1990 90 hp Johnson "low power under load"

[yogiselle]

I just bought this boat and have completly rebuit almost evertything. Power head gaskets, new fuel filter, new gas pump bulb, rebuilt fuel pump, rebuilt carbs, new spark plugs and wires with " not of correct name but the 4 little boxes the spark plug wires go to to make them spark" lol. Anyways motor starts on 1st crank and will idle all day. Motot runs great out of the water with no problems. Once in water motor slowly climbs in rpm's for throttle and will not get above 2200 in gear. Tried this many times and every now and again motor would run smooth for about 35 seconds max out and running then die off. Had wife start squeezing fuel bulb the next couple runs and motor ran perfect. had her stop for two more passes and motor would quickly die off and not go above 1800 to 2200 rpm's.
Should i replace all gas lines and what else could be my problem?

 

[lmuss53]

Re: 1990 90 hp Johnson "low power under load"

My '85 90 hp did the same thing and it was the fuel pump. Pumping the ball like you did made mine run better too. The complete VRO pump is expensive but there is a rebuild kit for the gas portion for around 100 dollars. Since my VRO was already unhooked by a previous owner I put the ready mix pump from an 88 Special on mine and eliminated the VRO pump. The complete 88 Special pump is about $50 to $60 from iboats. If your VRO is hooked up I would not unhook it to save $50. Do a search on VRO pump rebuild and you'll find the numbers for the VRO rebuild kit.

Read this thread and you'll know some more about your motor and the fuel delivery system.

http://forums.iboats.com/showthread.php?t=428223

ALSO PLEASE UNDERSTAND THAT IF YOU ELIMINATE THE VRO PUMP YOU'LL HAVE TO START PREMIXING THE OIL INTO YOUR GAS AT A 50:1 RATIO !!!

 

[wilde1j]

Re: 1990 90 hp Johnson "low power under load"

Your immediate problem appears to be fuel delivery problem, which can have a number of causes, such as:
. air leak on pump suction side (bad clamp, cracked hose, cracked tank pickup tube, etc., etc.)
. malfunctioning anti-siphon valve
. plugged tank vent
. trash blocking tank pickup screen
. plugged fuel filter
. collapsed fuel line
. water or trash in internal and/or external filter
. try an alternate fuel source (i.e. portable tank)

I don't think replacing fuel lines will help, unless they are very soft and collapsing.

 

[lmuss53]

Re: 1990 90 hp Johnson "low power under load"

I should have mentioned all the stuff wilde1j said too, sorry. I checked all that before I changed out the pump. I'd hate to tell you to change a pump that isn't bad, so check all those other things too. In most cases if the ball pumps up hard when the motor isn't running and stays that way for a while you don't have a cracked or leaking fitting anywhere.