Need help new boat think I'm running too big of prop plz help

[Maxumman2b]

HI guys I'm new to this forum I just bought a boat a 1992 maxum 1900sr it has a 4.3 mercruiser with a alpha one gen 2 outdrive I got in my lake this last weekend and floored the boat it had a hard time planing off it got up to 35 mph only me on the boat at 3900RPMs I looked at the prop and I have a mercury mirage plus 48-13702a4521p I think this prop is to big I do lot of tubing a cruising around and would love to get some top speed out the boat I usually will have 2-4 people on the boat with me my question is how do I find out what hp is the motor?and what kind of prop should I change out to to get best performance out of the boat?also what the redline of this motor is and what I should be running in rpm range? Thxs for your help I would love some alive and help

 

[steelespike]

Re: Need help new boat think I'm running too big of prop plz help

My info indicates 4400 to 4800 rpm. A 190 is 1.81 ratio ,210-,220- are 1.62.
My feeling is your motor should be doing a lot better with a 21" prop.
You really can't make up 900 rpm with a prop. A 17" prop would add about 800 Speed might make about 42
But a 4.3 should be making about 50 or more with a 21" prop.
A 18 or 19 ft 3.0 with a 21" prop would top out about 38-40 mph at about 4800.
Things to check ,Compression, is throttle opening all the way,is the timing set right and advancing as it should.
Is the bottom clean and smooth?

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

Everything is running fine don't know how to do the timing because it has the thunder bolt Iv ignition system throttle is opening all the way I just found a ss 15x17p prop which I might buy to see if anything changes I also checked fuel filters and they were clean also and I believe this is a 155hp or 175 because there is a sticker which says no more then 180hp on the transom any others tip would be great

 

[BonairII]

Re: Need help new boat think I'm running too big of prop plz help

Any chance that your boat is waterlogged?

 

[steelespike]

Re: Need help new boat think I'm running too big of prop plz help

The 17 will help your performance but suppose load up with people and want to do water sports the boat will likely still struggle.
If you reduce the pitch more you will be in the the area of what you need for a hard to push pontoon.
Did you check the compression?Is the bottom clean and smooth?If you weigh the boat it will tell you if it has absorbed water over the years. Not unusual if poorly stored or moored.
If you look up props here at iboats for your motor I think you will see a 17 is way down the list and your boat is a typical size and weight for a 5.0.The prop would come from the middle upper portion of the chart.
At 20 years old it wouldn't be surprising if the motor needed a major tuneup with a compression check.

 

[CHARGER2]

Re: Need help new boat think I'm running too big of prop plz help

You definitely have an engine condition. Go through this list:
http://forums.iboats.com/mercruiser...ives/list-possible-causes-low-wot-295070.html

I bought my boat (very similar to yours) I had the same problem. A carb rebuild, new plugs, wires, cap, rotor and timing adjustment brought mine to the appropriate rpm range. Timing thunderbolt iv is pretty easy. Look it up in the forums.

 

[Starcraft5834]

Re: Need help new boat think I'm running too big of prop plz help

When you get your engine conditon fixed, but a 4 blade prop on.... I have a 20 ft cuddy, replaced the prop which was beat up, first with a 3 blade Solas, boat came up on plane slow,, got to 4200WOT bout 35 mph,,,, decided to go to 4 blade prop,, 15P 4 blade, 14.75 in Solas,
HUGE difference......... I had 5 adults in my boat, that 4 blade pushed me up on plane in less than 10 seconds!! probably 7... 32 mph at 4500 WOT perfect for my 3.0 140 hp in line 4.... I cant say enough about going to a 4 blade... you will lose a few mph, but gain huge hole shot!!! it was the right move for me and my heavy cuddy..... good luck

