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#1 |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Spark Plugs What is wrong?
Ok...really does not miss...just runs ragged. These plugs are in order as
I took them out. From left top..1 3 5 7 and top right 2 4 6 8. Three of the plugs look like have never been run. Why are the center plugs that clean? I have tried two diff carbs...two hei's and two sets of wires that I know run well. Also...adjusted valve lash and it does not have a flat cam. The 350has a small cam...and 15 inches of vacuum. Pcv valve is good and has a baffle. Any ideas? I guess next is to pull intake manifold...? |
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#2 |
Registered User
Join Date: Nov 2014
Location: Bigfork, Montana
Posts: 1,137
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Re: Spark Plugs What is wrong?
How long were the plugs in the engine?
You are running mis-matched plugs (AC Delco vs Autolite) The four that are black are beside each other in the firing order (may or may not be an issue) 1,8 & 7,2 When does the engine run ragged? at idle, just off idle, etc. What carbs are you trying? Did you just put the cam in it & what cam is it? Did the engine ever run good? There's no need to pull the intake unless you know you have a vacuum/coolant/oil leak. Back up & start with the basics. Make sure you are not trying to tune a dead engine. do a compression test do a COMPLETE tune up. install new plugs ( all of the same mfg) new cap, wires & rotor confirm correct firing order go from there (it may be a fuel issue) |
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#3 |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
Okay...just bought the truck...running this way...compression test already done
and is good...I have had all ac plugs and made no difference...both carbs run perfect on my other truck...1406 stock eddy and stock600 holley. The cam already in engine...214 at .050 and 456 lift. One is a new msd street fire and the other hei is good I know runs perfect..been carrying as a spare...fires right up and idles well..its mid range and low on power almost like a wire is off...but not quite. Really does not smoke. Throttle response is good...fuel pump has 5 pounds of pressure. So you tell me? ![]() |
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#4 | |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Spark Plugs What is wrong?
Quote:
That vacuum is quite low like a tired motor. Did vacuum gauge needle bounce or move while truck was running? Do a leak down test to rule out rings seats, etc on those cycls. The autolite tells me that cylinder has had issues for a while and its not carb related. Anything else is purely speculation and the lack of wanting to do any diagnosing. https://mobiloil.com/en/article/car-...-leakdown-test
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC Last edited by demian5; 08-04-2017 at 12:32 PM. |
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#5 | |
Registered User
Join Date: Nov 2014
Location: Bigfork, Montana
Posts: 1,137
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Re: Spark Plugs What is wrong?
Quote:
If it has run like this since you bought it then you are chasing someone else's rabbit. There is a possibility that the cam was installed out of time. What heads are on it? If the heads have dual springs I have seen one spring break & the engine runs fine but doesn't run well up top. (the remaining spring keeps the valve operating & quiet, but "floats" at higher RPMs) I'm hoping it's a simple timing issue, sure you are too! |
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#6 |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
Well today I noticed the water down just a little in the radiator...so added some...let it warm and open the thermostat...guess what big bubbles
in the flowing water....never stopped doing the bubbles....it has turn down tailpipes so I couldn't see the exhaust. |
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#7 | |
Registered User
![]() Join Date: Dec 2001
Location: Pace, FL
Posts: 2,155
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Re: Spark Plugs What is wrong?
Quote:
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#8 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Spark Plugs What is wrong?
Does your intake manifold by chance distribute fuel to the inner ones from one side and the outer ones from the other? Then you could have a problem on one side of your carb. But you'd have to look at the layout of the manifold to know for sure...
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#9 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Spark Plugs What is wrong?
Timing!!
What's initial timing? |
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#10 |
Registered User
Join Date: Oct 2012
Location: Green Valley Arizona
Posts: 1,351
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Re: Spark Plugs What is wrong?
What's the gap on the plugs?...should be 45
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1970 C10 Short Stepper with 71/72 front clip. |
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#11 |
Registered User
Join Date: Jun 2014
Location: lakefield,mn
Posts: 566
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Re: Spark Plugs What is wrong?
Do a leak down test sounds more like a mechanical issue. Also check and make sure that the power feed for the distributer is a full voltage and not the factory resistance wire.
