140 E tube vs larger main jet

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.
 

toomanytoys

Well-Known Member
#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.
 

SAS289

Well-Known Member
#8
I put an NKG plug in for my ride trip this past Tuesday. After the ride the plug looks good. I guess it was around 72 degrees that day. That bike has a 35 or 36 jet in it with the 140 e tube. Only had one minor issue. It had a hard time starting hot. Had to open the choke and open the throttle a bit to start it. First time ever that it took more than 2 pulls to start it. Otherwise ran well.

In this case I may be running too lean for higher RPM operation. I didn't have the tach on the bike but I would say I never broke much higher than 4K RPM. Everything was 30 MPH or under in the recently cut hay fields I rode in.

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