2004 GTI 717 Hard to start when warm

[AnteSweden]

As topic, my newly bought 2004 GTI is hard to start when warm.

Yesterday we where out at sea and the problem occured.

Fired up nice, riding around, went in to shore and stopped the engine.
Tried to start it after a few minutes but it wouldn't start.
In between it fires but dies.
A last it fired up roughly, and then went smooth so we rode for a while.
Then the same all over.

Tried to start with fuel off, but no luck.

Did this a couple of times, and the last time, we had it on for about 40 minutes, riding, picking up/leaving people at shore and so on.
No problem at all, nice idle, fine feedback on throttle.
No hesitation.

It runs without problem, good and stable idle, answers fine on throttle.
Top speed/rpm no problem.

Maybe a slight misfire on low rpm's.

On land it fires up immediatly with no problem.

I've checked compression with two different gauges,
No brand gauge : 130/125
Hella gauge : 140/135
Full throttle, spark plug in the other cylinder when testing.

Seems fine to me.

Any ideas where to look?

 

[Riverguy42]

As topic, my newly bought 2004 GTI is hard to start when warm.

Yesterday we where out at sea and the problem occured.

Fired up nice, riding around, went in to shore and stopped the engine.
Tried to start it after a few minutes but it wouldn't start.
In between it fires but dies.
A last it fired up roughly, and then went smooth so we rode for a while.
Then the same all over.

Tried to start with fuel off, but no luck.

Did this a couple of times, and the last time, we had it on for about 40 minutes, riding, picking up/leaving people at shore and so on.
No problem at all, nice idle, fine feedback on throttle.
No hesitation.

It runs without problem, good and stable idle, answers fine on throttle.
Top speed/rpm no problem.

Maybe a slight misfire on low rpm's.

On land it fires up immediatly with no problem.

I've checked compression with two different gauges,
No brand gauge : 130/125
Hella gauge : 140/135
Full throttle, spark plug in the other cylinder when testing.

Seems fine to me.

Any ideas where to look?

I just bought a 1996 Speedster (jet boat w/717 motor) that is doing exactly the same thing. Starts instantly when cold, starts hard or very hard when warm. The problem seems to be worse if there is more than 5 minutes between killing and trying to restart.

What I have found is that if I advance the throttle to 30-50% and then try to start, it will fire up eventually (maybe takes two seconds of cranking).

Not sure what the problem is, maybe this is normal?

 

[mikidymac]

No, it isn't normal and fuel/carb related.

 

[Riverguy42]

No, it isn't normal and fuel/carb related.

Hmmm...tough to imagine a fuel related issue that only causes problems when the engine is warm, and disappears completely when the engine is cold.

I do know that ethanol mixed into fuel can increase the possibility of vapor-lock, but I'm only using no-ethanol marine gas. Still, vapor-lock is the first thing I suspected, but it did not clear when I tried the normal tricks.

Rotax Hard Start - Vapor Lock?

I've seen other Rotax techs (aircraft versions) talking about fuel pumps, that these get a little weak when the engine is hot, especially as they get older.

Maybe AnteSweeden and I should start there?

 

[mikidymac]

This is a sealed fuel system so vapor lock isn't possible. There is no place the liquid fuel can turn to vapor and these engines don't get hot enough either.