Diagnosing starting / low throttle issues 1993 40HP

mike__b

Seaman
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Oct 21, 2010
Messages
64
I got to take my 1993 40HP Evinrude (tiller, TTLETB) out on the lake today. It really pushed my boat well. I bought the motor a couple weeks ago and revived it after the previous owners said it hadn't been run in a couple years. Started right up with some blue smoke, probably because I primed the cylinders with some penetrating oil prior to attempting to start.

I had it mounted and a couple small things fixed at my mechanic. New primer valve, new fuel filter, some new fuel lines. The big expense was I went ahead and had them rebuild my carbs. I would have done it, but it was already there and they said it wouldn't idle and would die because of the carbs. The tilt is off while I'm repairing it, so it sits really low in the water right now. My mechanic said it runs a bit rough on idle due to that fact.

So I take my boat out from their shop. I run it up and down the lake probably 5 miles or so. We are mostly running WOT except for wide turns, etc. We did have to maneuver through a couple long no-wake zones at a slow idle. During this whole time the boat performed well, didn't kick or sputter except if I turned the idle all the way down where the throttle would go no lower. No wake speed was really smooth. We've been out for about 1.5 hours when we start to run out of fuel. I had borrowed a tank and didn't know how much fuel was in it and the gauge was broken. So we try to make it back to the marina. Well, we didn't make it. Ran completely out in a no wake zone about 100 yards from a marina. We threw the trolling motor in and drove over and got new gas. I used my handy-dandy mixing bottle to accurately mix 50:1 in the tank with 4 gallons. That would be enough to make it back plus leave the guy I borrowed the tank with plenty to spare.

Hooked up the tank, prime the bulb. And it struggles to start. Finally get it started, rev it up in neutral, idle it down and put it in gear and it dies. Did this several times, each time with it struggling to start. When it would finally start, it would blow out blue smoke. Normally, it didn't smoke at all, even on a cold start. Finally I grabbed the primer bulb and squeezed it and it seemed to have way too much slack. Pumped it up, it started, started to take off and it died. The fuel line had slack again. Repeated, and finally it started again, primed the fuel line again and started off and all seemed well.

We get to the marina and its rush hour at the ramp. So we idle down real slow trying to wait on a pontoon that was taking forever to move. We're barely moving at this point and it dies. We paddle over to the dock behind that pontoon that took forever to unload. Try and try to start it with almost no luck. It would start, throw it in gear and it would die. Priming the fuel line seemed to help, but failed to solve the problem. It would go into gear for a few seconds then die. Eventually we got it on the trailer with my bow line.

So before we got gas, the motor ran really good. I hope we didn't get bad gas. I have thoughts of it being a bad pickup in the tank or his hose or the fuel connection. But also, I was thinking about vapor lock. The motor would have been really hot after all that running. It was about 90 degrees F out today when this happened. Any ideas what the cause may be? I plan on starting it in my 30 gal trash can on Monday and also calling the mechanic too.

Also, if the carbs were rebuilt as described, should I have rough idling with the throttle all the way down? I have the idle speed adjusted up, but it still is rough and feels like it might die even when cold. I had them give a once over the engine and the carbs are all they suggested fixing.

TIA
 

fireman57

Captain
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Aug 24, 2004
Messages
3,811
Re: Diagnosing starting / low throttle issues 1993 40HP

Sounds like you picked up trash from the bottom of your tank when you ran it dry. Usually not a good idea. You said that you would have rebuilt the carbs yourself so if sounds like you are going to get your chance at a really good cleaning. Make sure that you blow everything out with compressed air. I'm betting that you have a low speed jet with junk in it.
 

mike__b

Seaman
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Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

I'll look into it if it doesn't run good cold. Does that account for the lack of fuel supply at low speeds? It really seemed that air was getting into the line or the fuel pump wasn't pulling strong enough at really low speeds. We were really feeling a fuel supply issue (pump, tank, line, vapor lock, etc), not a carb issue. But they are so closely related, I guess its possible.
 

Haffiman

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Dec 17, 2009
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2,454
Re: Diagnosing starting / low throttle issues 1993 40HP

If your VRO is hooked up, what happened was that the VRO pumped pure OIL into your carbs when it ran out of fuel.
Pull out the drain-plugs on the carbs, and 'wash through' with fuel by pressing the primer bulb on your tank.
Put the drain screws back, start the engine, put in gear as soon as possible and throttle up!
 

mike__b

Seaman
Joined
Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

If your VRO is hooked up, what happened was that the VRO pumped pure OIL into your carbs when it ran out of fuel.
Pull out the drain-plugs on the carbs, and 'wash through' with fuel by pressing the primer bulb on your tank.
Put the drain screws back, start the engine, put in gear as soon as possible and throttle up!

