1984 Johnson 90hp Speed/Power Problems

[Boat84]

Hi, Everyone this is my 2nd post. My first post was 2cylinders missing, and that was caused by a pinched bottom gas line, so now i'm on the water and atleast moving : ) I have a 1984 Procraft 1650V it's running 40mph @ 4500RPM WOT Seems like it should be doing more than that. When I took it out after fixing the pinch gas line I didn't have the TOP on it or the cap that bolts in front of the Carb it Seemed like it would tack up to 5200RPM pretty good without that stuff on it. But now with the cap installed and the top on it 4500RPM is all i'm getting..I have a friend that has a 15ft bass boat with a Evenrude 70hp and he blew me out of the water running about 45mph this to me doesn't seem right. Anyone have any idea why so slow are is this normal for this type of boat.

 

[HighTrim]

Re: 1984 Johnson 90hp Speed/Power Problems

So you are now getting fuel and spark to all cylinders? If so, what size prop are you running? Prop not spun at all? Any pics of your setup? Boat not water logged?

Your WOT RPMS are much too low, you are lugging the motor.

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

Are you saying that right now you can gain 700 rpm by taking the hood off?

If so, look at the #4 spark plug wire. It may be shorting to the hood latch.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

I'm new to boats how can i tell what size prop i have? Far as water not much I have taken all the carpet out and the lids to be recarpeted soon. Also when I got back from River i checked all my plugs and they looked really good to me like a Golden Brown look

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

I'm not sure if it just because i take the hood off or taking the hood and the carb cover off. when i tested it on the river the first time it ran good was with the hood and carb cover off and the RPM hit 5200. What RPM Range should i be looking at on this motor what should it be turning?

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

Still trying to figure out what's different between running at 4500 and at 5200. If you put the boat in the water right now and ran it with the hood on, how many rpms will it turn?

If you run it right now with the hood off, how many rpms?

4500 as a top rpm is really lugging it. 5200 is still lugging but better. We need to get it to run 5200 with the hood on without changing props or moving the motor. It should run the same rpm with the hood on as off.

If simply putting the hood on causes you to lose 700 rpm we need to figure that out. Then we'll work on improving the set up. My guess is that when you put the hood on you're losing spark to one cylinder.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

I put my boat in the water sunday with the hood and carb cover on and at WOT with motor trimed up my RPM was 4500 running 40mph. Friday when i took it out without the Hood or Carb Cover, it tached really fast and the RPMs went to 5200. Can't recall the mph i was just glad it was running for the first time.. I checked all the plugs when i got back from Riding Sunday and looking at the motor from the back the Right 2 plugs where burning Good golden Brown. Left top was good also but the Left Bottom was wet with gas... like it wasn't Firing but i check the compression again 125lbs and it has fire going to the plug and checked the plug and it was firing also. So filing out on the hood latch could be a possibility, i'll check that out next time i'm able to go out. Been raining everyday since sunday..

 

[56 rude]

Re: 1984 Johnson 90hp Speed/Power Problems

Check the bottom left coil very carefully,i say this as my 82 90 hp rude you had to be very carefull putting on the cover or you would eventually wear through the wires on the coil, thus causing a possible short.What i did for added protection was silicon the wires just as a added precaution.When i say the wires i mean the small wires not the plug wire though that bears looking at too.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems


Took my boat out today here's whats going on. Went out with the Hood on it Ran 4500RPM @38 to 40mph @WOT came back and took the hood off NO CHANGE same speed and RPM.. Motor sounds good in the water.. What are some changes that i can do? with 3 people in the boat barely planes out, I was told change prop and put a Hydrofoil (Whale Tail) on it to help get it out of the water.. MY PROP SIZE IS 13 3/8 X 17 is this to big?

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

It's very doubtful you prop is the issue. First we need to verify the compression is good. Are you sure the carbs are clean? Do all 4 spark plugs look the same? If all that is OK we need to make sure it's getting spark on all 4 all the time. A timing light is the easiest method to do that.

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

Hummmm.....at 4500 with a 17" prop your theoritical speed is a little over 36 mph. Are you sure your tach is set on position 6?

 

[mikesea]

Re: 1984 Johnson 90hp Speed/Power Problems

I like the earlier suggestion of something causing a plug not to fire.If you truly got 5200 and now lost 6-700 rpm.Be sure to check all connections to your coils.Both small and large wires as well as grounds.If you feel the one that wasnt firing is culprit,you can swap the coil with a different cyl.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

The compression on all 4 cylinders is good 115 to 125 lbs looking at the back of the motor left hand side bottom plugs seems alittle wet with fuel and the other 3 cylinders is dry and like a golden brown. doesn't sound like my motor is missing. I do know that that cylinder that is wet with fuel has a nice blue spark and good compression, Only thing i can think of if it's missing it's not at an idle. How can i check that cylinder with a timing light to see if it's sparking all the time?

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

you mentioned my tach being set on 6. I called my boat dealer and they told me the same thing i haven't had time to check I will check when i get up in the morning now it's 2:50AM WED .... I guess if it's missing on #4 cylinder thats why it's sluggish out of the hole, But I have no clue on what it could be cause I have Fire to that cylinder and Compression.. Carbs have been Clean over and over again theres really not much to the Carbs. Surely it's somthing simple i'm missing.. I Really Appreciate everyones REPLY.. I'm ready to get this thing in the water and running the best it can run

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

OK, bottom left (#4) is wet with fuel. That means it's not firing or the fuel pump diaphram is leaking. So yes, you're back to checking spark first.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

what is the exact way of checking the plugs to see if there firing or Burning good? WOT then shut it off and come to a stop and check all plugs. Is there a way of telling if it's loosing fire when it Rev's up.

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

As you mentioned, checking #4 with a timing light while under way is a great place to start.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

Okay will do that. Fuel pump diaphram doesn't seem to be leaking noticably
if all the other cylinders is getting fuel wouldn't that cylinder also be getting enough?

 

[Dhadley]

Re: 1984 Johnson 90hp Speed/Power Problems

You mentioned the #4 plug was wet with fuel. Two of the things that will possibly contribute to that is no fire to that cylinder and a leaking fuel pump diaphram. The fuel pump is operated off of pulses from #4. If the diaphram leaks it tends to put raw gas in #4.

 

[Boat84]

Re: 1984 Johnson 90hp Speed/Power Problems

Thank you Is there a way I can change fuel pump to a electric fuel pump. If so how many Lbs of fuel pressure are we talking about for a boat motor