New SS prop - now i lose thrust at mid throttle...what is up?

[spinfly]

1995 Suzuki DT40 w/ remote controls.
Installed a new SS prop. Now I lose thrust around 2000 rpms, and then the motor revs. But it is NOT a spun hub-I pulled the prop and it is fine(it is the newer hub-insert design, easily replaceable). I don't hear or feel a jolt or anything when this happens, it just seems to have slipped out of gear... When I slow back down, it will engage again.
I have heard switching to a SS prop can cause this. Why?
I really prefer a SS over aluminum for several reasons, so changing back is not an option for me.
What needs to be adjusted to correct this? I have actually already taken the lower unit apart as of now, but am looking for photos to compare my parts to to determine their condition.

Other info/questions: initial engagement to forward can be a little difficult but a little force will engage the gear. Also, on the throttle arm there is a lot of play, even in neutral without squeezing the button on the underside of the throttle arm. But this "play" does not move the shift linkage at the motor. So is this just play in the control box?

Also, gear oil was coffee black and STIIIINKS!

Thank you fellas. I appreciate any thoughts you have time to post up.

 

[99yam40]

Re: New SS prop - now i lose thrust at mid throttle...what is up?

Lower gear oil stinks even new.

Mark the prop and the hub to see if it is slipping when this happens.

what size props are the old and the new and what WOT RPMs did you get out of them.

Most of the time when changing to SS you do not use the same size/pitch as the aluminum

 

[spinfly]

Re: New SS prop - now i lose thrust at mid throttle...what is up?

This gear oil smells SOUR. I can even smell it in my house. Does not smell like new gear oil.

For the hub to slip, the rubber teeth on the hub would have to break. Not broken.

Old prop was 10 1/4" dia., 14P, put on by prev owner. WOT RPMs were 5500, which is too low.

New prop is 11" dia., 13P. Have not pushed beyond 3000 RPMs, since I lost thrust the 1st time out w/ new prop...

 

[99yam40]

Re: New SS prop - now i lose thrust at mid throttle...what is up?

what does your manual give for WOT RPMs for the DT40?
I always thought 2 strokes ran at 5500

all I can say it try marking and checking it as you said it is not jumping out of gear

Have you took a sniff of new lube?

 

[spinfly]

Re: New SS prop - now i lose thrust at mid throttle...what is up?

Manual actually says 5600 Max RPM @ WOT. There was a gap of 300 RPMs w/ the original 14P (my mistake, it was a while back when I tested the original prop), so the Max RPMs were right at 5300. So, 1" less pitch should put me at 5500-5600 max RPM @ WOT. Sorry for the misinfo.
Here is the rubber hub insert, and the actual hub of the prop. The fit is almost like a glove, and there are no scratches or shavings that would indicate any rotation had occured. For the prop to spin around the brass spindle piece, it would have to separate/tear the rubber, right? (Edit from previous post today: teeth are on prop, while the receiving grooves are recessed into the hub as pictured.)
View attachment 162627View attachment 162628

Yeah, I opened up a new tube of marine gear lube just to be sure, doesn't have the fowl odor that the old stuff does. I kinda wonder if the P.O. used automotive gear oil or something else not recommended. Or maybe it got burned at some point?

I also noticed that the amount of travel I can see at the adjustment point on the shift linkage (when moving the throttle arm) is noticeably LESS than the amount of travel I get by hand now that I have dropped the lower unit and have this exposed....

Thanks for your time, 99yam40.

 

[spinfly]

Re: New SS prop - now i lose thrust at mid throttle...what is up?

Anybody have any ideas?

I don't think there is any problem with my gears, pinion, or clutch dogs. I've inspected them and they look fine. There was only a small amount of metal shavings on the shift magnet, as I understand some is considered normal.

Now my question is basically this: Could this loss of forward thrust be corrected with an adjustment in the shift linkage?
Thanks all.