david r simpson wrote:
>
> To List
>
> I just recently got my 76 spitfire back on the road, and have replaced the
> Stromberg carb and reinstalled
> ....... The spark is fine & plugs are not fouled.
>
> Dave Simpson
> NE Ohio
> 76 spitfire
>
Dave
If it was not hesitating prior to installation of the old carb, look
first at the carb set up you are running.
A late ZS CD150 is very sensitive to everything: stuck choke valve,
messed up run-on valve, worn thottle shaft leaks, wrong air cleaner, the
list goes on.
Try plugging off that vac hose that goes to the electric valve between
the carb and the canister. Then cap off the vacuum fitting that the
distributor vac attaches to. (Idle rpm may go up, but thats OK for
testing here). Remove, clean and perhaps use a blanking gasket to
temporarily completely seal off the choke (acutally a cold start
valve). This will remove the possiblity of leaks or fuel dumping
through this avenue.
Make sure the main needle is in good shape. If it is the adjustable
type, follow the Haynes instructions explicitly. It works, but is
confusing. I found VERY little range of correctness on my 79. The
slightest bit too rich, and the cat glows red hot. The slightest bit
too lean, and the car runs poorly. You will need the special hex key
wrench, of just a long hex key and hold the carb piston TIGHT as you
turn the wrench. (otherwise you torque out the diaphram).
Make sure the piston and related parts are REAL CLEAN and oiled.
Speaking of oil, try different weights of oil in the carb piston. This
will change the response speed of the piston to various air flows
through the carb. Try thicker. Up to 90wt even. The longer the piston
stays down as the air flow increases (from more open throttle), the more
air velocity there is through the carb. The more velocity for a given
air mass, the greater the depression (low pressure). Hence the CD.
Constant Depression. (This is a term of carburetor physics, not owners
of smogged cars). The greater the depression, the greater the suction
over the fuel jet (the hole the needle rises and falls in.) Hence the
richer the mixture.
Another way to mess with the CD is to alter the spring. I recommend you
measure your uncompressed spring length first. Note this for retrofit
if necessary. Or use a second spring to experiment with. Stretch the
spring, trying various lengths. Add,say, 3/4". See how it works. Keep
trying.
This is how I solved a performance problem when I went to a free flow
air filter. The stock air cleaner really restricts air flow, and if you
free up air flow, it throws off the rest of the system. So the spring
adjustment compensated. This spring adjustment issue is the last
effort, not the first. You do not want to be using the spring
adjustment to compensate for some bonified problem that should be fixed
of itself first.
Happy wrenching. Happy driving
Brian N
65 Spit (Weber downdraught)
79 Spit (Weber downdraught) Except for smogging
63 Consul Capri (Weber downdraught)
Can you guess which carb works best?
|