Hey guys, new here.

I bought a 2001 Sportster (1200) last December and am finally getting it on the road. Excellent condition with only 5,000 miles.

She was running fine, but since I saw that the spark plug wires were welded to the plugs with rust, of course I decided to replace them

I replaced the plugs (gapped at .038) and the wires (Screamin' Eagles since the dealer was out of stocks).

Now I notice that the engine "misses" a lot on throttle-up and backfires upon deceleration.

Can you guys suggest some possible reasons for this?

Original plugs had no gasket, these new ones did. Gave them a firm-ish tighten and then an additional 1/8 turn.

Original long wire had an outer plastic "jacket" which helped insulate it from the engine. New one does not. I'm not sure if there could be some bleeding to the engine through the wire insulation.

Thanks lot!

 

First I think the plugs should be gapped to 40. What did the old ones look like when you pulled them? That being said ... I would turn my attention to the carb. It's a 2001 with 5,000 miles? There has been a point in its life that it has sat a long time. Look at the carb, problem is probably there according to your symptoms.

 

The old plugs looked very clean, maybe a bit white, which I think means she ran a little hot.

But definitely clean. They were gapped a loose 40. I'll pull the new ones and widen out to the same loose 40.

Yup, with those miles she has sat around, or lightly ridden around the neighborhood.

Thanks for the tips. If correcting the gap doesn't do it, then I agree the carb needs to be looked at.

 

If they were white then the bike is probably running too lean. A lean bike will backfire on deceleration as well. You can try taking the idle mixture screw out about a quarter of a turn and see if that helps. Ultimately though you should tear down the carb and rebuild it. I do it every winter. And make sure you replace the intake manifold gaskets while the carb is off the bike. Leaking intake manifold gaskets will cause a very lean condition that may not be correctable with jets or idle mixture adjustment.
Good luck to you.

 

Thanks. You're right, it is running lean. I noticed when I pulled the choke out the problem dissipated. She does seem to idle at a slightly low RPM, even with the old plugs.

I'll definitely take your advice & do a rebuild and won't forget the gaskets.

Again, I appreciate the advice.

 

Make sure both ends of your spark plug wires are firmly seated and connected.

John

 

 

Run some Seafoam gas treatment for a couple tanks as well. I haven't had my carb off in over 20 years and it runs the same as always. I do run Seafoam every few tanks or so, and she just keeps on purring. Need to replace choke cable, but I only use it for a minute or two, so no biggie.


John

 

Also check the inside of the coil towers, they can get water in them and end up with green corrosion inside them.
You may need to up the jetting, there are still lots of bikes out there that have never had there jetting corrected from the factory. A good sign that nothing has been done is the plug will still be covering the idle adjustment screw.

 

I definitely should run some gas treatment through. The gas in there is oldish. Still, with the old plugs and wires she fired and ran smooth as silk.

Now she's misfiring like mad (Haven't yet re-gapped. I'll do that in the morning). SO the issue seems to be directly related to my changing the plugs.

Is there any reason you guys can think of that the new plugs use gaskets while the old ones had none? The new plugs' numbers seem to be correct.

Also, could it be that the long spark plug wire shouldn't be touching the engine? Again, the old wire had a ribbed plastic tube shielding on it while the new one doesn't. I did split the shielding lengthwise with a razor blade so that I can put it on the new cable, but haven't. Can new cables arc when touching the engine?

jag, inside of the coil towers... Good advice. I'll check that. Clearly the bike has gotten wet so I expect some hidden water damage.

Thanks for putting up with my basic questions guys.