426 overheating

Took my 426 to the dunes. About half way through the day it started idling high and overheating. Any ideas?

How does it run now?

Seems to be running fine I havent riddin it since but I started it in the garage and seemed to be running fine.

Not sure what the problem is but when my 426 was giving me overheating issues I installed a Boyesen water pump no overheating issues since. :bonk:

High idle and overheat are symptoms of a vacuum leak. Start it up and spray carb cleaner around the flanges and carb and anywhere else that would be exposed to vacuum. When the engine starts to sputter, you found the leak.

Of course use care with the fire hazards involved with spraying carb cleaner.

what else can be exposed to vacuum

Take the Black 'Kehin' cover off the carb where the cables go in. Odd are its full of dirt there and need to be cleaned anyhow. Spray it. It can leak right there where the shaft for the throttle valve linkage is.

Where the airbox attaches, there is a plastic flange, that has an o-ring to seal that flange to the carb body. Spray around there.

Hot start knob could be leaking around its seals also.

Thats about all I can come up with right now.

Also, pull the carb off if you are confident in doing so. Take the cover off the top. If its full of dirt, its leaking air at the shaft seal.

Ok thanks. Another thing when I adjust the the fuel mixture screw it takes a while for it to adjust

When idling, can you bilp the throttle, and does it hang a bit when slowing down? Would you say that the idle is erratic?

If so on either of these, it is vacuum leak for sure.

the idle isnt erratic its just a little high when it was over heating it seems fine now ill try what you said tho just to see if it makes any difference.

the idle isnt erratic its just a little high when it was over heating it seems fine now ill try what you said tho just to see if it makes any difference.
What where the symptoms of it over heating? The circumstances?

A lot of coolant started shooting out of the overflow and the idle was high, and motor was really hot. It was about 100deg that day and we were going pretty slow through the dunes so there wasnt getting much air through the radiator so I figured it was overheating. Just did a full motor rebulid on and this was pretty much the first ride after break in. I did flip the bike forward while going down a dune could have something to do with it?

I doubt it. More probably just an heat issue. The only thing you can do about it now is to check it over to make sure it's OK, and check the valve clearances to be sure they don't have anything to do with the hanging idle.

valves were checked before the dune ride and they were good should i do them again?

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