I replaced the stock carburetor on the engine in my '51 Ford with a 2GC I rebuilt. I really like everything about it, except that if is sits a week or so, it's hard to start. If I crank on it for a while it'll take off, but it doesn't seem right. If I use my squirt bottle of gas and fill the carb through the vent before trying, it starts immediately. The choke seems to be functioning correctly, so I suspect the fuel is leaking out of the float bowl somehow. I have removed the power valve, inspected it and the seat closely, replaced the washer, and it seems to have gotten worse, if anything. I have experienced this problem on 94's before, and every time, it was a leaking or improperly seated power valve, so that's what I expect is happening here. I am planning on getting a new power valve and replacing it, but I realized I know almost nothing about them on these carbs. Do they have different "ratings" like those in a Holley? Where is a good source? Anything else I should know? Is there any other place where the fuel could be leaking out? Any information will be appreciated.
I don't think fuel can leak past the power valve into the throttle bores of a 2gc That it off and tear it down to just the float bowl body of the carburetor remove the jets and power valve and fill the bowl with gas and watch the bottom of it. Nothing should leak out.
Going from memory here... The power valve in that carb is open until vacuum is applied to the piston that is in the top cover... It has the plunger and spring attached to it that holds the power valve open when there is no vacuum applied or when vacuum drops at wot. That said, it won't bleed a carb down like the ones a Holley uses. You may have a pinhole in the casting... Seen that more than once. Pull it apart, clean and dry it. Set it on a piece of cardboard and pour some solvent in the float bowl. Watch and see if the cardboard gets wet. If it does, look for the hole! You can usually fix it with fuel proof epoxy ( JB Weld ). Sent from my Moto G Play using The H.A.M.B. mobile app
As already mentioned, I don't think the power valve can leak in such a way as to allow the float bowl to drain when the engine is shut off. I think if you remove the throttle plate and look at the bottom of the bowl you might find a soft plug that seals a passage into the bottom of the accelerator pump well. If that is loose or appears to be leaking you can reseal it with a bit of epoxy like graybeard360 says. But I don't think this was a chronic problem on 2G and 2GC carbs. You might also try using a thicker, insulator type gasket between the carb and the intake manifold. That might help relieve a fuel percolation problem in the carb during heat soak conditions. Also, since it seems to often be overlooked, grab the instruction sheet from your carb kit and double check the bowl vent adjustments.
When the above checks for proper functioning of the carb are complete, consider the following if this problem is still present. My rod, if I drive it everyday, as on a trip the cold start is immediate. But at home, where I might not start it for a week or two, it is hard to start due to fuel in float bowl evaporating. Seems that the corn alcohol / gasoline blend fuel available in my state evaporates that quickly, causing the long crank times on cold start after sitting a few days. Phil
As mentioned above, definitely NOT the power valve. On the Rochester 2-G, the power valve simply is an additional source of fuel to the main discharge nozzles to augment the main metering jets when low vacuum conditions exist. You could remove the power valve completely, and it still would NOT leak down the bowl (wouldn't run very well though ). The discharge points of the main discharge nozzles are above the top of the fuel level in the bowl. Here is probably your problem: http://www.thecarburetorshop.com/Troubleshooting.htm#Hardstartcold And just to be historically accurate, the carburetor that was responsible for the phase "leak down" is the Holley model 94 with the passage in the carburetor under the power valve that drains directly into the intake manifold. I cannot think of any other carburetor that can "leak down"; although early Rochester Q-Jets could back-fill a certain amount into the fuel line. The inlet filter with the check valve stopped this; and the bowl would never completely go dry, as does the Holley. Jon.
I've an Autolite 2100 that does this. The fuel in the bowl is not evaporating, if you check. It gets a good squirt from the accelerator pump through travel. It is strange. To save wear on the starter I got in the habit of pouring a teaspoon of fuel down the throat of the carb. Vroom! From the link above: "Difficulty starting a vehicle that has been allowed to sit for a number of days (that will then start well the rest of the day) is often caused by modern fuel. Modern fuel begins to vaporize (evaporate) at a much lower temperature than fuel before the 1970’s. Once the engine is shut off, the fuel in the carburetor bowl begins to evaporate through the bowl vent. If there is no fuel in the carburetor, the engine will not start." In my case, there's plenty of fuel in the bowl, after a week, because I checked. WTF?! ... Maybe it's the lighter ends are boiling off first... hadn't thought of that, makes a certain amount of sense I guess. Have to pump the $hi& out of it, if it's been sitting several days, it will then start right up. If driven regular it's never an issue. This is apparently a common problem that many people complain about. If you can figure out what causes it you'll be a hero.
^^^^^ Let me go off topic for just a second. I have 2 Honda 2000 generators that if I do not keep the fuel fresh within the fuel line and carb, it won't start. Bottom line, fuel has gone bad already and won't fire. Just another possibility to look at.
In Minnesota, we are lucky enough to have "non-oxygenated" (no alcohol) fuel readily available, so it is all I use. I did not have this problem when I had the stock carburetor (94) on it. Are you saying that the construction of a 2GC is such that it is more subject to fuel evaporation? I think I'll start looking for a leak in the bowl or soft plug. At least you guys saved me the effort and expense of replacing the power valve.
Make sure the air bleeds at the top of the carb around the venture are open they can cause fuel to siphon through the idle circuit.
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