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06-13-2020, 11:59 AM | #1 |
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Join Date: Feb 2019
Posts: 16
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239 / 2gc idle issues
This is a long story about why this even happened but here's my dilema: I have a 239 mated to a mercomatic medium case trans w/ 2gc carburetor, mallory dual point. I cannot seem to get it to idle low enough and strong enough to handle transmission engagement. Could the torque converter stall speed / rotating mass be an issue? I figure with the difference of 16 cubic inches vs the merc's 255, It should be able to handle this.
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06-13-2020, 01:05 PM | #2 |
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Join Date: May 2010
Location: East Hartford, Ct
Posts: 5,898
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Re: 239 / 2gc idle issues
Believe the idle speed spec. for the automatic is 485 RPM.
Mine is happy with 500-550 RPM. What is your idle RPM? Engine displacement has nothing to do with it.
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DON'T RECALL DOING SOMETHING FOR MYSELF BASED ON SOMEONE ELSE'S LIKES OR DISLIKES Last edited by 51 MERC-CT; 06-13-2020 at 01:14 PM. |
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06-13-2020, 01:28 PM | #3 |
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Re: 239 / 2gc idle issues
My way of thinking is that there is not enough mass / inertia to maintain idle speed properly. I cannot get my idle speed much below 700 or so. Are you running a mercomatic? what is your idle speed in gear? thank you for responding...
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06-13-2020, 01:36 PM | #4 |
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Join Date: Apr 2019
Location: Kansas
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Re: 239 / 2gc idle issues
1. Are you running a stock cam? A performance cam will exaggerate this problem.
2. Is the timing set at approx 4 degrees at idle speed? 3. Does the engine try to die when put in gear or is it just too harsh a shift into gear? 4. Do the idle mixture screws have any effect when turned out or in? Terry
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"It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302 |
06-13-2020, 01:43 PM | #5 | |
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Re: 239 / 2gc idle issues
Quote:
Don't over think the mass/inertia thing, get the RPM down to the appox. 500 range then see what happens.
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DON'T RECALL DOING SOMETHING FOR MYSELF BASED ON SOMEONE ELSE'S LIKES OR DISLIKES |
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06-13-2020, 01:44 PM | #6 |
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Re: 239 / 2gc idle issues
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06-13-2020, 01:51 PM | #7 |
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Re: 239 / 2gc idle issues
Ok. Something's not right in the tuning if a lower idle can't be achieved. Maybe a vacuum leak (although rich running doesn't point to that) or maybe an idle circuit problem in the Rochester. That carb should work fine. I'm running a small base 2GC on my Merc and it'll idle at 400 if I want.
How does your engine sound when trying to run lower than 700 rpm? May get a clue from that... Terry
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"It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302 |
06-13-2020, 02:43 PM | #8 | |
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Join Date: May 2010
Location: East Hartford, Ct
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Re: 239 / 2gc idle issues
Quote:
If you are using a Merc. manifold to mount it that had a divorced choke. There is a vacuum port/hole that has to be plugged where the old choke mounted.
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DON'T RECALL DOING SOMETHING FOR MYSELF BASED ON SOMEONE ELSE'S LIKES OR DISLIKES Last edited by 51 MERC-CT; 06-13-2020 at 03:32 PM. |
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06-13-2020, 05:12 PM | #9 |
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Join Date: Jul 2016
Location: Lake worth Florida
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Re: 239 / 2gc idle issues
How much vacuum is it reading , is it steady ?
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06-13-2020, 06:05 PM | #10 |
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Join Date: May 2010
Location: Chester Vt
Posts: 8,860
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Re: 239 / 2gc idle issues
The stock distributor won't work with the 2GC distributor.
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06-13-2020, 09:18 PM | #11 |
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Re: 239 / 2gc idle issues
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06-13-2020, 09:43 PM | #12 |
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Join Date: May 2010
Location: Chester Vt
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Re: 239 / 2gc idle issues
Yea, I read that after I posted. Stupid factor vrty hi today .
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06-14-2020, 10:06 AM | #13 |
Junior Member
Join Date: Feb 2019
Posts: 16
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Re: 239 / 2gc idle issues
Ok, I have it worked out. I didn't mention the engine is a fresh rebuild. Ran it about 4 hrs and progressively lowered the idle, I believe the engine was built very tight and would not cooperate until it was bedded in. It will now idle correctly. Thank you all for your help.
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