Makin' popcorn
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Joined: Jun 2010
Posts: 83
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From: Door County, WI
Makin' popcorn
Went for a good 150 mile ride today to an area dealer for a party. When we went to leave, and other times before, ahen I would go to start my bike it would backfire out the exhaust real bad. Also does in between gears too. Real bad on decel. I have screamin'g eagle slip-ons without baffles. I was told that when I got the bike, the guy thinks it is running way to rich. Would running to rich cause this making popcorn sound? Unused fuel maybe? I want to get the cause and fix it. The carb is stock- no s&s or other. It has a SE aircleaner too.
Road Warrior
Joined: May 2005
Posts: 1,301
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From: Minden LA
Yes, cams makes a difference. pull the plugs and look at the color of the electrode area. if it is black and sooty it is too rich, if it is white or very light tan it is too lean. a light to medium brown is what you are looking for. if it is lean, put in the next bigger jet than what is in it and if rich, go down 1 jet size. this is basic jetting stuff and other tweaks may be necessary as well, such as pilot jet or needle raise or different needle, but this should get you headed in the right direction.---jack
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Joined: Oct 2007
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From: Palm Harbor fl.
you got no baffles... essentially your running drag pipes. They're gonna pop like mad and also th lack of backpressure makes it very hard to tune the carb correctly for running at low to mid rpms So, get some bafffles for the pipes! Or a good new exhaust system. Also you can have intake and posssible exhaust leaks as well... If you don't know what your doing tuning wise, take it to someone who does. if you want to tinker and leave the bike without baffles, you need to first find out where the idle speed screw is set at, and try some adjusting there. Be sure to seat the screw and count the turns before it seats so you know where you started. The more it is turned out, the richer the idle mix becomes(anything more than 4 turns out and you definitely have a problem there with the float position, low speed jet size or intake leak). Now you also ned to find out what jets and needle you have in there and if the float is adjusted properly as well...as you can see, if you don't know what your doing, this can be a lot to figure out. A good mechanic can figure this out and tune you up quite easily for a couple hours labor. Even if the bike gets tuned correct and no leaks are evident, the open system will have decell popping no matter what you do. I bet when the bike is hot, you can probably rev it up while on it's stand and watch the pipes blow flames out the exhaust...
Last edited by rounder; Jun 20, 2010 at 12:53 PM.
Cruiser
Joined: Jun 2010
Posts: 196
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The low restriction of the SE aircleaner and the lack of baffles pretty well guarantee that you're running lean, at least in the lower rpm range. CV carbs will self-adjust over a narrow range, but you're outside of that.
When tuning, always start rich and work back leaner. Have several sets of clean, preferably lightly used, plugs handy, as you may fuel foul one during tuning.
Carb swaps and modifications are among the most popular mods done to HDs. Yours may have something done, like a tuning kit with different jets, softer spring, drilled out vacuum port, and different needle. This may complicate your tuning, if you don't know what mods have been done. Did you own this from new?
You can raise the needle, which controls most of the operating range in a CV carb...from about a quarter throttle to three quarters, by putting small thin washers under the needle flange. You will also need to richen the idle mix, from the sound of it. This is hard to reach, coming up from the underside of the carb, toward the rear. Stock, this is sealed off with a welch plug, but almost everyone has removed that to get to the screw. LIGHTLY bottom the screw and then back out 360 degrees. Two turns, one revolution. Then work in by as much as 180 degrees or out by 360 degrees. Always tune when the engine is fully warm.
When tuning, always start rich and work back leaner. Have several sets of clean, preferably lightly used, plugs handy, as you may fuel foul one during tuning.
Carb swaps and modifications are among the most popular mods done to HDs. Yours may have something done, like a tuning kit with different jets, softer spring, drilled out vacuum port, and different needle. This may complicate your tuning, if you don't know what mods have been done. Did you own this from new?
You can raise the needle, which controls most of the operating range in a CV carb...from about a quarter throttle to three quarters, by putting small thin washers under the needle flange. You will also need to richen the idle mix, from the sound of it. This is hard to reach, coming up from the underside of the carb, toward the rear. Stock, this is sealed off with a welch plug, but almost everyone has removed that to get to the screw. LIGHTLY bottom the screw and then back out 360 degrees. Two turns, one revolution. Then work in by as much as 180 degrees or out by 360 degrees. Always tune when the engine is fully warm.
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Joined: Jun 2010
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From: Door County, WI
I bought this ride used. I took the carb apart today. The main jet has a 176 number and the slow jet is a 46. I pulled the plugs and they are VERY white. Lean for sure. Should the main jet be upsized? What number would be a good starting point? I'd rather be running rich. No wonder I got such good mileage!
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Road Warrior
Joined: May 2005
Posts: 1,301
Likes: 24
From: Minden LA
I bought this ride used. I took the carb apart today. The main jet has a 176 number and the slow jet is a 46. I pulled the plugs and they are VERY white. Lean for sure. Should the main jet be upsized? What number would be a good starting point? I'd rather be running rich. No wonder I got such good mileage!
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Joined: Oct 2007
Posts: 7,562
Likes: 11
From: Palm Harbor fl.
so you know, the only way to read a plug properly is to use a new plug and do a full throttle run when the engine is hot. You then want to kill the motor at full throttle and coast to side of the road. Then pull the plugs and read them. the plugs can then give the correct reading of afr, idle and timing. All the experts say you can't read a used plug properly. You still may not be lean, you may have an intake or exhaust leak. The main jet will not help much for your cruising range and idle. it will help starting over 1/4 throttle with the main change coming at 3/4 to full throttle. If you do increase the main, a 185 would probably be good to start for stage1 on your evo, and also you need to do the idle mix screw as well as I mentioned before. This may help in what you should look at...https://www.hdforums.com/forum/engin...-properly.html can you see what needle you have in there.... I recommend changing the needle to the NOKK needle or the 88 sportster needle. 27094-88 is the sporty one 27241-95 is the NOKK. The needle is marked so you can tell what it is. List of Harley needles.... http://xlforum.net/vbportal/forums/s...d.php?t=436467
Last edited by rounder; Jun 20, 2010 at 12:52 PM.
