Bike stops after 30 minutes of riding.

The Virago uses 20W-50 oil in warm weather. If you ask any bike shop they will recommend moving to a 10W-40 in cold weather down to about 30ish F, and if you plan on riding down to extreme temps of about 20F and below, then a 5W-30 or 5W-40 is recommended. For the 5-7C temps you list, you could really just use the same oil you use for summer. Just take a little extra time in letting the bike warm up and don't ride it hard the first couple of miles to let the oil come up to full temp. If you prefer to err on the side of caution, then use the 10W-40 oil. I had a Yamaha 650 Classic and I used 20W-50 year round and never had issues as long as I made sure to warm it up properly first.

Your Serow should get around 70 Miles per gallon (28 kilometers per liter). I find that the oil in my bike is thrashed after 1000 miles of riding. It only takes one quart of oil to change it so that is probably the best interval for a single cylinder dirt bike. In you case every 1600 to 2000 kilometers. You should use only a JASO MA certified motorcycle oil. 10w-40 for cold climate/year round. 20w-50 for warm climate/touring. Car oils use different additives and may cause scoring in certain types of cam bearings. Do not use any oil that says " Energy Conserving " on the label . It will shorten the life of your wet clutch and transmission gears. If you choose Synthetic oils, they will help your bike run cooler and shift easier. Shell Rotella T and Rotella T Synthetic 15w-40 are inexpensive JASO MA oils. Trials bikes use tire pressures around 10 PSI (.7 kg/cm). Lower pressures are used for better traction off road. Street bike tires run higher pressures around 30 to 35 PSI (2.1 kg/cm to 2.4 kg/cm)for road driving. This gives better cornering and tire wear. For good all around performance for on/off riding you probably want to run 25 to 30 PSI (1.8 kg/cm to 2.4 kg/cm). For mostly street use 30 to 35 PSI (2.1 kg/cm to 2.4 kg/cm). There is probably a sticker on the frame near the side cover that tells you the factory recommended tire pressure for your model. Ride and make adjustments from there.

Id start at replace spark plugs.. too this bike may have sensors that tell an ECM info one of these may be out of spec after a set time or temp .. id get a manual & check the locations of them. In manual the often have a trouble shooting guide..

Check the fuel tank breather pipe and fuel flow from the tank.

takes a long time to run the rediness test since there are 6 different tests to complete...

PROCEDURE 1
EVAPORATIVE EMISSION SYSTEM LEAK MONITOR
Inspection Conditions
Engine coolant temperature: 30°C (75°F) or less (The engine is stopped before the test drive is started).
Atmospheric temperature: 5 - 30°C (41 - 113°F).
Condition of A/T: Selector lever D range.
Fuel remained in fuel tank: 30 - 50% is recommended.
Time required: 16 minutes or less after started the engine.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position. Well be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 89 km/h (55 mph) or more and travel for 16 minutes.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position.

