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Top Gear Wide Open Throttle Time Limit


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Back in 1986 I quickly learned the importance of jetting as I seized a practically new Honda CR125R

in less than 10 seconds holding it WOT down a gravel road in 5th gear.

You can't blame insufficient oil as 20:1 was the recommended ratio back then!

 

A super rich main jet is the answer if you want to turn an MX race bike into a road racer but,

be prepared for it to be too rich everywhere else (trail & track) and, any engine braking should be avoided.

 

For relatively short MX courses, a leaner main jet (stock) usually promotes quicker revving and good overrev 

but is not sufficient to cool the internals for sustained WOT riding.

 

Always a favorite example to show kids :

 

 

Edited by mlatour
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Outboard boat motors run WOT all the time. 2 stroke bikes can too. But as mentioned you’ll want a big main jet and an oily mixture. 30:1 or less. My old Merc 90 “tower of power” called for 20:1 so that’s an indicator.

 

High RPM doesn’t allow time for the oil to drop out of the fuel mixture as well to protect parts so you need more oil.

 

Even with a very large main, you can get a bike to run reasonably well below WFO if you tune your needle and pilot accordingly. Not great, but rideable.

 

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4 hours ago, Doc_speeder said:

Outboard boat motors run WOT all the time. 2 stroke bikes can too. But as mentioned you’ll want a big main jet and an oily mixture. 30:1 or less. My old Merc 90 “tower of power” called for 20:1 so that’s an indicator.

 

High RPM doesn’t allow time for the oil to drop out of the fuel mixture as well to protect parts so you need more oil.

 

Even with a very large main, you can get a bike to run reasonably well below WFO if you tune your needle and pilot accordingly. Not great, but rideable.

 

:thumbsup:

Chain saws, yard equipment, and even them gas scooters, all run WOT for a long time @ 50:1. Boat engines are cooled by the water they are in. So, has to do with cooling, jetting, and a few other factors. WOT on a dirt bike sitting still will kill it, no fan, minimal cooling, and improper jetting main factors. 

Releasing the throttle and starving it on the deceleration is just another factor. 

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The problem is that if you jet your bike for wide-open roads, it's not going to run very well on the trail or track.  An old-timer trick for long road runs is to just hit your kill button periodically for a second or two while holding the throttle WIDE-OPEN.  As soon as you release the button, the motor will restart.  The wide-open throttle will allow a large volume of fuel mix to lube and cool the engine.  

 

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5 minutes ago, rpt50 said:

The problem is that if you jet your bike for wide-open roads, it's not going to run very well on the trail or track.  An old-timer trick for long road runs is to just hit your kill button periodically for a second or two while holding the throttle WIDE-OPEN.  As soon as you release the button, the motor will restart.  The wide-open throttle will allow a large volume of fuel mix to lube and cool the engine.  

 

Genius, lol.

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