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Carburettor jet size
Posted: 21 Aug 2021, 12:10
by Asw
Hi.
My CU engine has twin Brosol 40 carbs. One runs really well the other is very rich. Does anyone know what the stock jet sizes should be so I can check? Thanks in advance
Re: Carburettor jet size
Posted: 21 Aug 2021, 14:33
by bigherb
Main jet 135, idle pilot jet 50
Re: Carburettor jet size
Posted: 21 Aug 2021, 14:47
by Asw
Thank you
Re: Carburettor jet size
Posted: 10 Sep 2021, 21:19
by Asw
Just an update. Finally had time to strip the carbs and they were fitted with 145 / 60 jets. From what bigherb said it’s no wonder it was running a “little rich” . So I’ve got 135 / 50 and a lean option of 130 / 45 on there way.
top tip Don’t trust websites that say jetted for a standard……. Engine….
Re: Carburettor jet size
Posted: 11 Sep 2021, 19:43
by Rosie n' Jim
You say that one runs well, the other runs rich. Are you judging this from colour of plugs? Assuming you plan on changing both left and right carb jets, you will still need to address this. Running lean with the CU engine will cause damage, rich won't.
Start by balancing them at idle and at 2-3k revs. If that's okay, there may be a blockage in one carb, or an air leak at or after the carb. I'm also assuming you are using the standard airbox?