rotax carb

Amongst all the weighty deliberations on improving safety,
maybe someone experienced and knowlegable about diaphrgam carburetors
could give me guidance.
I fly a PIK 20E , Rotax 501 unreliable engine which has been behaving erratically, surging but not misfiring that I can detect.

From the plugs I see rear cyl lean, front cyl a bit rich.
Does a split carb diaphragm enrich or lean the mixture?

thanks

John F

On Friday, May 15, 2020 at 8:34:29 AM UTC-7, john firth wrote:
Amongst all the weighty deliberations on improving safety,
maybe someone experienced and knowlegable about diaphrgam carburetors
could give me guidance.
I fly a PIK 20E , Rotax 501 unreliable engine which has been behaving erratically, surging but not misfiring that I can detect.

From the plugs I see rear cyl lean, front cyl a bit rich.
Does a split carb diaphragm enrich or lean the mixture?

thanks

John F

I am surprised that it runs at all - the diaphragm is critical for regulating fuel flow thru the carb:
https://www.youtube.com/watch?v=jWBre4-tHsg
You need to overhaul the carb which includes replacing the diaphragm.

Tom

Before you get too excited about pulling that carb apart check the rubber mount between it and the engine. I’ve heard of them cracking out.

On Friday, May 15, 2020 at 11:34:29 AM UTC-4, john firth wrote:
Amongst all the weighty deliberations on improving safety,
maybe someone experienced and knowlegable about diaphrgam carburetors
could give me guidance.
I fly a PIK 20E , Rotax 501 unreliable engine which has been behaving erratically, surging but not misfiring that I can detect.

From the plugs I see rear cyl lean, front cyl a bit rich.
Does a split carb diaphragm enrich or lean the mixture?

thanks

John F

An air leak was found at the shutoff valve , and fixed.
The carbs were pulled and the diaphragms examined; one is a bit stretched
but no holes found. Search for Tillotoson HC spares unsuccessfull.
Rebuilt everything with diaphragms swapped.
Engine now runs smoothly slightly lacking full power.
Rear cyl still hot as shown by EGT.
JMF

An air leak was found at the shutoff valve , and fixed.
The carbs were pulled and the diaphragms examined; one is a bit stretched
but no holes found. Search for Tillotoson HC spares unsuccessfull.
Rebuilt everything with diaphragms swapped.
Engine now runs smoothly slightly lacking full power.
Rear cyl still hot as shown by EGT.
JMF[/quote]

Hi John

I had a Pik30E in an earlier life and the rear cylinder always ran hotter due I expect to reduced cooling airflow as it is partially shielded by the front cylinder.

Regards
Brett