1986 150 HP Johnson Low rpms again??

[Steve135]

Ok Long story as short as possible. Motor is a 1980 had a new powerehead put on. A 1988 with oringinal 1980's electrics . Only lasted 25 hrs think water was getting in thru new head gasket? Had one really dry plug and piston looked melted hot after the motor failed and I inspected it. The problem I was having was only able to get 4300 rpms at WOT and 30 MPH/GPS. But At some point during my trouble shooting I was able to get 5500 and 37MPH/GPS for a short run but it when back to the 4300 rpms Then the motor seized one piston. Now I bought a new used powerhead a 1986 with 50 hrs on it. Now I replaced the old one with a complete power head nothing came off the one that was on the boat. Just removed the 4 bolts and 4 nuts and replace the gasket and put this one on. So There aren't any old fuel pumps, coils, carbs, powerpacks nothing from old engine.<br /> I have the same problem 4200 RPM I am thinking its the fuel system. Do you thing this could be the problem? I am going to see if the check valve in the built in tank is failing I have changed the water seaperater, I have had the fuel pick up out of the tank. The screen at the end is not clogged or dirty. But that anti syphon valve might be bad. Any help here before I go thru another powerhead. Because now I am thinking fuel starvation running lean at WOT without enought fuel was the cause of the first powerhead? steve

 

[Walker]

Re: 1986 150 HP Johnson Low rpms again??

Did you overhaul the carbs when you put the new top end on it?

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

No The carbs were rebuilt just 50 hrs before. They came with the new powerhead not off the old motor. Its too weird to have the same rpms on two different powerheads with different components. And yes the tach is new set at 6p and has been known to run at 5500 rpms at some point and the boat was able to do 37 mph.

 

[Walker]

Re: 1986 150 HP Johnson Low rpms again??

I'd go through the carbs again. Are you running a VRO pump or standard fuel pump. Those big motors used 2 standard pumps to supply enough fuel for all 6 cylinders.

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

ok Listen carefully we took it off a boat that was running perfect at 7am in the morning and at 1:30 pm the same day it wasn't working perfect on my boat! It can't be the carbs!

 

[Walker]

Re: 1986 150 HP Johnson Low rpms again??

Well, you got me then. Must be gremlins.

 

[DHPMARINE]

Re: 1986 150 HP Johnson Low rpms again??

Some things to do ...<br /><br />Pull the plugs.Do they all look the same ?<br /><br />Shoot the Gremlins.<br /><br />Are you propped right ?<br /><br />Generally a head gaket doesn't let water in,as compression blows it out,instead.<br /><br />Has the gearcase been off lately ?<br /><br />DHP

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

The gear case was off to install the powerhead. The boat turned 5500 rpms and 37 mph with the other powerhead before it started ackting up then it just fried once cylinder. The top of the piston melted mechinic said it was due to water getting in I though head gasket could have been from a cracked head or sleeve. The 3 plugs on tht right side look light brown and dry as compaired to the 3 the plugs on the left side they are dark and wet but not really wet wet just darker. There not fouled!

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

Update I took the fuel line off at the water seaperater, stuck it in a 6 gal can of premix and went for a ride. Well I got the same rpms about 4300. The only thing I did find was the fuel ball not hard after the short high speed run. This indicates to me that its a fuel starvation problem. The ball regained its firmness at a slow troll of about 1500 rpms. The only culprit left at this point is the fuel ball its self! tomorrow I will run it with out the ball and the 6 gal tank. See what happens tomorrow. This is supposed to have 3/8 fuel line correct?

 

[Walker]

Re: 1986 150 HP Johnson Low rpms again??

Its normal for the ball to lose its hardness while running. When you pump it by hand it buuilds up pressure between the carb float needles and the check valve in the bulb. When the motor starts and the fuel pump takes over the bulb becomes nothing more than a fat part of a suction hose.

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

Update is I found that one whole side the left side as you face the engine off the boat, spark plugs were dark and wet.The other side is lite brown and dry (all) I today replaced the power pack on the wet side. It was not just a plug and go deal. I have a 1987-88 electrics and all I had a 1986 powerpacks the plugs aren't the same pattern so I was forced to cut and splice plugs to match. I must have done it right cause it starter right up. But didn't make a differance in the rpms at WOT. It did seem to clear up the center plug on the wet side only? Its now lite brown and not wet. So I next swapped the coils for #1 #2 and it didn't make any differance in the wet plug at idle! The motor starts right up and sounds great even at WOT but thats only 4300 rpms and 30 mph. And yes it did reach 5500 and 37 mph with the current prop boat set up at one time!

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

Ok went to look things over again. I did find the timing base was not moving full throw, wire harness wass preventing it, or spring is bad? I rerouted the wire bundle to alow the timming plate to move full throw. I am able to get 4900 rpms and about 33 mph better but not perfect. I tryed to re do link and sync and just about screwed it up totally. So Whats first? Throttle cable, Timing, Cam follower. I can't get the Cam follower to meet the small line at throttle movement, with amplifier tool installed!

 

[steamboatwilly]

Re: 1986 150 HP Johnson Low rpms again??

Are those plugs supposed to look light brown and dry?? I thought they supposed to look dark and wet.Seems to me like theyre running lean.

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

Still lugging around 4900 rpms This week it slowed while at WOT and then recovered. I still have two wet plugs on one side. And now there is no charging again, This is a new retifier. I am thinking its the stator. I have fixed the timming so it moved full throw. I will replace both the stator and timming base along with two power packs and six coils today. Then see where I am. I have these off another motor that ran fine.<br />steve

 

[haybarn]

Re: 1986 150 HP Johnson Low rpms again??

Hey stinkey How are ya? I have a 85 Johnson v6 and am having the very simular problems. So please let us know what you come up with so I can do the same to mine. The left side bottom two plugs are light brown and wet and the top plug on the left side is black and dry???? Although for some reason Sunday it jumped up to 5500 and man it flew. Then today it would jump up to 5500 and drop in and out every now and then.

 

[haybarn]

Re: 1986 150 HP Johnson Low rpms again??

Sorry it is also a 150hp

 

[Steve135]

Re: 1986 150 HP Johnson Low rpms again??

update I have replaced all electrics timer base, stator, all coils, both power packs, fly wheel. took it out and it ran better but still never reached 5500 rpms. about 5200 and 34 mps (gps) after a short run I pulled the cowling and just took a look see. I saw a little smoke comming out from around the #3 plug. Pulled the plug and found that the plug was cross threaded and most of the threads are gone. So this will end up being most of the lost RPMS. I will helicoil the plug this weekend. let you know whats up then.