Dan,
This is a stumper, all right.
Are BOTH carbs suddenly running rich? Or just one?
The spark plugs will tell the tale.
By any chance did you replace the overflow tubes
recently? If they stick down below the frame, at
high speed you'll get a little bit of a vacuum
in the float chambers... viola the fuel level will
rise causing the carb to run rich.
How old are your floats? The replacement items are
the black plastic type. Still wondering if some
fuel treatments/additives might make them take
on "gas" sooner. If they are heavier, the fuel
level will increase, too. Also might explain
the need for the pressure regulator.
FUEL PUMP SWAP... any chance you left out the spacer
between the pump and block? If so, the fuel pressure
goes sky high! (3 psi is normal, suddenly you see
15 psi!).
Oh, when Pat Horne suddenly had problems with his
carb running too rich, I had joking suggested the
only thing left to check was for a muddobber (wasp
common in these parts) building in the overflow
tube. Uh, pure luck on my guess... but couldn't
figure anything else out!
Cheers,
Tom Walter
Dan Neff wrote:
> I am stumped y'all. Any idea's?
>
> Short version:
> All of a sudden my (SU) float bowls started overflowing on high speed
> downhill decelleration (and gagging and sputtering the engine when resuming
> cruise). I have Ztherapy carbs, and Scott Bruning hasn't a clue. The best
> improvement I've gotten is by putting a fuel line regulator in (with a
> mechanical fuel pump!!?) -- setting it to 2psi eliminates the problem about
> 95% of the time, but am suspicious it might be leaning it out a hair on
> acceleration (6,000rpm+) - getting intermittent 'bumps' in the acceleration/-
> power.
> I don't think I've fixed The Problem, just found a workaround. Any idea's
> what the REAL problem is?
> I'm wondering if the Grosjets could be that touchy about fuel pressure,
> except I'd still want an explanation as to why they worked fine for 11
> months!
>
> Long version:
> [When she gets mad about something...]
> Back around the end of June (I'd already put over 5,000 trouble-free miles
> on it since a valve/cam job, 10,000 miles since Ztherapy carbs), I seemed to
> have gotten a bad tank of gas. Sputtering and spitting off and on. Alternator
> seized 400 miles later.
> What's weird is about that time, I swapped my fuel pump into a 1600 to
> determine if 1600's pump was bad. When I put mine back (and replaced alt,
> checked and re-checked connectors), I started having problems with float
> bowl overflow on low-grade downhill decelleration (usually above 40mph)!
> Did plugs, points, rotor, condenser, cap, swapped an old air filter
> (being unemployed I had to draw the line somewhere), swapped plug wires,
> fuel filter, checked floats and Grosjets, and checked with Ztherapy. still
> having problems.
> Last year, my fuel line gas-tank return reed valve was leaking, so I had
> put a "T" in and run a straight line with a restrictor in it back to the
> tank. It's been fine until now. So when overflow started happening, I tried
> running without any gas tank return restrictor (leaned it out too much on
> uphill/load). Drilled out restrictor and improved it significantly. Put an
> EI distr'r in, with a 12v coil (which eliminated ballast resistor - a suspect
> at that point). Nada. 'Borrowed' a reed valve to go back to stock. Problem
> was worse!
> That's when I tried the fuel line regulator. I'm comfortable daily driving
> it at this point, but wouldn't want to take it on a road trip.
>
> thanks,
>
> Dan Neff '69 2000
> Colorado Springs, CO
> www.wycroc.org
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