Here...
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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.
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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. |
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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. |
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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. |
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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. :) |
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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. |
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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. |
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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. |
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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. |
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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. |
UPDATES: |
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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. |
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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. |
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Click
an image to view a larger version. |
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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
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Venturii |
Main Jet |
Idle Jet |
Pump Jet |
Air Correction |
Emulsion Tube |
30mm |
1.45 |
0.65 |
0.75 |
1.60 |
F24 |
Stock 1600TP
with a 1 1/2" 4-1 header and twin mufflers
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Venturii |
Main Jet |
Idle Jet |
Pump Jet |
Air Correction |
Emulsion Tube |
30mm |
1.55 |
0.70 |
0.70 |
1.65 |
F24 |
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. :-)
Log:
Carb and manifold fitted: May 2005
Air box fitted: Nov 2007
Warm air tube fitted: Jan 2008 |