1993 Johnson 70HP 2stroke: won't start when WARM

[ReedMikel]

Just inherited a 1993 JC Pontoon boat with a Johnson 70HP, 3 cyl, 2 stroke. Engine starts when cold or hot without a problem. But if it's warm (e.g. run for an hour, then off for 30 mins), it won't start. Sometimes it would cough like it was about to start, but then nothing (just turns over). When I'm out on our lake and this happens, only way to start it is to remove 3 plugs, spray starter fluid in all 3 cyls, and then it starts. I am no mechanic, but doesn't that sound like a fuel issue? I have the shop manual for this series of motors, and in the fuel section I saw mention of a "fuel primer solenoid" that from what I understand sprays fuel into manifold when key switch is activated (I think it means when I push in on switch for choke?). I'm thinking that when the motor is hot, there's still some fuel in the system and no choke is needed. But when WARM, there's no fuel and choke might be needed? And if that solenoid is flaky, maybe no fuel is getting in? My local marina mechanics are probably not going to solve intermittent problems like this, so I guess I'm on my own (with all your help too

Appreciate any suggestions!!

Thanks,
-Mike

 

[ReedMikel]

Thinking it's a fuel issue, could it be vapor lock/boilover? How would I tell?

 

[interalian]

When you're doing the "warm" start, are you lifting the fast idle lever? Priming? On mine, "warm" starts need a lot of idle boost but no priming.

 

[ReedMikel]

Yes, I'm lifting the idle lever just like I do for cold starts. I've tried pushing in the key switch (choke) as well as not choking. On first try I did not squeeze the priming bulb, but tried that later and still no start.

 

[ReedMikel]

The more I research this on Internet, the more convinced I am this is a classic vapor lock problem. Lots of folks, even with newer motors, reporting same symptoms. Some have suggested that "winter" gas (with a higher ethanol level) could be the culprit. Some suggested using higher octane gas (I've been using 87). I guess I'll start with the simplest and start using high octane gas. I wonder if there is any additive to prevent this?

 

[ReedMikel]

Just found that a nearby marina sells 91 octane gas with NO ethanol, so I'm going to try that first. Apparently ethanol lowers the boiling point, which can lead to vapor lock.

 

[Silvertip]

Higher octane gas is actually harder to ignite than 87 octane. Octane is not the problem, nor is ethanol, and I seriously question vapor lock. A 30 minute rest after a hard run should clear a vapor lock anyway. Is your overheat alarm working?? Check for vacuum leaks. The fuel pump on your engine works by vacuum pulses. Any vacuum related issue would affect fuel pump operation. Once started (as when cold) the engine can overcome a small leak. When warm, that leak may worsen thus preventing proper fuel delivery and carburetor operation. 1/2 up on the fast idle lever should be adequate. If the primer solenoid is not delivering fuel when warm then it is suspect. The small orfices related to the primer system can also plug creating a hot/warm start problem.

 

[racerone]

You may not agree, but I would take the starter apart for a simple inspection and OHM check on the armature.--Ask how to check when you have it apart.----A " no money spent " step to take.

 

[ondarvr]

This isn't uncommon on older carb'd 2 strokes, some do it frequently, others never. And like they said, octane has nothing to do with it, although there's a slight chance ethanol may. As the warm motor sits there it may evaporate fuel out of the carbs, so sometimes squeezing the primer prior to starting helps. So can holding the key in and squeezing the bulb, then trying to start it. I haven't seen a foolproof method, but if required just spray the starter fluid into the air box, you shouldn't need to pull the plugs, this would be a last resort though, not the first step.

 

[ReedMikel]

Hmmm, I read many articles and posts that said ethanol is definitely a factor with vapor lock, as it lowers the boiling point. And a marina owner told me they only sell ethanol-free gas. Why would they do that if it wasn't an issue? Oddly, I have read conflicting stories about octane and vapor lock. Some said higher octane gas is made by adding alcohol/ethanol, which would mean higher octane could be worse for vapor lock. I've also read that an engine gets HOTTER after being shut off, which can lead to vapor lock as the gas boils in carbs or lines. And the tech article I read said that the vapor lock could easily last 1.5 hours. I don't think I ever waited 1.5 hours, as I've just pulled plugs and sprayed starter fluid if I got tired of waiting out on lake. Good to know I can just spray into air box instead If engine had a vacuum leak, would it only affect WARM starting? I have no problem starting cold or hot. Ahhh, the pleasure of owning a boat

 

[ReedMikel]

I think it starts when HOT because the gas has not had a chance to boil...

