Re-jet?

[jmking42]

I bought a 2005 Midnight Venture from a friend in Texas,elevation 1000ft,and brought it to Colorado Springs,elevation 6,000 ft.I've noticed that when decelerating,it will sometimes backfire.....not real loud,but it does backfire.Seems to run fine and don't really notice any loss of power at higher (12-13'000 ft) altitudes.Just wondering if any other people live at higher altitudes and whether they had to rejet.

[V7Goose]

Re-jetting is neither needed nor advisable IMHO.

 

But the high altitude does have the engine running a bit rich. So tuning the carbs can help.

 

Generally, popping or banging on decel is caused by some problem with the ignition or mixture. On these bikes, the most common problem is a vacuum leak form the vacuum port caps or damaged vacuum hoses on the other two ports, so always best to check those out first. The caps on the two vacuum nipples will get hard and crack in about two years, so start by replacing them. Another common problem is an exhaust leak at the Y joint; this is covered in numerous older posts.

 

After making sure you do not have any vacuum or exhaust leaks, it is time to tune the carbs. Remove the anti-tamper covers from the mixture screws and carefully start to turn each one in until the RPMs begin to drop - this verifies the low-speed circuit is working. Now open the screw to reach the highest RPM, and repeat for each carb.

 

After you have completed this process, if you still have problems with afterfire, you will need to check out other things that affect the combustion process. Good luck.

Goose