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  1. #1
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    Hopped up 60deg Johnson not performing as expected after rebuild

    I have a 96 johnson fast strike 150 on a 96 stratos 282. I purchased the boat cheap with the powerhead having two cylinders down.

    MODS....

    Just finished a full rebuild .020 oversize oem piston and rings, new bearings, seals, water pump, thermostats ect
    Had the block casting junk cleaned up and the block was polished up nicely.
    Exhaust ports raised to 175 HP block specs
    Idle relief holes plugged off using JB-weld
    Installed FICHT reed cages with Boyesen dual stage carbon reeds
    Rebuilt carbs and went up three sizes on main jets (69D- 72D)
    Disconnected VRO oil line, plugged off, unplugged harness
    Exhaust tuner modified by plugging and welding passage between port/stb exhaust passage
    Installed 1991 fast strike cylinder heads pn 335195
    Installed 6" jackplate 3.5" below the pad

    Emptied fuel tank and lines, removed anit-siphon valve, blew out vent hose with air
    First run was with 93oct no ethanol fuel premixed 25:1
    I have ran less than a tank through it so I am still mixed rich

    Complaints..

    Runs rough at idle and up to 2500ish rpm.. A few short full throttle runs top out at 61gps.. My step fathers bone stock non fast strike model runs 63 on a similar hull without jackplate and same prop. (23p renegade)

    I have tried anywhere from 5.5-7.5 turns out on the mixture screws to help the low end. It will not stall but seems to get really close and shakes the boat badly until the revs build up some.

    some troubleshooting on the ignition showed #1 coil was infinite resistance( others were 275ohms)
    Replaced switchbox, optical sensor, and all coils with new CDI at the same time....no change on running performance
    also running recommended QL78YC at .030 gap

    Link and sync looks good, timing looks good while running. Compression tests cold with throttle open show 105,110, 108 port and 108,110,110 stbd.

    Battery voltage shows 11.85 on my mulitmeter. A side note, cdi instructions say that I can disconnect the port temp sensor and ground the tan wire from the harness to set the timing. I did just that and only get a single flash from the timing light while the engine turns over. I can not see the timing unless the engine is running even though cdi says there is a work around by jumping the tan wire to ground. I have performed resistance checks on the stator and they appear to be good.

    I can only turn the 23 renegade 5600-5700rpm at 61mph
    I plan to play with the jetting and go up to a 74D to see if that helps the top end I am looking for, I am stumped on how to clean up the bottom end. Seems as if it is dropping a cylinder at idle to 2500rpm.

    I know theres alot of info here and probably more indepth than most care for. Any performance gurus or johnson/evenrude gurus see if yall can help me find the power I am missing. It should be an easy 180HP engine after these mods, and should push that 17'stratos closer to 70mph than 60.

    Thanks

  2. #2
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    did you change to 175 carb set up
    Certified Experimental Engineer.

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  4. #3
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    You can't add more fuel without adding more air,you'll just run rich.You need the larger carb bodies and throttle bodies from a 175,and I would start by going up one jet size from stock,Chris

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  6. #4
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    Thanks for the tip on the jet size.

    My understanding of the carbs is that the fast strike/intruder model uses the same large diameter carbs as the 175hp engines.

    My carb has p/n 436798 on the body. came with 69D jets stock.

  7. #5
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    No i did not change the carbs, only the main jets during rebuild.

    I thought the fast strike carb was the same diameter as 175hp?

    I read around on some of these forums and that old bass and walleye article, I didn't see any mention of swapping the carbs. I hope I did not over look that.

    heres a link the the article
    http://www.dynomitedynamometer.com/a...up_article.htm

  8. #6
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    After some searching it appears the throat size of my carbs is the larger style. So maybe just play with low speed screw and high speed jetting from here?

    some info on the carbs
    http://forums.iboats.com/forum/engin...erchangability

  9. #7
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    If the engine runs very rich it will make less power.


    18 ft Speedcraft - Offshore

    Bottle Fed Merc tuber 2.4

  10. #8
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    Monty from monty racing was kind enough to give me some info over the phone, he says they run a size 74D in their engines but I know there is more head work than slapping on a pair of 91 heads as I have done, and more port work.

    I had my intake and crank ports cleaned up really well, and exhaust ports opened up to 175hp specs. Nichols Outboard engineering did my block work, I have used them several times in the past and always do good work.

    The plugs did look blacker than coal after a short run but I wasnt sure if that where from running rich on fuel, or the 25:1 oil mixture.

    It is symptomatic of being rich, but one of the best in the business says jet up. This is going to get expensive at $15 per orifice

  11. #9
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    as a side note,if its still in break-in,i wouldnt run wot until your done with the break-in schedule.ive burned down a couple like that in omc motors(too much lead in foot!).better that it it runs rich than lean,especially while breaking in.

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    Proper break in is vital after a rebuild , if you run it hard early you will scuff the bores and the engine will not make the power it should


    18 ft Speedcraft - Offshore

    Bottle Fed Merc tuber 2.4

  13. #11
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    Yes you guys are right on the break in, I have probably opened it up prematurely.

    Did a few idle runs in the driveway, then maybe 30 min run time before cracking it open momentarily.

    I have done several WOT runs on the first tank, only opening it up prop 10-15 sec each time before backing down to 4500rpm.

    You guys think ive jumped the gun and scored it up already based on the compression numbers I have posted above?

  14. #12
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    if you only have 30min. on it under load so far,your getting too high on the rpms WAYY too soon!did you get a break in schedule?what type of oil are you running?

  15. #13
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    It has probably 3 hrs under load on it now. I have the service manual that outlines a break in procedure. Ive always thought varying the rpm range, and avoiding lugging the engine was more important than babying the engine for 10hrs.

    Something to do with the way the rings are shaped with a bevel edge facing up, the pressure in the cylinder pushes the rings outward against the cylinder wall and fully seating when cracking the throttle open here and there.

    The oil is cheaper penzoil 2 cycle. I will prob switch to omc oil once I no longer mix 25:1 Figured double rich would provide plenty of lubrication regardless of oil quality

  16. #14
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    so long as its not synthetic,or a blend.i did this on my efi merc motor and it took twice as long to get the rings broken in.

  17. #15
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    Thanks for the heads up, i will avoid synthetics until broken in.

    I want to get a little more in-depth than just the jetting. CDI says i should be able to time this engine with a timing light by using 1 jumper wire from port temp sensor to ground. i get one quick flash from the timing light when the engine first starts turning, and then another flash on the last rotation of the engine. The switchbox, coils and optical sensor are brand new cdi componets. I cant help but wonder if this is related to the low rpm hesitation and stumble.

    I am not grounding all plugs while checking, only the #1 that I am trying to see with the timing light.
    All plugs fire with a visual check, and timing light while running.

    Any ideas?

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