1971 70HP Chrysler OB correct prop size and pitch?
 

I've seen everything from 12" x 13P to 13" x 17P for this motor as the standard
size and pitch.

I know the new prop (that I got from the guy I bought the boat from) ain't
cuttin it at 13" x 19P.

Anybody?

Harvey Gerst

"Harvey Gerst" wrote in message
...
I've seen everything from 12" x 13P to 13" x 17P for this motor as the
standard
size and pitch.

I know the new prop (that I got from the guy I bought the boat from) ain't
cuttin it at 13" x 19P.

Anybody?

There isn't a single answer to which prop is best. One factor is certainly
the horsepower of the motor, but the characteristics of the boat can play
into the equation as well.

What isn't "cuttin it" now?

How does your boat perform (what speed and RPM) under Wide Open throttle
(WOT) ?

Is this a two cycle or four cycle engine?

The motor is 33 years old, could it be losing horsepower?

If you need more hole shot then the standard answer is to go lower in pitch.
Keep in mind your top end, however. If you reduce the pitch by 10% then
your RPMs at top speed will be 10% higher, or perhaps your top speed will be
10% less or some combination of the two. It may be possible to find a shop
that will loan you a prop to try out. This is really common for I/O units
but it might be hard to find a shop that deals in props for a Chrysler
outboard. If you can find a loaner it will allow you to try it out before
you invest in a new prop.

Rod

"rmcinnis" wrote:

"Harvey Gerst" wrote:
I've seen everything from 12" x 13P to 13" x 17P for this motor as the
standard
size and pitch.

I know the new prop (that I got from the guy I bought the boat from) ain't
cuttin it at 13" x 19P.

There isn't a single answer to which prop is best. One factor is certainly
the horsepower of the motor, but the characteristics of the boat can play
into the equation as well.

According to the Chrysler manual, the 13x19 is primarily recommended for their
high performance 150hp engine.

What isn't "cuttin it" now?

It either dies when I try to open it up, or takes a very long time to get up on
plane. If I "goose it", and IF it doesn't stall (which it does about 50% of the
time), it'll eventually get up on plane, after a long time.

How does your boat perform (what speed and RPM) under Wide Open throttle
(WOT) ?

Max, right now? About 32MPH @ 3,800 RPM (which is current WOT).
Recommended WOT is 4,400 to 5,100 RPM.

Is this a two cycle or four cycle engine?

It's a two cycle, three cylinder engine.

The motor is 33 years old, could it be losing horsepower?

It seems to be meeting specs, according to two different mechanics.

If you need more hole shot then the standard answer is to go lower in pitch.
Keep in mind your top end, however. If you reduce the pitch by 10% then
your RPMs at top speed will be 10% higher, or perhaps your top speed will be
10% less or some combination of the two. It may be possible to find a shop
that will loan you a prop to try out. This is really common for I/O units
but it might be hard to find a shop that deals in props for a Chrysler
outboard. If you can find a loaner it will allow you to try it out before
you invest in a new prop.

Rod,

First of all, thanks for the help. The confusion for me lies in seeing
different specs being recommended for the "standard" prop. One piece of
Chrysler literature has the prop listed as 12x13, another has it listed as 13x14
(and 13x15), and another prop (suggested by several people) was 13x17. The
13x19 "digs in" too much, I think, and loads down the engine.

I'm getting a 13x17 (and I'll keep an eye out for a 13x15 as a spare), but it IS
confusing to me.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

When is the last time the carbs were professionally cleaned or rebuilt? That
sound more like the problem with that engine.


"Harvey Gerst" wrote in message
...
"rmcinnis" wrote:

"Harvey Gerst" wrote:
I've seen everything from 12" x 13P to 13" x 17P for this motor as the
standard
size and pitch.

I know the new prop (that I got from the guy I bought the boat from)
ain't
cuttin it at 13" x 19P.

There isn't a single answer to which prop is best. One factor is
certainly
the horsepower of the motor, but the characteristics of the boat can play
into the equation as well.

According to the Chrysler manual, the 13x19 is primarily recommended for
their
high performance 150hp engine.

What isn't "cuttin it" now?

It either dies when I try to open it up, or takes a very long time to get
up on
plane. If I "goose it", and IF it doesn't stall (which it does about 50%
of the
time), it'll eventually get up on plane, after a long time.

How does your boat perform (what speed and RPM) under Wide Open throttle
(WOT) ?

Max, right now? About 32MPH @ 3,800 RPM (which is current WOT).
Recommended WOT is 4,400 to 5,100 RPM.

Is this a two cycle or four cycle engine?

It's a two cycle, three cylinder engine.

The motor is 33 years old, could it be losing horsepower?

It seems to be meeting specs, according to two different mechanics.

If you need more hole shot then the standard answer is to go lower in
pitch.
Keep in mind your top end, however. If you reduce the pitch by 10% then
your RPMs at top speed will be 10% higher, or perhaps your top speed will
be
10% less or some combination of the two. It may be possible to find a
shop
that will loan you a prop to try out. This is really common for I/O units
but it might be hard to find a shop that deals in props for a Chrysler
outboard. If you can find a loaner it will allow you to try it out before
you invest in a new prop.

Rod,

First of all, thanks for the help. The confusion for me lies in seeing
different specs being recommended for the "standard" prop. One piece of
Chrysler literature has the prop listed as 12x13, another has it listed as
13x14
(and 13x15), and another prop (suggested by several people) was 13x17.
The
13x19 "digs in" too much, I think, and loads down the engine.

I'm getting a 13x17 (and I'll keep an eye out for a 13x15 as a spare), but
it IS
confusing to me.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

"Illinois Fisherman" wrote:

When is the last time the carbs were professionally cleaned or rebuilt? That
sound more like the problem with that engine.

Carbs were rebuilt last month.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

Tank pickup may be clogged? Was the problem there before the rebuild,
Harvey?


"Harvey Gerst" wrote in message
...
"Illinois Fisherman" wrote:

When is the last time the carbs were professionally cleaned or rebuilt?
That
sound more like the problem with that engine.

Carbs were rebuilt last month.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

"Illinois Fisherman" wrote:

Tank pickup may be clogged? Was the problem there before the rebuild,
Harvey?

Before the rebuild, it would die everytime I took it out (and I had to use a
trolling motor or paddles to get back to the dock). It was a combination of
gunked carburator needles, a bad gas tank with no venting and really misaligned
control cables. I think all that's left is changing out the prop.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/