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evo backfiring/missing

Engine, Fuel and Exhaust

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Old May 23rd, 2009, 07:55 PM     #1
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evo backfiring/missing

Hey guys, this is my first post on this site. Maybe you can help me out. I have a custom bobber I built with a 97 softail motor. Stock CV carb and Harley ignition, open air filter and 2 into 1 pipe with HP power baffle. I've only had it running for about 700 miles now, still working out the bugs. Anyway, I got it on the road and ended up rejetting to a 45 and a 180 main jet. Bike ran great until just recently. I noticed it was running a bit lean in the midrange (like cruising on the freeway) and put a small washer under the needle, which really seemed to help. A few days later and it started spitting back out of the carb when riding and sometimes at idle too. The plugs looked lean again, like they did before I increased the jets when I first got it running. I had a really big backfire getting on the freeway one day and it hasn't really been rideable since. I replaced the slide and diaphram, which was torn by the backfire I presume, because it was fine a week before. No change. I increased the jets, no change. Seemed to have an intake leak, so I replaced all the seals (I ended up doing this several times), and no change, but I don't seam to be leaking around the seals anymore. Checked the compression, checked the pushrods and the valves to see if they were opening. Put in new exhaust seals. Checked the timing, checked the coil. The VOES is working correctly. I've got good fuel flow. I even put another CV from my buddy's bike on and no difference.

Anyway, I am stumped and don't know what to try next. Right now the jetting is back at 45-180 where it was running well before. It starts fine (kick only) and idles well, usually it even runs fine if you are using very little throttle, although I seem to feel a little surging even then. When you go to give it some throttle though, it starts spitting back through the carb and missing. Especially under a heavy load, like riding up a hill. If you power through this missing, it starts going well at higher revs, but still misses a bit. The plugs look relatively good, but the electrodes get white and the engine gets hot like it's too lean. Any ideas? Sorry for the long post, but I wanted to give all the info. I could. I am a pretty decent mechanic, but this is my first Harley and I'm stuck!
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Old May 25th, 2009, 09:17 PM     #2
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Re: evo backfiring/missing

a few things first, Check very carefully for intake leaks, spray some carb cleaner around the mounting point, secondly, i would verify that the voes is functioning properly, how did you come to the conclusion that it was alright?? Next, every bike needs proper jetting, even on a stock evo, i run a 46 to 47 slow jet depending on altitude, secondly, I recommend changing the stock needle, some people use 89 sporster needles, i use bob woods kt1 needles in all my bikes, and then the main should fall between 180-190 main, depending on altitude. also you did not mention the idle mixture screw, if you havent touched it, drill the aluminum plug out and start at three turns out, everything ive mentioned is on the fat side, it tends to keep these air cooled motors running cooler and better. just my two cents.
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Old May 26th, 2009, 01:44 AM     #3
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Re: evo backfiring/missing

Thanks for the response. I have sprayed carb cleaner around the seals, which is how I figured out I had a leak in the first place. Turns out one of my flanges was warped, so I replaced both. Now I get no response when I spray around the intake mounting points. The VOES seems to be working because the engine slows down when the hose is removed (low vacuum so it switches to the other ignition curve), and it switches at 6psi with my vacuum pump. I am running a jet kit in the carb but cant remember the brand, it does have a slightly slimmer needle though. I'm running a 45 idle jet, which came with the kit, but I am at sea level (seattle) so I don't know if that has any impact. I tried the 48 idle jet and a 185 main and still had the same problem. The main thing is that I was riding this bike with no problems with the 45 and 180 and suddenly can't even ride it. Also, the plug is drilled out of the carb so I can adjust the idle mix. Thanks again, jeremy
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Old May 26th, 2009, 10:53 AM     #4
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Re: evo backfiring/missing

This may sound like a stretch, but it has happened to me. Check the fuel valve. I rejetted for 3 days once trying to get the cough out of my sporty. Plugs looked great, still acted lean. Finally checked fuel flow.....dribble. It ran rough at low RPM, started fine, idled fine. After about 5 minutes at 3000+ it sounded like a machine gun until I would back down.
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Old May 26th, 2009, 12:09 PM     #5
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Re: evo backfiring/missing

Also may not hurt to ohms check or even swap out the plug wires. I had a weak foward cylinder one that drove me crazy for a while.
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Old May 26th, 2009, 12:23 PM     #6
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Re: evo backfiring/missing

Quote: Originally Posted by Shifter View Post
Also may not hurt to ohms check or even swap out the plug wires. I had a weak foward cylinder one that drove me crazy for a while.
Jeremya72,

Welcome to the Forum.

As Shifter said above, check your plug wires. Don't know what your cover on your coil looks like, but on my Dyna it was a sheet metal cover with a couple of half-moon cutouts that the plug wires came through. The sheet metal had actually cut through the insulation on the boot allowing the coil to periodically fire to ground on one plug. The symptoms were similar to yours. This was worse when it was wet (like raining). Had a heck of a time trying to find this until it bit me one day!!

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Old May 26th, 2009, 03:35 PM     #7
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Hey thanks guys. I have checked the petcock, and it seems to flow fine, a nice steady stream. I'm not sure what the ohms should be for a good plug wire, but the rear one is about 150 and the front one (longer) is 300. I think I'll try another set of wires off a buddys bike. There is no coil cover on this bike. I'll re-post again after trying this.

No change, same if not worse. Still looking at wiring, maybe the ecm? Also, noticed the "sealed" battery is leaking. Maybe that is a problem too.

Last edited by TQuentin1; Jun 6th, 2009 at 10:10 PM. Reason: follow on post
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Old Jun 6th, 2009, 06:21 AM     #8
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Re: evo backfiring/missing

Make sure to clean the area where the battery leaked with a solution of baking soda and water to neutralize the acid or it will eat up the finish anywhere it contacted.
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Old Jun 6th, 2009, 07:43 PM     #9
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Re: evo backfiring/missing

Let me ask you something. If you don't close your petcock while the bike is off does the carb overflow?
While you're at it make sure all your carb seals are not leaking air.
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Old Jun 7th, 2009, 12:39 AM     #10
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Re: evo backfiring/missing

It seems to me that you may not have battery voltage at the primary side of the ignition coil or the coil may be bad check the resistans on the coil. And check the spark plug and spark plug cables. Good luck.
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