78 johnson 175 wet plugs only turning 4200 rpm

O

Orlando

Member
78 johnson 175, it bogs when i try to accelerate and will die if i dont pull throttle back most of the time, a couple times it has accelerated properly first try but usually it takes multiple attempts of slowly inching the throttle forward and backing down a hair, then giving it some more. tach works intermittantly and at WOT highest rpms i've seen is 4200. plugs seem to be wet with fuel when pulled. compression is 90 cross the board +/- 2psi. got good spark, jumps 7/16 inch on tester and shocks the hell outa me when i pull wires while it is running. its not overheating, highest temps i've seen with infrared thermometer is about 147. carbs are all opening closing properly,and are synched per my manual. not leaking out the fronts when primer ball is squeezed. checked bowl drain holes on carbs, seem to be pumping decent amount of fuel from all three.previous owner said he had them rebuilt last winter. fuel tank vent lines have been cleaned. have tried portable tank with no difference. its got the proper champion ul77v plugs, no gap to these to worry about. i've ran about 120gallons of fresh fuel through it since ive owned it and its been acting this way the entire time. power packs check out. im out of ideas on this one, did alot of looking here and on iboats to find a solution. just out of ideas, i know its not over propped has factory omc 15x17 aluminum. any thoughts suggestions or ideas would be greatly appreciated
 
checked the idle timing, havnt had help to check wot timing yet, but the stop looks like its never been touched. will run the gauntlet today and get my wife to help, shes about as good with anything on wheels or with moving parts as my two year old son. so hopefully i'll have enough fingers left to type the results later on.
 
probably do a seafoam decarb as well, although im pretty sure it dont need it, got to put the boat in the water today anyways to fix some rollers on the trailer. gonna get another set of new spark plugs too, decarb and use the two month old ones as spares. the compression seems a bit low, even if it is even between all cylinders. so a decarb couldnt hurt i guess. i'll do the timing on muffs without starting engine, that should eliminate the odds of my wifes driving throwing me overboard.
 
ok, time for an update. timing checked out ok, did a decarb and changed plugs, no difference except my compression came up to between 97 and 105 psi per cylinder, or might just be i was using a different gauge.but no improvement in running
 
ok, just noticed i got a little water leaking around the outside of one of the head gaskets, not much just a very slow drip, maybe one drop every 8-10 seconds. but compression is good. i changed that head gasket a couple weeks ago, so probably get by with just tightening it up a touch.
 
just changed the oil in the lower unit, nothing looked amiss. got one idea left, this engine has fixed high speed jets from what ive been told, but could the low speed jets be pumping out to much fuel causing my symptoms? and are they adjustable?
 
Check the timing advance, it maybe hanging up if the motor has ever sat for some time. I doubt your low speed jest are pumpng to much fuel. Tach going haywire is usually a bad rectifier, your tach reading of 4200 may be wrong as well if the pulses are set incorrectly.

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