Owen: My experience with clogged heat risers is that any problem I've
ever experienced is worse in cool damp weather rather that cold
weather or hot weather. Carb icing can make the car run really
rough, barely idling. Do you notice any frost on the manifold? On a
38 degree day with a light mist falling I used to get a significant
frost buildup on the manifold throat right below the carb, even
after a fairly long highway drive. Several methods for unclogging
the riser including the clutch cable-roto-rooter method (See John
Henry's site of technical help at
http://www.thebugshop.org/gotech.htm scroll down to "Clearing carbon
clogged heat riser tube"). The other method is the oxy-acetylene
torch method where the torch is used to heat the carbon plug to red
hot and then the acetylene is cut off an oxygen is used to combust
the carbon out. Real easy except that you can burn a hole right thru
the riser if you're not careful and be forced to get a new manifold.
Before you do any thing, though, check for vacuum leaks along the
air-fuel path. Rough idling is often a symptom. Most folks recommend
spraying WD-40 around the manifold boot joints and gaskets to see if
a change in engine speed occurs (signifying a leak drawing in the
WD-40). Check also to see if your idle cut-off solenoid is loose or
working properly. Maybe others will have some more ideas. Good luck.
Clancy
Owen wrote:
>
> Hey there - I've got a 1970 Campmobile with a 1600, and have had
some
> problems with idling, and with the engine cutting off when I let off
> the gas quickly after revving the engine. The carb is fairly new -
> less than a year - as are the fuel pump and filter. I'm pretty sure
> I've got the carb tuned right, and it's clean.
> I was wondering if these would be symptoms of a clogged heat riser
> tube - when I pulled the engine last summer to install new rings,
> heads, valves, etc., it was clogged and I wasn't able to get it
> unplugged - I put it back on as is, thinking that I would deal with
> it another day. I've probably put less than 100 miles on since the
> work I did, and it was running fine until recently. Has the day come
> for me to deal with that heat riser tube? I wasn't sure about the
> effect on the engine of a clogged heat riser, and thought you guys
> might have some input.
>
> Thanks for the help,
> Owen
>