Johnson Fuel Problem, Help!

[zarnah]

Hi all, brand new to the forums, all the way from New Zealand! I recently purchased a 90hp V4 VRO Johnson outboard, think its the 1988 model, it has had a full rebuild etc, my problem is that it is drinking way to much fuel for some reason? Got it all wired up etc last week and took it to our local lake for a bit of trialling this weekend, and down low in th revs its not running well at all, I suspect because its over fuelling and struggling to burn the fuel, a 28 litre tank of fuel lasted me only around 20-25 minutes! I have checked for leaks etc and have come up with nothing so all that fuel is definately being fed to the engine. Is there a way to adjust this? or anything else I should be doing?

 

[kenmyfam]

Re: Johnson Fuel Problem, Help!

Your motor will use approximately 10% of it's rated horse power in US gallons per hour at WOT (wide open throttle) it should use significantly less at cruising speeds. Therefore it will use about 9 US gallons per hour at WOT.
Have you checked for evidence of leaks in the lower cowl ??
What was included in the "full rebuild" do you know ??
Can you explain more about the low rpm issues ??
Welcome to iboats

 

[Vic.S]

Re: Johnson Fuel Problem, Help!

I think I would be considering the possibility that one of the carbs is flooding due to its float valve not seating correctly.
There are no mixture adjustments that can be made.

But also check the operation of the primer ... got the red lever set for normal operation.

BTW a 1988 model should have the date letters CC in the model number
as in J90TLCCA

(Be aware that a US gallon is not as big as a "proper" English (Imperial) gallon . It is only 3.785 litres )

 

[kenmyfam]

Re: Johnson Fuel Problem, Help!

(Be aware that a US gallon is not as big as a "proper" English (Imperial) gallon . It is only 3.785 litres )

I still have trouble with the US gallon when I am there. Loved the "real" English gallon. Living in Canada for over 20 years I am used to litres now.

Worst thing is a pint of beer in the US is only 16 oz !!!

 

[ezeke]

Re: Johnson Fuel Problem, Help!

In either system a pint is 1/8 of a gallon. For beverages, I think we need to bring back the Scottish pint.

 

[kenmyfam]

Re: Johnson Fuel Problem, Help!

For beverages, I think we need to bring back the Scottish pint.

I'm all for that !!!

 

[zarnah]

Re: Johnson Fuel Problem, Help!

at low rpm the engine struggles and if it is out of the water (with water hooked up to the water intake of course) then the exhaust blows a lot of black smoke at low rpm, which tells me its running very rich and struggling to consume the fuel thats been thrown at it, which probably is leading to my fuel consumption problems, along with the fact that it just wont perform at low rpm so is pretty much WOT all the time to keep it happy. The rebuild included new crank bearings, new pistons, new rings, and all new seals and gaskets. Which way does the red lever have to be set for normal operation? full clockwise or full anti-clockwise?

 

[ezeke]

Re: Johnson Fuel Problem, Help!

The red lever on the primer solenoid is parallel to and aligned with the cylindrical base for normal running. This closes the valve unless the ignition key is pushed inward.

In the emergency position the valve would be left open, flooding the engine.

 

[R.Johnson]

Re: Johnson Fuel Problem, Help!

Rebuilt, or not! Compression test first.

 

[James R]

Re: Johnson Fuel Problem, Help!

Does sound like one cylinder is not performing.

 

[zarnah]

Re: Johnson Fuel Problem, Help!

as far as compression goes im not entirely sure what the readings were, the boat shop that checked it over before I bought it did tell me but I have forgotten for now, have it written down somewhere, from memory it was something like 126,126,125,127, does that sound about right?
So if the little red switch is facing inwards (towards the boat) its in the emergency position and floods the engine? would that cause it to use a lot of gas? I do know its a real bastard to start, the best way I found was to not prime it with the hand bulb at all and then it would start but still didnt like to idle, the best I could get was to have the warm up lever on full and that would JUST keep it ticking over.
Is it much of a hasle to take off the carbs to check for a stuck float? I have had a lot to do with two stroke dirt bikes and even do my own rebuilds etc on my current one but this outboard looks a hell of a lot more confusing than a single cylinder 250cc engine to pull apart to me!

 

[ezeke]

Re: Johnson Fuel Problem, Help!

First, try it with the primer solenoid handle correctly positioned.

Click the thumbnail for section from page 5 of your owners' manual.

The only time that you should need the manual position is when the battery is dead and you need to rope start the engine.

 

[kenmyfam]

Re: Johnson Fuel Problem, Help!

Compression numbers are fine.
My 2 cents on that.