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View Full Version : 24 MPH at 3800 RPMs 1981 Stars and stripes


zetalampi999
05-30-2008, 12:26 PM
Boat 1981? Stars and Stripes 351 w/power slot transmission?

Engine runs strong but tops out speed at around 25 MPH with RPMs reading 3800. What can be causing this?

Ben
05-30-2008, 12:38 PM
Seems awfully slow, you don't still have the trailer connected do you? You're supposed to leave that at the ramp.

Just kidding, this seems like an insanely wrong prop, or something else I know nothing about. A good start would be to check your prop for the size (hopefully stamped at the center, maybe 14x18 for a powerslot) & post on here to compare w/others who would know the correct prop size.

TRBenj
05-30-2008, 01:03 PM
Dollars to donuts you got a 13x13 on there instead of the proper 14x18.

I would suspect that you should be able to turn 6k+ RPM's with that 13x13 if your motor was tuned properly. I think you you have other issues, but start with the prop.

Hollywood
05-30-2008, 01:06 PM
Or you have your tach set on 4 cyl. mode and are really only turning 2500 rpm!

EricB
05-30-2008, 01:51 PM
Lets start back at the beginning.... when did this first occur? Did it do it last year? Last time out? New Boat? Did you replace/change anything recently?

Sounds more like a powerslot prop (14 x 18) on a non-slot drivetrain (1:1).

ShamrockIV
05-30-2008, 02:41 PM
did the prop fall off??????

ShamrockIV
05-30-2008, 02:42 PM
[QUOTE=Ben;497877]Seems awfully slow, you don't still have the trailer connected do you? You're supposed to leave that at the ramp. [QUOTE]



man that is funny!!!!!!

454Prostar190
05-30-2008, 02:53 PM
You're on a roll Shamrock!:)

ShamrockIV
05-30-2008, 02:55 PM
You're on a roll Shamrock!:)

thanks!!! lol

man i had a 84 but it was a slot and ran alot faster than that!!!
and beat ur brains out too!!!!

TMCNo1
05-30-2008, 03:07 PM
"Reb tha mutha up!"

Evan Jones
05-30-2008, 03:35 PM
Tranny slippage.....???

ShamrockIV
05-30-2008, 03:38 PM
too much ballast?????????????????(human type)

zetalampi999
05-30-2008, 03:58 PM
This has been the case ever since I've owned the boat. Me driving and one skiier or no skiiers at all this is how it runs. I thought the speedos might be clogged but they are not and you can tell when slalom skiing that it is not fast enough, so I think they are reading correct. I will look at the prop when I pull it out this weekend.

zetalampi999
05-30-2008, 04:04 PM
I'm not sure how to tell if power slot or not any sure tell signs.

east tx skier
05-30-2008, 04:08 PM
I'm not sure how to tell if power slot or not any sure tell signs.

Look at the tag on the transmission. Not sure about the 80s, but later era slots had a 1.125" diameter shaft versus a 1" shaft for a 1:1.

EricB
05-30-2008, 05:16 PM
Looks like the back of the transmission has the gear reduction housing of a 1.5:1 trans, which would mean it has a powerslot transmission.
Check your prop size and shaft diameter. That boat should hit 42 to 45 mph at about 4400 rpm.

ski_king
05-30-2008, 06:09 PM
That is a Powerslot (1.52:1) Transmission.
It should have the 14 x 18 prop.

When running right, it should be able to top out around 44-45 mph at 4400-4500 rpm.

Once it is up on plane, it should be close to the rpm should be real close to the mph..... 3000 rpm = 30 mph etc.

Sonds like a power issue........ maybe just needs a tuneup?
How is it running otherwise? Is it backfiring, sputtering on take off, etc?

Jim@BAWS
05-30-2008, 07:01 PM
Inpossible a 13 x 13 will not fit on a POWERSLOT shaft
Power slot shaft is 1 1/4

Adjusrt your speedos

20 MPH is 2000-2100 RPMs all day long

Jim@BAWS



Dollars to donuts you got a 13x13 on there instead of the proper 14x18.

I would suspect that you should be able to turn 6k+ RPM's with that 13x13 if your motor was tuned properly. I think you you have other issues, but start with the prop.

Willski
05-30-2008, 07:05 PM
Seems like my RPMS run just a little over my speed. ~ 3800 RPM for 35-36 mph. Top out about 4400-4500.

TMCNo1
05-30-2008, 07:18 PM
I always had the understanding a PowerSlot shaft was 1 1/8", ICBW!