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

Thxs guys for all the info I picked up some things today a new thermostat because the boat is running extremely cold and won't heat up past 100 degrees thinking there is no thermostat or stuck open one also new fuel filters and a quicksilver ss 14 1/2 x17p I already did cap rotor ignition sensor plugs and coil I haven't done wires the boat is running smooth but has a little mist and pops through carb at cold start up or at holding the revs at 1500rpm thinking the timings off tommorrow morning I will be putting on the new stuff and reading up on timing for tommorrow also thinking the timing might be off I also realized that the outdrive has been changed and some one might of put the wrong gear ratio outdrive the boat is not water loged the boat sat for a couple of season the engine was frozen I got the motor sling freely I did a tune up of the ignition sites and got the boat running I replaced the sea pump and all gaskets and did a whole bellow job including a new gimbal bearing I also redid the floors with new wood and fiber glass just giving some info on the boat and what I know will update tommorrow to see if things change

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help


Just showing some pics so u guys see what I'm working with for visual I will post pics and maybe a video of engine running to show what's happening

 

[jestor68]

Re: Need help new boat think I'm running too big of prop plz help

Timing a Thunderbolt 4 is easy. Just hook your timing tight to #1 plug wire and setting timing to 8 BTDC with engine idling at 650 rpm. The timing advance is controlled by the ignition module.

Your 1992 4.3L is 175 hp or 205(4 barrel).

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

So I brought the boat out on the lake with the new prop when floored plained a little faster but kinda hestitated at first the rpms got up to 4400rpm at max trim up only me at 34mph I am now believing there is a issue with the motor could it be a carb issue there no adjustments that I can see can it be the shutters stuck on the exhaust any other things I could check timing will be checked is there way to put the ignition system in base timing mode

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

Update just pulled fuel filter really dirty changed to a new one thermostat was put in upside down and all the gaskets were wrong hopefully will fix problem

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

 

[CHARGER2]

Re: Need help new boat think I'm running too big of prop plz help

Next time post the pic upside up. I was really confused when I looked at it for a second! At that age I strongly suggest a full carb rebuild. Sounds like you have the know-how. Just get a carb gasket kit and rebuild it one afternoon. I bet it fixes your problem.

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

All right guys in long hard work I found it to be the timing I got it perfect now but still not getting those mph with one person trimmed all the way up WOT I'm getting 37mph 4200rpm witha 15x21p with the 14x17p I'm getting 35mph at 4900rpm almost 5k what should I get I'm thinking a 14 1/2x19p ss let me know what u think

 

[steelespike]

Re: Need help new boat think I'm running too big of prop plz help

37 @ 4200 indicates about 19% slip.Thats high.The somewhat low rpm would account for some of that.
A ss 19" prop assuming 4600 rpm and 14% slip speed would be about 39.
If slip is 10% speed would be about 41.
Does the boat respond to up trim?Did you check compression?
Are you running a hydrofoil? or trim tabs? Is the bottom clean and smooth with no distortions,flaking paint?
NADA says the sr is 130 hp so your 4.3 must be an upgrade.And indications are 175 hp.
I still feel that your rpm should be higher with the 21.And speed over 40,mid 40s.
Your dry weight is about 2400 Not bad for a 20 footer.

 

[Maxumman2b]

Re: Need help new boat think I'm running too big of prop plz help

37 @ 4200 indicates about 19% slip.Thats high.The somewhat low rpm would account for some of that.
A ss 19" prop assuming 4600 rpm and 14% slip speed would be about 39.
If slip is 10% speed would be about 41.
Does the boat respond to up trim?Did you check compression?
Are you running a hydrofoil? or trim tabs? Is the bottom clean and smooth with no distortions,flaking paint?
NADA says the sr is 130 hp so your 4.3 must be an upgrade.And indications are 175 hp.
I still feel that your rpm should be higher with the 21.And speed over 40,mid 40s.
Your dry weight is about 2400 Not bad for a 20 footer.

Thanks for the info what is slip exactly how do I fix the slip its not the hub in the prop because that's all new