here is just a little guide to installing either single or twin down/side draft carbies. Im not going in to much detail as I would recommend buying a book on the subject, and im no expert just trying to help.
To start off with obviously there are a number of different carby types that can be used in this application. I would like to link you to an awesome thread on here http://www.ozgemini.com/forums/tech/vie ... hp?t=19014.
Pretty much explains everything needed to know about sidedrafts there is to know. So there is no need for me to explain that.
So you have just bought yourself a new setup and are planning to bolt it on and you think the car is going to have trouble sticking to the pavement. Wrong…… although you bought “tuned for a Gemini” doesn’t mean they are going to be strapped on and go, you have to assume the last person to own the setup had no idea, they turned any screw they could find until giving up and selling to you, or they bought them many years ago from apparently a rally team tuned and sat in their shed until they found them buried in the bottom of the shed and sold to you.
Apart from not being tuned correctly, stale fuel has now gone from liquid to jelly to rock hard and is blocking anything it can, so that means don’t even bother attempting to bolt the setup to your car until a thorough cleaning has occurred. I would definitely suggest a complete rebuild if you want a reliable setup, either professionally or do it yourself as I have but I wouldn’t suggest unless you know what your doing.
here is mine.
Once you have a clean working carby/s it’s time to bolt to the manifold, and it is so important to use the correct gaskets and/or soft mounts. Soft mounts will honestly save you breaking the side off a carb as it can happen so easily, and without the correct good condition gasket a vaccum leak could be a tiny avoidable problem that will have you pulling your hair trying to find out whats the problem. A vacuum leak can be found by spraying a little start ya bastard or similar around the gaskets with the engine running if the revs rise you have a problem.
Next is linkages. Linkages are the number one thing to cause tuning problems, if you have twin carbs they must be in perfect sync to run properly. Im sure anyone that has twins has experienced this problem before. Stuck in the hungry jacks drive thru may even happen.
there are a couple different linkage types, the rod setup or the direct I think alfa type linkage. The alfa setup has a single adjustment to synchronise the carbies.
This is definitely the go for twins, im not sure if you can use this on downdrafts though. If you use a rod style keep away from plastic and try to use the hexagonal shaped rods to prevent slippage.
To get a base tune for first use of your twins obviously you cant use a carb balancer unless they are near synced. The method I came up with involved first setting one carby at an idle setting where the butterfly is slightly open, where I then used a torch to shine from the engine side of the manifold and i was able to see how much light was visible through the small opening of the butterfly. The amount of light should be the same on each barrel of the one carb, if not the butterflies may need to be adjusted on the shaft. Then do the same thing on the second carb and adjust the linkages to achieve the same amount of light. Try different idle adjustments to allow more or less light to achieve a better result.
To fine tune the settings I first set the sweep adjustment on my dellorto’s all the same and placed my mouth on each barrel and compared the amount of back pressure on each carby. I did this a few times with different idle adjustments to get a better feel, I found I was close on my initial setup using the light and then double checked again with the torch to see if it still looked right. This should give you a good enough sync to drive the car, somehow I pulled it off well enough for the car to run amazing so hopefully this works out for you too.
So to mount the carbies to the head a couple things may change, seeing as these carb setups are mainly designed for race setup you will find things such as pollution gear and heater hose fittings missing, depending on your manifold will depend on what will and wont be there. There is usually methods to keep your heater but if you don’t you can use 12V hair dryers to keep it legal for demisting purposes. There is a hose on the front of the head that runs to the standard manifold, Its pretty much a water bypass for when the thermostat is closed, it can be just blocked off at the front of the head, but I wanted to keep it as I feel more confident with it set up correctly. I removed the old rusty fitting and tapped a fitting into the head to run a braided hose to the manifold.
As for pollution gear the main thing is the rocker cover breather that must be plugged back into the air filter, if running filter socks this is really difficult I ended up running a hose under the edge of the sock and cable tied it there.
So you have removed the old manifold and gone to bolt on your new twins and found they hit the brake reservoir, the solution is a remote reservoir. This can be done by using a Tx setup, mounting the standard reservoir remotely or using another cars remote reservoir. Old RWD mazda 323 is perfect, you want the reservoir and the push in plugs that go into the master cylinder.
I mounted my Td/Tc reservoir by flaring some aluminium tube and gluing it onto the bottom of the reservoir to allow a good fitting for the hoses to mount. I also used some nylon right angle pipe fittings that are barbed and fitted tightly into the rubbers in the master cylinder. I bought these fittings from Bunnings in the irrigation section. In some cases the master cylinder can be avoided by using a spacer under the drivers side engine mount for some extra clearance.
this is my setup using the Td/Tc reservior.
Lastly after correctly fitting the manifold to the head and connecting all water hoses and wiring for temp sensors, you will find a few extra wires that are no longer needed from the old carbies solenoids. You will also need to have the correct fuel pump setup, im pretty sure a standard electric or mechanical pump is fine for most setups but I would definitely recommend a fuel pressure regulator especially if using a higher pressure high flow pump, the wrong fuel pressure can cause flooding and fuel level problems so a regulator is a great idea.
So hopefully this should give you a good idea on what is required to fit side or down draft carbies and answer a couple common questions and be able to synchronize twins enough to run until a carb balancer can be used, but first read through the thread i linked at the start for jetting for a good start.
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