Best way to check for intake leak

[400-416EX]

I have an intake leak on my 400ex. The idle is very erratic. What is the best way to check for this.

What year 400 do you have. I believe the 99 and 00 models had airboot problems from the factory and were changed out in 01.

Mine has came loose from the carb before and it was on the bottom side, very hard to see.

I would also pull off the bottom of the carb and pull out the pilot jet to make sure it's not clogged.

[red2004 TRX450R]

How we check to vacuum leaks on our racecars or any car for that mater is we use a house hold propane torch. You take the torch (not lit) and run it around areas that may leak if the idle goes up u found a leak.

Works real good for cars, why not bikes. Just be careful.

[MIKE400EX]

I've seen 2000's that had new and old style carb boots. The old ones had the rubber boot bonded to an aluminum flange. The new ones have the rubber boot bonded to a phenolic (heat-insulating) flange and seem to last much longer.

[frankies4hundy]

you can also spray some WD40 where you think it is leaking, while the motor is running. idle speed will pick up if the WD is getting past a gasket.

[UglyMotha™]

starting fluid

[Samson]

Originally posted by UglyMotha™
starting fluid

Amen, wd40 don't work worth a durn. Can't believe it says flammable on the side of the can! :p