 

[ReedMikel]

1993 Johnson 70HP 2 stroke: 2nd/thinner hose going from fuel fill to gas tank?

On my pontoon boat there are 2 hoses that go from gas tank to the gas fill neck area - one is a 1.5" hose that supplies gas to tank, other is 5/8" hose that terminates in a small metal thingy mounted on outside of boat, just above gas cap. Is that some sort of vent line? I am experiencing what I believe is hard starts when WARM because of vapor lock and wondered if this smaller hose/vent should be checked/replaced?

TIA,
-Mike

 

[canadalooney]

What exactly happens when you attempt to start it? Is the motor cranking quickly from the starter?

 

[ondarvr]

People say lots of things, it doesn't mean they're accurate.

I said there is a chance ethanol may increase the odds, but it depends on the exact reason for it not starting.

Octane can be increased by adding ethanol, but that's not how they increase it when you're switching between regular and premium of the same brand of E-10. There are places where the premium is E-0, this could make a difference, but it still depends on the exact reason it's not starting. If you are getting the premium fuel at the marina and it's E-0 it may help, but only because there's no ethanol in it, not because it's premium, regular E-0 would do the same thing.

 

[GA_Boater]

On my pontoon boat there are 2 hoses that go from gas tank to the gas fill neck area - one is a 1.5" hose that supplies gas to tank, other is 5/8" hose that terminates in a small metal thingy mounted on outside of boat, just above gas cap. Is that some sort of vent line? I am experiencing what I believe is hard starts when WARM because of vapor lock and wondered if this smaller hose/vent should be checked/replaced?

TIA,
-Mike

Moved this post into your thread. Starting a new thread on the same problem only confuses people.

Yes. the small hose is for venting the tank. I doubt it is the cause of your warm starting issue, If it were plugged, the boat would die after a few minutes when the fuel pump can no longer draw fuel out of the tank.

To verify, the next time the boat is hard to start, open the filler cap. If the motor starts, check the vent/hose for blockage. Is you still can't start, then keep chasing the vapor lock.

BTW - Vapor lock has been around as long as carbs and gas motors. In other words, far longer than ethanol laced gasoline. Ethanol is not a contributing factor.

This might sound off the wall, but I would look at the fuel pump. If the diaphragm is weak due to age, it has a harder time filling the float bowl.

In answer to the question about marinas selling E0 - It's a profit thing with a captive audience because they can and do charge more than for E10.

 

[ReedMikel]

BTW - Vapor lock has been around as long as carbs and gas motors. In other words, far longer than ethanol laced gasoline. Ethanol is not a contributing factor.

Wow, then there is a tremendous amount of misinformation on the Internet concerning ethanol and vapor lock! Are you saying adding 10% ethanol to gasoline does not lower its boiling point? I'm a gasoline newbie, but it seems to make sense that if an additive like ethanol lowers the overall boiling point, then vapor lock is more likely to occur. What's wrong with this logic?

 

[ReedMikel]

This might sound off the wall, but I would look at the fuel pump. If the diaphragm is weak due to age, it has a harder time filling the float bowl.

Why would a weakened pump only affect WARM starts? I guess "warm" is misleading, as temps actually rise after shutting off the motor. Temps go from hot (while running or just after shutting off), to hotter (while off for a period of time). That's assuming all the threads I read about this are accurate?

 

[ReedMikel]

This might sound off the wall, but I would look at the fuel pump. If the diaphragm is weak due to age, it has a harder time filling the float bowl.

Not sure if it's relevant, but this Johnson motor is the VRO type that has (had) an oil injection system. A couple years ago the marina disabled it (because I feared it failing and blowing the engine). From what I've read, the pump is a combined oil and gas pump(s). I seem to recall seeing an oil line that the marina cut and plugged (with a threaded screw if my memory is any good). I imagine they also cut a wire or two related to oil sensor. If they only plugged that line with a trheaded screw, could that cause an air leak? Vapor lock?

 

[GA_Boater]

When did this problem start?

 

[ReedMikel]

When did this problem start?

I got the boat in 2012. It had been in storage at marina for a few years (prior owner). Marina had to rebuild carbs and some other items before I took possession. I asked about the VRO feature and was advised to have marina disconnect it. So VRO was disabled from day one for me, and the warm start problem was always there. So I don't know if the marina's disconnection of VRO is a factor...