I have an idle problem with a 1990 Johnson 40 two stroke Model# TJ40ELESR

[Jehu1]

Motor compression is very good and even on both cylinders. Spark is good, new plugs.
All new Carb and Intake gaskets, all new fuel hoses and new fuel pump (converted from VRO to traditional pump). Link and sync has been done on the carbs.
Complete carburetor rebuild kit has been installed including new idle air jet and main jet in carb bowl. The carb has been dissembled twice and thoroughly cleaned in an Ultra Sonic cleaner and then all passages blown out with compressed air before reassembly.
Further the Idle Circuit core plug and lead shot plug were removed and the idle passages cleaned including “rodding out” with some solid wire the tiny capillary tube/venturi tube that picks up fuel for the idle circuit from the bowl. This is one of the older style carbs that has the main jet in the bottom of the bowl in line with the bowl drain screw, so the more modern needle-jet/jet needle configuration is not present. All fuel flows through the main jet then makes a 90 degree turn to enter a small area where either the fuel is pulled up through the main vacuum tube into the carburetor throat or through the little capillary/venturi tube the runs through the center of the vacuum tube to the idle air passageway in upper portion of the carb. This model still has the old idle adjustment needle which is currently set approx. 1.6 turns out where it seems runs best. The Motor will start fairly easily especially if I choke it ( this model has the electric choke that injects fuel directly into back of the carb throat to insure fuel gets to the cylinders. The problem is it will idle for about 30-45 seconds then slowly die out. If I keep hitting the choke while the motor idle speed is decreasing it will immediately speed up and keep running for a few more seconds till that fuel get used up and then it resumes slowing down and dying! It acts like its running out of fuel in the idle circuit. I tried opening up the old idle air jets with a small drill bit and installed them back in the carbs but that did not seem to help. So I reinstalled the new jets back in the idle circuits. I am very puzzled, the only thing I can think of is that the old capillary/venture tube is not functioning correctly, of course like any of these old tubes, it is bent inside the main vacuum tube and looks heavily oxidized, but I did “rod” it out the first time I cleaned the carbs so they should work. Anyone have any experience or thoughts about what I could do to fix this issue?

 

[racerone]

Need to tell the folks here what the compression is in numbers.----" good compression " means different things.----Flywheel key checked ?------Tried opening slow speed mixture needles 1/4 turn at a time ?---Throttle plates fully closed at idle ?

 

[Jehu1]

thank you for the directive, i did not post the numbers because i know my compression gauge is reading very low (cheap harbor freight gauge) and that would skew the advice i get here. but it does read consistently, i brought it with me once to look at a motor once and the man who owned the motor had several compression gauges which i compared to mine reading from his motors, his gauges would read from 125 to 135 psi while mine around 80 psi. that being said this motor reads 88 psi on both cylinders cold or warm, so i believe the real pressure is in the 130's at a minimum. my gauge never reads above 100 psi even on my other good motors (90hp Yamaha and 8hp tohatsu) The engine sounds very strong when running at WOT and when your spinning the flywheel with the plugs out to can audibly hear the compression ( suction ) getting pulled into the cylinders.
to answer your other questions I did do a link and sync, butterflies are completed closed at idle and open evenly, i have tried to set the idle many times moving a 1/4 turn to just a a blade width CW and CCW. without success. I am not sure what you mean by "flywheel key checked" if you mean that the flywheel is locked in place and not free to rotate on the crankshaft and change the timing randomly, i believe it is secure.

 

[jakedaawg]

Did you check that core plugs and lead shot actually sealed I use just a teeny bit of goo of one brand or the other. If that lead shot is leaking it becomes yet another air bleed that will slow the motor down.

Two carbs, right?

Will it improve if you raise base timing just a smidge? What rpm is it attempting to idle at? Is this happening in a tub, on muffs, or in the lake? Getting idle mixture set correctly between carbs on some of the '89's-91's can be a bear, I suggest you keep trying.

 

[Jehu1]

thanks for the advice, i can tell you have fooled with a few Carbs by your sealing advise around the plugs and lead, I found out how important that can can be several years ago working on a little Johnson 2hp, the smaller the engine the more critical everything be sealed properly so now when I work on a carb, after i install the plugs i seal around them to make sure there are no leaks disrupting the idle air flow, i have even gone so far as to seal on the inside of the carburetor throat where the main jet/vacuum line enter the housing and in cases like this one where the capillary tube enters the idle circuit at the top of the throat and gotten some amazing results doing that from stubborn outboards that don't want to idle. so bottom line is there are no leaks anywhere to decrease/disrupt the idle vacuum which is kinda why I'm stumped. to answer your other questions i have it on muffs in the yard.. past experience has shown there is no need to take it to lake lake if you cant get it idling right at home, as the lake water back pressure never has helped anything run better in my experience! as to your timing question it looks to be good, as you know there is a lot of slop in these old engines and when i stand back by the engine with it idling i can manually advance the timing a little without opening up the carb throttle plates. the engine will speed up a bit when i do that but will still slowly decrease its speed and die. very frustrating.. though i have a ton of experience rebuilding all kinds of carburetors i and not at all an expert in adjusting them on an outboard. so any insight you would like to share is very welcome!

 

[racerone]

If back pressure does not matter why do some of the newer motors have a factory installed valve to control backpressure.----Valve is in the exhaust housing ??----I would be taking the cylinder head off for inspection of cylinder walls.-----Would only cost a new head gasket if there is nothing wrong there.