PROCEDURE 2
FUEL TRIM MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or less.
Atmospheric temperature: -10 - 60°C (14 - 140°F).
Condition of A/T: Selector lever D range.
Time required: 30 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 89 km/h (55 mph) or more and travel for 30 minutes.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 3
CATALYTIC CONVERTER MONITOR
Drive Cycle Pattern
Inspection Conditions
Atmospheric temperature: -10°C (14°F) or more.
Condition of A/T: Selector lever D range.
Engine coolant temperature: Not set.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 89 km/h (55 mph) or more.
Travel for 300 seconds or more while keeping the vehicle speed at 89 km/h (55 mph) or more.
Decelerate until the vehicle speed is within 80 km/h (50 mph) or less.
While traveling at 56 - 80 km/h (35 - 50 mph) for 10 minutes or more, fully close the throttle at least once in 2 minutes and decelerate for 10 seconds or more.
Do not repeat deceleration too often.
Vehicle speed may go below 56 km/h (35 mph) after the deceleration.
Stopping and braking are permitted. (If stopped or drive at 56 km/h (35 mph) or less for more than 5 minutes the monitoring may be stopped. In this case please restart monitoring from the beginning.)
After completing the above deceleration, bring the vehicle speed back to 56 - 80 km/h (35 - 50 mph) and keep it in the range until starting the deceleration again.
Repeat the above deceleration at least 5 times.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 4
HEATED OXYGEN SENSOR MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or more.
Atmospheric temperature: -10°C - 60°C (14 - 140°F) or more.
Condition of A/T: Selector lever D range.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 56 - 80 km/h (35 - 50 mph).
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 56 - 80 km/h (35 - 50 mph) and travel for 16 minutes or more.
Stopping and braking during this operation are permitted. Keep the accelerator opening degree constant for 1 minute or more after each acceleration.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 5
EXHAUST GAS RECIRCULATION (EGR) SYSTEM MONITOR
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature: 100°C (212°F) or less.
Atmospheric temperature: 5 - 60°C (41 - 140°F).
A/C switch: OFF.
Condition of A/T: Selector lever D range.
Time required: 16 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start.
Accelerate until the vehicle speed is 56 - 80 km/h (35 - 50 mph).
While traveling 16 minutes or more at 56 - 80 km/h (35 - 50 mph) with engine speed 2,000 r/min or above, fully close the throttle at decelerate for 5 seconds or more until the engine speed reaches 1,000 r/min or under.
Do not repeat deceleration too often.
Stopping and braking are permitted (Rapid deceleration and sharp steering are not permitted).
After completing the deceleration, bring the vehicle speed back to 56 - 80 km/h (35 - 50 mph) and keep it in the range until starting the deceleration again.
Repeat the above deceleration at least 8 times by fully closing the throttle valve.
Return the vehicle to the shop, then turn the ignition switch to "LOCK" (OFF) position

PROCEDURE 6
OTHER MONITOR (Main Components, Sensors & Switches, Wire Breakage & Short Circuit)
Drive Cycle Pattern
Inspection Conditions
Engine coolant temperature:
100°C (212°F) or less (Except engine coolant temperature sensor monitoring).
30°C (86°F) or less (Engine coolant temperature sensor monitoring).
Atmospheric temperature:
5°C (41°F) or more (Except engine coolant temperature sensor monitoring).
-10°C (14°F) or less (Engine coolant temperature sensor monitoring).
Condition of A/T: Selector lever D range.
Time required: 21 minutes or more.
Drive cycle pattern: One trip monitor (from start to ignition switch to "LOCK" (OFF) position). Will be completed while traveling with the following drive cycle pattern.
Test Procedure
Engine: start
Accelerate until the vehicle speed is 56 km/h (35 mph) or more.
While keeping the accelerator pedal opening degree constant, keep the vehicle speed at 56 km/h (35 mph) or more and travel for 16 minutes or more.
Return the vehicle to the shop.
After stopping the vehicle, continue idling for 5 minutes, and then turn the ignition switch to the "LOCK" (OFF) position. Moreover, the vehicle should be set to the following conditions for idling.
A/C switch: OFF
Lights and all accessories: OFF
Transmission: Neutral

you should get an average of 23 miles per gallon

It is most likely a thermostat. As your car gets older the thermostat begins to lose its spring like properties and stays open all the time causing your car to never warm up.

If you can't tackle right away, start your car in the morning and let it run for about 15 minutes to warm up. Be sure to turn the heat on full blast and recirculate the air.

replace crank sensor. It gets hot and stops working.

I had one and they do get warm,but not hot.I went to a ST2.Main reason is the cost of servicing the 4s is way over the top.Maintainence is a big issue with them.Same with the Monster models.There is not a lot of difference in performance unless you really want to wring its neck around a track.They are both great to ride on the road.Hope this helps

Yes! You will open those things up, and they will probably look pretty clean, but the problem with your carbs is in the Idle circuit - too small for you to see into. If you do a search of carb cleaning or related topics, you'll see that alot of folks with cab problems try to clean their carbs ... only to have to open them up again due to improper cleaning (They are difficult to clean properly, require alot of patience) So, I would suggest that you have them cleaned professionally, or at least buy good carb dip to get them really clean. Spray cans of carb cleaner are worthless. Might as well wash em with dish soap.