Blocked Heat riser

[aab]

Busy with beetle engine , painting engine tin etc. When removing manifold found heat riser totally blocked . Is it necessary to unblock in our hot
climate ?. Thanking any help from those in the know.

[retrovan]

Best to have it open regardless of weather.

Helps with the ignition of the fuel .

Herman

[fourier]

If the heat risers are blocked, the car will not run properly.

The manifold will ice up, causing the atomised fuel to condense along the length of the manifold, forming larger fuel droplets, which will not burn as efficiently as atomised fuel.

The exhaust system also needs to be properly designed to support heat riser operation. It needs a low and high pressure tap off, to create proper flow through the riser. A lot of aftermarket exhaust systems have two tap-offs at equal pressures, tied into the no. 2 and no 4 exhaust runners, just after the exhaust port. This design does not create a pressure drop across the heat riser, resulting in no or very limited flow through the heat riser. You should have an exhaust system where one end of the riser is connected to close to the exhaust port, and the other end connected to the silencer box. This creates proper pressure difference, to have sufficient flow through the heat riser.

I have unblocked heat risers by using a length of old clutch cable in a low speed drill. Be sure to rotate the cable in the correct direction, otherwise it will unravel. I also use deoxidine (carefull, nasty stuff, bought at the hardware store) to let it soak over night. Be warned, it is not a quick job, and could take several days.

[aab]

Many thanks Retrovan and Fourier .

[retrovan]

If as said the two are connected to the same place but on different sides, you can fit a small casket on one side and a full size casket on the other, this will ensure flow, regardless of exhaust build.

Herman

[aab]

Thanks to all regarding info to clear heat riser. After unwinding the first piece of cable a few whips , and copious amounts of carbcleaner, success at last!