 

[Jehu1]

Sir, I agree completely back pressure DOES MATTER, it just has never made any IDLE problem i have had better if i couldnt get it working at the house first. Have you ever seen the situation where you could not get one idling right out of the water but it did better in the water?? as I said I am far from and expert so if you have please let me know, I had a small leak in the head gasket when i first got the motor, I took the head off replaced the gasket and cleaned and inspected the piston and cylinder wall, everything looked good and the new gasket has sealed the leak so we are good there.

 

[Fed]

I've had Mercs that wouldn't idle on the muffs but were stable in the water, turned out to be air leaking in through the lower crank seal which was getting sealed by the water due to the motors sitting very deep at rest.

 

[weaverunner]

Just a thought, but did you check the float level when you had the carbs apart? I had the same issue when I installed new floats and forgot to check/adjust the float level. Sounds like yours may be adjusted too low (or too high when inverted). 45 seconds sounds about right to drain the float bowls.

 

[oldboat1]

Older carbs with idle needles in the top front used an initial setting of 1 1/2 turns open, subject to further adjustment. Your smaller needle probably angles off the top of the carb -- initial bleed setting is usually more than the older carbs. Might try 3 1/2 to four turns open.

Your model should have a nozzle gasket between the carb top and bottom -- might make sure that's in place, or the carb isn't likely to draw correctly. Make sure lead shots were replaced.

 

[Jehu1]

Thanks to all who responded for the advice.. Just so i don't leave this post hanging open Ill post a final update..
The Problem is SOLVED!! (-:
I considered everything and mulled it over on Friday Night, thought about taking it to a seasoned outboard mechanic on Saturday but as I thought through everything i had done and tried to predict what a mechanic would do I decided I would be wasting his and my time as i was sure this wasn't a standard carb issue. so I got up Saturday and decided to take the carbs off one more time and unseal the Idle circuit pathways and really check it out, once i had cleared the area at the top of the Carb where the Capillary/venturi tube met with the Idle air (area where the lead shot goes) i got my 24 gauge solid wire out and started "rodding out" the venturi tube, I was really difficult getting through the top carbs tube and after ramming the wire through and pulling on both ends like it was dental floss i thought i had cleared it as good as possible. once i withdrew the wire and then started squirting for carb cleaner through the venturi low and behold a piece of wire popped out from the bottom of the tube. I pulled it all the way out and was very surprised, it was about an inch and a half long and heavily oxidized indicating it had been in the venturi for a while. It wasn't from the wire i had been using as it was stiffer and had ridges cut into it kind of like type cleaning tool you use to clear and air paint sprayer jet. So somewhere along the way somebody was attempting to clean the carb, got it jammed up in the tube and it broke off.
Anyway I cleaned out the bottom carbs idle circuit the same way. Reassembled everything and fired it up...I RUNS LIKE A CHAMP! Idle is strong and smooth and as an added bonus the working adjustment range of the idle mixture screws is well over a 1/4 turn which is as it should be.
So after the motor had been started using the electric choke (injected fuel) it was running at a higher RPM than normal due to the extra fuel the broke wire started eventually restricting the fuel flow through the top carbs idle circuit which cause the gradual slowing down of the motor till is stalled and died after 30-45 seconds.
I don't know if any of the following helped as well but after i got the wire out i notice the nipple of the venturi tube where it rests below the Vacuum tube in the bowl to pick up fuel didn't look perfectly round as it should so I jammed one leg of a tweezer up in it an (wallowed) it out to re-round it and open it up a bit. I did the same for the bottom carb as well this would insure good fuel pick up and judging from the happy results it all worked out.
A few other notes someone may be interested in. I use a product called BONDIC to reseal the area where the lead shot used to go and around the edges of metal seals anywhere they are found on a carb, it’s a neat product, kind of a thickish liquid that dispenses through a needle and instantly hardens with exposure to an Ultra Violet light which is supplied with the product, this product allows me to remove things like the lead shot from a carb and reseal the area without fear which is really nice since Lead shot does not come in any carb rebuild kits i am aware of and getting to the areas sealed by them can sometimes be critical, as in this case. Got my Bondic through a website called "the GROMMET" if you’re interested.
One other note about the Carbs on these early 90's 40HP Johnson Evinrude motors, there is a brass elbow on the top of the carbs used to connect the idle circuits of the top and bottom carbs together, i have worked on a few 90s area OMC carbs and none of them had this strange connection on them, as a matter of fact I have never seen anything like this on any other twin cylinder brand of engines carburetors. I had one mechanic tell me he thought it was there to help "balance" out the carbs but he didn't seem real sure about that, after thinking it through and trying to get this engine to idle with it and without it hooked up and seeing no difference I decided to remove the elbows and seal the holes left behind with the BONDIC. Judging for the now happy results I believe i can safely say you really don't need that connection on your motors carbs so if you want to take it off and seal the area you should be fine.

 

[jakedaawg]

Good for you...I dont recall the two carbs being hooked together with a hose...I must be getting old. I have several of these motors, I'm gonna have to look and see what you refer to.

 

[Jehu1]

I had never seen anything like that on a carb either, I first thought it was there because of the VRO system but that apparently isn't right. I saw a few of these carbs for sale on Ebay and on the ones that had good pictures you can see the line hooked up between the carburetors Idle circuits, it's located at the top back of the Carbs 90 degrees from right where the idle mixture adjustment screw/needle is. If anyone ever figures out what it was there for I would love to know..