I'm new to carbs, so somebody please whip me into shape to troubleshoot this. 1970 small-block with a carb that was originally made for a '71 big-block, started ok when I bought it last summer and always runs fine once running. Lately if it sits all week in the garage, it won't start for me without giving it some starter fluid spray or a sprinkle of gas on the carb. Where do I start? It seems to me that the fuel is evaporating when it sits for long enough... possibly related problems: - a bit difficult to keep from stalling before engine warms up - on WOT, she pushes hard until 60mph, then shifts into 3rd and falls flat on her face for about 3 seconds (auto trans)
Fuel is probably leaking out of the bowl. Couple of questions. Is it a quadrajet you have? Is your 350 stock or any modifications? If so, explain.
Before you try to start it, look in the airhorn and operate the throttle to see if there is gas in the bowl. If the accelerator pump doesn't squirt fuel, the bowl is empty, which means there is a leak. It's common for the Quadrajet to leak under the main body (between the main body and the base casting). You will see two round areas on a protrusion under the float bowl about 3/8" in diameter. These typically leak. There are many methods to fix this problem, including drilling and tapping the area where the main jet passages are located, using epoxy to seal the leak, and just peening the metal where the plugs are located and using a sponge rubber material in the little well in the base below this area. The other thing you should be aware of is that the gas evaporates out of the Quadrajet in a few weeks. The large vent on the top of the carb opens the float bowl to atmosphere so the gas evaporates fairly quickly. You said your problem occurs in a week of not running the engine, so I don't think this is your problem.
What may be happening here is a combination of evaporation and the resulting sticking float. If, for example, the float is fully closing the fuel inlet, as it should, then the fuel evaporates, the resulting deposits make the needle stick in the seat. Unless something unsticks the needle, like some of the starting fluid getting on the needle, the bowl never fills, as the needle is stuck shut. Having experienced this myself, I ultimately changed brands of fuel, which eliminated the issue. Ray
The hard starting after a week is indicative of fuel evaporation. The Q-jet has a pretty small volume in the float bowl, after you subtract the float volume. FWIW, I drip a little fuel into the carb even if it's only been sitting for a week. I don't use ether. You have to be judicious with the fuel drip. I'd say that I probably only put in a teaspoon. Note that I have a 600 CFM Edelbrock, so there's more fuel in the dual float bowls than the QJ has. Falling on its nose is indicative of a clogged fuel filter, or you're low on fuel. My '68 Skylark gently reminds me it's close to being out of fuel by stumbling at WOT. If I back out of it, the stumble goes away, but I've typically got about 30 miles before I'm walking.
I first had trouble with Texaco, which I thought was only evaporation. Then, after trying one morning to get the van running, it appeared that the float was sticking closed, which was the result of deposits in the needle and seat. When I switched to Chevron, the float sticking issue disappeared, however, no matter which of the major brands I use, the evaporation issue has not been relieved. Going back to Texaco has not duplicated the sticking issue, however, Texaco and Chevron recently merged, and I suspect that both now use Chevron. I suspect that, since fuel injection has its own fuel delivery options, the fuel has been re-mixed for injection, leaving the carbureted cars out of luck. One thing I noticed was that the alcohol content fuel appears to evaoprate faster, disappearing in as little as three days. My q-jet is on an '85 Safari, and I know that there are NO issues of bowl leakage. Ray
Here is my take on this issue. If the ONLY problem with this vehicle is that it is a little slow to start initially, after sitting a few days, it is likely an issue of fuel evaporation. Once lit, my van runs perfectly, both hot and cold, regardless of the ambient temps. After sitting a few days, it starts a little slower, but still lights on the first attempt. If that is the case here, it is not likely to be addressed by any tinkering or adjustments. No fuel in the bowl is no fuel in the bowl. Fuel injection addresses this issue by having an anti- pressure loss valve in the line, which keeps the line pressurized. Further, the systems have a "prime pulse" in the pump circuit, which pressurizes the line when the ignition key goes initially to on, before the crank position. If the only issue here is a slow initial start up after sitting, then runs fine, it is likely one of fuel evaporation, which is a by-product of the Reid vapor pressure of the fuel, determined by the refiner mixing the fuel. Marathon fuels, which is what I use now, appears to minimize this problem, noticably reducing cranking times after sitting.
Here is my take on this. I don't drive my 70 GS everyday. It gets used 2-3 times a week in the Spring, Summer, and Fall. I try to get it out once a week in the winter as long as there is no snow, salt, or runoff problems. It isn't unusual for my Buick to sit for 2 days or as much as a week. I don't use a choke. I don't want the engine to start instantaneously. I don't pump it at all. I run the starter motor for about 10 seconds, then pause 5 sconds, then run the starter motor for another 10 seconds. Then I pump it. It starts right away then, and the oil pressure builds right away with no lag at all. I feel better about that. If I fill the carburetor with fuel by priming it with my pusher pump, and then pump the gas and start it, the oil pressure takes 2-5 seconds to build sometimes. I don't like that. Just my .02
This will cost you an early starter replacement, which is way cheaper than an oiled-part replacement, anytime.
I was just gonna say that.. starters are cheap. When starting my 72, I would always turn the key without pumping (I think I learned it from Larry actually:TU: ) Then pump and vroom.. instant oil pressure
I just want to point out that by using the big block carb you are asking for trouble unless you are willing to totally custom modify the carb. The stock application Buick 350 Q jet would be way better for you since it is setup to run on the engine. I have had 455 carbs on 350s, and they can work well depending on the mods done to the engine. I read the Q jet books and spent over 50 hours tuning and rebuilding my Q jets. On a stock 350 the 455 carb gives way to much idle air, not the mention the air fuel ratios will never be right.
