Thursday, June 21, 2012

Problem solved? Kinda

This may get confusing. 
Tis the nature of the DCOE

So I had a lean pop at the transition between the idle jets and main jets
Anytime you'd power on the throttle, VS roll on the throttle, the carbs would backfire
After a bit of research I decided a change in the accelerator check valve was needed
The accelerator pump itself can be altered to tune the lean spot out... 
...but a former Weber employee disapproved
You only need one check valve per carb
They are easy to take out, but the location makes them a pain to install

See item 12

Old accelerator pump check valves were 55s (.55mm bypass hole)
Changed to 35s (.35mm bypass hole)

Lean pop during transition pretty much disappears
Middle carb is still popping a little tiny bit
I think I know why
Much improved and good enough for now


So the Z runs pig rich at idle, 500rpm
Tried messing with the fuel pressure
No luck
Went from 60F9 to 55F9 on the idle jets
No luck
Messed with idle speed
No luck
What was the next logical step?
Even smaller idle jets

Package from Italia

Ohhh shiny idle jets


Scared him

New Jets in the stack

So started it up and still runs pig rich
Switched back to 55F9s
I've realized due to my high duration cam the engine does not pull enough vacuum @ idle
Therefore the fuel has trouble atomizing and burning completely
Out the exhaust it goes
I'm not sure if there is anything I personally can do about it
I may have to take a trip back out to Rebello to see if they can get it sorted

On a side note with the smaller jets the lean pop was horrible on transition
maybe I will go to 0s (no bypass hole) on the accelerator pump check valve
This will basically not allow any fuel to be put back in the float bowl during the transitional period
That should eliminate the lean pop completely
If not I've got bigger problems

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