I have an 87 virago 1000cc I know I need to sync the carbs but why do I lose power when I have it idling to warm it up before I ride? I have it plugged up to a battery charger when I don't ride for a while bc I know that was one of the problems, but I start it up a few times and the battery dies again. But also smoke comes out of the top exhaust pipe but not the bottom exhaust... need some answers please and thank you!

Adjust the idle/fuel mixture on the carb.

It could be an air leak, air being drawn in somewhere under vacuum from the engine. The first thing to check is your carb connections are okay. Get a can of carb cleaner and get the bike idling/ticking over. Spray the carb cleaner around the area where the carbs are clamped to the engine. If the engine stutters or stalls it means air is being drawn into the carbs screwing up the air/fuel mix. Check the rubbers and clamps if this is the case.

is the air filter good, not restricting air flow, is the choke turning off ok

Below is a diagram. Turn the air screw inward until it lightly seats then open it up two turns. Set the idle speed with the throttle screw. The throttle screw pushes against a lever on the outside of the carb. From there, adjust the air screw for best idle speed. Do this for both carbs. Be sure the air cleaner is clean.

Sounds like the idle is set too high. Around 900 rpm is good.
These folk may have a manual for you:

http://www.repairmanualclub.com/motomanuals/index.php

vapor lock? float level ? main needles to low

The rubber seals and fittings between the carbs and cylinder head get hard and brittle. They can develop small cracks and also loose the seal they had when new and pliable. This means that extra air gets into the air/fuel mix as it heads for the intake valves. The air that has not gone through the carbs leans the fuel mix and causes the high revs. The seals and fittings will need to be replaced. Dealers have parts in stock for 10 years. Your bike is 22 years old. Google yamaha virago 750 parts also Google vintage motorcycle parts. Babbitt's would be a good source if the '87 and '88 parts match up. They list an '88 and have all the parts in stock except one hose line.
Go to the site below where you can see a parts diagram for your specific bike. You will select the actual brand, year, model, etc., once you go to the site. Part numbers and prices are also shown. You can order parts from this site. In the event no price is shown on a particular part and/or the notation "Not Available" is in the description, the part is not in stock. www.babbittsonline.com/pages/parts/viewbybrandand/parts.aspx

Hi and welcome to FixYa,

Initially, your description of "...off and on it shows me it has the power it should..." is significant as it indicates that it would not be a mechanical / engine problem.

Offhand, almost always, erratic performance and/or intermittent power could be: 1) electrical (least likely), 2) air/fuel mix (likely) and/or 3) carb (most likely).

Interesting though if as you posted, the bike has "...new...carbs...". If it were so, then a possibility to consider is that the carbs need synchronization.

Preliminary checks:

• at cold start, determine which cylinders heat up faster / slower using water spray;
• determine the colors of the burns / tips of the sparkplugs at what cylinder;
• loosen the drain screws of each carb and collect the fuel from the drain hose. Compare the quantity and quality amongst all 4 bowls.

Incidentally, is everything stock or aftermarket items installed such as free/open breathers air filters and/or exhaust system?

Good luck and thank you for asking FixYa.

Sounds like:
A: The starter clutch is slipping and not letting the starter engage the crankshaft
B. The carbs need to be cleaned. If ti has sat unused for more than 30 days, the pilot jets are clogged up causing it to stall (off choke) and be sluggish on acceleration off idle.

check the intake gaskets. in the middle front and middle rear. If they are oily, it more than likely sucked part of the gasket in. When it warms up the leak gets bigger. The easy way to check is to get some carb cleaner and spray all around the intake while idling and warm. DO NOT SPRAY ANY EXHAUST PARTS , carb cleaner is combustible. The truck should stumble or even shut off when spraying with the carb cleaner if there is a leak.