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Sportster Models 883, 883 Custom, 1200 Custom, 883L, 1200L, 1200S, 1200 Roadster, XR1200, and the Nightster.
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  #1  
Old 01-08-2009, 08:27 PM
Razorback Rob's Avatar
Razorback Rob Razorback Rob is offline
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Default Vacuum Leaks????

I've been doing a little research on petcocks and vacuum hoses and such. I asked the guy at my local bike shop about the problem alot of you guys were trying to help me with before, and he said I have a vacuum leak. Anything that I've read said the motor will run lean if there is a vacuum leak. My motor is running extremely rich in the front cylinder. For those of you that didnt read my earlier post, I have an 06' 1200C. Front cylinder is running rich. I've done compression tests, good. Checked the coil, good. Changed plugs for the fifth time, since October I might add. I cleaned the carb. I rejetted the carb last February and it ran great all year. Then in October in started fouling the front plug. I dont even know if you would call it fouling, more like drowning. I put the stock jets back in it. Still crappy. So my question is can a vacuum leak cause the motor to run lean and rich, and if so can it cause it to do so in one cylinder???
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Old 01-08-2009, 09:31 PM
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Is it really running rich or just not burning the gas it's getting. If you had a carb problem it would show up on both cylinders. I agree with your changing the spark plug and you say the compression is good. Is it the same as the rear or at least very close? I think that model uses one coil for both cylinders and they both fire at the same time (wasted spark). So the only thing left if the spark plug wire or plug cap. You could also have a bad coil where there is an internal problem with the tower that goes to the front plug.

And yes I agree with you, if there were a vacuum leak it would be running lean. Now there is a chance that the petcock is leaking through the diaphram and if the petcock gets it's vacuum from the front cylinder then it might be sucking gas directly from the tank.

So you have at least two things to look at. I would start with the petcock as that would be easy to diagnose. After you start and run if for a few seconds unplug the vacuum line and see if there is evidence of fuel in the vacuum line or fitting on the petcock.

Good luck and hope you get it sorted out. Please let us know what you find.
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Old 01-08-2009, 09:55 PM
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I guess it could be either rich or not burning the gas. How do you tell? And I dont think its the plug wires because I switched them and the front cylinder is still the one causing trouble. As soon as I checked my compression I checked my dads. Hes also got a 1200 XL. Right at 140 psi. Both cylinders. Dads was right at 140. I checked the ohms on the coil. Is there any other way to check it?
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Old 01-08-2009, 10:05 PM
satosan satosan is offline
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Lay the plug against the cylinder/rocker box some source of ground and check for spark while turning it over. what plugs are you using. run a hotter plug in the front cylinder???
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Old 01-09-2009, 12:24 AM
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As for checking the coil make sure that between the towers where the spark plug wires attach, I would think there would be zero ohms or a direct short since both wires should be fed by the same spark voltage.

If the coil and wires aren't the problem then did you do like I said and run it for a few seconds then pull the vacuum line off of the petcock and see if there is evidence of raw gas?

Maybe also do a search, either here or on google or both, to see if some one else has had the front cylinder too rich. It may be something we're overlooking related to the carb and way it is mounted. Could be the enrichening valve (choke) but I would think that would make them both run rich.
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Old 01-09-2009, 05:15 AM
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If the plug ain't getting fire, it will be wet, fouling will be black, thick black soot. Have you checked the gaskets for the intake manifold? sounds almost like there is a leak there, more likely on the gasket that the carb seats into on the front of the manifold, but check them both.
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Old 01-09-2009, 12:20 PM
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My .02, Forget about the petcock, carb and the vacuum hose. Those things would show up common to both cylinders. Zimbob is right. Are the intake manifold gaskets tight? You can spray the seams with carb cleaner or something else flammable while it idles and see if it the idle goes up, or replace the three gaskets. Made a world of difference my '99 and the gakets are inexpensive.
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Old 01-09-2009, 01:47 PM
robzuc97 robzuc97 is offline
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I suppose it could be a leak in the rear cylinder and you're overcompensating for it by adding gas (too much jet) which causes the front to foul. Try using propane and a neoprene tube to check for leaks at intake seals: engine will sound different when idling (and won't catch fire from spraying flammables). May want to consider having it EGA'd to see what the AFR is in each cylinder, also: leaking cylinder would be noticeable esp. when compared to the other.
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Old 01-10-2009, 10:39 AM
mbwannabe1 mbwannabe1 is offline
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If it hadn't run properly from Feb to Oct without additional carb mods or adjustments, I would be in the same camp as rozuc97 - and the propane check is the best way to look for vacuum leaks.

Since you said the plugs are more "drowned" than fouled, I'm reading this as wet.
I don't know the vacuum line routing for your bike, but what JDVORCHAK said makes sense, and it's a simple check.

To me, a wet plug usually means a bad spark (unless it's an oily wet, which is posibly valve seals since your compression is good). I have seen coils work fine cold, then quit when hot. Since both plugs fire at the same time, try swapping the plug wires and see if the problem moves to the other jug (assuming the wires are long enough).
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Old 01-10-2009, 10:39 AM
 
 
 
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cylinder, davidson, drowns, fouled, harley, leak, lean, line, plug, plugs, rear, running, spark, sportster, unplugged, vacuum


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