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Tools: reciprocating saw, files, coat hanger wire, tubing cutter (for
the copper).
Parts: 3/4 inch copper tube, hose clamps, maybe hi-temp silicon sealant,
maybe heat riser gaskets and new bolts.
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The photo is a tad dark. This operation took place with the stock carb
and manifold, before the weber carb replacement. In the photo you see
the stock heat riser, with a 3/4 inch copper pipe clamped on. The car
was running bad, so I thought, maybe it's a cold manifold problem (not
likely in summer - it turns out to have been vacuum leaks). Anyhow,
I decided that the heat risers needed to work. They were totally blocked.
Getting a wire around the bend is impossible. So, I cut off both ends
with a reciprocating saw (aka SawsAll). The dotted line is approximately
where the heat riser is cut. I shoved a coat hanger wire in there rotating
constantly until I had drilled it through the blockage. Repeat on the
other side. It's a tiring, dirty operation. Happily, 3/4 inch i.d. copper
water pipe fits nicely as a sleeve to join the cut ends. I cut a slot
in each end of the pipe, and clamped with hose clamps. Seemed to work
well.
Now that I've put heat risers in my new intake manifold, sealed in
only with hi-temp silicon, I wonder if hi-temp silicon would have worked
here?
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When a Bug has a merged exhaust, this is almost always also an extractor
exhaust. The flow of gas out the merged part actually creates a negative
pressure on the cylinder that is not on exhaust stroke.
The result is that if you are using a modern, merged exhaust instead
of the factory exhaust, your heat riser is almost totally useless. Note
the negative part of the graph on the left. Hot exhaust gasses have
little positive flow. Instead, they just move back and forth.
I have confirmed this. My exhaust pipe can be very hot, and the heat
riser will be tepid or actually cold.
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