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Thread: lowered engine proformance Help

  1. #1
    Member rrjfish8's Avatar
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    Default lowered engine proformance Help

    I had my boat out the first time this year and was disappointed in the proformance. For staters my engine is a one year old 50 honda. Last year I was able to get 25-27mph at 5400rpm this time out I was able to get 22-24 at 6000rpm and did not run it there very long it also had a hard time with climbing some of the steeper rollers . Before I went out I changed the engine oil and lower unit oil checked plugs put a new prop on (same as old). The lower unit oil I put in was 75w-90 royal purple I am now going to put 80w90 honda which is what I had it it. The engine oil is to the top hole on the dip stick (where it is supposed to be). When I put the prop on I took all the washers off and put a lot of grease in and around everything. I had a about 1/4th a tank of old gas in it from last year that I did not put anything in for the winter but I ran it for about 15 min on 3 or four nice day in the winter, could out gas do this? I also had alittle residue around the exsaust. hopefully the gas or lower unit oil and nothing more but I would like to hear from some people that know more them me. Thanks Ryan

  2. #2
    Moderator Paul H's Avatar
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    Sounds like something is different with the new same as the old prop. If you're going slower at higher rpm I'd think your new prop has less pitch, but that would help you climbing rollers.

    I'd inspect the spark plugs and see what they look like. If they aren't tan/brown, put in new plugs, and definately new gas.

    Any chance you were carrying more gear on the boat, or have moved stuff around so that there is more weight foreward in the boat? Trim change can make a notable difference in performance, same as carrying additional weight.

  3. #3
    Member spoiled one's Avatar
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    It sounds to me like one of your props isn't the stated diameter and pitch. The one you just put on is turning numbers par with a lower pitched prop. A simple test would be to put the old one back on. Seems odd that it would turn higher rpms, yet have a lower speed and a tough time with the rollers. I wonder if it has a "bum" hub?
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  4. #4

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    Quote Originally Posted by rrjfish8 View Post
    I had my boat out the first time this year and was disappointed in the proformance. For staters my engine is a one year old 50 honda. Last year I was able to get 25-27mph at 5400rpm this time out I was able to get 22-24 at 6000rpm and did not run it there very long it also had a hard time with climbing some of the steeper rollers . Before I went out I changed the engine oil and lower unit oil checked plugs put a new prop on (same as old). The lower unit oil I put in was 75w-90 royal purple I am now going to put 80w90 honda which is what I had it it. The engine oil is to the top hole on the dip stick (where it is supposed to be). When I put the prop on I took all the washers off and put a lot of grease in and around everything. I had a about 1/4th a tank of old gas in it from last year that I did not put anything in for the winter but I ran it for about 15 min on 3 or four nice day in the winter, could out gas do this? I also had alittle residue around the exsaust. hopefully the gas or lower unit oil and nothing more but I would like to hear from some people that know more them me. Thanks Ryan
    Ryan,

    You didn't mention if your honda 50 has a carb or not. All the hondas I have ever had have carbs that are very difficult with old gas. They cough, sputter, flood over the floats, and run like crap. If they have one flaw, it is that they will not take having gas that is not fresh, dirty gas, or old gas. But with that said, after my gentle encouragement on not to abuse your honda, I don't think that is your problem. You didn't fill us in, but normally people don't just change a prop after one season (what did you do? It's ok we have all done it before LOL) and I suspect that the new prop is not the same as the old prop. Or it could be that whatever you are measuring your speed with is wrong (fish finders and water wheel speedos are notorious for this). If you are going by GPS, it also could be going against the tide instead of with it on this occasion.

    While there could be a number of reasons, the prop being different is what I'd look at first as you should not be running more RPMs and getting less speed if your prop is the same with an identical trim setting. It just doesn't compute to me.

    Pete, I am at a loss of how a bum hub of lower unit could cause anything but a catastrophic and immediate failure. Even without the thrust washers they just eat the housing all up and don't really fail exactly. What did have in mind on that?

    It even could be a combination of things. Like more stuff in the boat, a different prop, bad gas that has lowered your octane and engine's power, different tides and the wind. And I don't think anyone has mentioned this yet, sometimes some kelp will get under the boat and around the outboard causing light cavitation which does lead to more RPMs and less power. Normally, the skipper notices immediately, but sometimes it is more subtle. It has happened to me.

    Maybe you should put new gas into it, make sure your load is set like last year, set your trim to last year's setting, and take it out again before busting the wrenches out.

  5. #5
    Member rrjfish8's Avatar
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    is there a way to see if the hub is bad? no carb, the 09's are efi's The prop is stamped the same, I still have the old prop, it just has a very few bumps on it and thought I would use it as a spare. I forgot to say I did fill it up with new gas but 1/4th of it was old. The load was about average. I am getting great info thanks, I want to figure this thing out.

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    Member spoiled one's Avatar
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    Quote Originally Posted by T.R. Bauer View Post
    Pete, I am at a loss of how a bum hub of lower unit could cause anything but a catastrophic and immediate failure. Even without the thrust washers they just eat the housing all up and don't really fail exactly. What did have in mind on that?

    I was referring to the prop hub. Can they slip? I have heard of people spinning hubs, causing the rpms to sky rocket. My bet is on the prop. Just because it is stamped the same doesn't mean that it is. Quality control just isn't the same today as it used to be. I don't think it will be getting much better, either.
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    Member rrjfish8's Avatar
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    I just looked at the two props. They look the same. could you tell by putting them side by side?

  8. #8
    Member Alaskanmutt's Avatar
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    Default Yes the hub can be bad

    All it is is rubber and they can slip. The do not alway slip enough to make the engine race wildly either. They can sli[p enough to raise the rpms a bit (like 5400 to 6000) and then the prop won't grab (Think slipping clutch in a truck)

    You can take the prop to A-1 props on Potter here in Anchorage. The owner should be able to tell you if it is bad or not (had this happen to me a few times when in the Coast Guard)
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  9. #9

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    Quote Originally Posted by Alaskanmutt View Post
    All it is is rubber and they can slip. The do not alway slip enough to make the engine race wildly either. They can sli[p enough to raise the rpms a bit (like 5400 to 6000) and then the prop won't grab (Think slipping clutch in a truck)

    You can take the prop to A-1 props on Potter here in Anchorage. The owner should be able to tell you if it is bad or not (had this happen to me a few times when in the Coast Guard)
    That is new information for me. It sounds like just putting the old one back on would eliminate that once and for all though. I will keep that subtle slip in mind. Only once have I had a hub fail and it was immediate and catastophic. A-1 said it happens that way all the time as I was shocked it could just go like that. I couldn't even get it to bite enough to get back to the dock. Thank god for kickers....I think I'd take it back if the prop is toast. I wish him the best of luck.

  10. #10
    Member Rod in Wasilla's Avatar
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    I'd look at the prop as well. I've got a 15 horse that did the same thing. Prop hub was slipping. New prop, no more problem.
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