Typical main jet on MHR cylinder with open air filter??

[price.is.right]

Just as title says, where should be my basepoint for tuning?

[OveRReV]

not familiar with the arreche but for a 21mm PHBG carb i start at 90 then work my way down leaner.

[price.is.right]

Actually this is a dellorto carb, sorry my sig is out dated.

[burnt_toast]

Wow 90 sounds pretty lean for a 21 with open filter..

I'm tuning at 17mm with open filter and alum 70cc and even 95main was still too lean, I've had to file it to ~100 to work

Dellorto jets are different too, their #'s are actually smaller than mikuni, I recall using a 105main in a 17mm Dellorto on my Italjet w/ 70cc Malossi and Arrow pipe with open filter

[dvsjames]

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[price.is.right]

Ok, that's good to know they may be a bit bigger than others.

I was using a 90 main and things seemed to be going good. I just thought that was small.

If I try to tune with the stock airbox on I'm thinking a 70-something main. :o

[OveRReV]

jetting has no definite setting, every engine is different, as long as the engine feels & runs great whatever size you got in there is the ideal jetting. for AC engines use a +2 to +5 bigger jetting than the ideal to allow for extra cooling effect. LC engines need to be run leaner than AC.

[florida derbi rocket]

Thank You OR.. I Always believed Humidity and temp effected a tune from day to day. Everybody wants Lawnmower reliability from a scooter, unfortunately they have a different life than the mower and need more attention.About jets? I have looked through a few hex jets and could barely see through some of them. My Dellorto 5mm and 6mm jets have huge holes for 85-105.

[price.is.right]

That's exactly what I noticed too.

When comparing the arreche jets to the dellorto jets I noticed the arreche 105 was roughly the same size as a dellorto 90.

I know these motors are finnicky and require tuning almost on the daily. I'm just trying to find a good base point/compare with other tuners ect.

Thanks guys.

[OveRReV]

you are correct in that area, my DO 115 jet has the same jet hole size as a keihin 120 jet.