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  1. #1
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    200 Carb Powerhead making 1000 Less RPM than 175 Opti Powerhead

    Melted a piston on a 175 opti and reverted the exhaust plates back to the original Carb setup. Was originally a 175 carbed then 3 years as a 175 opti.

    Heavy fishing boat and the 175 opti and the previous 175 carbed would do 34 mph at 5100-5200 rpm with a 16 pitch prop.
    The new to me 200 carb powerhead is only getting around 4400-4500 rpm and 26 mph. There was a brief moment going through a wave it shot up to 28 mph for 4 seconds and 5000 RPM then fell back down.

    I might be imagining it but primer bulb never really gets firm like it did on the opti.
    I found the recitifiers were blown and the red and yellow stators lead were loose disconnected and likely shorted to engine or each other. Just rewired with good rectifiers and charging works now and it smoothed out a high speed miss that was present while the rectifiers werent working. But motor still does not seem to have as much power as the 175.
    Seller is working with me and took compression pictures at my request 125 to 129 on all before i purchased. He promises he had it running 5800 rpm on a much faster setup (although he said 6400 RPM another time). Seems like he's telling the truth for now.

    Sounds like fuel delivery at this point as the engine wanted to spin up faster for four seconds once but, but have a dva and compression tester to recheck electrical and cylinder condition if need be.
    Any tips or ideas with the primer bulb not getting super firm appreciated.
    Maybe my boat got heavier over time and the 175 opti could push through the rpm range but the 200 carb can't reach its top end without a lower pitch prop? All powerheads discussed are 2.5L btw.
    Last edited by Fishinmymission; 08-11-2020 at 11:38 AM.

  2. #2
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    Kinda hard to say exactly, but 1st thing id do is check ignition system and then go over carbs if necessary, do u know how index a flywheel and make sure its firing when its suppose to on all 6?

  3. #3
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    I have a timing light and the thing that lets me see TDC. Ive done it for a single cylinder before years ago and can probably find the instructions again for all the cylinders.

    That being said can i verify my choke system works and see it injecting fuel with the carb box off? And adding choke (enrichener) while going full speed and I don'y hear or see any rpm changes, is that a giveaway that the issue is not in the carbs(at least the lower two carbs that its hooked up to)?

  4. #4
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    Its a possibility it stuck on choke but doubt it or it wouldn't idle at all , if u have that clearish bleed line (tygon) u can use that to watch it go thru or pull line off and hit choke and c if runs out line, do u hear the click?
    Last edited by Merc 2.5; 08-11-2020 at 05:10 PM.

  5. #5
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    Its a lot of work.... but pulling the coils out of the plastic case.... than pulling the rubber boot off..... Make sure the black carbon that holds the coils are not cracked.....leads to weaker spark...also ck ground wires on coils. The fuel pump may need the round flapper valves.

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  7. #6
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    The choke clicks can hear it with engine off, but i heard no change in rpm or speed while running full speed and pressing choke.
    When the guy sold me the engine i told him it was going on a standard mid and to put on those studs, he also moved the rectifiers to under the coil plate(i think the bad crimps came undone when he did this), and without telling me he removed the nice blue ngk plug wires from the pictures and put on standard plug wires. Fishy cause i had already paid my deposit and at first i thought it was different engine. He has a shop on Long Island New York but I want to figure out the issue and make sure it's not something that's my fault before i flame him. Paid $2800 for a dropon powerhead and it doesn't seem very drop on at this point.

    I have a spare coil plate with coils and plug wires already wired to two fairly new cdi boxes i took off my 175 carbed when i blew the main bearings. Should i Just start by swapping all those components at once? I know they work. Then compression check and then dva and ohm test trigger and stator. Lastly circle back to carbs again maybe.

    I have a spare fuel pump to, im suspicious of the bulb not getting very firm that something is up with fuel pump or carb floats but maybe thats normal compared to going to the fuel pump of an opti when an opti is off and the bulb got rock hard.
    Last edited by Fishinmymission; 08-11-2020 at 06:27 PM.

