New sbc 400 blueprint engine keeps fouling plugs with gas

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
3,052
Reaction score
3,032
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
I’d contact Blueprint and see what cfm they recommend, I think 850 is overkill but it wouldn’t be the first time I was wrong. Good luck.
That's the Carb that blueprint engines provides, tunes, and dyno's the engine with... It might be a bit too big, but it is the provided carb and I doubt that the size is what is making it foul plugs. It might make it a little harder to tune and drive on the street though.
 

Green79Scottsdale

Full Access Member
Joined
Aug 8, 2010
Posts
2,457
Reaction score
5,151
Location
G.R. - MI
First Name
Bob
Truck Year
1979
Truck Model
K20
Engine Size
400
That carb was also most likely "dialed in" under full throttle pulls in a controlled environment, for dyno sheet needs. Now you have it in an ever changing environment, turning a consistent and lower rpm with not a full load. Different conditions require different tune ups. A change in air condition, hotter or colder weather, or elevation, can change the air fuel mixture ratio. As said before, best to get an AFR gauge on it. Also, make sure your ignition is up to the task, and the plugs are correct for the application. I don't remember what was said already.
 

HEG77k10

Member
Joined
Jul 14, 2021
Posts
37
Reaction score
14
Location
Adna, Washington
First Name
Hayden
Truck Year
1977
Truck Model
Chevy k10
Engine Size
400 stroker
When I talked to a technician from blueprint he said they don’t do any tuning on the carb, idk if they use a different carb for the dyno pulls or what. I’m thinking abt getting a 750 carb. I want to daily drive this so im not super concerned with getting every last bit of hp out of it. I think a 750 will also have some better low end throttle response. Any good experiences with a Holley sniper or other “self tuning” efi systems?? Maybe that would solve the whole issue…
 

Craig Nedrow

NADAR UNDER THE RADAR
Supporting Member
Joined
Sep 1, 2018
Posts
402
Reaction score
540
Location
Washington State
First Name
Craig
Truck Year
1973 (have two), 1985
Truck Model
K10, K20, C20
Engine Size
350, 454, 6.2 Detroit
I run a 454 small cam, low compression, 750 carb. Primary jets 73, secondary 83. The 73 run down the road A/f ratio about 13.8, the 70 primary ran 14.6. Secondary started at 80, now 83, about right at 12.8-13 WOT. I have an A/F gauge in the truck. This 400 sb at 6500 rpm, 90% volumetric efficiency would require a 677 cfm carb.
 

Attachments

  • IMG_3576~photo.JPG
    IMG_3576~photo.JPG
    169.5 KB · Views: 41
Last edited:

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
3,052
Reaction score
3,032
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
Get an AFR gauge on it. Buy a jet kit. Try to dial in what you have. If you end up not being able to get it driving right, you can always go down to a 750 and start tuning again from there, the AFR gauge and jet kit will work for both.
 

HEG77k10

Member
Joined
Jul 14, 2021
Posts
37
Reaction score
14
Location
Adna, Washington
First Name
Hayden
Truck Year
1977
Truck Model
Chevy k10
Engine Size
400 stroker
What would y’all recommend, a double pumper 750, or an avenger 750. Both Holley obviously. The avenger is quite a bit cheaper so just seeing what you guys thought.
 

HEG77k10

Member
Joined
Jul 14, 2021
Posts
37
Reaction score
14
Location
Adna, Washington
First Name
Hayden
Truck Year
1977
Truck Model
Chevy k10
Engine Size
400 stroker
biggest difference vacuum vs manual secondary’s?
 

Craig Nedrow

NADAR UNDER THE RADAR
Supporting Member
Joined
Sep 1, 2018
Posts
402
Reaction score
540
Location
Washington State
First Name
Craig
Truck Year
1973 (have two), 1985
Truck Model
K10, K20, C20
Engine Size
350, 454, 6.2 Detroit
Vacuum Secondary like a 4160, make sure it has the secondary block (adjustable) and not the plate non-adjustable type. Mine had the plat, so I bought a secondary metering block and I like the vacuum secondary's, better fuel mileage generally speaking. Also highly adjustable. I watch my A/R fuel gauge, and I will be running mid 13's a/f punch it, and hold, and the gauge reads 12.7-13 even. I just changed to this, big improvement. Today, we have aides (A/F monitors), that can tell you what is going on. Now that I have one, it's not a stab in the dark. If you had a gauge, it would probably show a very rich 11.8-12.5 range. If so, go down four steps on the primary's. Pull off the secondary metering block, and go down three from whatever is in there. Fire it up, and test it. Sorry so long, but go buy an A/F ratio gauge and put it where you can see it. Mine is incorporated into the stock dash, almost looks stock.
 

Attachments

  • IMG_3576~photo.JPG
    IMG_3576~photo.JPG
    169.5 KB · Views: 34
Last edited:

squareton

Member
Joined
Dec 9, 2021
Posts
48
Reaction score
30
Location
topeka ks
First Name
chris
Truck Year
1983
Truck Model
k2500 suburban
Engine Size
350
Have you checked to make sure your ignition system is getting its proper 12v? Maybe it only has enough juice to keep it running good enough but keeps fouling the plugs?
 

HEG77k10

Member
Joined
Jul 14, 2021
Posts
37
Reaction score
14
Location
Adna, Washington
First Name
Hayden
Truck Year
1977
Truck Model
Chevy k10
Engine Size
400 stroker
Yeah has full 12 volts at all the plugs. Changed plug wires too bc the last ones I had got all torn up by the looms. Actually cut down to insulation. Last time I get that Cheap hard plastic clip in junk
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
1,751
Reaction score
2,289
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
Get the wide band first. If the 850 is what blueprint provided with that engine, that’s what I would run. Don’t go second guessing the guys that built and dynoed the engine. For that matter, I’d call blueprint and ask what the suggest.

Disconnect the secondary linkage, drive around on the primary side. Get it dialed in, then worry about the secondary side.

Spray some carb cleaner on the air bleeds, maybe there is some gunk screwing up the calibration.
 

potent rodent

Full Access Member
Joined
Mar 22, 2020
Posts
148
Reaction score
76
Location
indiana
First Name
butch
Truck Year
86 and 78
Truck Model
1500
Engine Size
350 and 305
are u running vaccume adv , u need some serious tuning on that carb , make sure to check your float levels , check your transfer slots on your secondary nothing else would make your plugs sooty but the carb and timing
 

Latest posts

Forum statistics

Threads
36,142
Posts
763,446
Members
25,273
Latest member
juliannv07
Top