jet sizes

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konig44

konig44

New Member
Mar 20, 2013
46
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fort collins
I bought a Carb from thatsdax I was wondering what everyone suggests for jet sir. My engine is a 66cc flying horse with the FAX Carb and the expansion chamber from sickbikeparts.

Thanks for any help
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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best thing to do is run it and see what it needs (don't forget to wait until break-in period is done before tuning)
 
konig44

konig44

New Member
Mar 20, 2013
46
1
0
fort collins
I am past the break in period. I'm just topping out at about 25 MPH with the mentioned upgrades. I'm also 230 on an old heavy '59 jc Higgins with a 2 gallon motorcycle tank. I only out a gallon at a time in
 
biknut

biknut

Well-Known Member
Sep 28, 2010
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Dallas
First you'll need to check to see if your carb has 5mm or 6mm jets. The Dax come with both sizes, according to Dax. I have have one that came with 6mm.

Most people say the smallest one it comes with, the 70 is too rich. I would buy a 68, and a 66.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
You said a "FAX" carb? I'm assuming you mean DAX and that it is the RT?

At our altitude you'll want to go smaller on jet size. Up here, were we live the air is less dense so stock carburetors will always be a little on the rich side. Keep a watch on your spark plug color and don't be too concerned with performance until you get a couple hundred miles on the engine. You can still jet for a good 2 stroke sound but until the rings really seat and things loosen up a little you won't see what your engine will ultimately be able to deliver.

Tom
 
Wild Bill

Wild Bill

New Member
Jan 29, 2013
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Camarillo So. Cal.
The RT comes with the 75, I just finished break in and switched to a leaner fuel oil mix from 20:1 to 32:1 and changed the plug for an accurate plug reading. I ended up with the smallest jet that comes with the carb IIRC it was a 60.

With the 75 jet my speed topped out at about 27 mph also and the engine sounded way too fat, Once I got down to the smallest jet my top speed went up to 35.6 mph and the plug looks right. Im at sea level and you are much higher in altitude so im not sure what jet you will need.

Oh ya I weigh about 215.
 
Last edited:
konig44

konig44

New Member
Mar 20, 2013
46
1
0
fort collins
I have a couple hundred miles on the engine. All my spare jest I have 65 70 75 80 and 85. I should have it set up with the 60? If so at altitude should I try to go to the 65 or 70??
 
Wild Bill

Wild Bill

New Member
Jan 29, 2013
478
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Camarillo So. Cal.
The smallest jet in the set that comes with the carb is the 65 and thats what I am running. If you are familiar with reading plugs, check your plug and if it looks too rich go to the next smallest jet then test run and look at the plug again. If you change the jet it is helpful to use a new plug if you have one so you get an accurate reading with the new jet. Are you still running at break in oil mixture, if so that can make the plug look too rich, I didnt lean the jetting down until I went to a leaner oil mix after break in.
 
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