LCGB Forums

Hi all, I had a great running casa 185 set up but ancellotti a bit tiny/ loud for local Swiss authorities so have flipped to the deeper and very well built BGM big bore. Sounds great and quieter however it is now running flat at last 1/4 of throttle turn...I am running a 28m dellorto phbh carb through a ram air filter.

Main jet jet is currently 108. I am not too techy / experienced re carbs ( needles vs atomizer etc) . Mb have recommended and I have ordered some bigger main jets, but before they arrive thinking if there may be some other thoughts out there on what to do?

Thanks

Hi. Main jet seems far too small. I bought a ram air, the longer one. Did not like it at all as it had the same symptom's as yours. There are many historical jetting threads on here that may help, you will just have to search. Carbs on these bikes are pain as you will read in due course. I now run a 30 mm Oko on a 48 mm Clubman. If I had a standard crank I would go back to bog standard. Good luck.

Main jet doesn't seem far too small at all however I would go up 2 to 110 or even 112 then do some plug chops. I went up x2 when making the same change and all has been fine since.

Ram air filters are a little bit restrictive also, I prefer the breathe sweet.

Rich'

update: jets came..went 1 up from 108 main to 110 and then 112 and did chops and plug looked great..smokey grey/tan..very clean, but still was lumpy/bogy from 3/4s throttle up..given i am doing the euro in a couple of weeks have put the Ancelotti back on and will have another go/look when i return..shame because the MB is a really well built exhaust with some well throught through detail, relly robust and eays fit and sounds better/quieter which is what i need

Your description of last ¼ throttle is precisely where the main jet comes into play. So for somebody that claims to be:

“not too techy / experienced re carbs”

I would say that’s good information you've provided.

Now, I’m not contradicting any of the information you have received already.

But, if it were me, I’d get my head around what is ‘too rich’ & what is ‘too lean’ which is not as easy as it sounds.

Common sense (unusual for me!) suggests try & go deliberately too rich & work down.

Try a 120, say, because that should be rich but ‘safe’ & if so, will give you a comprehension of what ‘boggy’ is really like. If you get to, say 7/8th to full throttle & backing off cleans it up & it starts to pull, then yes, you are too rich. Carburetion wise, not Swiss standard of living…..

Joking aside, do you understand?

To help you more, we need to understand that you can start to ‘feel’ the difference between rich & lean.

My own interpretation of boggy is meaning too rich.

The other thing though, people often fail to check, is whether the atomiser is big enough. I suspect yours is, but a check of that is to leave out the main jet entirely. Gasp, horror! What that does is tell you if your set-up is capable of delivering enough fuel for the rest of the system to calibrate through the range.

I hope this makes sense.