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68 c10 swb stepper 68 c10 swb stepper 67 c10 lwb 06 gmc duramax |
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#12 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,193
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Re: Spark Plugs What is wrong?
Cyl 3,4 and 6 all look like water contamination within the combustion chamber...
Compression test and leak down test...most likely blown head gasket between 4 and 6... Could also be a lean out due to manifold crack...is this a two barrel or four barrel carb? Open plenum manifold or closed ? |
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#13 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: Spark Plugs What is wrong?
I would get a correct set of matched plugs gapped correctly and run it again before you get too crazy trying to diagnose whats wrong , the threads don't even look the same length let alone the heat range can't be the same .
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#14 | |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
Quote:
bought truck from....carbs are not the problem both that I have tried run perfect on my other truck. |
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#15 |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
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#16 |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
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#17 |
Senior Member
![]() Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,280
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Re: Spark Plugs What is wrong?
Is it a trick of lighting or camera, that Plug #2 looks 1/4'' shorter than Plug #1?
On closer look, you have 5 ACs and 3 Autolights. Running ragged, I wonder why?
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Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 08-04-2017 at 10:00 PM. |
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#18 | |
Registered User
Join Date: Jul 2010
Location: texas
Posts: 180
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Re: Spark Plugs What is wrong?
Quote:
Just bought a few autolites to try...made no difference. |
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#19 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Spark Plugs What is wrong?
Bump your initial timing up 6 degrees.
Your timing marks might be wacky. |
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#20 |
Registered User
Join Date: Dec 2009
Location: bisbee, arizona
Posts: 1,529
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Re: Spark Plugs What is wrong?
its easy to mix up 5 and 7 when hookin back up the wires.
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#21 |
Senior Member
![]() Join Date: Jun 2011
Location: burlington,iowa
Posts: 439
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Re: Spark Plugs What is wrong?
I think they are the wrong plugs, you might need long reach plugs, I ran across same issue, took me 2 years to figure it out. use a thin wire with hook on it and put in hole for plug and see if it needs a longer plug.
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Tom in Iowa 68 L88 C10 68 4x4 C10 soon |
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#22 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,193
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Re: Spark Plugs What is wrong?
Do the spark plugs screw into the heads at 90 degrees to the head or are they angled off center ?
Taper seat or (peanut) plugs are meant for heads that have angled spark plug threads....if the spark plugs thread in at 90 degrees to the crankshaft, these plugs are the wrong type...they may be the same as what was in there, but that doesnt mean they are correct... Post a pic of the side of the head showing the plug without the boot ....thanks ![]() ![]() ![]() |
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#23 | |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,431
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Re: Spark Plugs What is wrong?
Quote:
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#24 |
Registered User
![]() Join Date: Oct 2011
Location: Victoria, B.C
Posts: 3,794
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Re: Spark Plugs What is wrong?
...plugs look like a mix of brands and not the original sizes.....
Sounds like your basic parts group otherwise is in good shape so far....but you have some troubleshooting work to do. I think the 15 inches of vacuum is probably ok, depending on what rpm you were at. More important was the 'needle behaviour'...ie: steady? bouncing? intermittent drops? or? ...do the timing first....as Geezer said, bump it up. Then I would look like mad for a vacuum leak somewhere....brake booster?...intake manifold?....carb insulator gasket?....open port or line?....broken vacuum hose? ...more pics? All good Coley
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....for some men, there is experience, skill and effort....for the others...there is visa and UPS LOL 1966 Chevy 1/2 ton (Florida- Red/white) 1972 Chevy 1/2 ton (California- Blue/white) 2005 Chevy Silverado HD2500/Duramax 2000 Dodge Ram 1500 |
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#25 |
Registered User
Join Date: May 2008
Location: Mesa, AZ
Posts: 281
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Re: Spark Plugs What is wrong?
While everyone has already mentioned the differences in plug brands and sizes, there is also a chance they are of different heat ranges too.
I've used hotter running plugs to compensate for poor oil control in the past.
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I own 3 classic vehicles. 1971 LWB C10 Deluxe. 1974 VW Super Beetle. 1971 VW Fastback. The C10 and the Super Beetle run, the Fastback is just not there yet! Please visit my Super Beetle and Fastback profile on TheSamba. |
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