Team-BHP - Honda Unicorn Engine Dies after 30 KM

A friend (Newbee Bhpian: NosArt) of mine is having a weird problem with his 2006 Honda Unicorn.

This problem started after a normal service with a regular local Mechanic, The problem occurs after running about 25-30 Kms, the bike’s engine would Die whenever the throttle is reduced. And to keep the bike running he has leave ride the bike on the clutch while reducing the speed and constantly keeping the throttle open, or alternatively use the choke while slowing down.

He has taken the bike to several mechanics and also to the Honda Service center in Chembur, They suggested a wide array of problems
- Electrical including the alternator. ( Checked and seems to be fine)
- Spark Plug (checked and cleaned and working fine)
- Fuel Cap for not letting the air pass ( Ran the bike with the new fuel cap , same problem continues after 30 Kms)
- Checked and Cleaned the Carburetor (Haven’t verified but the Honda SS says its fine)
- Air Intake ( Checked and Replaced the AIR filter)

As I said the problem always happens after riding about 30 KMs , so most of the time when he takes the bike to a new mechanic and they do a test ride, it performs fine. But yet again only after running 30 KM it starts to give the problem again. But weirdly the problem occurs mostly at nights (Heat’s got to do with something?)

Any inputs on this guys?

I think your friend is revving the bike to insane levels, and the engine is getting heated up. It used to happen to my Pulsar as well. After few minutes of inactivity/cooling, the bike would start and function normally.
Does the Unicorn start after say 5 minutes of inactivity ?

It looks like the engine is over heating there can be several possibility.

Ensure that there is no obstruction of airflow to the engine.
Proper lubrication check quantity & quality of the oil in the sump.
If the engine oil filter is clogged then oil circulation will be impacted resulting in friction & overheating.

Some updates to the possibilities listed below.

Taking the Honda Mechanic on a long drive may not be possible as the last time he got it serviced from Honda, the bike was working fine for about 3 days (riding for more than 30 kms per day) and then the same problem started.

Also, he is not revving the bike too much, he rides mostly around 60 kmph if not slower. Also usually it takes about an hour of inactivity for the bike to start working normall, the problem then starts again in about 10-15 kms

The engine oil has been changed last week, also the air filter has been changed and the airflow has been checked by the Honda service station, checking the oil filter could be something that can be re-checked

This might be lame, but, have you checked the fuel tank?
This happened to me when I was cruising on my bike and when I
eased on the accelerator there was a sudden dip in power and
the engine used to cut off. Problem diagnosed: Fuel tank had
some cloggin and some water due to it being parked in the rain.

Check the breather. I dont know about the system employed in Unicorn, but in my present bike there is the air breather for tank under the front seat i.e. the breather pipe ends under the front part of front seat.

Overheating is generally not the problem with these bikes. I used to ride Caliber to 8K rpm before each gear shift.
Unicorn is not known to get overheated.
Check :
1) If the fuel is flowing properly from the tank. This might not involve riding. Just disconnect the fuel line ( if it not metal pipe ) and start to fill petrol in a bottle. If the flow of is sufficient to fill in one litre of petrol in the bottle then fuel supply is not the problem.

2) Check ignition coil, cable, sparkplug and that spark plug cap.

3) Check all filters, mainly fuel and air.