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90 Tohatsu

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Justaguy10825 View Drop Down
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    Posted: 09/06/2012 at 2:07pm
I just bought a 24" with a 90 Tohatsu. The prop on it now is just a little chewed on one of the tips so I'm wanting to replace it. The boat came with 2 props. The spare is a 13 pitch but the PO told me that with this prop on it, the RMP's were closer to where they should be (5200) but he was fouling spark plugs. This does not make sense to me because I would think that the higher RPM's would keep thngs hotter and be less chance of fouling. The chewed prop (15 pitch) runs in the neighborhood of 4200/4400 rpm and does not foul out the plugs......
Any ideas as to why it may be fouling at the higher RPM's? I have not seen it happen yet and am just going off what the PO told me. But of course, at the same time, he was wanting me to let him keep the spare prop (but since he had advertised the boat with two, I kept it..... )
Any ideas? Thanks!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 2:49pm
First off, don't put that 15 pitch prop back on, does more harm to the motor. I've never known props to cause plug fouling.  You could rebuild the carbs and never fix the fouling problem. So it also sounds the hotter it gets, something is letting more air get in and causing an incomplete combustion resulting in fouling.  I would pull the plugs, and soak the cylinders in SeaFoam to decarbonite it. My advice is to take it to a QUALIFIED mechanic who can do the testing properly (just my opinion). It will cost you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CajunDiver Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 2:52pm
Maybe he put too much oil in the gas
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 2:53pm
By the way, put specifics of your boat and motor in your signature line so we don't have to ask for the information. Like now we could use the year of your motor to track the specifics of it of what the prop SHOULD be on your motor. Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PS-Guy Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 3:27pm
I think you meant LESS air...more air = leaner burn Wink.  That motor should be oil injected so could be an issue there.  Higher RPMs alone will NOT cause fouled plugs...in a properly running motor it would be just the opposite. 
Feel free to contact me for help on your project!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Justaguy10825 Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 4:29pm
It is a 1993 / 24' Sweetwater with a 90HP Tohatsu. He told me that the engine was original equipment on the boat. Other than this, what information would be helpful or required? Startes right up, started it on the muffs first, then took it out for a test ride before I bought it. No noises or anything sounding "off" coming from the engine. WOT only got up to about 4200/4400 RPM & that's with the 15 pitch on it.. Thanks
1993 SweetWater 24"
1993 Tohatsu - 90HP
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 4:57pm
I would use the 13" prop. It will not cause fouling of the plugs and it is the proper one for your boat/motor combination.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/06/2012 at 5:06pm
info on the motor would be what year it is, don't assume its original equipment. If you're not sure of the year, post the serial # and/or model number for us to look it up for you. That way you'll know for sure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Justaguy10825 Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 9:43am
I will be up there tomorrow (I have it stored near a lake) I will get the serial number... I am also going to change the prop to the 13 pitch. Can anyone tell me what tools I will need to take to swap the props so I do not take a bunch more than I need. Also, Would anyone know what spark plugs the engine should have in it? I would like to take an extra set just in case there are any fouling issues. Paddling a 24' barge does not sound like fun. Thanks again!
1993 SweetWater 24"
1993 Tohatsu - 90HP
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Woody Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 10:05am
What lake do you keep her on? I grew up just north of you, loved Greer's Ferry Lake.  Do you have a manual for that motor? If not do an online search, you might find one. Also go to a website like iBoats and look up the parts schematic for that engine, it should tell  you things about the nut size, plug type, etc.
 
To remove the prop you will need a piece of wood (2x4) to wedge on top of the prop to keep it from spinning when you turn the prop nut. You will need a prop wrench or a deep socket and breaker bar. I think the standard size is 1 1/8 inch although mine was smaller, more like 15/16 inch as I recall. Remove the plug wires when you take it off so that you don't accidental crank the engine. Look at the locking tabs holding the nut in place, there are several types. Again the engine schmatic should show you. Take an extra with you if you can. They often break or soften, always best to replace it each time. Some may have wire on the nut so take wire clippers. Put the engine in neutral, be sure the key is off, block the prop  with the wood so that it won't spin and turn the nut to the left to remove.
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Boating in SE Louisiana and
Cedar Creek Lake, TX
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 10:23am
Get both the serial number AND model number, as some don't show by serial number what they are.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Woody Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 10:50am
Charles is right, those are important numbers to get and keep with you. I can't tell you how many times I've gone to look something up online and needed that info. I keep them on a text file in my cell phone now.
Woody & Marilyn
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Cedar Creek Lake, TX
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Justaguy10825 Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 11:10am
I have her stored indoors in Higden/Greer's. Did not want to deal with keeping her on the water & the issues that go along with it. I don't have a manual yet but I certainly am going to be needing one. The online ones your talking about, is that something that I will need to pay to download or are the free ones I can take a look at "As-needed"? Thanks!
1993 SweetWater 24"
1993 Tohatsu - 90HP
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 12:16pm
Get the paper backed ones. I would never pay for one you download as a pdf because depending on the source, they are probably illegal copies of copyrighted materials. iboats and others will have the books you're seeking. Somewhere on the forum we have links to books sources so a little bit of searching on your part (do advanced search) will or should work. Maybe someone will be kind enough to find the lines for you if you need help with that. Just be sure you're getting a paperback version from a reputable seller. I never liked something I had to print out (although a page or two is convenient) but I've got 4 different books on my older motors and sometimes you'll find 3 different answers. Some are better than others in describing mechanical testing with photo's.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Woody Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 2:22pm
Sometimes you get lucky and find something online for free although most manufacturers now sell them. A printed book is best, as Charles suggests. Personally I like to avoid the "one size fits all" manuals (covers all Tohatsu 1988-2004, 9-200 HP, or such as that). Those really get confusing trying to figure out just which engine is actually the one you have. A manufacturers service manual for your specific model and year is the best option although these can be expensive. Many companies that sell engine parts, such as iBoats, have skematics online that show you details of the various parts, and these are free to look at. I suggest you take a look at them.
Greer's Ferry is a great lake, I'm sure you'll enjoy the pontoon up there. I do understand what you mean about keeping a boat in the water. A lift is nice if you can swing that.
Woody & Marilyn
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Boating in SE Louisiana and
Cedar Creek Lake, TX
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Woody Quote  Post ReplyReply Direct Link To This Post Posted: 09/07/2012 at 2:29pm
Here is one manual on eBay:
 
I'm not sure if that one fits your motor or not. It would help people offer suggestions if you put info in your signature about your boat and motor (brand, year model, etc.) Even though you may have posted that info elsewhere most of us won't take the time to go search your threads to get the info.
Woody & Marilyn
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Boating in SE Louisiana and
Cedar Creek Lake, TX
Excellent Member of the Month Club 6/09
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