BillJ

My Feedback: (19)

Good in knife ...but sags like its rich when inverted...Can this be caused by rich low end needle ? Have a plate blocking the diaphram hole...

pe reivers

Our gas engines use chainsaw carbs. They do not go rich by just a change in orientation.
It is the pressure differences at the carb intake and diaphragm that alter the carb mixture in flight, so that is where you have to find the solution to the problem.
A cover plate is not a solve-all. Do a search for rich mixture. The subject has been discussed ad infinitum.

wifpwcf

hi bill,you need to solder a tube of the diaphragm hole & run a tube of it then run it into your fuse.
If it is still doing it you need to lean your bottom end.maybe do that first then run the tube
cg

pe reivers

Lean idle mixtures may cause your plane to crash. The flame-outs on gas engines I have seen were mostly due to the idle mixture being too lean.

DMcQuinn

My Feedback: (13)

I have been fighting a similar issue with my 3W 100. look for a long thread titled "3W 100 quits in knife edge" http://www.rcuniverse.com/forum/m_5133372/tm.htm

It is not due to in-cowl pressure. my problem is duplicatable on the ground with the cowl off. I think the engine goes rich when rolled on to its side or inverted. Fuel puddling someone called it. leaning the NV seems to help.

pe reivers

Good point. On some engines fuel puddling occurs, and may easily be mistaken for a carb going rich. However, the effect of puddling is shortlived, whilst a carb going rich due to extra reference pressure on the membrane will last as long as the adverse condition lasts. If an engine stays too rich as long as it flies inverted, or knife edged, or whatever, you can rule out fuel puddling.

DMcQuinn

My Feedback: (13)

Thanks, Pe. My issue only happens after the engine has idled in the upright position (carb on the bottom) for a while. At any medium throttle setting or faster it runs fine.

BillJ - does your issue happen at idle, full throttle, in-between? Have you tried it on the ground? (I remove the wings so I can pick up the plane while on the ground)

BillJ

My Feedback: (19)

I have tried mine at 1/3 1/2 and full ......Flip it upside down and it sags like its rich or dropping off....Go upright it comes right back up....I haven't tried eqtended inverted flight for fear of a flame out

rcdude7

My Feedback: (264)

Is this a rear carb 120 (120iB2)?

BillJ

My Feedback: (19)

Bottom (front) carb model