jet size question
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Joined: Aug 2016
Posts: 54
Likes: 4
From: Colorado Springs
^^^^This.
I bought every jet and tuned my stock CV for not only the altitude, but the enginework I had done to it.
So your small jet comes into play between idle and 4000rpm. After that the larger jet comes into play too. It was running so rich with stock settings that carbon had built up all over the intake valve, and I regularly had to back off the throttle to maintain speed on the highway, and anything above 75mph was unattainable.
So what I did was I bought every Keihin CV Carb jet I could get my hands on, and a new emulsion tube and the easy idle adjuster screw and the easy AFR adjuster screw. After putting in 10:1 pistons and my EV13 cam, I had to do my very first tune on any engine, let alone a carb engine.
It won't maintain idle with too small a pilot jet no matter the AFR screw's location. So what you do is you start lowest you can go and then work your way up until you can't get any additional seat of the pants feel out of it. Your AFR screw should be used to keep it sounding like a flappy wet thud rather than like a car's cylinder stroke. Good news is it's most of your driving range. Also put new plugs in when you do this so you get a good baseline.
After you get that dialed in start with the smallest jet size for the main jet and go from there. Should help you quite significantly. Each jet is only like $3 so it's not a huge investment, but if you're traveling, or going to exceed 5,000 feet of elevation change for an extended period of time, you should carry your jets with you. I live in Colorado and have a 5,000 foot elevation change no matter where I go, so they're in my bag just in case. Easy change kit comes with 4 allen heads that make dropping the bowl and changing the jets a simple under 2 minute process. Worth the dough if your ask me.
I bought every jet and tuned my stock CV for not only the altitude, but the enginework I had done to it.
So your small jet comes into play between idle and 4000rpm. After that the larger jet comes into play too. It was running so rich with stock settings that carbon had built up all over the intake valve, and I regularly had to back off the throttle to maintain speed on the highway, and anything above 75mph was unattainable.
So what I did was I bought every Keihin CV Carb jet I could get my hands on, and a new emulsion tube and the easy idle adjuster screw and the easy AFR adjuster screw. After putting in 10:1 pistons and my EV13 cam, I had to do my very first tune on any engine, let alone a carb engine.
It won't maintain idle with too small a pilot jet no matter the AFR screw's location. So what you do is you start lowest you can go and then work your way up until you can't get any additional seat of the pants feel out of it. Your AFR screw should be used to keep it sounding like a flappy wet thud rather than like a car's cylinder stroke. Good news is it's most of your driving range. Also put new plugs in when you do this so you get a good baseline.
After you get that dialed in start with the smallest jet size for the main jet and go from there. Should help you quite significantly. Each jet is only like $3 so it's not a huge investment, but if you're traveling, or going to exceed 5,000 feet of elevation change for an extended period of time, you should carry your jets with you. I live in Colorado and have a 5,000 foot elevation change no matter where I go, so they're in my bag just in case. Easy change kit comes with 4 allen heads that make dropping the bowl and changing the jets a simple under 2 minute process. Worth the dough if your ask me.
Last edited by avenger09123; Aug 5, 2016 at 11:22 PM.
Thread Starter
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Elite HDF Member
Joined: Jul 2010
Posts: 3,830
Likes: 302
From: Lorain Ohio
I pulled the carb apart an it looks like it has a 45 idle an 180 main....BUT....looks like the choke cable was frozen slightly open....could this be the problem? I just replaced it an put new plugs in....hope this helps.
Seasoned HDF Member
Joined: Jun 2010
Posts: 9,332
Likes: 3,873
From: Upstate New York
A stuck choke cable will cause a VERY rich condition, since you're driving with the enrichener partly on all the time.
A 45 pilot jet should be fine once you get the choke fixed.
A 45 pilot jet should be fine once you get the choke fixed.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
^^This^^
Road Master
Joined: Jan 2008
Posts: 1,187
Likes: 8
From: Montgomery, AL
That 45/180 combo should be great. I pull 45 mpg on mine with that combo. I verify you have the choke fixed. That would make it pig rich all the time. My plugs are light with no soot like you show.
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Cruiser
Joined: Apr 2016
Posts: 134
Likes: 2
From: Ontario, Canada
I just ordered the same pairing of jets for my CV carb as the bike ('95 FXDWG) is running too lean. After reading a few CV carb tune threads and looking into kits, this pairing seemed to be pretty widely accepted.
However, I also see that guys are drilling the vacuum port in the slide, replacing the slide spring, and raising the jet needle taper...
Any comment on that, or tried/tested/true settings for the above noted jets.
However, I also see that guys are drilling the vacuum port in the slide, replacing the slide spring, and raising the jet needle taper...
Any comment on that, or tried/tested/true settings for the above noted jets.