I have a 75 corvette L48 stick and last week I added 3 gallons of gas ran the car for 15 min
Now the take is empty. this happened before but I just added gas and scratched my head thinking dam I went through allot of gas running the car 4 time for 10 min
Things I have done in the past 2 week :
Rebuilt 2 carburetor "uses Rochester's (might go to Holley are carb 3) and it seems to be flooding , The oil does smell but I am only over 1 quart so were did the rest of the gas go? 2-3 gallons.
There are no leaks and no smell.
The car runs rich no matter how much you turn out the mixture screws.

 

Turn out the mixture screws?????
You turn them clockwise to lean the idle mixture.
Did you correctly adjust the float level, what did you set it to?
Did you correctly attach the clip on the needle to the float?

 

How hard is it to start once it has been sitting?
Electric or manual fuel pump?
Could be leaking from the carb (siphoning?) Into the cylinders?
My Holly was doing that until I had it rebuilt...but my oil smelled real bad.

 

I'd say it's sitting in the cylinders slowly washing out your rings and the rest went out the tail pipe

 

All great answers


Yes hard to start
1 Yes Mix screw ALL the way out not change all the way in no change but will try on 2nd carb
2 I have seen siphoning Gas Mist
3 float set 1 1/6
4 Seat installed correctly .
This was not a problem until I rebuilt my 2 carbs cause the car was sitting for 27 years and the car ran too rich on 1st few starts ( past 2 weeks)
I figured I should rebuild the carbs and i have done a few in my time so I don't understand what is wrong . It's not that hard to rebuild
I need to do another oil change ARG after only 40 min today running time, what a waste !@

 

You say that your crankcase is over a quart. If that is the case, you have a leaky fuel pump. Fix it and do not run the engine until you change the oil and filter. Jerry

 

DING DING DING!!!! I think we have a winner!

 

whats your fuel pressure at?. If its over 6 psi it wont matter what you set your needles to because you are flooding the bowl and you are just pumping the gas through your carb whether its asking for it or not. You need to change the oil before you fry your bearings

 

Thanks all !!! I will change the oil and filter and fuel pump Friday . I never knew a bad fuel pump could cause flooding ....

 

check the pressure before you replace it, it may just be putting out 7 to 9 psi like most do. A new one is going to put out the same psi and your problem may not go away

 

If you still have a mechanical fuel pump on the engine, pull the oil dipstick and give it a smell. If it smells like gasoline, that's where your fuel is going. Likely the diaphragm in the fuel pump has a rupture and some of the fuel is getting pumped into the oil/crankcase. If that is the case, DO NOT start the car until you have resolved this problem. Chances are that no real harm has come to the engine because of this; but further use could result in engine damage or fire, or worse....
If the crankcase oil does not smell like gasoline, I have no idea where the fuel is going....

 

Well as a precaution since the car sat for 27 years without being run I purchased a fuel pump I’m going to also replace the oil and filter. I’m gonna fix one of the carbs because one was flooding but not to the extent of 3 gallons of fuel missing. So one of the carbs is no longer flooding so I guess I’ll put that back in after the fuel pump oil and filter change and maybe call it for the season and store the car until the spring.

I have a side question holley carburetor or Rochester. The reason I ask is because I’ve had trouble with the last three Rochester’s that I personally rebuilt that seems pretty decent. Or do I have another problem why carburetors don’t seem to run right on my car

 

In my experience a properly rebuilt and tuned quadrajet runs great but there are details that need to be paid attention to during the rebuild and tuning to get it performing its best - not just swapping in new parts from a kit.

How experienced are you at rebuilding carbs? You say you've done the three carb rebuilds - I have to respectfully suggest that maybe the issue is not with the carbs if all three don't run right. It might be worth your time to send one of the carbs out to a respected rebuilder who flow tests or actually runs the carb on a test engine. It can be money well spent.

Good suggestions have been made to confirm fuel pressure.

I'm also of the opinion that the fuel pump is suspect. If that diaphragm has a leak, the fuel will flow right through it and into the block. Fuel in the oil is not a good combination and can quickly lead to internal engine issues if the engine is run that way for long.

I have always found Holleys to be a much easier carb to use and many people have done just what you are asking - throw the Qjet away and put a Holley on with good results. This causes them to think the Qjet is junk (and some are) but when it just needed more attention paid to it during the rebuild.

I've used both and rebuilt / tuned many of each over the years. They each have their pros and cons but each will do their respective job if built and tuned as designed.

If I remember correctly, Lars has a pretty detailed Qjet paper floating around this forum or somewhere in cyberspace.

Good luck getting your car sorted. I'm sure it'll be a good runner when you do.

Tom

 

Yeah I’m trying to do this at a respectable budget but I think that may be my problem (fuel pump) As far as experience back in the 80s I had a lot of muscle cars and I’ve rebuilt over 50 carbs on my own. All of them have always come out perfect and running perfectly.