No, the previous owner has disconnected the VRO. I run a 50:1 mix.

I was told there was a way to flush these carbs without removing / disassembling them, any idea?
 

fireman57

Captain
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Aug 24, 2004
Messages
3,811
Re: Diagnosing starting / low throttle issues 1993 40HP

There is no way that I would trust to "flush a carb". If you suspect the fuel pump then squeeze the primer bulb when it acts up. If it picks up and runs right then it is your fuel pump.
 

mike__b

Seaman
Joined
Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

Well, I've been running it for a while now. It's now on my tank with new gas mixed 50:1.

It did start easy and ran decent. No real problems starting it. I've even cut it off after running about an hour idling, and it started right back up even with the throttle on slow. It does still run a bit rough on slow. And when I first started it up, it would die after a couple minutes with the throttle all the way down. I have a tiny tach on order to make sure the idle speed is correct, so I can't check but it seems to maybe be idling low. If I had to guess, it sounds around 600 rpm.

Now it seems to be running stable on full slow, but if I throw it into gear at that speed (it's in a 30 gallon trash can) it will sputter out and die. It does seem to start up MUCH easier than when we were on the lake. Normally first attempt after just a couple revolutions. I wonder what continues to cause the rough low speed issues.
 

fireman57

Captain
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Re: Diagnosing starting / low throttle issues 1993 40HP

did you ever clean/rebuild your carb? Sounds like trash in the low speed jet.
 

mike__b

Seaman
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Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

Not since the weekend. It is currently running like when I picked it up from the marine shop. But I'll look into it.
 

mike__b

Seaman
Joined
Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

Well, I "rebuilt" the carbs again today. Fully disassembled, removed the low speed nozzles after noting their position. Soaked them in a gallon of the thick carb / parts cleaner, then sprayed all the residue off with carb / choke cleaner. It sure is a pain to removing the carbs on this motor with that VRO pump in the way. I also used a parts grabber to grab some of the dropped bolts and locknut from the air silencer the "mechanic" dropped.

I noticed a few things after taking the cover off. First, the carbs were never cleaned. Not cleaned anywhere to my standards at least. There was still old oil and gunk on the outside of the carbs and on the linkage. There is no way someone soaked these or sprayed them down with carb cleaner and wiped them off. So I'm not real pleased. Also, old papery gasket material was left stuck to the bowl parts. Second, I seem to have a fuel leak from the fuel manifold on the line that goes to the primer. I tied a new zip tie around it but it still leaked. I'll need to get a new hose to run from the fuel manifold to the primer. Odd, I had a cracked valve on the primer replaced too... But the line seems old... It's well stuck on the manifold.

I only put it back together enough to make sure it started up. I'll run it more tomorrow, I just ran out of time today. They didn't replace the gasket between the carbs and the air silencer and the air silencer gasket itself is all tore up and they didn't replace that either. So I'm going to reassemble it fully when I get new gaskets.

When my tach arrives, I'll adjust the idle speed, etc. I also may need to do a linkage adjustment. The top carb seems to be opening more than the bottom carb.

Edit: Looks like the mechanic actually cracked the fuel manifold on the leg that goes to the primer. So I'll be getting a new manifold and hose too.... fun.
 

mike__b

Seaman
Joined
Oct 21, 2010
Messages
64
Re: Diagnosing starting / low throttle issues 1993 40HP

This morning I fixed the fuel leak and got the air silencer back on. I did all the adjustments I can right now. I did a linkage and sync adjustment. Once I did that, it wouldn't run at full slow. To make it run at full slow, I needed to screw in the idle adjustment screw in significantly for it to idle.

The idle screw also advances the timing. I'm wondering if my timing is off. The length of the spark advance bar is the length my book says it should be. There is some "play" in the spark advance level where it connects with the throttle advance, this is normal. But when running, if I push the spark advance forward in that area of play (maybe 1/4") it seems to run smoother.

I do have it now where it will run at full slow and when I put it in gear, it doesn't want to immediately die. But If I left it in gear, it probably would.
 
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