WOT RPMs not there

[houstoncajun]

Re: WOT RPMs not there

Yeah. I'm looking at everything right now.. gonna start with the spark, then fuel, then prop. If it was cavitation, wouldn't my rpm go up though?

I couldnt get my rpms up at first either, changed plugs, cap and rotor, adjusted timing and got up to 4200 RPM. but still just churned water at 10 MPH max, changed the prop and it planed out and hit 25 mph (maybe the wind was helping) but am down to 3800 RPM. (I'm learning on the prop selection now and its a compromise between hole shot and top speed)

not sure if I should be giving you advise since i'm just learning it too

 

[houstoncajun]

Not getting WOT

Not getting WOT

I'm getting around 3800 RPM with a speed of about 25 MPH (22 - 25 depending on waves)

the boat is heavy 5500 LBs dry, 100 gal gas, 25 water, 9 waste and lots of beer and ice

its a 260 mercruiser 5.7 with an alpha 1 drive

I've changed distributor cap and rotor, plugs to ac delco, put good gas in it, timmed it a litte bit off though about 12 BTDC at around 800 to 1000 RPM (will fix that tomorrow) my compression checks as follows:

#1 125 #2 145
#3 140 #4 145
#5 125 #6 145
#7 150 #8 145

My specs are as follows from mercruiser:
WOT 4200-4600
Idle 650-700 @ 8 BTDC
1.50:1 overall drive gear ratio

In my manual:
The original prop Carver put on it was a 15 3/4" x 16, but there is a statement in there " 25 to 35% prop slip is common for a cruiser type boat operating at crusing speed"

"variations in load, operating conditions, enviornment, the individual engine and hull performance may necessitate the purchase and use of another prop"

Is there anyother way to find out if my engine is making the proper power without a dyno test? I dont want to change the prop if I have a engine problem instead

Any advise on where to go from here would be appreciated

 

[JustJason]

Re: Not getting WOT

Re: Not getting WOT

Double check your tach against a known good tach first... then have a look at this list courtesy of Don s.

http://forums.iboats.com/showthread.php?t=295070

 

[houstoncajun]

Re: WOT RPMs not there

Please take a look at this:

http://forums.iboats.com/showthread.php?t=309743

 

[Tail_Gunner]

Re: WOT RPMs not there

http://boatpropellers.iboats.com/Me.../9591/?**********=867741255&*******=759923513

Cost effective and the right blade design....

Product Info

Solas Amita

• High quality aluminum propeller.
• Universal blade design to fit wide variety of applications.
• Wide blade design works well with 4-stroke engines.
• Designed for outstanding acceleration and top speed.
• Tough heavy duty rubber bushing smoothes shifting and won?t slip.
• Exclusive Solas squeeze casting process nearly eliminates porosity making our aluminum propellers stronger and tougher than traditional die cast propellers.
• Solas aluminum propellers have 4 layers of paint applied using superior coatings and high-tech painting process to ensure excellent anti-corrosion performance.

Theres a very good design spefic prop again in ss
http://boatpropellers.iboats.com/Me...23177/?**********=867741255&*******=759923513

The BAY PRO III 4 blade series propellers are specifically designed for offshore fishing boats and offer great acceleration and improved midrange performance in rough water and adverse conditions.
The BAY PRO III series is available for 115 horsepower and greater engine with 4.75" diameter gear cases.
BAY PRO III utilizes the Stiletto Guardian Hub system.


Your old prop is cavitating badly and looks a little lean..At this point because of the lack of good data or info..(worn prop) id suggest you go with the 15 alum and if it performs well with the boat you can alway's use it as a spare and go to the SS which will give you lower planing and higher speeds ..but they will be not be that large of a gain

Just a question..a Alpha drive on a 26" boat???

 

[MikDee]

Re: WOT RPMs not there

Ok... so i went and changed the plugs and distributor cap, (3 of the cap screws sheared off in the body of it so I clamped the cap back on, just to run until I can fix it) It now will get 4200 RPM but is not gaining any speed, about the same at 2500 RPM as 4200, it just churns water, the spare prop is a 48-78118-17, i need to do a quick haul and change it out and test again. Here is a pic of the prop on it now. I tried trimming everywhich way and moving the weight around still not getting on plane. any thoughts are appreciated

After finally moving to this thread from the other one, and just now seeing the picture of that spare prop, Maybe it's me, but it looks like a magnet for attracting bubbles (cavitation, ventilation, whatever you want to call it, because the surface is rough!) something like having barnacles on the bottom slowing you down.

It appears the 17" pitch prop you had on it to start with works better, but IMO it is still overpropped! I still seriously doubt you'll be able to spin a 4blade

 

[houstoncajun]

Re: WOT RPMs not there

That prop pictured has been in the trash for a couple of weeks. The prop currently on it is a quicksilver aluminum 15 x 17 with the rubber torque 3 insert, thats where my numbers are coming from currently. I posted originally in the motor forum before doing my tune up and was just churning the water with that prop pictured, then ended up in the prop forum. (Tailgunner recommended jumping around in the forums to get answers) I've done the tune up but the timing is a bit off and will fix this weekend. I'll go with the suggestion of a 15 x 14 prop zero rake and let you know the numbers from that.
Oh and I ran some seafoam throught the gas tank and crankcase when I first purchased her and changed the oil last weekend

Thanks for the help