By the looks of the picture, that boat has/does sit real low in the water, by the apparent toilet ring/waterline mark along the sides. The wooden stringers and the foam may be saturated with water, therefore the boat may be carrying a lot of extra weight and it may be having a hard time reaching speed because of all the additional weight it could be carrying. Only about 6" of the hull should be underwater when measured at the corner of the transom.
35703

EricB
05-30-2008, 10:41 PM
TMC;
Good observation!!!! The tell tale lake water line (if left in the water) shold be at about the bottom red stripe. That could be a sign of an over-weight boat.

sk8salomon
05-31-2008, 09:01 AM
TMC;
Good observation!!!! The tell tale lake water line (if left in the water) shold be at about the bottom red stripe. That could be a sign of an over-weight boat.


so we are back to the ballast (human type) problem again? lol!

pilot02
05-31-2008, 09:08 AM
I always had the understanding a PowerSlot shaft was 1 1/8", ICBW!


By the looks of the picture, that boat has/does sit real low in the water, by the apparent toilet ring/waterline mark along the sides. The wooden stringers and the foam may be saturated with water, therefore the boat may be carrying a lot of extra weight and it may be having a hard time reaching speed because of all the additional weight it could be carrying. Only about 6" of the hull should be underwater when measured at the corner of the transom.
35703

Great observation and I'll vote for correct. That boat is sitting WAY too low in the water... Stringers and flooring are most likely saturated with water as already mentioned.

FrankSchwab
05-31-2008, 11:35 AM
Maybe the PO added a bit of ballast? Perhaps in the form of lead or steel weights?

I can't imagine saturated stringers weighing enough to lower the boat that much!

/frank

pilot02
05-31-2008, 11:49 AM
Lead is a definite possibility... Platform looks like it's been raised up as well. You'd be suprised how much weight saturated foam and stringers will provide though.. My previous boat was a 79 Galaxy I/O and when I replaced the floor/stringers/foam in it, there was a substantial weight difference for the better.

If he's running 3800 RPM's, he should be running at least in the mid to upper 30's speed wise..
3800 rpm's is way too low for this boat so....
First thing I'd check would be to hook up an external tach and put the boat through it's paces.. That boat should be running 42-4400 rpm and probably 41-42 mph without a slot and 44-46 with and just a driver in the boat. So, that leads us to whether there's a prop problem or something mechanical elsewhere...
Regardless, there's definitely a problem because he's not getting the rpm's. Having verified the tach (rpm's) and the prop size (stamped on the prop) I'd also check to see if there is tension on the shaft (alignment) to see how freely the shaft rotates.. If it doesn't rotate freely in neutral on the trailer, I'd star walking the floor looking for soft spots/stringer damage and then go from there.

If the boat runs to rpms out of gear and the prop looks good (no visible dings) no binds in the drive train and the floor and stringer's seem solid, etc., I'd bet the bands are shot in the tranny or the oil pump's going out and not providing enough pressure to fully engage the bands in which case, the bands will be shot soon as well.. If the fluid level is low in the tranny, it will slip and I've also encountered issues with my own when I switched from regular Dexron to Synthetic.. Suprisingly, I've found that I haveto keep my fluid level at the full HOT level or it will slip under severe load. Personally would have thought that synthetic would have been better in this respect.

Pilot's .02

zetalampi999
06-02-2008, 01:49 PM
as for the sitting to low in the water...it doesn't actually sit that low in the water. The water line is just below the bottom red stripe I'm not sure why in the picture it does look look like that. Here is a picture in the water. I wasn't able to take boat out this weekend to see the prop but I did feel that it is a 3 blade if that matters. The motor runs very strong starts right up no sputter/hesitation very responsive. Can you tell me how I can easily check proper rpms are reading. ( hook up an external one)

pilot02
06-02-2008, 02:05 PM
If you don't have one, check with your friends and find someone with an old style Dwell/Tach meter.. All you have to do is hook up the battery connections and one signal lead which should clamp over your #1 spark plug wire.. While your at it, check for a timing light and ensure that your base timing is 10 degrees before Top Dead Center and also that as you rev the engine the timing advances more (towards 25 degrees BTDC). There's a mark on the crankshaft pulley as well as a pointer to line up with it.. You may need to put a little white paint (white out works well) to be able to see them in motion. I'm not sure of the exact spec off the top of my head for the advance while revving but if it's not advancing and your not seeing at least 10 degrees of advance that would also explain the lack of top end RPM's.

454Prostar190
06-02-2008, 02:20 PM
C:\Documents and Settings\All Users\Documents\My Pictures\Kodak Pictures\2006-05-30\100_0660.jpg

Just an observation on my boat. I hope this works

454Prostar190
06-02-2008, 02:21 PM
Nope:(....