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Discussion Starter · #1 ·
Dynoed my car a little while ago, finally getting around to jetting my carb. Pulled the blocks off and can only see the primary jets, the secondaries have a "plate" over them, do I need a "security bit" type screwdriver to remove that plate??

Thanks

Eazy :welcome:
 

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Discussion Starter · #2 ·
I'd rather not hammer on it, I was going to take a picture of the screw, but I got one out with a small screwdriver, I'll take it to the hardware store and see if I can find a screwdriver tomorrow. I'm sure I've seen this type of head before...
 

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Since it's a 4160 the "plate" is your secondary jets - you have to replace or drill that plate to alter secondary size.

I recall having good luck getting out the screws by finding just the right size flat blade and not tearing stuff up. Hope this helps.
 

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CLUTCH

Used commonly in Chevrolet and GMC trucks, this screwhead is also sometimes seen on trailers. Comes in 2 common sizes: 5/32 and 3/16 inch , though occasionally you see 1/4 and 5/16 inch as well.
-SNAP-OFF CLUTCH HEAD SCREWDRIVERS-

This type was very popular with :pain: THE BOWTIE BOYS :pain: in the fifties. HOLLEY also used them extensively on period carburetors.
 

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thinking about how a vacuum secondary enriches the mixture, do you need to change it? set the primarys accoridingly for effiecency(usually not far from the intial jets). i have used a 600cfm VS holley on 289's to 440's. the one i got has a non removeable plate. although everything can be worked, or drilled.

i would work on your timming. change the vacuum and advance curve a little...maybe.
 

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Discussion Starter · #7 ·
spinn said:
thinking about how a vacuum secondary enriches the mixture, do you need to change it? set the primarys accoridingly for effiecency(usually not far from the intial jets). i have used a 600cfm VS holley on 289's to 440's. the one i got has a non removeable plate. although everything can be worked, or drilled.

i would work on your timming. change the vacuum advance curve a little...maybe.
I dynoed it in December and was running very lean (to the point of detonation before the engine revved out), even at idle, why I'm jetting it.(If I remember correctly, I was somewhere near 16:1 at idle) I had a cheapo distributor on it, and am now looking at a MSD 8360, and an RPM air gap manifold..
 

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Technical Support Barry Grant
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biggeazy-e said:
I dynoed it in December and was running very lean (to the point of detonation before the engine revved out), even at idle, why I'm jetting it.(If I remember correctly, I was somewhere near 16:1 at idle) I had a cheapo distributor on it, and am now looking at a MSD 8360, and an RPM air gap manifold..

What intake do you currently have? If its a smaller dual plane intake going to an Air Gap style can make your lean condition worse.
 

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what numbers are you putting down ?

a cheapo vacuum advance HEI distributor can do alot. never heard of someone gaining horse power from a disrtributor change...when it was setup up for the application correctly. a correct advance curve is the key.

if this is the elusive demon problem from hell, put a gauge on everything and tape them to the windshield. then go driving. you want to see fuel psi, engine vacuum / ported vaccum, oil psi, exhaust temp, the damn coil voltage, etc....find out what is going on.

unfortunately a vacuum curve will not do anything for your dyno #'s. but if the vacuum isnt set correctly its possible there are other ignition faults.

many years ago, i built a 350 performer package, self worked iron heads, PAW kit, 600 cfm holley, 9.5 to 1, summit headers, stock type HEI. made 260-ish hp at the wheels on a dyno.
 

