Author Topic: Mid Jet/Lift Control  (Read 527 times)

Offline MS

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Mid Jet/Lift Control
« on: May 18, 2019, 05:19:33 AM »
Hello everyone from up here in north Dakota. I just picked up an 07 GS500F for 1800 with only 1500 miles on it! The local Honda dealer got it on trade. I just happened to get there before they serviced it at the busiest time of year and they were ready to deal :icon_twisted: Then I found this awesome online community and loads of info. This bike seems to have quite a following :woohoo:

Anyway there are the obvious signs someone was already into the carbs (pilot screw caps gone) but they need to be done again. I tried fresh gas and it wound up in the crankcase. Good thing it needed a battery too or I may have tried starting it. I took them apart and was cleaning the jets when I discovered something about the mid jet (60). I hit it with cleaner and it sprays out near the top of the inside of float chamber? So I cover the hole, look through the bore and main jet passage and hit it again. Nothing. Plugged? So I look at the direction of the passages and they seem to head up to the top of the carb. I open the choke and hit it again and there it is. Choke port.

Bottom line is, I'm pretty sure that number 60 Mid jet is just the choke jet. I also think the reason parts websites call it a main jet is because that is the type of jet it is, not necessarily what it does. I have had probably between 40 and 50 bikes over the years and picked up almost all of them cheap because of carb issues, so I have seen a few things. Please correct me if I am wrong, but if I am not, there may be some jetting specs/data out there that need to be corrected.

I'm almost positive the lift control is just an amusing last ditch effort to run lean while avoiding an accelerator pump or full blown FI. It tames slide lift for less waste, better atomization, hides flat spots, ect. Jetting can eliminate the need for it with better power/acceleration but probably way less economy.

Also I have some pretty cool tricks for jetting that I haven't seen discussed yet here if anyone is interested. It is indeed a black art and I will keep you posted as I go.

Offline herennow

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Re: Mid Jet/Lift Control
« Reply #1 on: May 18, 2019, 06:46:43 AM »
Correct on the mid jet being a choke jet. There was a long thread I made way back where we identified that,along with lots of other carb jetting questions. Got a bit academic  but I'm really comfortable with carbs now.... especially because I had carb problems on an old britbike at the same time (which turned out to be something else entirely, but that's another looong story)