leaks around worn butterflies. b) ignition timing set wrong? Check it with the vacuum advance to the distributor off and plugged. Is the vacuum advance working, or is it jammed on "full advance"? c) are there manifold vacuum leaks? d) is the idle compensator set too high?
No, once the throttle is open too far, the engine runs off the mains, and is no longer on the idle system of the carburetor. That is why mixture the screws have no effect. Lead additive will do nothing to prevent the corrosive effects of ethanol. Better ethanol resistant kits are necessary, especially the accelerator pump. You have to replace the needle/seat.
Ok i did some tuning up. I did have my idle screw set for to high of idle. once i turned it down, the engine wanted to bog out but it was because of improper mixture screw setup. I took it for a spin around a few blocks and it ran fine. I didnt see any gas leaking when i shut the car off. I have to give it a few more runs before im convinced the leak has stopped. Id still like to look into the heat riser tho. ill have to look it up in the shop manual to find it. The vacuum advance seems to be working. I feel it spitting air when the vacuum hose is removed and the engine will bog down too...unless it should be pushing more air out then it is. Im not sure what you mean by (jammed on full advance) As for vacuum leaks, there still could be some. ill check the areas you listed. A buddy of mine said a way to check for vacuum leaks is to spray starter fluid in the areas i think theirs a leak at and if the engine revs, then there is a leak. If thats true then ill try it. ---------- Post added at 02:03 AM ---------- Previous post was at 01:37 AM ---------- I have a new needle/seat, mixture screws and up-to-date plunger ready for order. I think ill replace the stock glass fuel filter unit with something more modern one too.
What I meant by "jammed in full advance" is what condition is the diaphragm in? Does it move like it's supposed to or is it stuck in one position or another? There's a rod coming from the diaphragm into the distributor which moves the plates. Sometimes these diaphragms get stuck, fail completely or start to leak vacuum. If yours doesn't leak and still moves, leave it alone; it's not the problem. Yes, you can use starting fluid to look for vacuum leaks. A lot of old timers did it that way. I wouldn't recommend it though. Please have a fire extinguisher handy if you try it. You might want to use something that isn't as flammable though, just to be on the safe side. I've used WD-40 and it worked. Cleaned and lubricated the linkage too. Any aerosol can will work in a similar way; if there's a vacuum leak, the motor will quit instead of speed up. Another quick way to check for vacuum leaks; place your hands over the top of the carb and close off the intake; if there's a leak, the idle will increase, if there's not one, the motor will die. Sounds like you've got most of the problem licked except for the fine-tuning, good work!
Oh ok well it looks like the advance isnt jammed then. Doing the "hand over the top of the carb" trick makes the motor want to die out. Im still missing something tho. I drove it around this weekend and it'll still leak when i turn the car off. I think its defiantly leaking from the lower butterfly shaft ends. gas will leak from both sides of the carb in the same area. Is the shaft supposed to fit that tightly threw the base plate so gas wont leak? Is gas supposed to be pored on the lower buttlerflys and kept there when the engine is turned off?
Okay, it's close then. It is possible that the carb will leak raw gas, but I've usually found that it is a setting issue and not a leaky gasket or bowl. It is possible that it'll leak internally, and the seal on the butterfly shafts should be tight, but not impossibly so. If you can move the shaft up and down, or see up/down movement, or what we in the watch business call "sideshake", then the throttle shafts are too loose and there is your vacuum leak. Bushing this shaft might fix it. There's also a chance that the carb base is corroded through and causing a leak through the heat-riser, these are all things that will cause enough of a leak where you have to set the idle up higher and therefore, operate on the mains. When the carb runs on the mains, once you shut it off, vacuum into the motor stops, and the raw fuel that would normally dump hits the butterflies and flows out the compensator vents. So your initial observation of a potential vacuum leak may not be far off the mark; all it needs is a small one, check everything that uses vacuum by isolating them all off, then see how the motor runs. Then do the WD-40 trick, concentrating on the throttle shafts. If it dies when you do this, there's your leak. If it doesn't, well, then we'll all have to think about this some more, 'cuz then we still haven't figured this thing out...
