yes the air is denser which your getting more air compared to gas in cold weather

thumperclone wrote on 12/31/69 at 16:00:09:


I may be a sadistic S.O.B., but I can't help smiling from ear to ear when it does that at the gas station.  

In my experience the cooler weather and cooler pipes seems to magnify the small exhaust leaks. Mine backfires on decel when cold, but after getting warm they all go away. I checked last night and I have a couple small leaks at the adapter and muffler. Will need to address those with Fall weather coming on, but only ordered the new header gaskets yesterday. I had used up my supply and didn't ordered enough last time. FWIW as long as this is an exhaust topic. I recently blew the center baffle out of the HD-FXD muffler I had on for 7 years or so, changed the muffler to the 2nd one in the set,  but never looked inside the RAASK pipe I used for a header. While I had the exhust off to change the clutch lever cam, I happened to look in the RAASK and the inner liner was partly blown away at the very top.  Greg sold me a used OE pipe and I had an adapter made to go on the muffler I was using before. The sound is totally different with the stock head pipe, single wall adapter and HD muffler than it was with the old not really double wall header and no single wall connector. Much more distinctive sounding on low to med RPM run up in each gear. Louder but still OK i think. Not sure how much of the change is due to the exhaust not dumping some of the pressure pulse (and hence noise) between the heavy RAASK walls and the single wall connector not absorbing some of the noise. I know the single wall Highway Hawk Drag pipe I tired was noisy from the exhaust port on down as it was very this wall. I may try to find a foot of schedule 80 water pipe and have it bent for the adapter and try it as it is much heavier walled than the exhaust pipe. Did that years ago on a Dodge Crewcab PU and it outlasted the body on the truck. The sound is more HD like now where before I would have compared it to a Wing with aftermarket exhausts, more of a purr.  Apparently the new RAASK is dirrerent, has packing between the inner and outer pipe with perforations in the inner and packed baffle. Only available in 60 mm now, old one was 50 mm OD with a much larger inner pipe the than the OE one. Still like to find another used RAASK for a header as it works great with the HD mufflers. Max

Wow, I am glad to read all this comments and advises. I can tell that I am not the only one with this boom! problem (Well, I do not if this is a problem).
Now the question is: Is my engine going to be hurt from this backfire during cold days?
Is there a forum explaining or showing how to re-jet? I would like to know how is done, and what should I use to re-jet my carb.
Thanks again