96 Sport GT40 Fast at Idle when docking

[Canuck-Surfer]

Hey guys,
Had my maiden voyage on my 96 Sport restoration with new rebuilt GT40 and brand new 40A transmission. Im used to driving a 2008 211 with EX343 engine and have done so a good bit this summer. During my first ride in the Sport today, I immediately noticed she is VERY fast in gear at idle. We have a tight marina and the speed concerned me. RPMs are good...about 700. She’s just fast. She has a 4 blade prop (dont know exact specifics). Only other thing I noticed is that I do have to move throttle several inches past neutral in order to get in gear (though going into gear is smooth).

Is this normal? Do I just need to relearn how to drive? While dockibg this afternoon, a guy in a boat a few slips down even commented that “you may want to slow it down a bit next time” after watching me dock....

[Chris Parsons]

Do you have perfect pass?

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[Canuck-Surfer]

It’s in the box in my garage. But not installed yet. I wanna make sure I have the basics down before I go changing the set up

[Chris Parsons]

Gotcha. Was thinking it could be a pp adjustment issue

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[Jonny Quest]

700 RPM is fairly normal idle speed. Something like 600 RPM is typically too low and the damper plate or planetaries may chatter/clatter. Look at the prop. Standard OEM for that year was an OJ Legend 14 X 16 I believe. Most would recommend Acme 422 as the prop of choice for a Ski Nautique with a GT-40. Is the tach reading correctly? Do you believe the 700 RPM number?

JQ

[Chris Parsons]

I agree with 700 being fine. Id even take 750 if needed.

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[Canuck-Surfer]

I just checked...she currently has an Acme 422 (4 blade) on her. this weekend I will test RPM with a spare shop tach and confirm rpm.

[Jonny Quest]

Acme 422 Is the Gold Standard for a Sport Nautique with a GT-40. Good to go there...

Unlike an I/O with a steerable prop, an inboard with shaft, prop and rudder requires a sufficient amount of water flowing past the rudder for proper slow speed steerage. Hopefully you won’t take any grief for running at idle speed. If you were to drop 1/2” in prop pitch (go from Acme 422 to Acme 654) you would drop idle speed by 3-4%. The bow wave at idle speed really shouldn’t bother anyone.

JQ

[Canuck-Surfer]

Acme 422 Is the Gold Standard for a Sport Nautique with a GT-40. Good to go there...

Unlike an I/O with a steerable prop, an inboard with shaft, prop and rudder requires a sufficient amount of water flowing past the rudder for proper slow speed steerage. Hopefully you won’t take any grief for running at idle speed. If you were to drop 1/2” in prop pitch (go from Acme 422 to Acme 654) you would drop idle speed by 3-4%. The bow wave at idle speed really shouldn’t bother anyone.

JQ

So...some follow up. The RPMs are low. When she goes into gear the RPMs remain around 600.

I’m not concerned with my ripples or wake at high-speed. I’m more concerned about making 90� turns in a very tight docking marina at a significant clip.

Could it just be the 422 prop and lighter weight of the Sport moving me faster? Our 211 idols at significantly slower speed when entering the marina.


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[Canuck-Surfer]

On another note, When I am going faster on the water either cruising around or pulling a boarder and I pull back into neutral, the RPMs drop to 1000 and hang out there for about 5 to 10 seconds after we stop before dropping back down to 600. I know the ECU controls idle. Is that normal for a GT 40? It seems kind of odd pulling into neutral and hearing the engine still turning at 1000 RPM and then all the sudden it finally drops down.


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[DVskier]

Nautique calls the high idle “idle flare”. They corrected it in 1999, gthis was vdone in the ECU. I had a 97 SN GT 40 and it drove me nuts.

[SilentSeven]

Former GT-40 owner here. Nothing you describe sounds wrong. My 96 Ski idled about 700 RPM. Idle speed in gear was too fast around the dock; had to pull it in and out of gear to manage speed. My 2004 206 with an Excaliber 330 is also too fast..I think they all are. My boat had the idle flair described above...it was a bit annoying but never a problem.

My boat benefited from some general maintenance that improved the running. New cap/ rotor / wires / plugs all helped..wires in particular. I replaced most of the vac hoses under the manifold including the PVC valve and line to assure no vacuum leaks. I cleaned out the backfire shield and throttle plate and body with a rag and some carb clearner. Checked all my electrical plugs for corrosion, zapped the each connector with contact enhancer. Re-did the ground straps with some sandpaper. Hey...it's a 20 something year old engine and it all contributed. Finally, I had some odd run problems and they were fixed by installing a rebuilt distributor (you can use a re-manufacted unit from NAPA...likely $100...fixed a flaky hall sensor).

[Canuck-Surfer]

Former GT-40 owner here. Nothing you describe sounds wrong. My 96 Ski idled about 700 RPM. Idle speed in gear was too fast around the dock; had to pull it in and out of gear to manage speed. My 2004 206 with an Excaliber 330 is also too fast..I think they all are. My boat had the idle flair described above...it was a bit annoying but never a problem.

My boat benefited from some general maintenance that improved the running. New cap/ rotor / wires / plugs all helped..wires in particular. I replaced most of the vac hoses under the manifold including the PVC valve and line to assure no vacuum leaks. I cleaned out the backfire shield and throttle plate and body with a rag and some carb clearner. Checked all my electrical plugs for corrosion, zapped the each connector with contact enhancer. Re-did the ground straps with some sandpaper. Hey...it's a 20 something year old engine and it all contributed. Finally, I had some odd run problems and they were fixed by installing a rebuilt distributor (you can use a re-manufacted unit from NAPA...likely $100...fixed a flaky hall sensor).

Good to know. The engine is just been rebuilt and everything is new on the outside as well, distributor, cap, rotor, wires, alternator, distributor, the whole shebang!

I’ve got a spare ECM with the Motes chip with the new engine tune from 2002. I’ll swap that out sometime this week and see if that fixes the idle flare. Sounds like it will!


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[SilentSeven]

Yeah...I'd be interested if that works. Post back!

[Canuck-Surfer]

Yeah...I'd be interested if that works. Post back!

Okay update here. I have also noticed a surging idle when cold. Lots documented over at CCF about surging or loping idle on GT40. Seems like I got off easy...I took the IAC off and it was crazy gummed up. Put some throttle body cleaner in it and cleaned with a q-tip. Replaced and surging stopped. However, the idle went up to 1200. Restarting didn't change high idle. I unplugged the TPS cable (which killed engine) and re-plugged it back up and restarted engine and idle returned to about 650.

I also was able to switch out the computer with my homemade ECU using the Hope for GT40 ECM thread. I had tried to use it when we put everything back together after the engine rebuild earlier in the summer but the fuel pump did not work with the new one. So yesterday I went out and bought a new can of electrical contact cleaner and wiped in on the leads that the Moates chip slides onto. A lot of wax film lifted off. I reinstalled the Moates chip and put the ECM in the boat and boom, works like a charm!

The Moates chip had the last tune for the GT40 loaded from 2002 (version 300M). I can confirm that with the 300M ECU, the idle flair no longer happens!!