  8. #7
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    Ball won't b hard while running but should b hard while priming, if choke works and no rpm change. U have a cyl or 2 very lean (carb) and would explain rpm issues

  9. #8
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    Quote Originally Posted by Merc 2.5 View Post
    Ball won't b hard while running but should b hard while priming, if choke works and no rpm change. U have a cyl or 2 very lean (carb) and would explain rpm issues
    This confuses me a little. If my rpms are low due to a lean or fuel restriction in the carb jets and I choke i would expect rpms to raise while choking as choke would add more fuel but they dont. Meaning fuel pump might not being supplying fuel or everything is already rich and the issue is electrical or compression.

    The ball does not really get hard while priming like it did on my opti i had on last month, but also possible check valve blew on the bulb you never know lol.

    I guess i just have to go through everything in the end. Ill start with removing carb box making sure no air obstruction and that the choke actually injects fuel, and that my butterflies are compltely open at full throttle.
    Last edited by Fishinmymission; 08-11-2020 at 06:49 PM.

  10. #9
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    Ya I guess I worded that wrong after rereading

  11. #10
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    At boat now but need to leave for work. Found a nut came off for a ground wire of one of the ignition coils, wire still on post but no nut obviously. Think this is it and I should go test now?
    Last edited by Fishinmymission; 08-12-2020 at 08:52 AM.

  12. #11
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    lol 5300 rpm and 32 mph about performance i was getting with the opti. Seems correct. Might switch from the 16 pitch 3 blade black max propeller to the 15 pitch 4 blade turning point hustler prop to see if I get some better performance. I wonder if maybe a 14 pitch 4 blade would be even better if I dont see enough rpm increases.

    Should i make a new thread for idle adjustment issues?
    have been messing with idle adjustments on the throttle cable barrel nut and idle set screw three times now and my idle is 800 when i start to boat but on the way back to dock after a long idle in no wake it really struggles and stalls still. If i give it choke here it dies so maybe the carbs are too rich at idle when warm?

    I also noticed there is no hose running from my thermal air valve circuit. Sounds like this may be my issue? Anyone know the diameter of these lines I want to relower my timing back to 725 and try with this hose in place.
    Last edited by Fishinmymission; 08-12-2020 at 12:18 PM.

  13. #12
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    Quote Originally Posted by Fishinmymission View Post
    lol 5300 rpm and 32 mph about performance i was getting with the opti. Seems correct. Might switch from the 16 pitch 3 blade black max propeller to the 15 pitch 4 blade turning point hustler prop to see if I get some better performance. I wonder if maybe a 14 pitch 4 blade would be even better if I dont see enough rpm increases.

    Should i make a new thread for idle adjustment issues?
    have been messing with idle adjustments on the throttle cable barrel nut and idle set screw three times now and my idle is 800 when i start to boat but on the way back to dock after a long idle in no wake it really struggles and stalls still. If i give it choke here it dies so maybe the carbs are too rich at idle when warm?

    I also noticed there is no hose running from my thermal air valve circuit. Sounds like this may be my issue? Anyone know the diameter of these lines I want to relower my timing back to 725 and try with this hose in place.
    That thermal valve is for cold start. Does nothing when up to temp. I ran some wmv carbs with that hose plugged. Worked fine. Idle was very good. U really need take the extra 10 -15 min to do link and sync imo. Once u start turning stuff anyway ,

  14. #13
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    Hey yea mine isnt plugged though just open so it sees it as being a cold engine and puts in extra fuel. I think I'm going to go put this hose in or plug it like you said and then back down my timeing again. Once again idle is fine when engine is cold, once warmed up it stalls going back to idle.

  15. #14
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    same problem with the thermal valve plugged. I also tried raising the idle timing set screw while warm and i cant get a good setup. I can set it to have great rpms while cold but then once the engine warms up after or after a full throttle run it wont idle.
    Im thinking I might have a small tear or hole in the fuel pump diaphragm. This would explain why my primer bulb got rock hard on the opti powerhead a month or so ago and now feels like a slow leak is present as it never gets firm.
    Maybe the engine doesnt mind the extra rich mixture when cold, but it becomes too rich once warmed up, or the hole stretches and fuel flow increases through it after running hard.
    Last edited by Fishinmymission; 08-13-2020 at 12:26 AM.

  16. #15
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    I have my fuel pump from my old carb engine and its the same part # but its been sitting dry for 3 or four years but i know it worked when i removed it. Also have the fuel pump that's still on my opti. Looks like fit is the same but its a different part #. Anyone know if any mechanical fuel pump can go on a carb engine? ill probably remove and if it looks the same swap the opti one on.

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