 Lean misfire
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Joined: Sep 2013
Posts: 23
Complete Newb
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OP
Complete Newb
Joined: Sep 2013
Posts: 23 |
06 america, bub pipes, duel K&N filters, 155 main jets, stock needles, stock pilot jets, air injection removed and plugged.
So everything seems fine for the most part but occasionally my right side carb will cut out with a little pop. This only happens while cruising (1/4 throttle) and intermediately at that. I have checked for intake leaks and that seems fine. This started happening after i did the air box removal and went with the K&N setup.
A friends claims this is a lean misfire and i should up my pilot jets by one size and see if that fixes it. What do you guys think?
Good friends, good drinks, good times.
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Re: Lean misfire
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Joined: Feb 2007
Posts: 23,194 Likes: 56
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,194 Likes: 56 |
Spray carb cleaner around all intake points and see if the idle changes if so you have a leak.If not then do a proper adjustment on the pilot screws. Then maybe up a jet size. This may not be the cause but wouldn't hurt to try before diving in farther.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Lean misfire
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Joined: Sep 2013
Posts: 23
Complete Newb
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OP
Complete Newb
Joined: Sep 2013
Posts: 23 |
Thanks dog. Ive checked for intake leaks with carb cleaner and results were no leaks. Proper adjustment on pilot screws is between 2 and 3 turns out right?
Good friends, good drinks, good times.
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Re: Lean misfire
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Joined: May 2010
Posts: 5,720
Check Pants
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Check Pants
Joined: May 2010
Posts: 5,720 |
Two and a half, three quarters turns is where you start, the sweet spot is where you find it. If you need to go past three turns, consider going up a size with your pilot jets.
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Re: Lean misfire
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Joined: Feb 2007
Posts: 23,194 Likes: 56
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,194 Likes: 56 |
Best way is to turn the idle up just enough to run on one cyl. remove one plug wire and ground it. Now with the engine running on one cyl. turn the pilot screw in until the engine runs rough then back it out again until the engine runs rough counting the turns between those 2 points where it runs rough. The best setting is 1/2 way between those 2 points. Repeat for other side.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Lean misfire
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Joined: Sep 2007
Posts: 198 Likes: 1
Adjunct
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Adjunct
Joined: Sep 2007
Posts: 198 Likes: 1 |
If it's only 1/4 throttle cruise that's causing problems, add a shim to each needle, this should clean it up.
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Re: Lean misfire
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Joined: May 2012
Posts: 46
Greenhorn
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Greenhorn
Joined: May 2012
Posts: 46 |
Quote:
Best way is to turn the idle up just enough to run on one cyl. remove one plug wire and ground it. Now with the engine running on one cyl. turn the pilot screw in until the engine runs rough then back it out again until the engine runs rough counting the turns between those 2 points where it runs rough. The best setting is 1/2 way between those 2 points. Repeat for other side.
Is there an advantage to doing this with the plug out, so as to avoid vacuum drawing fuel and flooding that cylinder?
That's how I have done it, but I'll be honest, I have found it difficult to notice where the running cylinder gets rough; it happens gradually both in and out. I don't see how there would be a difference in how the running cylinder performs with either method (plug in vs out on dead side).
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Re: Lean misfire
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Joined: Feb 2007
Posts: 23,194 Likes: 56
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,194 Likes: 56 |
If you can't make it run rough you need to change the jet or have a clogged passage. No need to pull the plug, you don't need to run it long enough to do any harm.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Lean misfire
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Joined: May 2012
Posts: 46
Greenhorn
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Greenhorn
Joined: May 2012
Posts: 46 |
It does get rough, it's just not a very precise change for me. Like I don't notice the change over a 1/2 turn, say. Going on memory here, but the rough running probably spans a full turn, making it hard to decide if the best setting is say 2-1/4 vs 2-1/2 out.
Separate question, but my understanding is it's normal for each carb to have it's own setting (reason for doing them both separately). What would be the cause of different settings?
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Re: Lean misfire
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Joined: May 2010
Posts: 5,720
Check Pants
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Check Pants
Joined: May 2010
Posts: 5,720 |
Minute variations in valve adjustments, actual cylinder/ring condition, the carburetors themselves and air/fuel passage profiles as to side to side. Add it all up and one side differs from it s almost twin brother. The exhaust or the final product of combustion being correct at all throttle positions being made the same on both headers is the Holy Grail we seek. I settle for usable power at a fuel air mix that doesn't harm my engine as I'm anal enough about enough things as they are.
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Re: Lean misfire
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Joined: May 2012
Posts: 46
Greenhorn
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Greenhorn
Joined: May 2012
Posts: 46 |
Makes sense. Thanks. I also find that balancing my carbs is kind of the opposite - VERY slight adjustment to the screw makes for noticeable changes on my manometer. It would help if the darn thing wasn't so tough to reach and adjust.
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Re: Lean misfire
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Joined: Feb 2008
Posts: 2,671 Likes: 15
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,671 Likes: 15 |
Quote:
Makes sense. Thanks. I also find that balancing my carbs is kind of the opposite - VERY slight adjustment to the screw makes for noticeable changes on my manometer. It would help if the darn thing wasn't so tough to reach and adjust.
That is normal.
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