1991 20HP Evinrude no acceleration

[67Mirro]

Ok, I’ve been fighting a problem with my boat for quite some time and think everything has made sense to me after using it this past weekend just want to know from all you guys if this would make sense to you. I’ll explain it all and let me know if that’s what you think it is.

So I first took my boat out in the spring and it was running fine but then When I would get on plane the boat would be going fine then all of a sudden slow down but the rpm’s would still stay high until I let off the throttle on the tiller. And then I would rev back up and go and another 30 seconds would do it again or it would catch it self and take off again. I initially thought it was the fuel pump and fuel delivery so I changed it all and rebuilt the pump then went back out. I went back out and started doing the same thing again so it had me stumped. Then this past weekend I took it out ran fine on plane for 5 minutes then kicked down and rpm’s stayed high while my speed went down to 4mph and if I went to accelerate it would rev up but not go any faster than 7mph but would rev up high and sound normal just would not grab the water and go and after that it was like in limp mode and would only got 5mph no matter how much throttle I gave it it would just rev higher(kind of like when a clutch is slipping in a car) . After doing some online research I came to realize that maybe my prop had spun on the hub? And leading up to my boat finally shutting down for good made me think was it failing before when it would do it occasionally and it would slip here and there and then this week I did it in and finally wrecked the bushing in there? Has anyone had this issue before? Thanks in advance, just going down to the lake next weekend and want to try to get this resolved.

 

[saltchuckmatt]

Ok, I’ve been fighting a problem with my boat for quite some time and think everything has made sense to me after using it this past weekend just want to know from all you guys if this would make sense to you. I’ll explain it all and let me know if that’s what you think it is.

So I first took my boat out in the spring and it was running fine but then When I would get on plane the boat would be going fine then all of a sudden slow down but the rpm’s would still stay high until I let off the throttle on the tiller. And then I would rev back up and go and another 30 seconds would do it again or it would catch it self and take off again. I initially thought it was the fuel pump and fuel delivery so I changed it all and rebuilt the pump then went back out. I went back out and started doing the same thing again so it had me stumped. Then this past weekend I took it out ran fine on plane for 5 minutes then kicked down and rpm’s stayed high while my speed went down to 4mph and if I went to accelerate it would rev up but not go any faster than 7mph but would rev up high and sound normal just would not grab the water and go and after that it was like in limp mode and would only got 5mph no matter how much throttle I gave it it would just rev higher(kind of like when a clutch is slipping in a car) . After doing some online research I came to realize that maybe my prop had spun on the hub? And leading up to my boat finally shutting down for good made me think was it failing before when it would do it occasionally and it would slip here and there and then this week I did it in and finally wrecked the bushing in there? Has anyone had this issue before? Thanks in advance, just going down to the lake next weekend and want to try to get this resolved.

Yes, you've spun the hub, take it to a prop shop or buy a new one. There is a chance that your engine is mounted too high and you are ventilating the prop. But I don't think so and if it ran fine a long time ago and it's definitely your prop. By the way when your prop slips and you're over-reving that's very bad on your motor.

 

[67Mirro]

Yes, you've spun the hub, take it to a prop shop or buy a new one. There is a chance that your engine is mounted too high and you are ventilating the prop. But I don't think so and if it ran fine a long time ago and it's definitely your prop. By the way when your prop slips and you're over-reving that's very bad on your motor.

Yea I think I’m just going to buy a new prop trying to figure out what pitch still. And keep the old one and have the bush in replaced. I just kept the RPMs super low and putted in I wasn’t reviving the crap out of it lol wouldn’t want to blow it hahaha

 

[jimmbo]

The Dia, Pitch and Part# are usually located under the Nut and Washer that hold the Prop on. Sometimes the Dia and Pitch are also on the outer hub.

 

[saltchuckmatt]

Yea I think I’m just going to buy a new prop trying to figure out what pitch still. And keep the old one and have the bush in replaced. I just kept the RPMs super low and putted in I wasn’t reviving the crap out of it lol wouldn’t want to blow it hahaha

Yes, I agree with Jimmbo. Here are a few pictures of a prop off a 25hp. 10 inch diameter by 13 pitch. Common pitches are 13, 15, 17 pretty sure yours is a 10inch dia. Without a tachometer it's hard to dial in a prop so do your homework.

 

[tphoyt]

Sure sounds like a spun hub.
I always carry a spare prop thrust washer nut and pin. Just for this reason.
You just never know where or when it’s going to happen.

