No power

[Iswing]

I know someone knows why:  Story, purchase a 99 IS, ran OK but hesitation at 1800 RPMs.  The previous owner had it desmog.  Rode in for a while and it kept getting less and less power; give it gas and bike started shaking.  Took out carburetors and took them apart and all looked good.  Previous owner said they were rebuilt.  I replace the timing belts and replaced the jets, and put it all back together.  Starts great, runs fine, until you ride, turn the gas and no power and backfires.  I think it getting gas ok, seems not a gas issue.  I replaced the plugs, sounds good when sitting, give it gas and sounds great.  Could I have done something wrong with timing belts?  All vacuum hoses are good, and all hoses connected back.  Your help is greatly appreciated. 

[Chrisj CMA]

Double check that the up marks and 1/2 mark are all level together. One tooth off makes these thing run poorly

[Jims99]

What Chris said. Also did you check the air filter? Make sure all intake tubes are seated properly and clamps are tight. Have you tried any fuel additive? That may also help.

[Bagger John - #3785]

In addition to the above, how's the fuel flow?

[Iswing]

Thanks for the help. Spark plug wire 4&6 were reversed. 

[Mooskee]

That would do it!