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Hi, I have an aftermarket ali inlet manifold with a Holley carb which keeps giving me trouble so I am going to rebuilds the original Quadrajet and fit that. The manifold will take the Quadrajet so no issues there however I have a few questions.
Firstly I have looked at youtube video's of how to rebuild them but my one is slightly different in as much as the primary needle also activate a "plunger" that is directly behind them, this "plunger" is screwed into it's position and has a spring arrangement, do I just wind this down until it is firm? The only way to do this is by use of pliers.
Secondly I want to do away with the choke as I do not have a heat riser on the Ali manifold so I was going to wire the choke open or is there an alternative way of doing the choke.
Lastly can I just plug the all the take off's apart from the fuel vapour, vacuum take off, and the timing take off points?
Google "power piston stop screw", you will find a thread on this site from 2005. A member named Lars goes into detail on the adjustment procedure.
Concerning the choke depending on which Quad you have an electric choke can be used.
You can have Lars work on it or get his papers and Cliff Ruggles book and you can do it yourself. I was amazed the performance gains after I worked on mine. I have a wideband O2 sensor which assisted in my tuning which informed me just how lean I was running.
Thanks gents, getting Lars to work on it is a no no as I'm in the UK, I'm happy to do rebuilds when I know where everything is meant to go and as I said the youtube video's show a number of different Quadrajets getting rebuilt but the one for my vehicle is slightly different (it is the standard one that came from the factory), from the ones that they are rebuilding, even the one showing the early C3 carb rebuild.
MelWff Thank you that is exactly what I am referring to and thank you to Lars for explaining in that thread what to do, I am now a little happier that I can sort this carb out. I will also look to see if I can locate an electric choke before just doing away with it altogether.
Well, I have rebuilt the carb and it is certainly better, starts well and rev's quickly, however, if left for some while (a couple of days) the fuel in the carb leaks out somewhere so I have to turn the engine over on the starter for a while before fuel gets back in the carb and it will start.
If I put fuel down the carb from a can it starts right up and if not left for more than a couple of days it will usually keep going.
I have read about syphoning of the fuel due to no check valve or the valves in the fuel pump not very well, so the last time I ran her up, after switching off I clamped the fuel pipe from the pump to the carb and left it for a week (went on holiday), when I came back there was no fuel in the carb except in the plastic "bucket" on the opposite side of the carb from the accelerator pump.
With this information I decided to remove the carb and take out the well plugs, I have done the four main ones, tapped them and am ready to fit threaded inserts with JB weld, however, the fifth smaller plug I noticed has two holes inside the well plug area, my question is do I tap and insert a thread plus JB weld and cover the hole that is in the side of this area or does this hole need to be there to feed the other hole.
I know I have not explained that very well but hopefully someone knows what I mean,
If the photo is of any use, the main hole is on the left and the smaller one is on the right, if I put a plug in I will more than likely close off the hole on the right.
Also just realised that I probably need to do this plug as well, it is the one below the accelerator pump area.
Well, I have rebuilt the carb and it is certainly better, starts well and rev's quickly, however, if left for some while (a couple of days) the fuel in the carb leaks out somewhere so I have to turn the engine over on the starter for a while before fuel gets back in the carb and it will start.
If I put fuel down the carb from a can it starts right up and if not left for more than a couple of days it will usually keep going.
I have read about syphoning of the fuel due to no check valve or the valves in the fuel pump not very well, so the last time I ran her up, after switching off I clamped the fuel pipe from the pump to the carb and left it for a week (went on holiday), when I came back there was no fuel in the carb except in the plastic "bucket" on the opposite side of the carb from the accelerator pump.
With this information I decided to remove the carb and take out the well plugs, I have done the four main ones, tapped them and am ready to fit threaded inserts with JB weld, however, the fifth smaller plug I noticed has two holes inside the well plug area, my question is do I tap and insert a thread plus JB weld and cover the hole that is in the side of this area or does this hole need to be there to feed the other hole.
I know I have not explained that very well but hopefully someone knows what I mean,
If the photo is of any use, the main hole is on the left and the smaller one is on the right, if I put a plug in I will more than likely close off the hole on the right.
Also just realised that I probably need to do this plug as well, it is the one below the accelerator pump area.
Any advise much appreciated.
I had the same problem with my double pumper and noticed if I kept the tank full it doesn't do it as bad.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
You should look for the Cliff Ruggles quadrajet book.It covers all your questions and is how I modded mine and tuned it. I also have a AFR gauge like SSTOPCZY does. It is also possible the bottom of your carb bowl has become porous and the fuel can seep straight through the case. After you get your plugs filled in, fill the bowl with fuel over the top of a clean piece of paper and see if it seeps through. Do you folks have ethanol in your fuel over there. We unfortunately do and the heat of the engine can cause it to evaporate quicker. Edelbrock has a base gasket that is a rubber compound and acts as a heat sink so that the engine heat wont heat the carb and cause it to evaporate quickly. I had to add a .5 inch phenolic spacer to solve my issues. I now trun a 1 inch spacer and just have to deal with a little evaporation
Hi,
We have between 5 & 10% ethanol in a gallon of fuel, I need to stop the fuel evaporating or seeping out as we pay the equivalent to about 6.50 dollars a gallon and that is cheap to what it has been in the past.
