85' Evinrude 150XP powerhead

Hey guys new to the site and have a couple questions about a 85' 150XP. I recently bought an 82' V-king w/ an 84' Johnson 150 and it came with a 150 XP powerhead. The powerhead runs good but I was told 2 of the cylinders have low psi (90psi) due to minor scuffing. I am taking it to my mechanic this weekend to see how the compression is on the other 4. What PSI should this motor be turning out and if they aren't within 10% of each other what kind of work (and cost) should i expect?

I am currently seeing 68-70 with a 26P trophy, nose cone/low water pickup and sits on a manual jack plate with 6.5" set back. What kind of speeds can I expect with the 150XP and a prop change to a 27P OMC SRX?

Thanks guys any feedback would be great.

John

It is in my opinion, so important when asking hypotheticals the rpm. reading be included thanks:).

Welcome to Scream and Fly! :)

That motor has loose heads on it, so 90-100 psi would be my guess.

A rebuild, it depends on a lot of variables. Whether it needs to be bored and one or more pistons replaced, or just honed and new rings, whether you want to replace the bearings or not, etc, etc.

5500rpm with a 26 is 68 at 10% slip, then 5500rpm with a 27 at 10% slip is 70 according to my calculator.

Did you buy that blue V-king on craigslist in NY?

Thanks for input. Would a compression test diagnose those other possible variables or would they need to tear it down? Assuming that compression is between 90-100 for all cylinders, am I taking a risk by potentially blowing out a piston if minor scuffing does exist? Would I be better (and also a cheaper) off just taking the heads and carbs off the XP and putting them on my current motor? Sorry for all the questions, I've been driving fast boats for 15 years but haven't worked on them much.

@gregpro50 yea I got it in Galway,NY a few weeks ago.

So what is the final reading on the compression on the other 4 cyls? Keep the carbs, but ditch the heads. Look for a set of 1979 heads, either the basic 150-175-200 456/457 (110 lbs) or the 235 heads 872/873 (120 lbs)

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Originally Posted by EMDSAPMGR

So what is the final reading on the compression on the other 4 cyls? Keep the carbs, but ditch the heads. Look for a set of 1979 heads, either the basic 150-175-200 456/457 (110 lbs) or the 235 heads 872/873 (120 lbs)

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I have a mint set of those 200hp heads that I'll sell to you for a good price if that's what your after. Pm me and we'll work something out.

Take the air box cover off both motors. The 150 XP should have 1 5/16" carbs. The 150 may have smaller carbs. In that case, yes swapping to the larger carbs would be better.

How much scuffing does it have? Can you post some pictures?

I haven't had the time to pull apart the XP just going on what the previous owner told me. Thanks for all the input ill keep ya posted and let you know in a week or so where I'm at once I get the powerhead back.

Leak down test would probably reveal scuffing if it was bad.