Vapor Lock? 1978 restored Nautique

Hello Forum members,

I need your help and ideas. I have a 1978 Nautique that I am restoring. I have professionally replaced floor and stringers. This winter she is getting a brand new gel coat head to toe. Top to bottom. I have owned and used her for 2 full summers now. Her engine was rebuilt before I bought her and is working great. I did have the carb. rebuilt this summer. Here is the issue I need help with. If I drive at closed throttle/ clicking gear, or keep her ideling too long. (between skiers) driving in clicking gear for too long like when my kids are learning to ski off the boom, I appear to be struggling with what my mechanic thinks is vapor lock. When I try to accelerate it just boggs out. Sounds like she is getting too much or too little gas. My mechanic thinks the gas is getting too hot creating " vapor lock". His diagnosis might all make sense becauseif I pull the engine box up when driving at clicking gear through channels the problem does not happen as frequently. Or if it is happening and I turn the boat off for 15 minutes it stops happening. The temp gauge always reads well below 180. I always run 92 octane gas with no ethanol.

From my description are there any other ideas of what my problem could be? And if it is vapor lock what can I do to fix it? My mechanic says we could try to put some kind of device that cools the gas before it gets to the carb???

What is frusterating is it seems to be getting worse or happening more frequently this summer vs. last summer. The only difference this summer is I had the carb rebuilt and I have a modern fuel filter vs. the original one which was on there when I purchased the boat and started leaking.

The boat is going to look like it just off a show room floor next summer when this gel coat is done and I want to not be dealing with this annoying engine/ vapor lock issue.

I appreciate any ideas as I am not a mechanic and need help in this area. I have a good one who loves working on this engine but we never got it fixed this summer even after carb. rebuilds and new water seperator fuel filters etc.

Good Idea Kap.... I would also check

- Primary's dripping at idle?
- accelerator pump adjusted correctly?   
- primary floats adjusted correctly?
- clean spark arrestor?
- are your bow vent tubes clogged or smashed? especially after a floor rebuild?

PS... it's not vapor lock, that only happens when the engine is not running, and from what I understand, it doesn't happen much on boats, although it gets talked about a lot here.   The Holley carb site calls it "heat soak" if you want to understand more of the principal and the cause.

another thought - fuel pump is bad, or not providing enough pressure?

The strangest thing about this problem is it doesn't happen unless I idel for too long. The rest of the time it runs like a dream. Which make me think the fuel pump, etc. are all working fine. Maybe not though.

this boats arent meant for idling. too much fuel gets on the intake and generates a bogging

Can anyone speculate as to why I don't have an issue if I open the engine box while going through channels? I can fix the problem by doing that. It just isn't a reasonable solution.

Luchog wrote: this boats arent meant for idling. too much fuel gets on the intake and generates a bogging

I agree with the need for a new mechanic or possible an old(Er) mechanic.

As for these boats not being meant for idling that's news to me... My experience is Properly running boats will idle indefinitely (a couple hours at least) without any issues.

The mains should be doing nothing at idle.
Given how conservative the cams are, I concur with Joe, they should idle indefinitely.
A 2-3 hour blub is nothing.
A boat that can't has something amiss.

yes you are both right on the jetting, I didnt give it enought brain time and 9 hours under the sun today must have done some damage.

Agreed, and no issue should arise while idling between skiers.

I will stand on my though, this boats are not meant for idling. That doesnt mean you cant or that it will harm anything.
The overal design/tune on this engines is for a different use, fuel mixture, plugs heat range, valves, etc.
Of course, this on the theorical case the boat is mainly used at idle speeds.

On the subject, carb tweaking is in order.

Don't give up, don't throw money at it either. It is possible this guy is right. I have had cars in the past that loaded up when hot, probably were set too rich. Carbs can't adjust on-the-go like FI can now.

There is a reason for this problem, you just need more data.

Get a IR thermometer (they are cheap now) & take some temp readings of your engine, carb, etc. Maybe take some readings of someone else's boat under similar usage.

If you look close enough, you will detect the cause.

Good luck!

Thanks Eric, Good idea and I think he might have talked about the coil before. It is not hard to make this problem come up. It is becoming very consistent. I just need to have him over next spring and we can drive in clicking gear for 10- 20 minutes and it should rear its ugly frustrating head. It used to be only some of the time which made me think I was getting bad gas. I even switched stations..But it is becoming very predictable now which is only good in that with him on site (always comes to my place and works on it in the water) we should be able to figure it out. Thanks for all the replies as I can print them and share them. He will understand them better than I. Thanks again for the ideas.

FFF - Now that you mention it, I had an evinrude with bad exhaust manifold, did the same thing.

That is actually a great idea and reminds me of something I forgot about. One of my hoses is attached together with a clamp. It was set to be fixed this spring by a different mechanic ( guy next to shop who replaced stringers) who pointed the potential problem to me. I told him to replace both and then he couldn't get the parts before I was scheduled to pick it up. I remember the mechanic thought they were expensive too. He said that is probably why the guy before fixed it that way. Clamping two pieces together. He said I would probably be fine since it worked the summer before.

So I will fix this either way. Are there any recommendations on what kind of hose to use? Is there a type that would enhance the sound? As in louder.

I did try to drive with the motorbox open once (after it had started bogging out) and it back fired a little which was unsettling to myself and a friend of mine who both know little about engines. I called my mechanic to check it out. That is when he said to turn it off and try it an hour later. An hour later, after it had cooled, it worked fine and I continued to pull my buddy barefooting. I need to replace those hoses either way.

If the problem started and I tried to drive with the doghouse/motor box open, should the problem solve it self quickly? If it should then this is probably not the issue. It seem like the boat needs to be turned off and something/part needs to cool off.

Sometimes...When this problem is happening it is when I try to take off quickly. It just sputters and bogs. But if I back off the throttle a little or accelerate slowly I can massage it's way to faster speeds. It is like it works it self out. I can only get this done if it hasn't been run or idled too long which again makes me think it is heat related.

I am replacing those hoses whether it solves the problem or not so thanks again for reminding me.

John

It could certainly be an exhaust leak issue or a coil issue or a vapor lock issue (although I got to say a vapor lock would have to be due to a relatively hot running engine in my humble opinion) or even a sticky advance mechanism/timing related issues….
But if it quacks like a duck, and swims like a duck… it’s probably a general carb cleaning/tuning issue. It is the most common problem and it describes your symptoms perfectly.
Either an overly richly adjusted idle or dripping caused by improper float levels or nicked up needle/seat assemblies would fit the symptoms perfectly.. even the extra cool air helping a bit would indictate too much fuel.
However that may be a red herring and you may simply have an incorrectly adjusted or improperly working accelerator pump that causes you to bog, pop, or possibly die off the line sometimes. I see that at least once a season even on otherwise clean and well adjusted carbs.
Personally, at this point in my life if a carb even looks at me wrong I pull that son of a gone off and rebuild it (ok first I check fuel pressure, then I check voltage to the coil, then I make sure the advance assembly moves smoothly since all those things can be done in minutes without taking anything apart).   But other than that tear it down.