Racing motor pullcords?

[Tpdingo]

Racing motors like the Briggs Animal, Raptor series and some heavily modified clone motors don't have pullcords but instead have the end of the shaft and a wierd plate with holes in it. Why?

 

[mckutzy]

Typically as I understand it... The compression and lack of a release on the modded cams... Make it dangerous to start it by hand...
So they use an electric starter device instead..

The plate as I recall, has enough holes to allow a controlled amount of air flow(they are still air cooled) out to allow a proper start up temperature for the race...

 

[65ShelbyClone]

Race engine typically have high compression and cams with no compression release, making them extremely difficult or impossible to start with a recoil. Trying to will likely break the recoil anyway, so they use a starter box instead. Many of those engines also run methanol, so...

The shroud block-off plates are often for reducing airflow with methanol engines so they can come up to temperature. Some are adjustable and look like a barbecue grill vent.

 

[anderkart]

I agree,

The recoil-portion of some pullstart assembly's tend to seize up at the 7,000-10,000 RPM that some open-class racekart engines run at too...

 

[Tpdingo]

I agree,

The recoil-portion of some pullstart assembly's tend to seize up at the 7,000-10,000 RPM that some open-class racekart engines run at too...

I get it being too hard to start, but seizing? Why? The pull starter should be entirely disconnected from the motor once it turns over.

 

[anickode]

I get it being too hard to start, but seizing? Why? The pull starter should be entirely disconnected from the motor once it turns over.

Depends on the motor. On the old Briggs flattys, the square starter drive stub is affixed to the flywheel, and has a freewheel mechanism in it. That freewheel mechanism is what seizes up, effectively locking the starter mechanism to the flywheel.

You are right; on the newer engines, they have a starter cup on the flywheel, and the recoil mechanism has spring loaded pawls that retract when the cord is not being pulled on, so there is no mechanical engagement with the flywheel when it's running.

 

[mckutzy]

But the main reason for a Pull start kick/pull back, is that the instant the motor gets going, its going faster then a typical factory tuned engine, and thus it rips the cord out of your hand.
On a Honda/clone type starter it takes 1/4 of rotation of the starter pawl "engager", to fully disengage from the cup... Theres about 3/8"-1/2" of travel for the pawls to grab the cup.