1957 evinrude fastwin 18hp ventilation problems.

[K.C]

@Texasmark
What size boat did you use to waterski behind with the 18?

 

[K.C]

Seems a shame to hack down the transom on a boat rated for75+hp to accomodate an 18hp motor....

I agree, but I don't have money for brand new boat or long shaft motor. I really would like a larger motor but I can always just use short shafts right?

 

[WesNewell]

Boost Speed with Outboard Engine Height Adjustments - boats.com

Raising an outboard higher on the transom can reduce drag and raise top speed.

www.boats.com

 

[racerone]

Find the 5" extension kit.---They are not hard to find !----Your location ?----Find a kit at the local meet for the ----aomci-----Or find one on the aomci----website !

 

[K.C]

Found all the parts for it on ebay. Gonna be about $400 to do the 20" conversion. Might hold off a while on that cause I could probly get a bigger motor that I can fix up for that.

 

[K.C]

Find the 5" extension kit.---They are not hard to find !----Your location ?----Find a kit at the local meet for the ----aomci-----Or find one on the aomci----website !

I'm in maine btw @racerone
Gonna see if I can find the parts in a kit for cheaper than individually buying them.

 

[racerone]

These motors were essentially the same for near 20 years.-----Lots of used parts / kits available from collectors I think.

 

[K.C]

These motors were essentially the same for near 20 years.-----Lots of used parts / kits available from collectors I think.

Yeah, I'm gonna check my local boat yards.

 

[Texasmark]

Seems a shame to hack down the transom on a boat rated for75+hp to accomodate an 18hp motor....

That's a good response and I agree not just on the not hacking comment, but if it's rated for 75 the 18 will be a dog.....get another engine like a 50 or so......with a 20" leg.

 

[K.C]

So as I mentioned earlier I did not have money for new motor. So I made a 5" cut 1' across center of transom. Attached the motor and headed for lake. Now I remind you that before I could reach max rpm but it was ventilating. Now it's not ventilating, but when it planes off (with just me) I can only get the motor to rev to around 3000 rpm, max speed of around 10mph. I've tried clean fuel and carb cleaner. Changed plugs and pulled flywheel to check mag plate points and condenser. Everything seems to check out. And still nothing. Maybe a compression test? Idk. In a barrel it runs great and in reverse it will hit max rpm. But under the load of pushing me and boat it will not go past half throttle or so. And I've checked my throttle linkages and adjusted the high and low speed to factory spec and then adjusted once on water for maximum performance but still nothing. Any tips?

 

[WesNewell]

From previous photos it appeared that you only needed to lower the engine 2-3 inches to get the av plate even with the hull bottom, but you're saying you lowered the engine 5"? Now I have no idea of where your av plate is in relation to the hull bottom, and that is THE most important factor in regards to engine performance. But one thing seems obvious to me. Now that the prop is fully below the water line you need to get the proper pitch prop to allow your engine to reach the max recommended rpm at wot. But don't even think about prop pitch until you have the engine at the proper mounting height. Another photo like the first one you posted would help so we can see things as they are now.

 

[K.C]

From previous photos it appeared that you only needed to lower the engine 2-3 inches to get the av plate even with the hull bottom, but you're saying you lowered the engine 5"? Now I have no idea of where your av plate is in relation to the hull bottom, and that is THE most important factor in regards to engine performance. But one thing seems obvious to me. Now that the prop is fully below the water line you need to get the proper pitch prop to allow your engine to reach the max recommended rpm at wot. But don't even think about prop pitch until you have the engine at the proper mounting height. Another photo like the first one you posted would help so we can see things as they are now.

 

[K.C]

I believe I cut it to the exact measurements it needs to be. I apologize for saying exactly 5". It was between 3.5 and 4 that I actually took it down.

 

[WesNewell]

The height looks pretty good. Now you just need to find the right pitch prop to allow the engine to reach its wot max rpm, which I think is 4000-5000 rpm. But if that boat is rated for a 75 hp engine then you'll be lucky to even get it to plane with an 18 hp. It will surprise the heck out of me if you can even reach 20 mph.

 

[K.C]

The height looks pretty good. Now you just need to find the right pitch prop to allow the engine to reach its wot max rpm, which I think is 4000-5000 rpm. But if that boat is rated for a 75 hp engine then you'll be lucky to even get it to plane with an 18 hp. It will surprise the heck out of me if you can even reach 20 mph.

I've seen the same motor on similar 14ft boats do about 20-25mph. Apparently people have used water skis behind these motors. Mine is maxing out really really low. I don't have exact measurements but I'd say between 2k-3k rpms. It just gets on plane and then won't speed up. With 3 people my tops is like 5mph. I've gone over everything but compression test. Think that's next?

 

[K.C]

I have an original 9x11 prop on the motor now.

 

[Sea Rider]

If you have already modified the transom height, with deck load well distributed report at which lower leg height is the water flow paasing by, is it passing above the upper water plate, under it or towards the lower AV plate, for that must pull your head side of motor to check that out, no wild guessing nor wild assumptions here. If you sit the motor at a certain transom height for th AV plate to face or be even with the hull's bottom then you won't care at all at which lower leg height is the water flow passing by which it's of extreme importance as boats doesn't float same.

If the combo it's impossible to plane will need to install a less pitch prop to make it plane in order to check that out, boatig fun starts when the motor run towards its max wot rpm range while lightly loaded, say max 2 souls onboard, the issue is that being an oldie motor wil probaly have very few less pitch props to choose and go for. If not will have to content yourself achieving just fast displacement boring speeds....

Happy Boating​

 

[K.C]

If you have already modified the transom height, with deck load well distributed report at which lower leg height is the water flow paasing by, is it passing above the upper water plate, under it or towards the lower AV plate, for that must pull your head side of motor to check that out, no wild guessing nor wild assumptions here. If you sit the motor at a certain transom height for th AV plate to face or be even with the hull's bottom then you won't care at all at which lower leg height is the water flow passing by which it's of extreme importance as boats doesn't float same.

If the combo it's impossible to plane will need to install a less pitch prop to make it plane in order to check that out, boatig fun starts when the motor run towards its max wot rpm range while lightly loaded, say max 2 souls onboard, the issue is that being an oldie motor wil probaly have very few less pitch props to choose and go for. If not will have to content yourself achieving just fast displacement boring speeds....

Happy Boating​

Yeah I understand that. When its Just myself in the boat, the water is passing about a 1/4 inch above the av plate. That's at around half throttle 2500 or so rpms barely on plane. But that's as fast as it will go.

 

[Sea Rider]

Yeah I understand that. When its Just myself in the boat, the water is passing about a 1/4 inch above the av plate. That's at around half throttle 2500 or so rpms barely on plane. But that's as fast as it will go.

Can you measure the gap distance in centimeters between both lower leg's plates. That lower leg must have at least a 3 inches gap if not more in between both plates. Is the motor running strong throughout the whole throttle range ? if so that motor needs an urgent prop swap to at least a niner or less prop pitch to plane faster with 2 up.

Happy Boting​

 

[K.C]

Can you measure the gap distance in centimeters between both lower leg's plates. That lower leg must have at least a 3 inches gap if not more in between both plates. Is the motor running strong throughout the whole throttle range ? if so that motor needs an urgent prop swap to at least a niner or less prop pitch to plane faster with 2 up.

Happy Boting​

Runs strong up to about 2500rpms (not exact)but it won't go past that. While pushing me in boat. In a barrel and in reverse it will hit around 5000rpms.