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

[racerone]

Have you asked any other folks on your lake / in your area if they are having " vapour lock " problems or are you the only victem ?

 

[ondarvr]

An air leak would be a problem all the time, and would be the opposite of vapor lock.

 

[ReedMikel]

Have you asked any other folks on your lake / in your area if they are having " vapour lock " problems or are you the only victem ?

We are only at lake part time and most neighbors are renters, so we don't know if others are having this problem.

 

[ReedMikel]

We are using 87 octane gas from a local Mobil station, not marina gas.

 

[canadalooney]

Please answer previous post

 

[ReedMikel]

CanadaLooney - what post are you talking about?

 

[ReedMikel]

Hi GA_Boater - just checking to see if you saw my replies to your questions? I know this post has gotten kinda long...

 

[BobU]

ReedMikel - you pose some very good questions about vapor lock! I am anxious to hear answers from the moderator ga_boater. I too am under the impression that ethanol lowers the boiling point of gas, which should mean that vapor lock will more likely occur with ethanol present. I did some Google searches and found plenty of articles that support this theory. But let's hear what an expert like the moderator thinks? I recently started experiencing warm start problems too, so I find this to be a very interesting post.

 

[GA_Boater]

I am only a forum Mod, not an expert. Please don't let my forum title mislead you. I'm just a boater like you, nothing more.

I am opinionated though and ethanol is blamed for everything. From some of the comments in this thread, some of you believe all the words you read on the WWW, where every writer is an expert. You are free to believe or not believe what you want, including my non-expert, experience backed musings.

Let's prove or disprove if ethanol is causing these warm start problems.

Find a gas station - This is a good place to start http://www.pure-gas.org/ or a local marina with non-ethanol gas. Fill up a empty portable tank with E0 gas, add 2 stroke oil or leave it pure, depending on your motor, with no other additives. Go boating and duplicate your failure conditions.

Let us know what happens.

 

[BobU]

Agreed - I've seen many things inappropriately blamed on ethanol. But ReedMikel seems to raise some very logical points:
most gas stations sell gas with 10% ethanol added, ethanol lowers the boiling point of gas, and a lower boiling point is a *possible* cause of vapor lock. Are we in agreement on these statements? I agree with your test of using E0. I do not have such a spare tank, so I might just try running mine dry then adding the E0 mix.

As for your suggestion about the fuel pump - why would it only affect warm starts?

Thanks for all your comments and suggestions!

 

[ReedMikel]

Thanks for the list of E0 stations! I found one only a few miles away from my lake house in NY. Like BobU, I don't have a spare tank either to do the test. So I'll run my tank dry too and add the E0 mix...

 

[GA_Boater]

Fuel pressure can reduce or eliminate the possibility of vapor lock. A weak, stretched fuel pump diaphragm can cause reduced fuel pressure. I might as well add carbs to the list because a leaking carb can release pressure too.

I'm not concerned with the boiling point of ethanol when the other components of today's gas are far less than corn juice.

 

[interalian]

I remember the "good old days" when cars had carburettors. Vapour lock was a problem on really hot days and stressed engines with un-cooled exaust headers. Under hood temperatures on those cars was a LOT higher than an outboard would get, especially considering how low the thermostats are set (140 vs 195F).

If the fuel lines did get vapour locked, that would equate to no fuel in the bowls, which you should easily be able to overcome by squeezing the primer bulb (the float won't rise and close the needle if there's just vapour in the bowl).

 

[ReedMikel]

I'm still perplexed as to why the engine starts when cold and hot, but not warm? What is different about a warm engine?

 

[GA_Boater]

This so simple.

By hot you mean running for a while and then shutting the motor off for a few minutes. The fuel doe not have time to evaporate, so it starts right up.

By warm, you mean the same as above, except the motor has been cooling off for awhile, giving time for the fuel to evaporate.

 

[ReedMikel]

Yes, that was my assumption. Is the evaporation normal, or does it mean vapor lock has occurred?

 

[ondarvr]

The answer is, sort of, maybe, but not quite.

This has been happening since motors were invented, it may happen a little more now with ethanol, but it happened to me often enough prior to ethanol that I don't consider it be the cause. If just squeezing the primer bulb doesn't do it, try holding the key in and squeezing it, this bypasses the carb.

This will put fuel directly into the motor, so if the problem is fuel evaporation it will start.

 

[ReedMikel]

Thanks Ondarvr - you're saying to push key in (choke it) and squeeze bulb at same time?

 

[ondarvr]

Yes, that will force feed the fuel directly into the intake. I'm not saying this works on every motor, only that most of the time it solves the problem.

 

[ReedMikel]

Well guys, I think my warm start problem might be solved I was talking to a mechanic at our new marina and he told me that pushing in and *holding* the ignition key on this type engine actually injects a small amount of fuel into the engine. Holding it in does not do anything further - you get just one squirt of gas while it's held in. On a warm engine, where the gas has probably evaporated, you need multiple shots of gas. Simply push in the key multiple times to prime engine, then try to start it. I had mistakenly been under the assumption that when key was pushed in I was choking the engine using good old butterfly valves (I think that's what you call the plate, right?). Maybe some engines work that way, but this one injects fuel. I wonder how many other folks are fooled by this?