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I did buy a SE421 about a year a go. I love it. It work perfect and so far I have no problems. The only thing is with original Lower Unit my boat (I have Contender 23 with a 225 2 stroke Yamaha) will speed upto 48, 49 MPH. Since I change the lower unit with the SE421 top speed is 41MPH. Do I have to change propeller to gain back the previous top speed? Do not get me wrong, the lower unit had work perfect, it is just that little detail. If I have to change the propeller what will be the ideal prop for the SE421 lower unit?
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I'm sorry your having an issue. I will need a little more information to be able to help. Do you have the model number of your engine? Do you know the RPM that your currently maxing out at? And finally, do you know what prop you are currently running?
My first thought is that you have the incorrect ratio, or at least a different ratio than the lower unit you replaced. Do you know if it was original? It is possible that we built it wrong, or someone replaced yours with a different unit some time ago, or the wrong information was given at the time of order.
Finally, was the boat running just prior to changing the lower unit? Sometimes an engine will sit broken for quite some time before fixing it, and in that time things can happen. A bad fuel pump, bad fuel, stuck rings, etc.
Please get back to me with answers to these questions and we will see what can figure out.
Tech Support -
No a problem, I am happy with the product.
Eng. Model No: S225TXRU.
I can not see the RPM on the clock.
The prop I have is 15¼ x 19.
I do not know what was the ratio on the original lower unit. The one SEI sold me is 1.81:1. The Part no is 90-421-A25. SE 421, 1.81:1 25" Driveshaft. That is what the invoice says.
Yes the boat was and is running ok before the original lower unit incident. Everything is running, so far, perfect.
If I do not go fishing on the weekend I run motor for a bout 15min every Sat or Sunday. Also I use the YAMAHA RING FREE FUEL ADDITIVE.
Regards,Comment
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Let me ask a question the lower unit I have is standard rotation or counter rotation?tComment
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I confirmed that your unit should be a 1.81 ratio by the model number. We do also make a 2.00 ratio, it is possible it was built with the wrong gears, but to be honest I think I have only seen that happen once out of 90,000 units we have made so it is unlikely.
You could try to confirm it by turning the motor over two times and seeing if the prop makes one full revolution or is slightly short of one full revolution. A 2.00 ratio is 2 turns of the engine to one turn of the prop. It is best to do this with the lower removed, for safety reasons, but if you do it with the lower unit on the motor, then I would recommend disconnecting the battery and removing the spark plugs to make it easier to turn and to make sure it doesn't accidentally start.
If you have your old unit, you could also try to turn that one and count the revolutions, or if it is disassembled, just let me know the tooth count and I can do the math.
There is no reason that the RPM or top speed should be different, given the same ratio, same prop and a properly running engine, so I can only assume that the ratio must be different. Do you know if the old lower unit was original? I wonder if someone put a 2.00 ratio one on there for some reason.
Without knowing the RPM you are currently running, it is hard to recommend a prop. You could certainly try a different one, but I think it is better to research the ratio's first, just so we know what is going on, then we could make a recommendation.
If it is what I think, and you had a 2.00 on there for some reason, and now it has a 1.81, then you would need to go with a smaller prop. If it is the other possibility, which is we gave you a 2.00 ratio, then we would certainly swap out the gears for you, or you could try going to a bigger prop.
Tech SupportComment
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What a bout the rotation. What rotation is the lower unit I have is standard rotation or counter rotation?Comment
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Your unit is a std. rotation.
Tech SupportComment
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I did Check today the ratio and it is 2:1. When the eng turn twice the prop turns one
and two inches. What prop do you suggest ?Comment
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I sent you an email showing the positions of the shaft after doing the ratio check. If it wasnt at exactly 12 o'clock then it will not be a 2.00 ratio. Can you check the old one?
Tech SupportComment
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The old lower unit is broken that is why I purchase SEI product.
Technic how I did check ratio:
I remove all spark plugs. Put a pen inside cilinder one. Put the eng in fowar gear. Turn flyweel(FW) until piston head in cilinder one went all way to top. Mark FW with marker in a point and also mark propeller and lower unit in a spot. Turn FW twice and monitoring the rotation on the prop. As got to the second turn of FW the propeller mark pass one time and 2 inches more.Comment
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That should mean you have a 1.81 ratio which is correct from the factory. If someone had put a 2.00 on tbere, that might explain the speed difference. The math says you would need a smaller prop, so you could try a 17 pitch, but that is a guess since you don't have a tachometer.
Tech SupportComment
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So with the 2:1 ratio what size of prop should I buy?Comment
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It really depends on tbe boat and the current rpm. Unfortunately you can't tell me the rpm, so i can't recommend a prop. You could try to search for a prop calculator online, just remember you have a 1.81 ratio.
Tech SupportComment
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I installed a new tachometer and and prop 16x17. I will be testing it tomorrow. I will let you know my results RPM-SpeedComment
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I installed the tachometer and I installed the 16x17 Prop. I got 37MPH at top RPM 4200. I will be testing this week the original prop 15 3/4 x 19. I will give you the results latter this week.Comment
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