Speedster will not plane

[KBMWM3]

1997 speedster twin 720 recent purchase
Boat will not plane
Left motor 4000rpm then cavitates to 7000
Right motor 3000rpm then cavitates to 7000
Motors good compression
New carbs new jet drive housings new props
New fuel hoses and valves
Intake side of motor new gaskets when I removed oil injection
All new pump housing gaskets and seals all properly torqued
New carbon rings and boots
No water leaks

Thoughts on next step
Reseal intake grates???
Not much tension on new driveshaft boot
Retension???

Thanks in advance
Keith

 

[KBMWM3]

More info
Used sbt neoprene housing to body seal without any sealer

 

[FlyboyX]

i ran my boat for a year with no neoprene seals. i didn't have any cavitation issues.

what about your wear rings? have you checked the clearances of those?

 

[KBMWM3]

Yes
Checked twice
New housing
New wear rings
New props tight clearance
Unsure of driveshaft boot tension
And
Intake grates

Have no water leaks

Same as before with one wear ring gouged
And
The other side had bad bearings and damaged wear ring

 

[KBMWM3]

Thanks for ur thoughts and time and ideas

 

[FlyboyX]

some outdrives such as those on my challenger have a pair of air or water passages on the top of the housing. i don't know what they are for, but on my boat they were blocked with little plugs and a gob of silicone holding them in. i experimented with these a bit on my boat and found the drives would cavitate with those ports open. is it possible these channels are open on your boat?

 

[KBMWM3]

I will double check
Thanks

 

[rusty nail]

curious....would an engine terribly out of alignment with the driveshaft cause an unbalanced situation and send vibration and cavitation?

 

[KBMWM3]

Double checked ports blocked on hsg and plate
New driveshaft boots I ordered were 1/4 longer
More pretension than ones another supplied sent me
All reassembled and boot tension measurement is in specs
Will test out Wednesday

 

[KBMWM3]

Ordered second set of driveshaft boots
Second boots were 1/4 longer meaning more tension
All runs good now

 

[vission]

When I had my challenger I would also just simply slide the boot forward(tighter against the carbon ring) then use a zip-tie to fill in that gap against the hull. Will allow you to keep running without having to replace the boot.

 

[KBMWM3]

Thanks for sharing
I learn something everyday even after owning / working on my own original 95 GTS
But that is a different set up
Dealer that sold me the parts - said all the same - but the second set was different from the first set

Happy boat works now

 

[ottawaguy]

Glad you are up and running! I am a newbie and wondering what you meant here "Double checked ports blocked on hsg and plate". Are you saying something was plugged?

 

[KBMWM3]

Yes
On certain models two upper center water ports are blocked on the pump housing
And
Other models have hoses on the inside of hull and orings or sealer on pump housing
Depends on the set up from factory from my experience