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98 SN weird idle issue

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cragginshred View Drop Down
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    Posted: September-10-2018 at 5:46pm
We just replaced the distributor cap and that fixed the issue of getting out of the hole but after numerous adjustments the idle cannot stay at a consistent rate, it sounds good then idles down then comes back to normal then down again. Fuel filter was changed with good pressure under test, premium fuel in it with additive for injector cleaner.
Ideas?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 6:40pm
Is this a GT-40 motor or a carbureted boat?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 6:55pm
Originally posted by cragginshred cragginshred wrote:

after numerous adjustments

What other adjustments?


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cragginshred View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cragginshred Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 7:41pm
GT 40 Fuel injected
He was adjusting the bolt below the distributor cap.
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cragginshred View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cragginshred Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 7:42pm
To adjust the idle
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 10:25pm
A pic of the 'bolt' could help, but I'm a bit confused..... was he adjusting the idle screw @ the throttle body or was this bolt actually "under" the cap, as in inside the distributor? .... Because I can't imagine what you'd adjust under the cap to change the idle
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cragginshred View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cragginshred Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 10:44pm
@GT40KS it was just Below the cap not under it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 11:14pm
Idle issues with the GT40 are numerous so at this point you may have to just go through the checklist. Was the distributor moved at all (timing) when the cap was replaced? What about vacuum hoses, etc.? Did the IAC get unplugged? MAP sensor? All the plug wires seated well?

If all those check out, rolling idle issues with the GT40 could include a failing IAC, failing PIP sensor (inside the distributor), failing throttle position sensor, plugged or pinched vac hose to the map sensor or bad map sensor. I believe there are a couple of other likely suspects, just can't think of them right now
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cragginshred View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cragginshred Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2018 at 11:38pm
He was adjusting the timing not the idle

The boat pulls great out of the hole now......but to sell it the club will want the idle corrected.
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Gary S View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: September-11-2018 at 2:35am
Was the SPOUT connector disconnected when you/he was setting the timing ? You were using a timing light right?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-11-2018 at 7:56am
I guess a little background would help about now

What was the "getting out of the hole" issue? You don't seem to have any recent posts about this.

Was the idle smooth before the cap was replaced?

Was the fuel filter changed before or after the idle issues?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cragginshred Quote  Post ReplyReply Direct Link To This Post Posted: September-11-2018 at 12:07pm
He did NOT use a 'timing light' -good call. I will bring that up
He called the issue 'Hunting' he thought the engine would idle down from a 'normal' idle because it was 'hunting' for the correct timing.

**We had it on the water to make sure it had the correct 'giddy up' out of the hole which it did.........previously it did not and was missing. Because the fuel pressure checked out and the filter and just been changed he went to the Cap- which fixed most of the issues.

Will the timing light be key to 'fine tuning'?

Taking it to a real Marina shop this week. Hopeful they can get it sussed out.

Thanks fellas!
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