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In the rush for Weber IDFs and Dellorto DRLAs other carbs often get forgotten. I picked up a pair of good condition Weber DCNF 40s for £20 and decided to use one of them to spice up my stock 1600TP.

We did a dry run with one of the carbs on my brother's 1500SP (with a bought manifold) and it worked well, so I decided to go ahead and make a manifold for my car.

...and here.

1. For the main part of the manifold there are a couple of very useful parts you can buy, VW camper tailpipes! Go to GSF and ask for part number 20053 (EXH.DAMPER PIPE+BRACKET - T2 1.6 8/76 -> /79), they should be about £8.50 each.

The tailpipes are the same diameter as a stock 1600TP inlet manifold, so will fit in the stock elbows. For single port engines you can buy aftermarket elbows. I found some old EMPI ones for my brother's 1500SP.

2. Cutting the tube just next to the bracket leaves you with plenty of length.

3. Next you need to think about the carb base plate. I spent a long time carefully measuring my carb, but if you are using a Weber DCNF 40 you can use my diagram: click to view diagram. I was feeling lazy and had my plate laser cut from 5mm thick mild steel, but you could make it yourself. Make sure you use thick steel because ideally you don't want the plate to warp when you weld it.

4. Once the plate is made you can start welding bits together. Strap (or tape) the two tubes to a piece of angle iron. Use your base plate as a guide to get the spacing between the tubes correct because this is what the tubes will need to line up with. Then weld a plate between the tubes to join them. (I used bits that I cut off the exhaust pipe bracket.)

5. I used a bigger plate for the back of the manifold. If you do this remember that you will need to weld all the way around the tubes, so leave a gap to do this. I didn't and had to cut the plate after I had welded it on!

Turn the tubes over a weld another plate to the front of the manifold. You should now have a good solid join with no movement or flex.

6. For the next part it is very useful to have a spare engine! You need to chop the tubes to the correct length to ensure that you clear your generator or alternator. To do this I took off the stock manifold except for the (UK) driver's side elbow. This way I could keep chopping little bits off the tube that fitted into that elbow until it was the correct length. Remember to allow enough room for the carb base plate. Then you chop down the other side so that it is the same overall width as a stock manifold, which for my 1600 manifold was 44.2cm.

7. It is helpful to test fit the manifold on the engine to get the angle of the base plate correct. You need to angle it a bit to give enough clearance between the carb and the fan shroud. The angle that worked for me was 15 degrees. Just chop the tubes off at that angle and test fit it all to see if you need to tweak it. Balancing the carb etc can be tricky, but is possible. :)

8. I found that I didn't need to shorten the upright tubes, just cutting the ends so that they sat at 15 degrees was enough. In this photo you can see that the angle is only slight, but it gave me plenty of clearance for the float bowl at the back of the carb.

9. Once you have got the angle right you can weld the plate on. Weld the plate on slowly and carefully because you want to minimise distortion of the plate. Weld all the way around both tubes and make sure that you have no gaps. The manifold needs to be airtight.

10. To finish off the manifold you should smooth the join between the tubes and the plate. It doesn't take long to smooth out the join completely. Opening out the top of the holes so that it is a smooth transition from the larger diameter of the carb chokes to the smaller manifold tubes will also aid the flow of the fuel/air mixture.

11. With the manifold complete it is time to focus on the accelerator cable. When we fitted a DCNF to my brother's car I designed and made a plate to bolt on under the air filter. It is basically a cable stop for a longer accelerator cable that comes over the fan housing. As this design worked well I did some accurate measurements of my carb to create a diagram for the plate. Feel free to use my design: click to view diagram.

12. After spending ages cutting out and filing my brother's accelerator plate I had mine laser cut from 4mm thick aluminium. :-D (In fact I had two made, so get in touch if you want me to part with my spare one.)

I made three gaskets. One for the base of the carb, one for between the top of the carb and the accelerator plate, and one for between the accelerator plate and the bottom of the air filter.

13. With the accelerator plate on I made a throttle linkage arm out of spare bits from a stock carb. Once I had made this I could drill the hole in the accelerator plate at the place that lined up the best. I filed some thick aluminium washers at an angle to tilt the cable to take into account its path over the top of the fan housing. The stop that you can see bolted through the plate is the kind used on bicycles and is easy to get hold of.

14. Here is everything assembled ready to be fitted to the engine. You can see that I drilled the air filter butterfly nuts and joined them with an old carb spring. This stops them vibrating loose, and also keeps it easy to take off when you need to.

15. Here you can see the carb and manifold fitted. For the accelerator cable I used a Type 2 cable and cut it to length. The extra cable outer that I routed over the fan shroud was mountain bike brake cable outer.
16. Due to the lack of preheat tubes the manifold needs extra support to stop the carb from moving. My brother came up with the idea of this little mount, and it works very well. All the weight of the carb and the manifold is taken by the manifold elbows, so this 1mm thick steel plate is enough to hold the carb rock solid. The mount uses one of the carb-manifold bolts and the generator strap bolt.

U1. Due to that fact that I'm not using the choke on the carb I have found that the engine needs a little while to warm up before you can pull away. A couple of pumps on the accelerator pedal before starting, and then holding the engine at about 1500rpm for 2-3mins really helps. I have also added an electronic IMDU (Inlet Manifold De-icer Unit) to help with this.

U2. Since removing the rear scoop on my Baja I have noticed that at higher speeds in cold weather my engine struggles. To see if it was an increase in cold air being forced into the carb causing the problem I made a quick airbox to shield the carb. This definitely helped and I have since added a tube into the airbox to draw in warmer air from around the exhaust. It has definitely helped.
Click an image to view a larger version.

I have had the DCNF on for a while now and I'm definitely pleased with it. The carb (along with the 1 1/2" 4-1 header) lets my engine rev freer and higher. It isn't too great in the cold for the first few mins, but then neither was the stock carb I ran before (because my exhaust doesn't have preheat outlets). I had the engine tuned on a rolling road, and the engine is putting out about 60bhp. This seems pretty good for an almost stock 1600TP, and it feels like there is more torque than before too.

It is best to change the carb jets because the ones in the carb will be to suit a different engine. I got new jets from eurocarb, but you could also get an engine tuner to ream out the existing jets. Neither option is particularly cheap! Here are the jets that my brother and I are using in our carbs:

Stock 1500SP with a better flowing exhaust
Main Jet
Idle Jet
Pump Jet
Air Correction
Emulsion Tube
Stock 1600TP with a 1 1/2" 4-1 header and twin mufflers
Main Jet
Idle Jet
Pump Jet
Air Correction
Emulsion Tube

I have listed the jets only as a guide. If you are unsure then give eurocarb a ring, they are very helpful and can give you an idea of what you will need over the phone.

Any questions feel free to e-mail. :-)

Carb and manifold fitted: May 2005
Air box fitted: Nov 2007
Warm air tube fitted: Jan 2008