I will do all six plugs and then your test of seeing if the bowl is porous.
The carb has a thick base to manifold gasket, approximately 1/4" thick, however, I would not be able to run anything much thicker as the bonnet (sorry hood) of the vette only misses the air cleaner by 1/2" at the front..
I have now redone all the plugs and put fuel in the bowel for just over 24 hours, there was a drop in the level but I put that down to not fitting the top of the carb, however, there was no residue of any sorts on the paper I had placed the carb on top of so hopefully it has done the trick.
I have since put the carb back on the vehicle and will wait till next weekend to see if it has any fuel left in it to start it up without turning over and over. Fingers crossed.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
good luck...I would think you would get some evaporation still, but hopefully very little. Mine gets a few pedal pumps over night, if it just spins, I let it spin a bit to fill the carb. I pedal pump it 10 times and then it roars to life. If i drive it and its warm after I shut it down for a while I can just turn the key and it will fire up. If it has cooled usually one pump will get it. Good luck with yours, Im curious how it will go
Well, the carb is still leaking fuel somewhere but I have not done a test by clamping the supply hose after I switch off the engine to see if it is now just syphoning out, my previous test doing this was before I re-did the well plugs, so I will give it a go tomorrow and wait till the weekend to see if that does the trick, if it is then a rebuild of the fuel pump and replacement of the fuel filter in the carb will be in order. Currently have a large canister filter before the carb to stop any dirt but this does not have any check valves in it. Fingers crossed.
i sent mine from Australia for Lars to work his magic, it now works "upside down"......
I'm assuming that your Vette is the one in your avatar in which case originality is probably important to the vehicle but my one is a 79 and a general hack that gets abused and doesn't get a lot of TLC so originality is not important to me just want a reliable motor. I have looked at sending the carb to the states but in reality I would probably just go EFI as it would work out cheaper.
I'll keep plodding along witrh trial and error till I get to a point when I will just bin the carb and go EFI. Will keep you all informed as progress or otherwise happens.
Well three days and there was still fuel in the carb for the accelerator pump to pump fuel in and it started up easily. I have run the motor for a while and have reclamped the fuel supply hose again as I won't be doing anything to the motor for about a week so that will give me a better indication as to what is happening but from this last few days it does seem to be syphoning out after it is switched off so will be getting a rebuild kit for the fuel pump.
Chokes make starting your car much, much easier. If this is a 75+ carburetor (M4M), an electric choke conversion is fairly straightforward. You’ll need to power it to a switched ignition source, but otherwise no big deal. You take the hot air choke off and install and pre-tension the electric choke. Don’t reinstall the seal between the choke and the choke housing, as the electric choke grounds through the carburetor.
If you don’t know what kind of quadrajet you have, share pictures of the airhorn and choke assembly and I can let you know. If it’s using the stock 79 manifold with hot air tubes going from the manifold to the choke and from the back of the airhorn back to the manifold, it’s likely an M4M and really straightforward to convert.
Thanks. I'll get one of those, think there should have been a spring in the inlet where the filter goes but my one doesn't have either the filter or the spring, they must be obtainable.
Chokes make starting your car much, much easier. If this is a 75+ carburetor (M4M), an electric choke conversion is fairly straightforward. You’ll need to power it to a switched ignition source, but otherwise no big deal. You take the hot air choke off and install and pre-tension the electric choke. Don’t reinstall the seal between the choke and the choke housing, as the electric choke grounds through the carburetor.
If you don’t know what kind of quadrajet you have, share pictures of the airhorn and choke assembly and I can let you know. If it’s using the stock 79 manifold with hot air tubes going from the manifold to the choke and from the back of the airhorn back to the manifold, it’s likely an M4M and really straightforward to convert.
The actual starting if fuel is in the carb is not an issue. I didn't have the correct manifold for the heat riser but found a dual plane, ali one local to me so swapped that in adding the original choke mechanism and it works fine but the fact that the fuel is draining out means that I have to crank the engine for some while before fuel gets up to the carb and it will then start, I did think of going electric fuel pump but why bother if all it needs is a few small parts.
If it still won't do what it is supposed to do then I'll look at EFI, o2 sensor and an in tank fuel pump.
Well that didn't work then!!!! I left the vehicle with a completely clamped fuel supply hose but late today I went to see if there was any fuel left in the carb and the answer was NO!!! so seven days and not enough fuel in the carb for the accelerator pump to squirt any fuel what so ever.
Think the cheapest way to resolve this is to fit an electric fuel pump and be done with it, at least then I can prime the carb before trying to start it instead of having it turning over and over on the switch. It seems to run fine so generally the carb must be there or there abouts.
I will look further into a possible swap to an EFI system but from my initial investigations it's going to be around the £800 (might add I just missed out on a second hand unit over here for £600).
05-11-2020, 02:51 PM
79 quadrajet modifications
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