Possible vapor lock?

[Mattyman]

The starting problems with my 86 TS6M continue to haunt me. Last year I resolved some issues with hard cranking due to a bad starter solenoid when warm. This year I seem to be facing an issue, which seems like possible vapor lock.

When first taking the boat out, it fires up right away. After running for a period of time and upon shutting down, I have a hard time getting it to restart. It cranks and cranks but nothing.

Some info on yesterdays fun (water was warm and air temp was hot):

Took boat out and it started without issue. We ran it pretty hard for about 30-45 minutes without me shutting her down and it ran fine. At one point it stalled but fired right back up without issue.

We ran around for about another 10 minutes and then we anchored for about 30 minutes. I attempted to restart but all she did was crank. I then opened the cover, removed the air cleaner on the carb and used the throttle to dump some fuel into the carb. Cranked away for awhile and still nothing. Gave it some more fuel and finally it started up but would not idle correctly and then died. I got it started again by just cranking and giving it more fuel and it idled properly and ran fine until I got it on the trailer.

My exhaust manifolds were hot to the touch (I could not leave my hand on for very long). The temp gauge shows an acceptable level when we are out cruising (I think ~140-150?). When cranking I also saw that fuel was coming out of the jets and going into the carb.

Does this sound like the symptoms of vapor lock? Are there any other tests I can do to help narrow down the issue. I just saw that pouring cold water on the fuel pump may help? Or a new impeller to help out with vapor lock (even though I think mine is still pretty good).

If it is vapor lock, what can I do to fix it? I'm getting tired of only being able to shut down my boat at the docks ;) Thanks for the help.

[csuggs]

If you have fuel to the carb then it is not vapor lock. Sounds like an ignition (electrical) problem to me. I had a similar problem (see the following thread)

http://supraboats.com/bbs/showthread.php?t=9206

Turned out it was the coil.

[rludtke]

I think that this does sound like vapor lock. The fuel could be vaporizing in the float chambers. Your description of the exhaust risers sounds too hot to me. I have experienced this very thing with my Supra.

In my expereince, the exhaust risers begin to run hotter when the raw water impellor begins to lose efficiency. The engine coolant gauge will continue to indicate adequate cooling, and the engine gets harder to start.

When this occurs you will probably be able to get the engine started by cranking with the throttle wide open. This helps introduce fresh (cool) fuel into the float chamber. After some cranking the engine will light, and probably idle ok after a little throttle play. Do be careful to reduce power as soon as the engine starts. Alternatively, you can open the engine cover and allow the heat to dump. When the fuel cools, the engine will start normally.

The solution is the replacement of the raw water pump impellor. In my experience, replacing the impellor with new returned the riser temps to normal (you can touch with bare hand without burning). I also recomend that you add a thermal insulator beneath your carburater, to further reduce the likelyhood of this problem reoccurring. The thermal insulator will help reduce conductive heat transfer from the engine. Of course it will not help with radiant heat.

On extremely high ambient temperature days, it is possible that you could experience vapor lock even with a good impellor. Fuel vaporizes at ~140 F if memory serves me right, and under cowl temps could be expected to reach that temp on a really hot day. The thermal insulator will help in this case.

[oward1202]

I was experiencing the EXACT same issues with my 1985 comp for the past year so I know how frustrating it is. It may vary well be vapor lock so go ahead and replace your impeller, especially if the exhaust risors are too hot to touch. I just solved my problem this past weekend by simply replacing the ignition coil. Both are simple and cheap repairs that are well worth it. Both are also related to heat under the hood. The impeller will lower your temp under the hood by cooling off the exhaust risers and the coil is most likely going bad by not operating when hot. I would almost guarantee that one of these is the issue so do both before next weekend to ensure a less frustrating day on the water. Let us know what happens. Happy boating.

[rludtke]

I was experiencing the EXACT same issues with my 1985 comp for the past year so I know how frustrating it is. It may vary well be vapor lock so go ahead and replace your impeller, especially if the exhaust risors are too hot to touch. I just solved my problem this past weekend by simply replacing the ignition coil. Both are simple and cheap repairs that are well worth it. Both are also related to heat under the hood. The impeller will lower your temp under the hood by cooling off the exhaust risers and the coil is most likely going bad by not operating when hot. I would almost guarantee that one of these is the issue so do both before next weekend to ensure a less frustrating day on the water. Let us know what happens. Happy boating.

Oward has a real good point about heat affecting ignition components such as the coil.

[csuggs]

If you have fuel to the carb then it is not vapor lock. Sounds like an ignition (electrical) problem to me. I had a similar problem (see the following thread)

http://supraboats.com/bbs/showthread.php?t=9206

Turned out it was the coil.


That's what I said . . . . and I suppose vapor lock is possible, but it sure sounds like ignition problem to me. It can never hurt to install a new impeller, but I think you'll find it's the coil.

[bdumas35]

"We ran around for about another 10 minutes and then we anchored for about 30 minutes"

30 min. is a pretty good while to cool off. May rule out vapor lock.

[Jetlink]

That's what I said . . . . and I suppose vapor lock is possible, but it sure sounds like ignition problem to me. It can never hurt to install a new impeller, but I think you'll find it's the coil.

Installing a new impeller might lower the temp and resolve your problem however, if it truly is an ignition problem like what csuggs said, all you are doing is placing a band aid on the problem. As for the 30 minute sit, that is a significant amount of time for the engine to heat sink, the temp will continue to climb from 150-160 as there is no more cool water circulating through it. If you want, see if you can find one of those thermometers that you can point and shoot at the engine from a couple feet away and get some readings both underway and sitting in the water with the engine off after sitting for about 15 minutes or longer. You might surprise yourself.

[csuggs]

Installing a new impeller might lower the temp and resolve your problem however, if it truly is an ignition problem like what csuggs said, all you are doing is placing a band aid on the problem. As for the 30 minute sit, that is a significant amount of time for the engine to heat sink, the temp will continue to climb from 150-160 as there is no more cool water circulating through it. If you want, see if you can find one of those thermometers that you can point and shoot at the engine from a couple feet away and get some readings both underway and sitting in the water with the engine off after sitting for about 15 minutes or longer. You might surprise yourself.

I did that when I was trying to diagnose my problem. While the engine was running I was even able to shoot the temp near the thermostat housing and "see" that the thermostat was opening and closing as the temp changed. When I shut down the motor is just a giant heat sink and the whole thing will climb to 160-170 - almost anywhere you shoot the temp. In my case, the coil was too hot to touch even after being shut down for about 3 hours! Changed the coil - problem went away.

Here are the specifics in my case: I have a 1st generation Pertronix ignition, and according to Pertronix you need to measure the resistance across the two terminals of the coil to determine whether or not to use a ballast resistor. If the resistance is less then 1.5 ohms then they say to use the resistor, and if more than 1.5 ohms not to use the resistor (this according to Richard at skidim). I had it wired correctly, but I think that the coil was actually a bad one.

Mattyman - it sure sounds to me a lot like the problem I experienced most of the season. I was chasing what I thought was a fuel problem - once I realized it was an ignition problem I changed the coil and life is good.

[oward1202]

[QUOTE=csuggs;61574]
Mattyman - it sure sounds to me a lot like the problem I experienced most of the season. I was chasing what I thought was a fuel problem - once I realized it was an ignition problem I changed the coil and life is good.[/QUOTE

Ditto! Same problem with similar boats.