1 inch pitch causing all the problems!

Jimmy C · 24 June 2008, 11:14

Hi

I am currently running a suzuki 65dt with the factory fitted 11 3/4 16" ali prop which has good holeshot and acceleration but as i run the boat quite light wanted to go up in pitch a little. The new prop i have is a 17" s/s with the same diameter but the engine just cant get going and it stalls. Is this a case for mixture/idle speed adjustment or is the engine on its way out?

Cheers

Jimmy

Nos4r2 · 24 June 2008, 11:42

Going up 1" AND going to stainless can be as much as the equivalent of going up 3 to 4" in pitch depending on how agressive the cupping is. The SS prop is probably most of your problem.

it shouldn't stall though-does it stop completely?

Downhilldai · 24 June 2008, 12:54

15" pitch was standard on the DT65. I'm surprised you're looking for a 17" pitch. What max RPM are you hitting with the 16"? Has it been re-profiled?
As NoS says, shouldn't stall the motor, unless it's fouling somewhere

9D280 · 24 June 2008, 15:36

I'd disagree with the stall comments. When I got mine, it was fitted with a waaaaaay too small prop (first time out chickened out & throttled back as the tacho passed the 6500 mark on an engine supposed to max at 5500!

)

Changed the 10.25 diameter / 12" pitch for a proper G- series 11.25 diameter / 14" pitch and first time with that prop if I just knocked it into gear without then following through to a "proper" acceleration within about a second it stalled. Was Ok like that in open water, but a bit of a pain in the marina!

One small tweak to the idle screws later and it's fine now. (also maxes out at around 5300 @WOT, so it would appear to be about right for the setup)

Downhilldai · 24 June 2008, 17:52

Quote:

Originally Posted by 9D280

I'd disagree with the stall comments. When I got mine, it was fitted with a waaaaaay too small prop (first time out chickened out & throttled back as the tacho passed the 6500 mark on an engine supposed to max at 5500!

)

Changed the 10.25 diameter / 12" pitch for a proper G- series 11.25 diameter / 14" pitch and first time with that prop if I just knocked it into gear without then following through to a "proper" acceleration within about a second it stalled. Was Ok like that in open water, but a bit of a pain in the marina!

One small tweak to the idle screws later and it's fine now. (also maxes out at around 5300 @WOT, so it would appear to be about right for the setup)

So that was a problem with your idle settings, not your prop

9D280 · 25 June 2008, 10:51

It idled fine in gear with the old small prop but stalled with the new big prop until I tweaked the idle settings.........

I refer you back to the original question!

Downhilldai · 25 June 2008, 12:15

Your old 12" pitch prop was too fine and your new 14" pitch correct, so as your motor wouldn't idle with the new correct prop, the idle setting was the problem, in your case.

Jimmy may be suffering the same problem, but I wouldn't expect a 1" increase in pitch to cause this, particularly as his motor runs fine with the original. As always, armchair analysis isn't the easiest way to find a fix.

I still think a 17" pitch prop is too coarse for his set-up though.....

9D280 · 25 June 2008, 16:30

The old prop on mine was correct for the original life it led (loaded most of the time) and so the idle setup was tuned to that "small" prop. As I am now rarely more than 2 up, the old prop was incorrect at planing speed, so I changed it.

Thing is that by changing it, the original idle settings for the old prop were now wrong for the new, so it stalled. 1/4 turn of the idle stop screw in the "more throttle" direction later, problem solved.

If JimmyC's setup is not absolutley bang on nominal, and his idle screws are, say , 1/4 turn on the low side, that extra small load may be enough to push it over the "stall " cliff, because if it needs a 1/4 turn clockwise to optimise it, and its already 1/4 turn the anticlockwise, the set screws are now 1/2 tun off optimal......

Agreed ref. the armchair. All I'm trying to say is Jimmy, go tweak your idle settings, I suspect your engine needs

!

Downhilldai · 25 June 2008, 17:29

Yes

.....and then find the 17" prop is too coarse

Jimmy C · 27 June 2008, 16:46

well thanksfor all the comments...

I consulted the brownspoint website and it appears (?!) that my specific engine was supplied with a 16 inch pitch ali prop, whether it is the same i do not know?

With the orginial prop there are no problems throgh the range, although it revs to 6200 with 2 up and the manual says 5800-6100
So strictly i didn't think there would be a problem going up 1 inh pitch, but as nos points out s/s could in effect be as much as 3-4inch more.
I didn;t realise thois at th time.
The engine does need a little more playing with at idle as it smokes a bit, so i think the mixture might be a tad too rich, but we'll see how it goes.
Probably should put this in the other props bit, but does anyone have a 15" 11 1/2 or 11 3/4 s/s going that i could try??

I'll let you know how i get on....

Jimmy C