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  #1  
Old 05-15-2012, 10:31 AM
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AkioOhtori AkioOhtori is offline
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Default 392 V8 Dies under 1000RPM

First: I would like to apologize. Searching through the forums I have seen a number of these threads, but haven't really found my answer.

My setup:
1970 IH Scout 800A 4x4
IH 392 V8
Edelbrock 1406 carb (new)
Pertronix Ignitor II (new) w/ Ignitor coil
Also new: fuel system (pump, lines, filter, switcher, and tank), valve cover gaskets, thermostat, battery, spark plugs (Autolite 85s), etc...

I am trying to get my Scout road worthy. Sadly, when trying to adjust my idle screw on my carb I noticed that the car doesn't really like to run under 1000RPM warm, 1200 cold. Anything less and it begins to sputter and eventually die. When running the throttle seems responsive and the engine roars pretty well. Didn't seem to have any problems driving (though I've never taken it out of first...). It probably needs an oil change, but I can't imagine that being the problem.

Searching through the forums, I have found the following possiiblites:

Vacuum leak: Most of the vacuum hoses are new. People seem to recommend pulling off hoses but I can't really say which I should/ should not pull and where to test. Total newb. I did just replace the valve cover gaskets, and while I have been REALLY conservative with tightening those, I think they are tight enough (but not too tight). I used a rubber seal w/o any gasket epoxy or that sort of thing.

Running to rich/ lean: This is actually my primary guess for the moment. The exhaust smells "gassy" to me, even when the engine is at temp. My understanding is the Edelbrock carbs don't need adjustment out of the box though. Furthermore I have literally no idea how to adjust this. (Always willing to learn!) The manual that came with it isn't super helpful, but it is possible I don't know what I am looking for.

Not enough fuel: Brand new pump (Carter M6959). You can view the fuel flowing through the filter and it does seem not great. I don't really know what that is supposed to look like though. Is it possible the 1406 is just too thirsty for the pump?

I could post a video later if that would help?
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  #2  
Old 05-15-2012, 10:38 AM
john breeze john breeze is offline
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Default Re: 392 V8 Dies under 1000RPM

what is the timing set at. that might help
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  #3  
Old 05-15-2012, 10:49 AM
Doc Stewart Doc Stewart is offline
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Default Re: 392 V8 Dies under 1000RPM

Weak fuel pump would give problems at speed not at idle.

Really sounds like a vacuum leak. Valve cover gaskets would not be the problem. Get the engine warm and use Brake Clean or even WD40 to spray around the carb base and any vacuum connections and along vacuum hoses. Be slow and observe the engine's reaction.

Edelbrock carbs definitely CAN use tuning right out of the box. See their website for details. Not difficult.
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  #4  
Old 05-15-2012, 10:52 AM
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scoutboy74 scoutboy74 is offline
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Default Re: 392 V8 Dies under 1000RPM

Verify timing and correct routing of plug wires first. Timing adjustments with a timing light are done off #8 which is the rear most cylinder on the passenger bank (LHD). Timing will be difficult to adjust accurately at engine idle speeds above 800 revs. There's virtually no aftermarket carb in existence that doesn't require at least some minor tuning for operating elevation and optimum balance of performance and economy.
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Hooty - '74 SII 4x4 - 392/TF 727/D20/3.73 D44 FA + Spartan/Trac-lok RA/4" SUA/33" TSL's/33g-fuel
Mongo - '71 1210 Reg Cab 2wd - 345/TF 727/RA 17 4.10 Trac-lok D60 - "Mongo love candy!"
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  #5  
Old 05-15-2012, 11:27 AM
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AkioOhtori AkioOhtori is offline
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Default Re: 392 V8 Dies under 1000RPM

I have verified the plug routing and it is all OK. I had a mechanic friend out to veirfy the timing, but we ended up not as it was running well and had good throttle response (and was smoking quite a bit thanks to some leaky valve cover gaskets). I can see about checking it anyway. What are the challenges of checking timing over 800rpm?

