18HP saga continues. Can’t get past 14mph and 3,900 RPM.

[billw]

I know you have tried three power heads. However I still would like to know the compression. 18s are unstoppable and get used and abused until the cows come home. Thus, they are often found with high cylinder wear. They will still run like a fine Swiss watch at lower speed, even with this wear. If you haven’t got 115 psi or better, you may not ever make it to 4500. Many times, you see them with 90, even 80 psi compression and they are smooth as silk; but the power just isn’t there.

At this point, you have been whipping this thing forever; so it is more of a matter of pride than money, that you get it to work. If I were you, I would rig it up with an adjustable high speed jet carb bowl or whole carb, at least as an experiment and see if that helps.

Long live American manufacturing!

[kerry]

Since I have an early 60’s 18 on the back shelf for later, I may as well ask- will an earlier carb with an adjustable high speed fit ? Unless I get lucky at the dealer, and he has a kit #278623 in stock, I might as well keep my options open.

If you have too many, AND not enough, you're a collector.

[fleetwin]

quote BillW:

I know you have tried three power heads. However I still would like to know the compression. 18s are unstoppable and get used and abused until the cows come home. Thus, they are often found with high cylinder wear. They will still run like a fine Swiss watch at lower speed, even with this wear. If you haven’t got 115 psi or better, you may not ever make it to 4500. Many times, you see them with 90, even 80 psi compression and they are smooth as silk; but the power just isn’t there.

At this point, you have been whipping this thing forever; so it is more of a matter of pride than money, that you get it to work. If I were you, I would rig it up with an adjustable high speed jet carb bowl or whole carb, at least as an experiment and see if that helps.

I like this idea…..The high speed needle might be too long and interfere with the lower pan though…
I have quickly reread this thread, but I don’t see anything about the prop style/pitch, pictures of the boat, or a description of the tachometer you are using….15MPH does seem way too slow for an 18hp though, have you tried it on a different boat?

[stephenspann27]

Mumbles, The missfire at idle i was chasing was either form a worn mag plate, or a bad plug wire. I bought a mag plate off ebay with the coils, points, wires, condensers etc already installed. I double checked the points gap and put it on my motor and the low RPM missfire went away. I’m not sure what my boat ways. i’m running a 14′ v bottom aluminum lone star boat, with a little bit of wood, bow mount trolling motor and battery. I’m willing to change from 40:1 to 50:1 but I dont’ see that small of a change making a big difference at WOT. I can see it making a difference with fouling plugs at idle etc. Since I know now I only have two main jet size choices, and I was already running the smallest available I think I’m going to try to get the older style carb with the adjustable high speed circuit.

[stephenspann27]

quote BillW:

I know you have tried three power heads. However I still would like to know the compression. 18s are unstoppable and get used and abused until the cows come home. Thus, they are often found with high cylinder wear. They will still run like a fine Swiss watch at lower speed, even with this wear. If you haven’t got 115 psi or better, you may not ever make it to 4500. Many times, you see them with 90, even 80 psi compression and they are smooth as silk; but the power just isn’t there.

At this point, you have been whipping this thing forever; so it is more of a matter of pride than money, that you get it to work. If I were you, I would rig it up with an adjustable high speed jet carb bowl or whole carb, at least as an experiment and see if that helps.

Bill, I’ve got another thread on here from a January when I was talking about not being able to reach max RPM. Someone said the exact same thing you are telling me, and that’s what lead to me buying the 3rd powerhead.

viewtopic.php?f=2&t=10394

I completely tore down two previous powerheads after removign them. The original one (which I never ran on a boat) was indeed worn out, all the cross hatching was gone, the crank was purple from being hot, corrosion had worn away a huge amount of material in the water jackets. I think it had about 95 PSi of compression. The second powerhead (off ebay) which I did run, the ebay add I think sayid 125 PSi, my gauge showed 105PSI. That’s the powerhead I was running when I started the post in January. When I took that motor apart I found that it wasn’t worn out but it had been hot, the pistons were scored, the bore was scored,and the crank journals were purple. The third powerhead which I’m running came from a AOMCI member, and is supposed to my "known good" powerhead. I think it has around 125PSi of compression as well. I’ll have to double check. I sort of put this project aside for the summer, and I’m working on it again, so some things are fuzzy .

A agree with you on the adustable jet carb. That is my action plan.

[stephenspann27]

quote fleetwin:

quote BillW:

I know you have tried three power heads. However I still would like to know the compression. 18s are unstoppable and get used and abused until the cows come home. Thus, they are often found with high cylinder wear. They will still run like a fine Swiss watch at lower speed, even with this wear. If you haven’t got 115 psi or better, you may not ever make it to 4500. Many times, you see them with 90, even 80 psi compression and they are smooth as silk; but the power just isn’t there.

At this point, you have been whipping this thing forever; so it is more of a matter of pride than money, that you get it to work. If I were you, I would rig it up with an adjustable high speed jet carb bowl or whole carb, at least as an experiment and see if that helps.

I like this idea…..The high speed needle might be too long and interfere with the lower pan though…
I have quickly reread this thread, but I don’t see anything about the prop style/pitch, pictures of the boat, or a description of the tachometer you are using….15MPH does seem way too slow for an 18hp though, have you tried it on a different boat?

Around January last year I had this rig out, along with my father in law’s 14′ flat bottom, which is bare bones, and his 1990 15hp evinrude. I did swap the motors and boats around at that point. I think my boat ran 19-20MPH with his 15hp. I don’t remember for 100% sure what my 18hp pushed his 14′ flat bottom to, I think it was around 15mph. He is boat has less drag for sure, and is probably lighter.

As far as the adjustable carb fitting my lower plan. There is already a hole in the pan I think the bass shaft can go through. I’ll enlarge it if i need to. I’m determined to make the older style carb work.

[stephenspann27]

Oh, prop pitch. I was running the stock 9×10, but I installed a 9×9 yesterday. No change at all in speed or RPM.

Here are some vidoes of the motor idle, reving to max (I know this is bad to do), accelerating, and starting.

https://www.dropbox.com/s/vowb22skkj0n5 … 0.mov?dl=0

https://www.dropbox.com/s/3i59j6msbwjj8 … 2.mov?dl=0

https://www.dropbox.com/s/69o36l1n0ny1c … 1.mov?dl=0

[billw]

Yeah, revving in neutral doesn’t really prove anything. It takes very little effort to make it WAY past 4500 when no-loaded. It would probably do it with one plug wire off. Very bad form. 😉

As for the adjustable jet thing, I was thinking that even if it didn’t fit in the lower pan, you could cut one short, file a slot in the end and tune it with a screw driver, or something of that nature, just to prove or disprove a point.

By the way, 18s do use a ton of fuel. Even good ones. Maybe it’s the relatively small carb bore of the earlier ones. (Pre-’69) I don’t know why; but they do. I don’t want to start a crap storm but Mark 25s are way better on fuel, in my experience.

Long live American manufacturing!

[Steve D]

on Ebay right now…
http://www.ebay.com/itm/Johnson-Evinrud … Mx&vxp=mtr

[stephenspann27]

quote Steve D:

on Ebay right now…
http://www.ebay.com/itm/Johnson-Evinrud … Mx&vxp=mtr

Crap I didn’t see that. I already ordered a 1964 model carb that’s the dual knob style. It was only $40 shipped, so I didn’t pay a ton more than the needle kit.

[Author]

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