pungent

Ok been going to do this for a while and finally got here. Firstly for most of the general specifications etc it's a good idea to get a Gregory's manual for the VH or VK 253-308 as most general settings are all in there. For a more performance tune check out this thread tunning a carbi and this will sort out any problems you may have. One thing I will mention is quadrajets are very tempermental if the gaskets are old and the accelerator diaphram is worn, so I highly recommend buying a new kit to put through your carb if you seriosly want it to operate properly no if's or but's on this one as there only about $50.
The carb I will be putting pic's up of will be a later model carb of the VH to VL commodores and I highly recomend if you have a earlier carb try and get hold of one of these ones.

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Can i just do one more burnout please.

pungent

What I am showing are modifications and nothing to do with tuning the carb and will not help your carb run correctly but if your carb is running correctly will help it perform much better. I will also assume you already have a reasonable understanding of the carb to start with. Ok I will start with opening the secondary passages as there is a restriction half way up due to the factory casting. You will see the spot circled in the pic there are two plugs, these are located at the bottom of the secondary passages. What we have to do is remove these two plugs. I find using the angle grinder very lightly scimming the surface area where the lip is till the lip is gone and it becomes smooth to be very effective. Now the trick here is being able to reuse the plugs so what I do here is drill in the centre of both plugs deep enough to get a small easy out in. Put the easy out in and keep turning and the plug should spin and slide out and what you are left with is what you see in the second picture.

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Can i just do one more burnout please.

pungent

Now here you need a 5mm drill bit and very carefull hands. I wont put pics up for this as I dont think it will help. Look down the secondary passage from the top and then look through it from the bottom and you will see half way up there is a big turn creating a restriction. What you have to do is drill from the top and bottom carefully to remove the restriction But if you drill to deep either up or down you will put a hole out through the side of the carb. If you mark the drill bit with a texta 1/4 inch from the tip and don't go past this point up or down and then go little bit further at a time looking through the passage till the restriction is removed. First pic is a undrilled one and the second pic is a drilled passage and you can see the difference.

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Can i just do one more burnout please.

pungent

Make sure to blow the passages out really well after drilling. Now if you drilled to deep into the plug as I did in the pic and go through the otherside,fill the drill hole up with fibreglass so it drips out the bottom and when the fibreglass sets sand the base of the plug smooth so the fuel can run smoothly across it. To refit plugs I put a tiny coating of fibreglass around the top edge then insert the plug back into the carb and cover the top of both plugs with fibreglass to make sure they will not leak. In the pic you can see it looks a little messy but you can sand it smooth but really nobody is going to see it.

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Can i just do one more burnout please.

pungent

Ok next step is to make the secondary's much crisper when you snap the throttle. What you will see in the picture on the outside fuel tubes are 4 small holes. These holes start 5mm from the bottom and are at intervals of 2.5mm. The size of the holes are obtained using a 1mm drill bit. To do this file one edge of the tube slightly flat and prick punch carefully and drill very carefully all the way through both sides. It don't matter if this job is not done perfect but as long as it's all very very close to the measurment's I have said. What this does is helps draw the fuel out much quicker for the first little squirt of fuel when the secondary's first open. The 2 inside tubes are for the main part of the secondary's . So what you do here is push them up through the carb body till they are only through the carb 1 inch and once again at this height it will let the fuel move up to the secondary's passage much quicker. You may have to pull the inner 2 tubes out and polish them very well or very lightly sand them with 1500 wet and dry to be able to slide them up through the body.

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Can i just do one more burnout please.

pungent

Now for the last little secondary trick. What you do is get a straight edge and scribe a line from centre of the tiny little fuel hole that is just above the secondary air flap's all the way down to the centre of the hole in bottom of top of carb. Now drill two holes just below where the secondary flaps close once again very carefully. You will have to remove the airflaps to do this and will have to go at a slight angle upwards. drill in untill you go through to the existing tunnel going to the top holes. Fill the top holes with fibreglass and sand back smooth. What this does is instead of the air flaps having to open and then create air flow past the holes to start flow of fuel, as the secondarys open and the air starts to open the air flaps the air is already passing the holes so the fuel will come through much quicker. In the picture you can see where I have moved the hole from B to A but you can probably move it down a little further than this.

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Can i just do one more burnout please.

pungent

One little mod that I will mention I dont recommend doing unless you suffer really badly from a flat spot when you are doing a burnout and opening the secondary's and shutting them quickly on and off. In the picture you will see a small hole, what this does is let fuel run into the small fuel storage area for the tubes that feed the first part of fuel delivered to the secondary's. Due to time filling up you may encounter a very small flat spot with on off full throttle driving due to this small resiviour not having enough time to refill. You can drill this hole out larger BUT BUT BUT in doing this if you are drag racing under full throttle and the hole has been drilled to large your main fuel supply from the bowel is being upset as the fuel now wants to move towards these holes instead of the secondary's jet holes. IF you do decide to modify this due to the mentioned flat spot go in very small incriments with drill sizes.

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Can i just do one more burnout please.

pungent

With all these mods done you should now be able to tune you secondary's so they will come in a lot quicker and harder.The primary's have not been touched so you will hold the same econemy but gain better performance. I have not been as detailed as I could have been and could have put up more pictures but if you don't understand what I have done here I personally think you should be looking at the tuning link I put up at the start and when you understand how to tune and rebuild properly you will be able to understand and do the mods. Just to finish off secondary metering rods should be changed if you have modified the engine, the picture has the standard DP rods that came out in all the standard later carbs and also a set of CV rods to show the difference in diameter. Hopefully this info can get a little bit more out of the quadrajet for you as these mods have worked wonders for me and a few mates cars. Happy quadrajetting.

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Can i just do one more burnout please.