The idea of spraying with carb cleaner is when you spray the vacuum leak the engine rpm changes, yes? I will certaily check that before getting all wild and crazy.

With playing with the carb I am concerened more than anything about screwing something up haha. If I don't find a vacuum leak I will man up and see what I can do.
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Old 05-15-2012, 11:37 AM
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scoutboy74 scoutboy74 is offline
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Default Re: 392 V8 Dies under 1000RPM

Base timing for a 392 should be no more than 7 degrees of advance (BTDC). This is to be verified on a warm engine with curb idle around 600 rpms. The reason for the low speed is to ensure that mechanical advance is not in play which will effect your reading. Your seat of the pants feel is a factor, but it is far from being the only determining one for verifying that things are as they should be. The key to successful diagnosis and repair is eliminating variables in a methodical fashion, starting from the easiest and working out from there. You make one minor adjustment, followed by testing to see what effect that has on the issue. Then you make another. One thing you want to avoid is the shotgun approach. By that I mean changing fifty things at once hoping one piece of mud will stick to the wall. Maybe you get lucky and maybe you don't. If you do get lucky, which one out of elevendybillion was the cure? You have no idea. Plus it can get rather spendy in a hurry.
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Hooty - '74 SII 4x4 - 392/TF 727/D20/3.73 D44 FA + Spartan/Trac-lok RA/4" SUA/33" TSL's/33g-fuel
Mongo - '71 1210 Reg Cab 2wd - 345/TF 727/RA 17 4.10 Trac-lok D60 - "Mongo love candy!"
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  #7  
Old 05-15-2012, 11:43 AM
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IH64Scout IH64Scout is offline
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Default Re: 392 V8 Dies under 1000RPM

Before you do anything get the timing set. I run it usually around 5 degrees. I've had luck around 10 too but I wouldn't take it that high until all the problems are fixed. If its still high after id look for a vacuum leak. Now by not touching the carb out of the box, you did at least adjust the idle screw right?
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4.10 D60's SOA on 4" springs
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  #8  
Old 05-15-2012, 11:48 AM
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fredsterra fredsterra is offline
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Default Re: 392 V8 Dies under 1000RPM

Where do you have your dist. advance ported to? I have a 1406 on my 345 / 392 non EGR intake. And I found it better to hose to manifold vac. vs. carb.
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1978 Terra 345 V8. Edelbrock 1406 carb, MSD,Pertronix, 392 4V Intake.

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  #9  
Old 05-15-2012, 12:24 PM
Jeff Jamison Jeff Jamison is offline
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Default Re: 392 V8 Dies under 1000RPM

There are 4 screws you need to adjust to start with on the carb,you have the fast idle adjustment for when its cold,the regular idle adjustment that is by where the throttle cable is hooked up,and the air mixture screws on the front base of the carb(I think these are you problems)These should be out about 1 1/2 turns to start with,start it up and see what you have,turn the idle adjust ment down some,keep going if it will let you.Now back to the front,turn one at a time until it smothes out,and rpm increases,keep going until it starts to slow down then turn back in to where it was the highest rpm,do the same for the other screw.Now you should be able to bring the idle down more.
To check for a vacumme lleak,take the air cleaner off,and hold a rag in the carb to block off all air,it should kill the engine,if it does not,you have a vacumme leak
Jeff
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  #10  
Old 05-15-2012, 01:12 PM
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IH64Scout IH64Scout is offline
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Default Re: 392 V8 Dies under 1000RPM

That'd be a pretty huge vacuum leak if it stays running with the carb blocked
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1980 Terra Scout II
6.9L Diesel/6.32:1 t19/NP205
4.10 D60's SOA on 4" springs
39x13.50x16 Iroks

-'91 Ferd F350 CCLB 2wd dually 7.3 IDI banks sidewinder equipped, ZF5
-'71 Travelette- DT466 power....
-'73 25' Starcraft motorhome
--Piles-o-parts--
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