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  #1  
Old 08-06-2009, 04:22 PM
wavesailr wavesailr is offline
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Default 1978 Scout II 392 V8 Engine Problems...

I've got a 1978 Scout II with a 392 V8 engine that's giving me problems only after it gets to operating temperature.

The engine backfires, misfires, stumbles badly, and has nearly no power after the engine gets to operating temperature. Before it's warmed up it runs perfectly and has lots of power.

I've replaced the mechanical fuel pump and that didn't help. I then bypassed the mechanical fuel pump and used an electric fuel pump. That didn't help either. The fuel pressure is about 3 PSI when the engine is running no matter if the engine is cold or hot at full throttle, or idle.

The timing is good at 3 degrees btoc using the #8.

The carb (Edelbrock Performer 600 CFM, electric choke) was replaced before I owned the Scout, but it looks fine.

The distributor and coil were replaced and didn't help.

All of the fuel lines are routed away from hot-spots.

Please help!!
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  #2  
Old 08-06-2009, 04:31 PM
Doc Stewart Doc Stewart is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Vacuum leak. Use your propane torch [don't light it!]. With the engine running, pass it over the carb opening: the engine will either speed up or lug down from the extra fuel intake. Use that as your indicator. Now pass the torch around the base of the carb and the various fittings on the carb including the shaft pivots. Watch for the engine response. When it responds, there's your leak.

Also check any of the vacuum fittings on the intake manifold especailly thee brake booster. Do the whole test in 5 minutes.
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  #3  
Old 08-06-2009, 04:41 PM
wavesailr wavesailr is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Thanks for the quick response. I"ll try it tonight.

The bogging and backfiring is only under load/acceleration. The engine idles perfectly both when it's cold and at operating temp...
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Old 08-06-2009, 05:31 PM
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Default Re: 1978 Scout II 392 V8 Engine Problems...

What Doc suggested has plenty of merit and should be followed. From your description, this could also be an air/fuel ratio problem. When cold, your engine craves more fuel than air, but this changes as the engine approaches operating temperature. Verify that your choke plate operates smoothly and that it opens fully as the engine warms up.
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Old 08-06-2009, 05:59 PM
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Russ McLean Russ McLean is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

>> The carb (Edelbrock Performer 600 CFM, electric choke)...

>> Verify that your choke plate operates smoothly and that it opens fully as the engine warms up.

Verify that the electric choke has 12 Volts and is properly grounded. Measure this on a warm, running engine.
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  #6  
Old 08-06-2009, 06:35 PM
wavesailr wavesailr is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Thanks,
Electric choke works fine. Choke plate opens smooth and is 100% open after running for a few minutes and stays open while hot and running.
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  #7  
Old 08-06-2009, 08:24 PM
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1975IH200 1975IH200 is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Be sure the electric choke is NOT powered from the ignition system.
The has caused several people here problems, caused by the PO Monster.
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Old 08-06-2009, 09:40 PM
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Default Re: 1978 Scout II 392 V8 Engine Problems...

i had a blown head gasket do the same thing. cept it was blown between 6 of the cyl's to each other
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  #9  
Old 08-09-2009, 04:48 PM
wavesailr wavesailr is offline
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Okay,
I just sorted it out.

There was a missing ballast resistor. 12v was going directly into the coil and causing the coil to get REALLY hot.

So, I bought a resistor and installed it. There's now about 6v going to the coil and distributor.

That fixed the problem perfectly. Now there's tonnes of power when the engine is cold AND hot!!

I tried the propane torch and it didn't change the rpm at all, even when I shot the propane directly into the carb... It sounded like a good idea though.


Thanks for all your help guys!!

Rob.
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Old 08-09-2009, 08:47 PM
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Default Re: 1978 Scout II 392 V8 Engine Problems...

Quote:
Originally Posted by wavesailr View Post
Okay,
I just sorted it out.

There was a missing ballast resistor. 12v was going directly into the coil and causing the coil to get REALLY hot.

So, I bought a resistor and installed it. There's now about 6v going to the coil and distributor.

That fixed the problem perfectly. Now there's tonnes of power when the engine is cold AND hot!!

I tried the propane torch and it didn't change the rpm at all, even when I shot the propane directly into the carb... It sounded like a good idea though.


Thanks for all your help guys!!

Rob.
if you're only getting 6v something is wrong.
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100 , 3.4 , brake , carb , coil , distributor , engine , fuel system , head gasket , idle , ignition , key , lock , number , pickup , power , scout , scout ii , throttle , timing

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