Back with a tuning problem

[NCScooter]

Been gone, lurking a bit. Got a new Triumph Trophy SE last August. Doesn't engender the love of the old 'wing. Anyhow, also got a C5 ignition for the 77 wing and when I set it the way it says in the instructions, I get a lot of backfire in the exhaust on deceleration. If I advance it like a degree or so it helps. Leaning (tightening) the idle mixture screws a 1/4 turn helps also. My gas mileage has decreased from around 30 (with points, Hondaman and a pair of emgo coils) to a little better than 25. Bike is fully dressed and I'm fully fed. Any helpful thoughts or humurous anecdotes would be appreciated. Thanks in advance.

[CYBORG]

Does not compute. I would review the install of the C5 very close. Mixture screws are more a low speed/idle thing. After a higher speed run look at the color of the plugs. Could be a carb problem

[Whiskerfish]

I have never setup a C5 so I can not offer any ideas on that but leaning out the idle mix screws is backwards to your issue. Like Cyborg said "does not compute"

[CYBORG]

I have one. The set up is the easiest I have ever seen. Even easier then a Dyna system

[ericheath]

It’s a jealousy thing. Wings get jealous when you start carrying on with another bike, especially if you flaunt it.

Check fuel filter? If it sat for a while, it may be a carb issue that’s reared its ugly head causing you to connect the dots with C5 install. If leaning helps, you may have leaking floats or gaskets. That would affect your mpg as well. After warmed up turn the fuel off. If after a minute or so you have ten seconds where it starts running well, it hints towards leaky fuel somewhere. Plenum floor dry?

[NCScooter]

Does not compute. I would review the install of the C5 very close. Mixture screws are more a low speed/idle thing. After a higher speed run look at the color of the plugs. Could be a carb problem

It is when I'm down shifting, so the butterflies are closed on the carbs. I have been riding it every week to 10 days. Thanks for the advice, I'll check on your suggestions.
I changed to Iridium plugs when I installed the C5, also rode for several weeks before I got the Trophy and noticed the drop in mileage then.

[CYBORG]

Because of the multi firing on each cycle the C5 has, sparkplug settings and condition can cause a plug to fire late.
Just saying, don't over look the plug condition as a problem

[NCScooter]

Checked the idle screws, they were in too far. (Doh!) Backed 'em out to 2 1/2 turns, no backfire on decel. Looked at the floor of the plenum with the bike running for a couple minutes, no sign of any gas. Have not checked the plugs yet. Thanks guys!