140 E tube vs larger main jet

Mini Bike & Go-Kart Parts

SAS289

Well-Known Member
#2
The 140 e tube should get improvements throughout the RPM range because it's supposed to give a better fuel signal. I would think the e tube is better for the low and middle more so than a large main jet. The larger (36-39) main jets probably helps the most at higher than 3600 RPM.
 
#3
The 140 e tube should get improvements throughout the RPM range because it's supposed to give a better fuel signal. I would think the e tube is better for the low and middle more so than a large main jet. The larger (36-39) main jets probably helps the most at higher than 3600 RPM.
I always thought the emulsion tube would richen it throughout the range. When I changed the emulsion tube I thought my throttle response got better. From idle to half then cruising and going from half to full. It seemed to get rid of the stumble I had in those situations.

I've never put much thought into it. I just put the 140 e tube and I ended up with a 37 jet in my tillotson and predator. Tillotson does little more than 5 grand and the predator hits 4000 peak.

There are so many variables when jetting what works for one won't work for someone else in a different part of the country.
 

SAS289

Well-Known Member
#4
I also never put too much thought into it. I re-jetted and put in the 140 e tubes before I even rode my bikes. So I wouldn't know if there was a difference. Never bothered to try the stock e tubes. The bikes run well.

I should try the stock e tube on my stock bike with the 33 main. It's possible that the 140 e tube is too much for a jet that size. And the autolite plugs you can't really get a good read on.
 

SAS289

Well-Known Member
#6
True, that. I can feel a performance/tuning difference between a hot afternoon and a cool evening.
Next couple months are a good time to test for that. If it runs noticeably better at 45 degrees than it did at 85 degrees then it was too rich at 85 degrees. Then down size the jet once it gets warm again next year. An upper section of the RPM range should be targeted. You wouldn't want great jetting at 3K RPM but already leaning out by 4500 as an example.
 

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