1988 175hp powerhead on a 1986 150hp

[300mag-hunter]

I've got a 1986 150hp (J7153506 J150TCLDC) Johnson that runs great, but seems to be slow on top speed. Compresson is 84-86 psi on all 6, taken by only removing one plug at a time. If I put the lynard back on and fired the motor quick with the gage in the top right cylinder it hit 110 psi, I only tried that on the one cylinder to see if it showed higher. With a 19 pitch prop, on a 18 foot ranger bass boat I'm running around 5400 rpm @ 43-45 mph gps fully loaded with gear and fuel. I steped up to a 21 pitch prop and it dropped the rpm to 4600 rpm and it increased the speed to 45-47 mph gps, but very slow out of the hole. It seems to run fine with the 19 pitch just slower than I like, most of these boats run near 60 mph.

I'm considering repowering, or swaping out the powerhead. I'm wondering what power heads will bolt right on to my 1986 Johnson, and be ready to go. Horsepower is not a concern of mine as long as it is at least 150hp, so if a 175 or 200 powerhead would bolt on I'd be fine with it, just have to stay off the throttle some. I've read info different places and found info on spacers, low compression gaskets, different reed spacers, etc used on these motors. I don't want to have to deal with that, just looking for a bolt on application.

I've found a 1988 175hp powerhead, recently rebuilt for a very reasonable price. Is there any difference below the power head on a 150 vs a 175 or 200. Or can I just bolt on the 175 powerhead on my 150 midsection and have a 175 motor. Or will I have to swap carbs, heads, manifolds or etc. to get it to run right. Also If this powerhead won't fit my midsection what years and horsepowers of powerheads will interchange with mine.

Thanks for any help.

 

[jtcarter]

Re: 1988 175hp powerhead on a 1986 150hp

You should remove all the spark plugs when doing a compression check. The 175 should be the same size as the 150.... carb jetting is usually the only difference. 200 is probably going to be a bigger bore and stroke, might not work.

 

[etex driller]

Re: 1988 175hp powerhead on a 1986 150hp

Those are lower lower compression motors sounds more like a setup problem to me I have a 18.5ft dyna trak bass boat with 86 150 gt with 6in jplate with prop shaft sitting 3.5in below pad with a 14.5 by 24p maker prop running 64mph @ 5600rpm with med. Load how low is your motor sitting sounds like a lot of drag to me most all my buds with this motor run 22-24 pitch props.

 

[dpd2483]

Re: 1988 175hp powerhead on a 1986 150hp

i have a 150gt on a 17ft boat with a jack plate and a 26 prop im geting 68 to 70 mph

 

[emdsapmgr]

Re: 1988 175hp powerhead on a 1986 150hp

A 1988 175 will not fit on a 1986 150 midsection. The 150 is a flatback engine. The 175 is a bubble back detuned 235. The midsection adapters are different. You do have a few options to consider. Your current 150 is the base model-at 150 hp. If you could locate a complete 150 from an XP/GT engine, it makes nearly 165 hp and would fit. Many of these later XP/GT models are propshaft hp rated. Also, the older flatbacks will fit, (1979 and later) they came in assorted 150, 175, 185 and 200 configurations-all crank rated.