Carby JET Sizing Question?

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Jul 2, 2016
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#1
Ok I'm interested in tuning my MB ASAP. I have several Jets already and I'm prepared to solder and drill if need be. What I'd like to know is that since I'm at a lil over 700 feet above sea level here in Erie PA. has anyone adjusted their carb to this level or does someone know the approximate jet size? Thx
 


FurryOnTheInside

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#2
I think it's probably a bit rich with the stock jet but you won't damage the engine running it a little bit rich. Just make small changes, one or two sizes at a time until you get the four stroking reduced to what you feel is right. I think it's really nice when you get to hear that little pop pop! anyway. :)

Your elevation is only one factor that's particular to your engine; there is also your air filter, your porting work, the effectiveness of the scavenging, your tuned pipe.. So many factors that, I believe, you really have to find the right jet by riding, feeling what it's like, and seeing what works for you.
 

Street Ryderz

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#3
Ok I'm interested in tuning my MB ASAP. I have several Jets already and I'm prepared to solder and drill if need be. What I'd like to know is that since I'm at a lil over 700 feet above sea level here in Erie PA. has anyone adjusted their carb to this level or does someone know the approximate jet size? Thx
With a more or less stock engine it can be ports cleaned or not at 700 ft and stock or simular 14-15mm carb start at #68 if still four stroking try #66 if not your good then run it for awhile see how it is and read the plug.there's many threads I'm sure that can guide you through jetting and how to read the plug.
 

gary55

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#4

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#5
I read up on jetting in the threads and while learning alot I did't see a particular jet size for my footage above sea level. Since this is mt first MB I wasn't sure what a tuned engine should exactly sound like, hell I just learned what 4-stroking was a few months back. I didn't know so many things play a part in jetting as FurryOnTheInside pointed out, I thought it was just the sea level but this is what makes me a newb and thus this thread.
 

gary55

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#6
I read up on jetting in the threads and while learning alot I did't see a particular jet size for my footage above sea level. Since this is mt first MB I wasn't sure what a tuned engine should exactly sound like, hell I just learned what 4-stroking was a few months back. I didn't know so many things play a part in jetting as FurryOnTheInside pointed out, I thought it was just the sea level but this is what makes me a newb and thus this thread.
Yes their are a lot of variables. Smaller jet with a tuned pipe, larger jet with a reed intake, but the chart will give a good starting point on a relatively stock engine. Ryderz is probably pretty close with a 68 summer and a 70 winter if stock or close to stock engine and carb..
 

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#7
Hey I'm from pa too south of ya. I want to know what jet I would need for my 74cc build I'm thinking of using a 19mm delorto clone what size jet would I need a #90? its 48mm x 41mm stroke and 40mm port.
 


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