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

Home › Forum › Ask A Member › 18HP saga continues. Can’t get past 14mph and 3,900 RPM. › Re: 18HP saga continues. Can’t get past 14mph and 3,900 RPM.

October 7, 2017 at 2:12 pm #65847
stephenspann27
Participant
    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.