low top end speed 1998 Johnson 90hp outboard

[wrench001]

Good afternoon guys. I have a 98 Johnson 90 hp. My top end is only 22mph this year. last season I put in a new VRO fuel pump, all the lines back to the tank with new pick up tube and strainer. new fuel filter and spark plugs. same prop that used to do 30 + mph.. seems to run great at idle and at cruise. its just at WOT i'm steady at 22 mph. Thoughts or advise?
thanks in advance
Steven

 

[kjdunne]

Re: low top end speed 1998 Johnson 90hp outboard

Do you have a tach? Is your WOT rpm the same as last year?

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

Do you have a tach? Is your WOT rpm the same as last year?

great question. I did not look honestly. I will take it out in a bit and let you know

 

[boobie]

Re: low top end speed 1998 Johnson 90hp outboard

Do a cylinder drop test on it and see if it's running on all 4 cylinders.

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

125 lbs compression on all cyls, spark at idle with timing light is good. tach is erratic and unreliable. fuel gauge is erratic also. runs great at idle but wont go over 9 mph

 

[boobie]

Re: low top end speed 1998 Johnson 90hp outboard

Read post # 4 again.

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

cyl drop test showed no change. tach tops out at 3200 rpm. spec is 5000- 5500 wot. because i'm a auto tech and i was sure it was a miss under load. I threw some parts at it. new power pack, 4 coils, plugs and wires. no change.. thoughts please?

 

[Chris1956]

Re: low top end speed 1998 Johnson 90hp outboard

Have you checked to see that the ign timing advance linkage works? Sometimes that can stick. Idle timing is 4* ATDC, with SLOW disconnected. Max spark advance is 20* BTDC. Check them both with spark plugs 2-4 removed, and motor cranking at idle and at WOT.

You are using the original prop? The boat is not waterlogged?

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

Timing was dead on. Advance moves freely. Linkage good. No water in boat. Same prop from last year with no damage. Freaking mystery

 

[Chris1956]

Re: low top end speed 1998 Johnson 90hp outboard

Check the spark plugs. Maybe you are getting some water on one of them, to put out the fire? Just a SWAG (Stupid Wild ***** Guess).

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

No water. Although all plugs seem wet with fuel like it's burning ****ty. All look the same

 

[Chris1956]

Re: low top end speed 1998 Johnson 90hp outboard

Are you using the OMS Oil injection? If there is an air leak in the gasoline supply lines, the OMS will inject more oil than necessary. Maybe one of your plugs fouls out? Another SWAG.

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

Brand new OEM VRO pump installed. New lines, clamps etc. No air or fuel leaks. No change pumping the ball or engaging the choke

 

[Chris1956]

Re: low top end speed 1998 Johnson 90hp outboard

Wrench, That motor has a vapor separator, so pumping the primer ball will not change the fuel supply to the carbs. Just a point, in case you didn't know. Not sure it is relevant.

Maybe choke primer lever is in manual? Maybe choke primer is stuck open flooding the intake manifolds with fuel? More SWAGs.

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

No choke lever is correct.

 

[Chris1956]

Re: low top end speed 1998 Johnson 90hp outboard

OK, last SWAG... maybe one of the carbs is flooding?

 

[wrench001]

Re: low top end speed 1998 Johnson 90hp outboard

It turned out to be contaminated fuel. I ran it empty. Filled it with super and a can of sea foam and after about ten minutes it was like someone hit a switch. 4800 rpm and 30+ mph. I feel dumb and happy at the same time. Thank you for all the help

 

[HenryB]

Re: low top end speed 1998 Johnson 90hp outboard

Try squirting gas (mixed in a squirt bottle) to see if any improvement.

 

[82rude]

Re: low top end speed 1998 Johnson 90hp outboard

id be a lot happier seeing the rpm,s at 5500 than at 4800 your lugging basically.