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1988 Johnson 90hp v4 2 stroke bogging out at almost full throttle

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Jj718

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1988 Johnson 90hp v4 2 stroke bogging out at almost full throttle just bought the boat 2nd time I take it out and starts bogging down at almost full throttle and then turns off just wondering if anyone has been thru this and could help me out? Also new to boating but pretty good with cars
 
Check flywheel key.-----Post actual compression values.-----These motors have a history of broken piston rings.-----Running with VRO in service or 50:1 mix?----Did you install a new water pump impeller ?---Tested the overheat warning horn ?-----Test run with another tank and hose.----Remember I can not see , touch or hear your motor.
 
50:1 mix I just bought the boat from someone I don’t know if he changed the water pump impeller out but when I keep it a low throttle she can go all day no problem and then there’s days that she will go full throttle but not all day it’ll go back to bogging down
 
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It is almost a golden rule to install a new impeller on a " new to you " motor.-----Post the actual compression values to get further input.
 
Just a few clicks on this site gets parts info-----Do not spend any beer tokens until you have determined overall condition of this motor.!
 
One quick thing to check is to take the breather or whatever cover you have over the carbs off. Check to make sure that at full throttle, the butterflies on the carb are perfectly horizontal. If not adjusted correctly, the butterflies go past fully open and start to close back up. I ran into this on an outboard motor just a few weeks ago. RPM's would go up, up, up until the last little bit of throttle left and it would decrease RPM's instead to continue increasing. Just a thought. Racerone is the man to take advice from though.
 
This type of symptom can be lots of things but is most classically, carbs or fuel delivery.

Check compression, yes. Check temp sensors & warning horn - good idea too, as is installing a temperature gauge so you got a clue before it's already too hot (although testing temp sensors requires removing water jackets on heads, which is usually easy but can be tricky if a bolt is stuck).

Sanity check link and sync for anything goofy, yes - ie carb butterflies run together and are closed at idle, trigger assembly turns as expected with throttle before carbs start opening, everything all connected together.

A new-to-you engine, you replace water pump and any thermostats/poppet-valves AND it's a good idea to service both the fuel pump (what is applicable), any hoses that look questionable, replace any filters involved, and rebuild the carbs. Removing the heads, checking the water deflectors, removing the covers, cleaning out the jackets on the heads, putting it all together nice and clean with new gaskets, is also great to do, however it can get you in trouble if bolts are stuck (usually aren't but can be).

Bad fuel usually shows up as a problem starting an engine. Something that runs well at idle, likely has good fuel. But that doesn't mean you don't have a filter that is plugged up due to bad fuel and is restricting flow.

Bogging, stalling, when you try to go wide open, is usually clogged up carburetor/jets - it's a common every 5 years sort of job, you get the kits, remove, disassemble, clean, rebuild, and put the carbs back on. Usually even if you didn't note anything wrong the problem is corrected.

If this engine is using a non VRO fuel pump, ie the style that the 88 SPL has, the style from back prior to VRO's that mounts to the block, when the diaphragms go they tend to come apart and clog the carbs. It's a good practice to replace the fuel pump, or put a rebuild kit in what you got, each time you do the carbs for this reason - new fuel pump components will outlast your carb rebuild but do not last forever.
 
Do not spend any beer tokens until you determine condition of the motor.----These motors have a history of broken piston rings.----Do yourself a favor with a compression test.----Post the actual values here !
 
racerone said:
Do not spend any beer tokens until you determine condition of the motor.----These motors have a history of broken piston rings.----Do yourself a favor with a compression test.----Post the actual values here !
Click to expand...
For sure going to buy a compression testing tool today thanks for the advice
 
Jj718 said:
For sure going to buy a compression testing tool today thanks for the advice
Click to expand...

The standard thing on the shelf, that screws in, you'd find at auto zone, is just great - have bought a couple of them over the years. Be careful though, some extensions they sell with them might be longer than the spark plug (ie you don't want a piston hitting it :) ). You only need to use the gauge and the short hose w/ the short threaded fitting they come with for these engines.

If you don't mind spending a few extra bucks to make it easy, it's very handy to have a couple jumpers w/ alligator clips and a momentary switch - this allows you to crank the engine right off the relay while standing on the ground next to the engine, versus hopping in/out of the boat again and again.
 
So I found out what the problem was I was only running on 3 cylinders one of the wire for the coil pack rotted off and I found another one in the same condition replaced them now she turns on and runs like a champ I did the compression test as well everything checked out good I just want to thank you guys for you help 🙏🏽
 
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