Carb joints dry-rotted - 1996 Yamaha Royal Star XVZ 1300 A

Backfire when throttle down can be;
1. dirty carbs that are running lean and need cleaning. Also the rubber grommets that hold the carbs can be leaking at the backside or even dry rotted.
2. no air filter
3. broken or open vacuum lines
4. an aftermarket exhaust that needs rejetting or an open exhaust system

Check if carbs floutlevil is ok and check if needle is not stuck

could be: control arms/bushings, strut seals/bearing, stabilizer arm bushings. dry rot on any rubber part, lack of lubrication of any swivel joint.

If the lines dry rotted, some of it probably go into the carburetor. There is a very fine mesh screen inside the carb that traps this sort of trouble. Take the carb off and remove the cover on the end of the carb that doesn't have the hole in it. Find the screen underneath the fuel pump diaghram and clean it with non-flammable brake cleaner spray. This is a very common problem on all these machines....

Sounds like jets are plugged in carb. Take off carb and take apart and spray with carb cleaner. Use jet tools and clean out jets, spray with cleaner real good then put back together. You may need to get a carb kit if gaskets are dry rotted.

CHECK THE DOUBLE SIDED BOARD, IF ANY OF THE TRACKS IS DAMAGED OR GOT ROTTED BY HEAT, IF ADJUSTING DOSNT WORK..DRY JOINTS MAY HAD OCUR, TRY TO SERVICE IT (PC BOARD).

what grease boots if its ball jionts or tierod ends you have to replace them(ball joint)//oz

First, you sould have one with a filter in the tank going to carb. Next run one from tank to primer bulb and from one from primer bulb to carb.

If it just starting happening, probably dirty carbs. If its been this way, you may need a carb sync. Also, check to make sure your carb boots are not dry rotted so they are sucking air. Take some wd-40 and spray around your carbs, especially around the mounting boots while the bike is running. If the rpms change while you do this, you probably have rotted boots or possibly just loose ones. But my first guess would be dirty carbs.

could be tranny mount has dry rotted on you/ or engine mount. Have a friend get in the car and put it in gear while holding the brake down, get under the car (carefully) before this happens and see if the tranny or engine jumps more than it should. Also inspect for worn/dry rotted suspension bushings on your shocks, a-arms, panhard bar, etc...

If you can't find anything out of the ordinary, take it to a AAMCO to get the tranny inspected. Could have a faulty sylinoid in the tranny.

Could be alot of things unfortunatly.