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Discussion Starter · #10 ·
Tech @ BG said:
What intake do you currently have? If its a smaller dual plane intake going to an Air Gap style can make your lean condition worse.
the lean condition is to be corrected with jetting the carb, the intake came with the engiine, and i believe is a summit polished dual plane
 

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Discussion Starter · #11 ·
spinn said:
a cheapo vacuum advance HEI distributor can do alot. never heard of someone gaining horse power from a disrtributor change...when it was setup up for the application correctly. a correct advance curve is the key.

if this is the elusive demon problem from hell, put a gauge on everything and tape them to the windshield. then go driving. you want to see fuel psi, engine vacuum / ported vaccum, oil psi, exhaust temp, the damn coil voltage, etc....find out what is going on.

unfortunately a vacuum curve will not do anything for your dyno #'s. but if the vacuum isnt set correctly its possible there are other ignition faults.

many years ago, i built a 350 performer package, self worked iron heads, PAW kit, 600 cfm holley, 9.5 to 1, summit headers, stock type HEI. made 260-ish hp at the wheels on a dyno.
it was an ebay 90$ vacuum advance HEI, I plan on running a MSD external coil, the fact that I sold that particular distributor helps my decision to buy a MSD. I didn't look too far into it, but with the cheapo dist, I was getting erratic primary voltage (when put on lab scope), I figured it was either a problem with the dist, or something I could figure out later (but with a better dist in place)

The cheap dist didn't come with advance springs, weights, so whatever it was out the box was what I was running. After dynoing the car (and hearing spark knock at 146hp & like 3500rpm, I was told by the shop owner that the car was definitely too lean for the appliaction (street (soon to be street/strip) small block chevy, 268h cam, .45 lift, unknown (believe to be close to stock) heads, 1.5 roller rockers, holley 600, and th350 with shift kit (not transpak)..

And he suggested jetting the carb up a little bit (+4 secondaries, +2 primaries to be exact)
 

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Discussion Starter · #13 ·
spinn said:
that jetting was going to cure a spark knock , or detontion at 3000rpm ?

no weights? have you adjusted your mechanical curve? with the vacuum hose disconnected ?
on the old distributor, no weights, no mechanical/vacuum curve adjustments..

pulled it out the box and fired the engine up..

and, yes, it was detonating real early, i don't remember looking to see what mph it was at, but this specific dyno is rated up to 1300whp, so I'll say there was a decent sized load on the engine, and it started knocking(pinging)

I pulled the air cleaner off and noticed hp gains right away, but again, started pinging pretty early. I am supposed to be making another trip out soon after I do the carb, throw a new dist on, and new intake if I can get some cash to do so. I'm also planning on baselining on another dyno closer to me, but I'd like to see what jetting and a free-er flowing air cleaner would do for me first.
 

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Discussion Starter · #14 ·
spinn said:
that jetting was going to cure a spark knock , or detontion at 3000rpm ?

no weights? have you adjusted your mechanical curve? with the vacuum hose disconnected ?
The jetting was supposed to cure a lean idle, as well as lean up to 3500-4000 where it started pinging
 

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Technical Support Barry Grant
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biggeazy-e said:
the lean condition is to be corrected with jetting the carb, the intake came with the engiine, and i believe is a summit polished dual plane

Don't change too many things at once!

Going from a low profile dual plenum intake to an Air Gap style intake WILL make the engine run even leaner! So you may want to fix your ignition, and fuel delivery problems before doing anything else.
 

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Discussion Starter · #16 ·
Tech @ BG said:
Don't change too many things at once!

Going from a low profile dual plenum intake to an Air Gap style intake WILL make the engine run even leaner! So you may want to fix your ignition, and fuel delivery problems before doing anything else.
That's exactly what I'm doing.... :) Jet the carb and see where I'm at, along with a new dist. From there, I was planning on starting some deeper modifications...
 

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Technical Support Barry Grant
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Remember you will most likely have to rejet again once you change intakes.
 

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Discussion Starter · #18 ·
Tech @ BG said:
Remember you will most likely have to rejet again once you change intakes.
Yup, for that, I was looking at the 64-99 jet kits on ebay..

I was thinking to get primary & secondaries now, and see where I'm at (at least start toying with A/F, Spark..), and this summer, pick up a new intake and jets, and dyno it with the new intake, change the jets/plate at the shop..
 
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