jet size question
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Elite HDF Member
Joined: Jul 2010
Posts: 3,830
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From: Lorain Ohio
jet size question
my bike is running very rich...I thought I'd adj the AFR adj...I tried to turn it in to back out to 2.5 turns for a base starting point, turns out it's all the way in. I'm off the week of labor day an plan on taking a look at it then.....should I down size the idle jet one size or two? I don't know what it has in it now so I'm just going to take a look an go a smaller one.
Seasoned HDF Member
Joined: Jun 2010
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From: Upstate New York
It would help if you mentioned what bike you have and what carburetor you're running.
The pilot jet and mixture screw tune the mixture from idle to 1/8 throttle in general. If you're running rich at larger throttle opening you will need to look elsewhere.
On a Keihin CV carb, the mixture screw meters fuel, and turning the screw in leans the mixture. On a Mikini HSR, the mixture screw meters air, so turning in the screw makes the mixture richer.
The pilot jet and mixture screw tune the mixture from idle to 1/8 throttle in general. If you're running rich at larger throttle opening you will need to look elsewhere.
On a Keihin CV carb, the mixture screw meters fuel, and turning the screw in leans the mixture. On a Mikini HSR, the mixture screw meters air, so turning in the screw makes the mixture richer.
Last edited by Uncle G.; Aug 5, 2016 at 09:36 AM.
Seasoned HDF Member
Joined: Jun 2010
Posts: 9,324
Likes: 3,869
From: Upstate New York
Poor fuel economy is usually an overly rich pilot jet or jet needle. A well tuned CV carb is capable of 45-50 MPG on the highway (at least that's what I used to get with mine).
What air cleaner/exhaust are you running? Have you changed anything lately? It sounds like the pilot circuit and/or jet needle is very rich, or you're running it VERY hard.
What air cleaner/exhaust are you running? Have you changed anything lately? It sounds like the pilot circuit and/or jet needle is very rich, or you're running it VERY hard.
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Elite HDF Member
Joined: Jul 2010
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From: Lorain Ohio
I don't run hard a lot but I'm not afraid of the throttle either......the plugs look pretty black after a few tanks of gas. I'll take a pic of the ones I just took out if I still have them. The first time I changed the plugs they were showing indications of a rich condition. I have a patriot defender short 2 into 1 an k&n filter with aftermarket backing plate so I could ditch recirculating the oil that's vented. the bike starts up fine an runs great.....it's smooth as silk cruising around town an back roads at 2300-2650, I cruise in that range since it seems to be the smoothest.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,062
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From: Haslet Texas
I don't run hard a lot but I'm not afraid of the throttle either......the plugs look pretty black after a few tanks of gas. I'll take a pic of the ones I just took out if I still have them. The first time I changed the plugs they were showing indications of a rich condition.
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Elite HDF Member
Joined: Jul 2010
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From: Lorain Ohio
here's a pic of the front plug....the rear is a little cleaner but not much:
maybe I can just run some seafoam through it....works for traildog!
maybe I can just run some seafoam through it....works for traildog!
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