[Spridgets] Spitting carbs - again...

[Andy Webster]

Dave,
so the engine has behaved like this since you got the car?
I'd be pulling off the rocker cover and watching while the engine runs. make
sure there isn't a poorly aligned rocker pad over an exhaust valve
I'd also be looking for a valve spring that wasn't up to the task or broken,
Are all 1275s double valve sprung? I know mine is.

I'd have expected fuel starvation to cause it to die off, not so much backfire
through the carbs. Having had a dodgy SU pump in the past, the car used to
just lose power, until I thumped the rear shelf with my fist, and knocked the
pump into life.
With the air filters off, does one carb spit harder than the other? that might
let you narrow it down to either cylinders 1&2 or 3&4 or all over the place.
Have you had the head off this engine?

Andy

--- On Mon, 8/6/09, Dave G. <kk7ss at verizon.net> wrote:

From: Dave G. <kk7ss at verizon.net>
Subject: [Spridgets] Spitting carbs - again...
To: "spridgets" <spridgets at autox.team.net>
Received: Monday, 8 June, 2009, 9:46 AM

Continuing the saga; a never ending series - starring me and the many
DPO's.

Still not able to hold the engine speed abobe 2500rpm without
spitting back, I decided to strip both cabs at the same time and
compare the parts from both back and front catbs at the same time (I
hadn't done that before!)
Lo and Behold (Poetic - aint I?) the spring from the rear carb was
2.4" longer than the front one!  (Insert choice of obligatory swear
words here!)
So I took the bits of 4 carbs - both from 1275 motors, and proceeded
to match the springs, piston drop rates and needles (spring or swing
type) re-assembled and reset them, then went through the basic tuning
procedure.
Result??
Good idle at 800rpm, pistons rise at the same rate, no miss or
stumbling, nice pick up when I 'blip' the throttle, runs nice at
2000rpm.
*BUT*
If I try to hold the rpms anywhere above 2500, the carbs still spit
back!!
No manifold leaks, timing spot on, etc., etc., etc..

I'm beginning to suspect low fuel flow at higher rpms is causing it
to lean out....
Is there a simple test I can do to check how much the stock pump can
flow??
How many ounces of gas in how much time is what I'd ideally like to
know...

Sorry to be a pest.. and Thanks  ;-))

--
Dave G.   KK7SS
'65 MK III Sprite in Richland, WA

If I wake up in the morning, and I hurt, it means that I'm still
alive !!
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