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no mid-range

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defluiter

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I have a 1987 175HP 0n a bass boat. My problem is it has no mid-range. I have rebuilt the carbs, rebuilt the oil pump, rebuilt the fuel pump, ran Seafoam in the gas, checked the stator, dis-connected the idle stabilizer, checked compression and all cylinders were 90 psi and all even. The motor will start and run fine up to about 1200 rpm's, but if I try to go past that the motor dies. If I slam it to wot it will take off and after it planes out it will go 65 mph all day. I don't know if it is carburation or ignition. Any suggestions will be appreciated
 
In my non expert opinion it sounds like you have a link/sync or mixture problem. First check the basics.

All carbs should be operating in sync, from idle up until a point around 1/4 throttle or something the position of the internal butterflies should not change (in that first part of the throttle range it's all done by spark advance, the trigger turns under the flywheel).. After about 1/4 throttle then the carbs come into play. There's a lot more than can be done here but I'm just explaining a quick sanity check incase something is way off.

If the above looks about right then most likely I think you've got your mixture wrong on the low speed jets. When rebuilding the carbs did you set them? They should have come out for cleaning for sure. After a rebuild, when it's time to adjust the jets, it's totally normal for an engine to run seemingly perfect at idle and lower speeds but not well at all at different speeds underway. The simple thing is to start how the book says (believe it's 1.5 turns out but I always go 1/4 over that so 1.75 turns out - good to count how many turns they are set at currently first)..

The book may tell you to start the engine and go through a process of turning them in all the way until you note a problem, then back out until you note a problem, etc.. I start a little richer than where they tell you to and if the engine runs OK I start testing on the water, with the error always placed on the rich side of adjustment.

My way (not necessarily the right way) - start engine up and get the idle adjusted right (you will likely need to mess with the idle as you make mixture adjustments).. If it will idle OK without "loading up" and stalling itself out then it's probably not too rich (it will idle OK at first, smoke alot, then slowly die out with wet/fouled plugs), otherwise go in 1/4 turn on each carb and check result until it seems sane. Slowly push throttle forward, if you get a bog then bring each screw out 1/4 and repeat, if it's loading up at idle go in with the screws. Eventually you get it about right - then after 5-10 hours of use, pull the plugs and read how the individual cylinders are doing (if one is lean bring the screw out a bit).

Jon
 
I am sorry that I didn't mention that I have wh-34 carbs that have no adjustments. I did run pipe cleaners and tip cleaners through every orifice in the carbs when I rebuilt them.
I also did a link and sync.
 
defluiter said:
I am sorry that I didn't mention that I have wh-34 carbs that have no adjustments. I did run pipe cleaners and tip cleaners through every orifice in the carbs when I rebuilt them.
I also did a link and sync.
Click to expand...

FYI - you really shouldn't run pipe cleaners or wire through anything, more of a chance of causing a problem. Carb cleaner through the straw that it comes with should work fine (I tend to use lots, like at can per carb)..

To me it sounds lean. Try this test to verify - when it bogs hit the choke. See if that momentarily recovers it. If so then you can be fairly sure it's a lean condition at that RPM range.

Jon
 
I took the boat to the lake yesterday and this is what I found.The motor will idle just fine, but when I put it in gear the engine dies,unless I jam it to mid throttle, then it chugs along at 1200 rpm’s. If I try togo above 1200 rpm’s it will die, unless I jam it to wot then it hesitates untilit builds rpm’s and then it will take off and plane with no miss. I can take itdown to 3000 rpm’s and it runs fine but not below that. I am thinking eitherstator or switch boxes. Any thoughts?

 
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