Logo
FULL SITE MENU

Johnson VRO 90 - 3K rpm at full throttle

R

rburke

New member
Good morning all. I have a Johnson 90 VRO Model No. J90TLESB, 90 HP When operating in gear at full throttle it is getting barely 3000 rpm. If I run it out of gear it easily hits 5k, but in gear its 3k. Do i need to have it looked at by a mechanic? It seems to run great, no sputtering, starts right up, it sounds good. I am just concerned about those RPMs, and we never topped 15 mph. The motor is on a 2000 Aqua Patio AP240. Thank you very much.
 
Revving in neutral means nothing !----It will do that on 3 of 4 cylinders.----Start with a compression test.-----Then a spark check.-----Is VRO in service or mixing at 50:1 in your tanks.----How did this motor run for you last year ?
 
I just bought the boat a few weeks ago so not sure how it ran last year. VRO seems to be working fine. I am a complete newbie in this world of boating and engines, but I am a DIYer and take on projects all the time. We bought this boat knowing it was a project. I will figure out how to do a compression test and see what that shows. Thank you!
 
These motors are famous for broken piston rings.--------Lots of new boat owners learning in these pandemic times I say.
 
Thanks for the info. yep we are learning this new world in the pandemic! As good a time as any, everyone starts somewhere :)

Just a follow-up on this, if it had a broken piston ring or some other cylinder compression issue, would it run like crap? Sputtering, smoking, etc? I see none of that on this motor. I agree that a compression test is the first step, been researching out there and thats what I have to do. I just hope I can do it while its in the water.
 
I do not have enough fingers and toes to count how many motors I have had myself with this issue.----So if one individual has a bunch how many failures have there been over 25 years of this piston ring style ????----And I have seen some with issues on more than 1 cylinder.----That means with broken rings they still run quite well because owners had lots of hope until the second one went !!-----But you may have a bad sparkplug or a bad plug wire.----I can not see , hear or touch your motor.----Trouble shooting on your part has to be done.
 
Last edited:
I do have one more question, some of the research I am seeing indicates these low RPM readings may be due to a prop issue. I am banging my head trying to determine what prop should be on my boat but I have not been able to find a definitive guide. I believe the prop on the boat is a 14x13. but the only reason I say that is because there is a spare prop on the boat with those specs. I cant see any markings on the current prop. Maybe I should replace the p prop?engine2.jpg
 
rburke said:
I do have one more question, some of the research I am seeing indicates these low RPM readings may be due to a prop issue.
Click to expand...
Yes, this is entirely possible. However, 14X13 is a very common prop on pontoons so I'd be very surprised if you're over propped. Please follow Racer's well-founded advice and do some basic troubleshooting before you start swapping parts.

A 2-stroke engine needs these things to run:
1) Fuel
2) Compression
3) Spark

Spark and compression are extremely easy and cheap to test.

Compression Test = $0
First, go to your local auto parts store and rent a compression gauge. Remove all spark plugs, make sure your battery is at full charge, and test each cylinder. You should see about 120PSI and less than 10% difference between all the cylinders. Return the gauge to the store and they'll refund your deposit.

Spark Test = $13
At the same store pick up a Lisle #50850 air gap spark tester. With the spark plugs still removed use the tool to test each individual spark plug lead. They should be able to jump a 7/16" gap with a clear blue flame.

If spark or compression fails on any cylinder stop and fix the problem. If all 4 holes are good then move to the next step which is spark plugs. Depending on the age spark plugs will foul and can result in poor performance like you're seeing. Get a fresh set of Champion QL82C plugs, gap them at 0.030" then retest the engine. If you're still limited in max RPM you then need to start tracking down the fuel system: carbs, filter, fuel pump, etc.

The thing is you've bought a 31 year old engine and you're relying on the seller (who was looking to make money) that the "engine ran good last year". You have no information on the service history, when plugs were changed, when the water pump was changed.....nothing. In these cases it's really the most safe option to assume none of that has been done and to install these routine service items before you go out and use the boat.

KJ
 
this is awesome! Thank you very much for the advice, it is mucho appreciated. Ill come back after the weekend and report what I find. Thank you!!!
 
A 2 stroke engine needs that 4th component to run.-----That is CRANKCASE compression.-----An often overlooked thing and a complete mystery to some owners.
 
There is no doubt there is an element of trust when buying used, especially in this sellers market. I knew the risks buying a 31 year old motor and accepted those risks. I got a deal on the boat such that if I need to replace the motor with a "new" used motor I am ok with that, but I also know most things can be fixed with some knowledge, the right tools, some elbow grease and patience - or a good mechanic! I appreciate all the advice I get on this forum and other places.
 
racerone said:
A 2 stroke engine needs that 4th component to run.-----That is CRANKCASE compression.-----An often overlooked thing and a complete mystery to some owners.
Click to expand...
Very true, if a crank case seal is bad or reeds not sealing it will cause loss of crank case pressure. I was using the most basic principles for the owner to go through troubleshooting.
 
Back
Top