I sent this over to Vintagebus a while back, and have a few replies, but I
thought I'd see if anyone over here still has an upright!! :)
Sorry for the ska ref...
I have been battling carbs for some time now, and have at last decided that
my REAL problem is:
Excess fuel pressure.
I finally got the 30pict1 that I had rebushed by Rimco to work pretty darn
good, but still have the initial problem I started with, ie, waaaay too
rich at idle, boggy takeoff, excess consumption at all speeds.
I've come to this conclusion since I have had the problem with four carbs,
including 3 different models.
I am currently running a stock 1600 sp, with the 30P1 and a 205 (67 bug)
vacuum dizzy. So my soggy bottom can't be due to a 009 - in fact, the 009
gave me a HECK of a kick off the line, where the 205 doesn't really seem to
cut in until 2800 rpm. Advance curve is on spec and smooth according to
timing light. Timing total is slightly high at 32 deg, which helped both
idle and pickup; I keep a cocked ear for ping!!
Acceleration is slow but steady up to 35 or 40, and then the thing audibly
winds up and gets GOING.
I have a 117.5 main, a 130y emulsion tube, the non-crimpy kind of
accelerator squirter tube, and the accel pump is on its innermost (smallest
squirt) hole; the float is new, and the needle valve has two washers under
it, one fiber and one brass.
Putting the accel pump on the big squirt setting causes black smoke and
engine to stall, classic overrich stuff; same problem w/ higher size main,
or smaller emulsion tube.
Have tried 3 diff fuel pumps, and got varying results:
Brasol 'generator' model had a weepy check valve (would allow gas to siphon
thru it when parked after running), so I replaced it with a alternator
style Bocar. Recently I changed that to a Brasol T3 pump. At first, all 3
were shimmed to book, 13mm. Each one was then shimmed up in an effort to
lower the fuel pressure; only the original gen pump really responded to
that, dropping to 2.5 psi at 3000 rpm. The alt pump dropped from 3.5 to 3.
The T3 pump has REMAINED at 3.5 psi with every shim - right now, there are
a total of EIGHT shims under it :P
Pushrods were the correct ones in each case... I even dug out one w/ the
point worn down to try and help on the T3!
So I am thinking that A) ya, too much fuel pressure.
B) this leads me to under-jet my carb in an attempt to lean out idle.
C)This is causing my doggy acceleration.
D)When the emulsion tube takes over, it is closer to what the motor needs
in total air/fuel mixture, and the car clears its lungs and gets moving.
Does this seem reasonable?
Its also possible that even w/ the 117.5, too much gas is getting to the
lowend and accel circuits and I am actually still drowning the carb; the
emulsion tube is closer to correct for the mixture it is seeing, however.
I am puzzled as to why 3 pumps would all read too high (tho it might be
possible that the T3 pump ALWAYS puts out this psi... anyone have a T3
Bentley to look?); the only thing I can think of is the distributor drive
gear - would too little play here cause this, ie, too many (or too-thick)
shims when installing the drivegear?
Any other suggestions?
It seems from the folks who did reply that most 30P1 runners have something
like a 125 main and a 140 or higher emulsion; if I can cure the excess gas,
I bet that's close to what I'll end up with.
But this excess fuel problem has me jiggered.
BTW, I noticed some needle valves are stamped 1.5, some 2.5, one I have
says 2.7; is this some sort of pressure ref?
Craig K
70 Neunsitzer
65 Pritschenwagen
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