[6pack] high RPM, won't come down

[Glenn Rattmann]

Gents,
The car is 74.5 with stock Strombergs (175 CD-2 SE) and stock engine, .
The last carb rebuild by me was probably 2002, but maybe only 4,000 
miles since then.  My occasional driver; it has about 105k miles on 
it.  The car had one DPO, he did a valve job at aroung 75k 
miles.  I'm certain carb shaft bushings were never re-done.

Problem is-- Engine hot, after a few minutes of stopandgo driving, I 
might reach say 3500 RPM in normal shift sequences.  When I let off 
the throttle during shifting, or want to decelerate, the RPM 
sometimes stays at the high peak-- like 3500!  A few frantic kicks of 
the pedal will "usually" bring things down to normal  idle-- but it's 
dicey.   There is no stumble on acceleration.

I have inspected the action of the pedal/carb linkage when car is at 
rest, and nothing there seems amiss.  So I don't think the linkage is 
hanging up somewhere (externally).

Dashpots are losing oil 'too quickly' and I always have to top them 
up after the car sits for extended periods (weeks) following, say, a 
90 mile drive.  Yesterday I pulled the air cleaner for a look, and 
noticed both carbs have oily gunk on the piston and the contact area 
of the carb bottom interface  The rear one is worse than the front 
one.  Not much doubt that the bypassing oil is responsible for the 
gunk-- but can the gunk be the cause of the symptom?

After some carb cleaner spray, and cleaning out the reachable areas, 
and adding some oil, I notice the pistons lift normally, falling with 
a normal 'click' .  Prior to the cleaning, the pistons didn't fall 
normally, but were hanging up slightly when falling.

I pulled the carb tops and lifted out the 
diaphragm/piston/needle.  The diaphragms seem ok to me (no obvious 
tears or cracks) and the alignment tab was correct.  I suppose 
"pinholes" could be there, but not visible...?   Pistons look fine, 
the needles are straight and move correctly against their spring 
action internally.

I have some spare o-rings for the dashpot oil chambers so today I 
will install them.  Could the leaking oil and subsequent gunk I 
mentioned be the cause of the throttle staying high, as 
described?  If so, then the cleaning plus adding the new o-ring on 
each dashpot should eliminate the problem.  Any comments appreciated.

I'm aware that anything beyond this procedure (relatively easy, carbs 
remain on car) will likely require pulling the carbs .  Then we are 
looking at things like butterfly hang-up... float behavior...float 
valve... bypass valves... and so on, right?

Who sells the best quality float assembly replacement?  And which 
vendor's carb rebuild kits  are "best", which partly means "they 
include the dashpot o-ring" as they should.  ISTR years ago, some 
kits didn't have that o-ring.

Thanks,

Glenn/San Diego
74.5