Now some of the stuff I’m buying is not perfect I know. I’m cleaning the ports the Jets I’ve got small tools to clean out everything and make sure there’s no clogs. I soak them in a bucket overnight. I have a feeling it’s something else there’s no way three carburetors could be ****. Now as far as the flooding scenario I don’t get that either I mean it’s pretty straightforward. You pay attention to the needle and seat you measure the height of where the float comes up with the carb I think mine is 1 1/16.

I still have to install the rear bumper work on some lighting issues I don’t plan on driving it to the spring so I think I’m gonna take a break over the winter. I’m gonna look for a good Holley carb but I had one of my Z 28 I had a 69 it worked great there to feed double pumper 650. I’m doing an oil change and replacing the fuel pump this Saturday. I do get oil and fuel are not good together especially the damage they can do the bearings if they’re not properly lubricated. Also when I run the cards generally for about 3 to 8 minutes at the most

 

You have three Quadrajets and none of them work properly? Firstly I'm not saying you can't rebuild one properly but what was the history of the ones you have? There are heaps of posts in this forum about these carbs especially the rebuilt ones that look very pretty but are next to useless as built from mismatched parts and incorrectly setup. Read the posts on the forum by Jebby and Lars on the "adventures" of trying to make a new Chinese clone of a Quadrajet work properly as an example. If I were you I would be sending one I had to someone such as Lars who can verify its correctly built and prove it on a test engine, that way you can eliminate the carb as the cause of your fueling issues.
Some of the early mechanical fuel pumps had tiny weep holes on the upper casing that fuel would leak from if the diaphragm was leaking rather than dump the fuel into the sump. In my case the fuel started to leak from these very fast, I entered the basement garage one morning to find the fuel running out from under the car

 

To replace the fuel pump, do yourself a favor and jack the right-front up and remove the wheel. Makes it a snap to get to the pump. Replace the "S" molded hose from the metal fuel line to the pump. Very important that you buy the molded hose and not use 'regular' fuel line (which will kink and block fuel flow). The 'drive rod' will likely slide out of the block; put grease on it and push it back in (so you can't forget it). Also, if the pump is difficult to press to the block surface when you try to reinstall it, 'bump' the engine over until the cam lobe is no longer pushing on the drive rod. It will then be easy to install the bolts.

My advice on carbs: Put a Q-Jet back on the engine if you have one that can be rebuilt properly. To help you decide if a Q-Jet has a good chance of being rebuilt properly, take some pics of the carb (or carbs) you have [from upper angle view and both side views], then send them along with a request to help you decide if any are good candidates for rebuilding to Lars Grimsrud via e-mail ONLY at V8FastCars@msn.com .If one is a good candidate I would also advise that you ask if Lars would be willing to rebuild it for you. He is very reasonably priced and will be set up BETTER than a new factory carb. He will run it on his test engine so HE knows it is right before returning it to you. Best "carb" money you will ever spend.

 

To make life easier when installing a new fuel pump, bump the engine to top dead center. That will place the cam in its furthest position. Pinch the rubber fuel line at the tank. I use needle nose vice grips with rubber hose sleeves over them. On the front of the engine is a bolt that is perpendicular to the fuel pump rod. Remove it. Get a bolt with the same thread and diameter size, just an inch or so longer. Screw it into the block hand tight. The bolt's job is to capture and keep the fuel rod pump up and out of the way. Remove the fuel lines and remove the two upper bolts on the pump. As mentioned above, remove the right wheel and go through the wheel well to access the pump bolts. I use two long extensions on a power driver. Once the old pump is out, it may be easier if you loosen the long bolt you installed and push the pump rod up higher. Again finger tighten the bolt to keep the rod up. Install the new pump with fresh gaskets and sealer. Reinstall the hoses and any hard fuel lines. Remove the long bolt and replace the short bolt with a ring of sealer. Remove the clamp or vice grips at the tank. Put the wheel on and check for leaks. Start the engine and again look for leaks. That should do it. Find a friend with a lift to make the job easier. Jerry

 

Wow this forum is so awesome I mean those steps are so helpful I love it when I can get shortcuts I appreciate all this info and you know what I think I might take you up on that idea send the carburetor to someone that can actually run it and test it this way I’ll finally know that it’s not the carb but something else

 

Can someone tell me the hose size to the fuel pump (2) of them I want to change . Are they 3/8 my guess or smaller 5/16 or 1 of each ? hard to tell today when I was underneath getting ready to remove the pump.
When I change it I want to do the lines too.

 

Do not buy a straight piece of hose from an auto parts store!!! You need to get a molded piece (first link below), or you risk crimping the hose and cutting off your fuel flow. The second link below, for the return line, COULD use a straight piece, but if you're ordering the one, you may as well order both.


https://www.zip-corvette.com/70-82-f...ed-s-hose.html

https://www.zip-corvette.com/68-82-f...e-cz-1175.html