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05-18-2023, 07:48 AM
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#1 |
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Registered User
Join Date: Dec 2004
Location: Highland, IN
Posts: 2,328
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Fouling plugs
I am fouling plugs on cylinder 1 & 2. I am running NGK R5671A-7 plugs. Should I change these?
350 Gen 1 bored 40 0ver, 400 crank, 750 double pumper. New build mostly idle time, around the block a couple times, but not driving daily yet
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Chris _______________________________ 1979 Chevy Stepside SPORT 2018 Chevy Silverado, 39 years apart  My build 2008-2016. http://m.imgur.com/a/bURrE |
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05-18-2023, 10:43 AM
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#2 |
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Senior Member
 Join Date: Mar 2003
Location: Colfax-California
Posts: 8,720
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Re: Fouling plugs
The 750 double pumper may be putting too much fuel into the engine
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05-18-2023, 12:21 PM
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#3 |
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Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,663
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Re: Fouling plugs
Its not even started to break in. Verify timing and run it. Check the plugs again after a couple hundred miles.
Double check for a vacuum leak on the back cylinders. A brake booster can leak while still providing boost. |
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05-19-2023, 09:47 AM
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#4 |
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Registered User
Join Date: Feb 2012
Location: So. Cali.
Posts: 2,673
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Fouling Spark Plugs
It depends on how they're fouling ~ oil or fuel ? .
What's the gap ? . Points or breakerless ignition .
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-Nate Geezer '49 3100 235 W/ Muncie SM420 SOLD '69 C/10 shortbed sidemount survivor 250 L6 W/ 350TH 
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05-22-2023, 12:32 AM
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#5 | |
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Registered User
Join Date: Oct 2015
Location: Ottawa, Ontario, Canada
Posts: 780
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Re: Fouling plugs
VWNate1
Quote:
Should be HEI 43-45 gap. As said by VWNate1. And I would use a vacuum Gauge to adjust the carb check the timing. Did you have the head seat seals changed make sure the plugs are not oiling fouled. Go back to basic re-ID: the plugs again to find out the problem.
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 1977 REG cab Long Bed with a 1984 Front Clip, 82 305 .60 over 9.0.1 flat top pistons, 4bbl, TH350, w/84 SS-intake & cam , w/ 1977 big block rad, 1975 gear box, 1984 master w/ metric fittings top & SAE fitting @ portion block, 1975 3.42 gear open diff. Duel 77-87 Factory air cleaner, duel inlet from rad support . Down sized 9' to new 8' Steel flat bedWas a 77 454 w/308 gear. Taken out 550 lbs. up front with motor clip change. |
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05-22-2023, 07:30 AM
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#6 |
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Registered User
Join Date: Dec 2004
Location: Highland, IN
Posts: 2,328
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Re: Fouling plugs
It is carbon fouled
HEI Distributer I think the gaps are about 0.55
__________________
Chris _______________________________ 1979 Chevy Stepside SPORT 2018 Chevy Silverado, 39 years apart My build 2008-2016. http://m.imgur.com/a/bURrE |
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05-22-2023, 08:08 PM
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#7 |
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Registered User
Join Date: Feb 2012
Location: So. Cali.
Posts: 2,673
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Fuel Fouling Plugs
Okay ;
Now you're getting some where . Time to check the timing and then look at the fuel system as carbon usually means running too rich and there are myriad simple reasons for this .
__________________
-Nate Geezer '49 3100 235 W/ Muncie SM420 SOLD '69 C/10 shortbed sidemount survivor 250 L6 W/ 350TH
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05-23-2023, 07:21 AM
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#8 |
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Registered User
Join Date: Dec 2004
Location: Highland, IN
Posts: 2,328
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Re: Fouling plugs
I have heard my carb is too big
Double pumpers are used for manual race cars, not drivers
__________________
Chris _______________________________ 1979 Chevy Stepside SPORT 2018 Chevy Silverado, 39 years apart My build 2008-2016. http://m.imgur.com/a/bURrE |
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05-23-2023, 08:01 AM
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#9 |
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Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,778
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Re: Fouling plugs
New build, mostly idle time you said.
We’re assuming you did the required cam break in. Normally 2000 rpm for 20 minutes. A double pumpers not too big. If the floats are set too high or the power valve is not the right one you can get a rich carb. Lack of enough timing can cause fouling too. |
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05-24-2023, 07:24 AM
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#10 |
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Registered User
Join Date: Dec 2004
Location: Highland, IN
Posts: 2,328
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Re: Fouling plugs
I did the proper break in I have an 8.5 power valve & 73 main jet and a 77 secondary jet
__________________
Chris _______________________________ 1979 Chevy Stepside SPORT 2018 Chevy Silverado, 39 years apart My build 2008-2016. http://m.imgur.com/a/bURrE |
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05-24-2023, 08:11 AM
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#11 |
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Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,778
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Re: Fouling plugs
What’s your idle rpm?
What’s your initial timing? What’s the vacuum reading at idle? What do the plugs look like on 7 and 8? |
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05-24-2023, 01:24 PM
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#12 |
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Registered User
Join Date: Feb 2012
Location: So. Cali.
Posts: 2,673
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Fuel Fouling Spark Plugs
Plenty of double pumper carbys are factory stock .
Yours -may- be too big, keep following the basic questions here, in my long career most times it will turn out to be a simple thing once you find it .
__________________
-Nate Geezer '49 3100 235 W/ Muncie SM420 SOLD '69 C/10 shortbed sidemount survivor 250 L6 W/ 350TH
Last edited by VWNate1; 05-25-2023 at 10:20 AM. |
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05-24-2023, 07:42 PM
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#13 |
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Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,663
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Re: Fouling plugs
Hard to get a good plug read 'just idling'. Drive it 20 or so miles to a good place to eat, get lunch, come back and when it cools off, see what the plugs say. Plus it will be a good start on the break in process.
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05-25-2023, 07:21 AM
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#14 | |
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Registered User
Join Date: Dec 2004
Location: Highland, IN
Posts: 2,328
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Re: Fouling plugs
Quote:
thanks
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Chris _______________________________ 1979 Chevy Stepside SPORT 2018 Chevy Silverado, 39 years apart My build 2008-2016. http://m.imgur.com/a/bURrE |
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