Question about Harley Davidson XL 1200 C Sportster Custom Motorcycles

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93 1200 evo, rough idle, stalling, back firing while coming to stops (using the bikes motor to slow down). power knocks when starting from a complete stop

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  • rudog2 Jul 31, 2010

    hi steve

    thanks for a reply.. the idle was low, it normally idled about 1200 to 1300 rpm, (that was for the charging system). it was idling low about 800, I did boost it to 1200 again, and filled the tank with high test. the more I think about it I feel maybe a spark plug is weak and I will change them tomorrow. I increased the mixture screw almost a 1/2 turn, will change plugs, hopefully that will solve the problem. I doubled checked the air filter, it may have been misaligned, the cover was off right before the problem started, I didnt replace it at that time, it was done by someone else. I did redo it after reading your reply. once again thanks .

    I'll post what happens after the plugs are replaced......

  • rudog2 Jul 31, 2010

    new plugs helped a little, didnt solve the problem... if this was a car, I would say the timing was too far advanced. I do not know how to check the timing. my manual is giving me no help at all. I will try a internet search. thats it for now... thanks again

  • rudog2 Aug 01, 2010

    thanks for a quick reply.. I was speaking with a harley rebuilding guy. he said it has electronic timing (won't jump timing). I will check any hoses. the pipe connecting the top of the jugs was re-routed early last year, that was the last time the mounting plate was taken off. the bike was not sitting any length of time. I will also check for vacuum leaks. what part of the country are you from, i am in ne PA.. thanks again rudog

  • rudog2 Aug 08, 2010

    I found a pin hole in the fuel line, changed that, next check will be the voes line, work has kept me far too busy to research may other things yet, I'm gettting the impression the rods for the valves may be misadjusted. I pray it is easier to fix than that. i took it out for a ride last night, ran great when engine was totaly warmed up, but backfifing and carb was acting up until engine was running for about 20 min. will check again tomorrow, changed fuel line tonite, i fell it may have been sucking air in.

    later rudog

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  • 4,565 Answers

Sounds like a combination of things. First, are you using high octane fuel? If not, try a couple of tank fulls of that. You mentioned "Power Knocks" when starting off from a complete stop. This is typical of detonation due to low quality fuel.

As for the backfiring and stalling. The engine should idle at about 1000 RPM or so. If it's idled lower thant this, stalling is a possiblity not to mention poor oil of the bottom end. The backfiring could be caused by an air leak into the exhaust system. The mixture in your exhaust system should be overly rich for combustion when you backing down using the engine. If the system is sucking air in at a joint sometwhere, it leans the mixture into a combustable mixture and it ignites causing the back fire. If you've removed the "anti-tamper plug" giving you access to the idle mixture screw, back it out about a half turn and see if that helps.

Good Luck
Steve

Posted on Jul 30, 2010

Testimonial: "thanks, will try new plugs also. I thank you for your help"

  • 2 more comments 
  • wd4ity
    wd4ity Jul 31, 2010

    Ok, I hope it helps. Doing this is sometimes pretty rough. All I can do is take a SWAG (scientific wild a** guess) as I can't ride the bike or even hear it run. I used to tell people that I couldn't fix their bike over the phone and now look what I'm doing. I just try to help as best as I can but I have to admit, there is a lot of the electronic problems that I know nothing about. I'm an old school biker that specializes in Panheads, Shovelheads, and Evos.



    Good luck

    Steve

  • wd4ity
    wd4ity Aug 01, 2010

    If you'll look on the right side of your engine cases right where the base of the two cylinders come together, there is a plug. This is a timing plug. If you take this plug out, you can see the timing mark on your flywheel.



    Now, there is a lot of crankcase pressure that will blow out of the hole when the engine is running so don't get your eyes anywhere near the hole. I would also cover the timing light I was going to use with some kind of clear plastic wrap to keep oil off of it. Harley makes a clear plastic timing plug that you are supposed to be able to see through to go in the hole. But, if the oil hasn't been recently changed, a drop of black oil will get on the thing and you can't see anything through it.



    To check the timing, loosen the plug but don't take it completely out. Connect a timing light to the front cylinder. Start the engine and make sure the light is working. Bring the engine to about 2000 RPM and remove the plug. It will blow a fine mist of oil out but shine the light into the hole. You should see a "dot" or "small circle" in the middle of the timing hole. If so, the timing is correct.



    One other thing might be the cause. You may have a vacuum leak around the carb or the intake. On the backside of the carb, there is a vacuum port where a hose plugs onto it to provide vacuum to your VOES switch. Check this hose for cracks or leaks. If anyone has had the air filter backing plate off recently, they could have moved the carb just a bit and that could be causing a vacuum leak.



    Now, has the bike been sitting up for an extended period of time or did this just start? If the bike had been sitting for a few months, you could have a stopped up jet or something.

  • wd4ity
    wd4ity Aug 01, 2010

    Your Harley technician is correct, the timing will not jump. That's why I didn't tell you how to SET it, just how to check it.



    Now there is one thing that I thought of and I've already told you to check it. That's the VOES. If you take the vacuum hose loose from the VOES, the timing will ******. The Vacuum Operated Electronic Switch controlles the timing. When cruising down the highway with moderate throttle, the vacuum in your manifold is high. This holds the switch open and allows your ignition unit to advance even further than the 40° maximum timing your ignition unit will advance the timing. Harley does this so that you get better fuel mileage. If left at that timing point when you rolled the throttle on, your engine would spark knock badly. So, when you roll the throttle on, the carb opens allowing more air into the intake causing the vacuum to drop. When this happens, the VOES closes and retards your ignition timing BACK to where it's supposed to be to keep your engine from knocking.



    Now, if you have a vacuum leak on the hose going to the VOES, it would be the same situation as opening the carb and the switch would ****** your timing. However, your throttle is not open and you are at idle with the timing retarded. This would result in a lower, erratic idle. Possibly causing the sputtering and stalling as well.



    I'd pull the fuel tank (makes it easier to get to the VOES) and check the hose. The way to test the VOES is unplug it with the engine running. The idle RPM should drop. If not, the switch is bad.



    I live in Forsyth, Ga. Roughly half way between Atlanta and Macon right on I-75. I've got a small place out in the sticks where it's nice and quiet. I also do a little work for the Old Mill Motorcycle Museum. If you're ever down this way, visit Juliette. That's where the movie "Fried Green Tomatos" was shot.

    http://www.antiquesofthelake.com/mill/in...



    Good Luck and Ride Safe

    Steve

  • wd4ity
    wd4ity Aug 08, 2010

    Rudog:

    I think I've got your problem figured out. Contact me directly at wd4ity@bellsouth.net. I'll have to send you some information that is simply too much to type in here. I can scan it in and e-mail it to you directly. I cannot do it through this forum. It won't allow me to send pictures. Remind me who you are because I get a lot of request coming in from other places.
    Steve

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