 

[67Mirro]

Yes, I agree with Jimmbo. Here are a few pictures of a prop off a 25hp. 10 inch diameter by 13 pitch. Common pitches are 13, 15, 17 pretty sure yours is a 10inch dia. Without a tachometer it's hard to dial in a prop so do your homework.

yea right now im pushing about 36kph (22 mph roughly), looks like common pitches on 20 hp are 10-11-12-13 thinking of going 11 or 12 to pull more top end as im on a bigger lake and like to get places when i need too

 

[jimmbo]

yea right now im pushing about 36kph (22 mph roughly), looks like common pitches on 20 hp are 10-11-12-13 thinking of going 11 or 12 to pull more top end as im on a bigger lake and like to get places when i need too

I doubt you will see any difference in speed, by going up in pitch. As mentioned above, you need a Tachometer to tell you what RPM the Motor is running when at WOT. The engine needs to be within a certain Rpm range, if it is to achieve it's HP and have any Longevity. I believe that with your engine it is 4500-5500 rpm. Going up in pitch will increase the load on the engine, resulting in a Lower Rpm at WOT, and very little difference in top speed. Sometimes the top speed drops as the pitch goes up, because the engine can't even get near the WOT Rpm range

 

[saltchuckmatt]

I doubt you will see any difference in speed, by going up in pitch. As mentioned above, you need a Tachometer to tell you what RPM the Motor is running when at WOT. The engine needs to be within a certain Rpm range, if it is to achieve it's HP and have any Longevity. I believe that with your engine it is 4500-5500 rpm. Going up in pitch will increase the load on the engine, resulting in a Lower Rpm at WOT, and very little difference in top speed. Sometimes the top speed drops as the pitch goes up, because the engine can't even get near the WOT Rpm range

I wholeheartedly agree with Jimmbo. For simplicity sake, if you don't want to do the homework, stick with same prop as you have and most likely you will be ok.

 

[saltchuckmatt]

Sure sounds like a spun hub.
I always carry a spare prop thrust washer nut and pin. Just for this reason.
You just never know where or when it’s going to happen.

I'm thinking you think this prop has a shear pin....it does not. It's a pressed in rubber bushing.

 

[racerone]

PIN-----Likely referred to the cotter pin for the prop nut !!

 

[jimmbo]

I'm thinking you think this prop has a shear pin....it does not. It's a pressed in rubber bushing.

OMC hasn't used Shear Pins since the early 50s. They did use Drive Pins of Stainless Steel, for many years after, but in 1968 started to transition to Splined Shafts and Hubs. In most cases the Props had Rubber Hubs to protect the Shift Mechanism, in some motors they used a coiled Slip Spring coupling on the driveshaft. They marketed these like they were to going to save the prop from damage on impacts.

 

[saltchuckmatt]

PIN-----Likely referred to the cotter pin for the prop nut !!

If you look at what he says, " sounds like a spun prop, I carry a extra pin for this very reason" to me, he's making it sound like this corrects this condition. Maybe I'm interpreting this incorrectly.

 

[racerone]

The party that posted #6 is not a dummy !----Read post #6 carefully.

 

[tphoyt]

Cotter pin for the nuts is correct.
I guess I should be more specific next time

 

[saltchuckmatt]

Cotter pin for the nuts is correct.
I guess I should be more specific next time

I see now!! There is no comma after spare prop. "I thought spare prop thrust washer" then I thought how are those things going to help you. I guess I'm the dummy but even that is up for interpretation!!!! Lol communication is key.

 

[jimmbo]

I see now!! There is no comma after spare prop. "I thought spare prop thrust washer" then I thought how are those things going to help you. I guess I'm the dummy but even that is up for interpretation!!!! Lol communication is key.

Poor punctuation caused that. Too many people write long never ending sentences that never end where they never use commas periods and still expect others to figure out what they said and meant even though it may be difficult they know what they meant and they figure we should know because they know what they meant clear a mud not

 

[saltchuckmatt]

Poor punctuation caused that. Too many people write long never ending sentences that never end where they never use commas periods and still expect others to figure out what they said and meant even though it may be difficult they know what they meant and they figure we should know because they know what they meant clear a mud not

Lol, so true!

 

[67Mirro]

Yes, I agree with Jimmbo. Here are a few pictures of a prop off a 25hp. 10 inch diameter by 13 pitch. Common pitches are 13, 15, 17 pretty sure yours is a 10inch dia. Without a tachometer it's hard to dial in a prop so do your homework.

does anyone know the proper pitch for a 1991 Evinrude 20 hp tiller? talked to a guy at local dealer and says 11-12-13 but wanted to know what's on it. but the boats at the lake in the water and i want to take a new prop with me he said he has a 12 pitch in stock thnking going with that but know beleive its a splined shaft in my year (14 splines) any suggestions?

 

[jimmbo]

The Proper Pitch is one that allows the Engine to run within the Engine's WOT rpm range, usually preferred to be in the upper half. To determine that, a Tachometer is needed. What is the Proper Pitch for a 14ft Car Topper, is not going to be the Proper Pitch on a 20ft hull.