Need tuning advice

I recently replaced the 40 year old coils on my 78 XS with new stock coils from Mikes XS. The old coils stopped working when they got hot. Im running points ignition and everything is new. After installing the new coils, the bike runs rough when cold, backfire and no power. After bike warms up. backfiring stops but still no power on low end. Then noticed that at higher rpms and at speed, bike will clean out and run great (better than ever) . Then when decelerating, bike runs rough again. Not sure what to do next. Does this sound like fouled plugs, or too rich mid range mixture? Thanks for any suggestions.

On a 40 year old bike, it could be anything, lol. Have you serviced the advance unit and advance rod? Cleaned and lubed them? It almost sounds like a failure of the timing to properly advance and retard with changing engine RPMs as it should.

I always break the glaze on new points surfaces. Make sure the gap is not too close, as that will cause problems. Be very sure it is timed correctly.

Thanks 5twins. Actually, I did replace the springs on the advance rod today. The springs now snap the weight back and seem to work as it should. Before replacing the coils, the bike ran good (at least until the coils got hot). Battery is new and charging properly. After installing the coils, engine now runs rough when cold and at lower rpm. After a few seconds at full throttle, the bike leans out and runs like a rocket above 3000 rpm. Its only when I slow down and transition back to low rpm that the power goes away and engine runs rough again. Feels like a 2 stroke coming on the pipe instead of a linear 4 stroke.

I started the bike tonight after work and the timing appears to have changed after installing the new coils. Can anyone tell me if changing the coils alone can change the timing? Either way I guess retiming the points is the next step,

No, timing shouldn't change with a coil swap. But points are a wear item. How long has it been since you set them and/or the timing? It can change in as little as a few hundred miles. That's why many of us choose to go with the Pamco.

Points and condenser are brand new and were set less than 200 miles ago.

As most guys know, the stock coils only put out low voltage, perhaps 13 kv at best.
Those stock coils were high quality, made in Japan.

Mikesxs sells low quality components made in Taiwan mostly. I'm suggesting that buying 13 kv coils, that are just a Taiwan reproduction, is asking for trouble.

Ignition coils is not an area in which you want to buy the cheapest product out there.

Also you may want to rule out the battery or charging components. I learned the hard way after weeks / months of tinkering that I had a crap battery. Does it run better if you have a charger on that battery?

I checked my original points 2000 miles after I serviced them. They were fine. I now have 11,000+ miles on the original points. Points are not a problem if they are greased at the foot and cam and the felts are lubed with a drop of oil. The point face should be cleaned with solvent on a paper card. The advance rod IS a known problem and needs pulled and greased. The last time I was having idle curiosities I correctly diagnosed the advance as the culprit. The rod was dragging. Your timing change probably was from the advance giving inconsistent timing.

I am going to make a guess that your points closed up because the rubbing foot was not lubed. Put a drop or two of oil on the felts. Put only a finger print of grease on the point cam in front of each foot. The foot will pick up the grease like a snow plow and hold it right where it will do the most good.

You are going to need to set, increase the gap on at least one point due to wear. Back fire strong enough to blow off a carb can happen when the points gap gets too small.

Use premium gas when you fill up. The extra octane will keep detonation from occurring on the highway. You do not want a holed piston!

Tom