Trying to locate '94 evinrude 140 vacuum leak

[L3600]

I have been reading endless forum questions/answers on the topic of rough idle, stalling so I'll try to condense my troubles. I have a '94 evinrude 140 that I am thinking has a vacuum leak that may not be accessible to diagnose with any carb cleaner spray externally. Is there a way short of pulling the powerhead off to see if it is leaking at the lower seal area?

 

[Joe Reeves]

Re: Trying to locate '94 evinrude 140 vacuum leak

What exactly is that engine doing at idle... spitting back (sounds like a mild backfire), drops a cylinder and vibrates, what?

With it idling, do you have the same drop in rpm when you pull the spark plug boot off of the individual plugs... also does a non firing cylinder (if it exists) suddeny start firing if you hold the plug wire slightly away from the s/plug (spark jumping to plug)?

Do you have even compression on alll cylinders?

With the s/plugs removed, does spark jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!?

Never have I seen a vacuum leak at a crankshaft seal. The only vacuum leaks I've ever come across was due to a bad or non existant gasket or "O" Ring between a carburetor and the intake manifold.

 

[L3600]

Re: Trying to locate '94 evinrude 140 vacuum leak

Joe- Thanks for taking time on this. I've been fighting this idle thing for awhile now. Idle is erratic. It varies between 800-1100 rpm on its own. It does not appear to be anything steady like dropping a particular cylinder. No vibrations other that running rough at idle. I've done the spark test and it seemed to look like it should. compression is between 95-105 on all cylinders. It runs fine anything above an idle.
Last season I went through the carbs. These things looked like brand new inside before I even started.I inspected each passage, used compressed air just hoping to find something. I followed each circuit to understand what each passage did. I installed new gaskets, needles,seats, checked float levels. I thought I was onto something when I found 3 of the 4 main jets backed all the way out. (I'm suprised it didn't fry a piston). Put it back in the water and the only thing it gained was better top end power probably because it was now actually getting fuel through the mains. I finally got frustrated and screwed the idle mixture screws all the way in to block off the air bleed holes and the thing actually almost idled smooth. It shouldn't have even been running at that point. Once again I used about 1/2 a can of carb clean trying to find some sort of external leak anywhere I could get to. That brings me to wondering if there is a leak somewhere else.

 

[Joe Reeves]

Re: Trying to locate '94 evinrude 140 vacuum leak

You say.... "It varies between 800-1100 rpm on its own."

The only time I've seen engines vary rpms up and down on a constant basis, over and over and over (and I've seen a few), the problem was that the throttle butterflies were not syncronized..... at least one carburetor had its throtttle butterfly opened ever so slightly at a dead idle.

This was a common problem encountered by novices when reworking the carbs on a cross flow engine that had more than one carb (linkage just a little too tight)... BUT it has happened with a looper now and then. It may not be your problem but it's something worth looking into... to check it off the list if nothing else.

Unless they've changed the design since I retired, the looper carburetors are separate from the throttle body (bent butterfly?).

Find the main operating hose that leads from the fuel pump/VRO to the crankcase and remove it from either the crankcase or the pump. Pump the fuel primer bulb up hard to see if any fuel leaks out that hose (slightly cracked pump diaphragm). This is unlikely but still worth checking.

Also, with the primer ball still pumped up hard, see if any fuel is leaking out the small primer outlets/hoses of the fuel primer solenoid.

 

[daselbee]

Re: Trying to locate '94 evinrude 140 vacuum leak

You MUST clean the throttle body passages when doing a carb job. Just cleaning the black carb bodies is only half the job.
Look up your carbs on shop.evinrude.com. On the side of the throttle body, there is a core plug. Item #2 on the drawing.
There are five(?) very very tiny holes behind that plug. They open into the throttle bore, right at the butterfly. They clog easily. I use a tiny welding tip cleaner to open them up.

Also, if your carb butterfly sync is off....in other words, if #1 and #3 are fully closed, when #2 and #4 are even open the slightest, it will idle like crap. All butterflies must be absolutely closed at idle. Some guys advance the idle stop to prop open the butterflies to increase idle. Can't do that. All butterflies closed. They must be perfect.

I am with Joe, you don't have some mysterious vacuum leak under the powerhead.

 

[L3600]

Re: Trying to locate '94 evinrude 140 vacuum leak

I will pull those plugs out and do some cleaning. That makes sense. I will also check for the fuel leaks Joe described. The throttle plates are in sync and are closing fully. I am glad to hear there should be no mysterious leaks I can't get to. Thanks for the input guys. I'm no expert. I'm here to learn.

 

[daselbee]

Re: Trying to locate '94 evinrude 140 vacuum leak

Consider.....the tiny holes I refer to allow idle fuel to pass to the cylinders thru the side of the throttle bore.
If those are clogged partially, the fuel/air mix getting thru would be very lean, right?
So, on your particular motor (you have that oddball carb design), the idle mixture screw adjusts AIR, not gas flow. When you turn the screws in, you are shutting off AIR, and that would richen up an already lean mixture.
You did say it ran better with the idle needles all the way closed, right?

Make absolutely sure the idle pickup tubes in the carbs are open. Those are the brass tubes that extend into the bowl.
They are not the same diameter throughout their length. They get small up at the top where they press into the plastic carb body.
And you know that the top of the tube opens into the labyrinth air/fuel flow passage on the stbd side of the carb that is covered by a metal plate. I have seen idle circuits clogged at the top of the brass tube. It doesn't help to blow air thru there, it is best, believe it or not, to suck on that brass tube and feel the flow of air on your tongue. You can really judge from carb to carb if they are the same, or if one is clogged.

I kid you not. Tastes bad, but only while you have the tube in your mouth.

 

[L3600]

Re: Trying to locate '94 evinrude 140 vacuum leak

At this point you would be suprised at what I'm willing to put myself through to get this thing running right. Thanks for the input, it gives me a couple new things to check out. It will be a couple weeks before I can get back to it but I'll let you guys know how it works out.