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SBC engine


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Dellb

Club Member

Sat 02 Dec 17 17:39

SBC engine


Hi All
At last I got round to firing up the beast after rebuild of engine. Alas all is not well.
The engine fires up fine and oil pressure is fine, but it is very difficult to keep going, and is heaving out clouds of black smoke.
The carb is a Holley 4160, and I have overhauled it with new Holley parts etc. Float levels are fine, and I canít find anything amiss with the carb. There is no backfiring through the carb and I think the timing is ok.
Anybody out there had similar probs?
Delb


--------------------
Derek L G

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sssammm

Club Member

Sat 02 Dec 17 18:27


Have you got the right needles?


--------------------
2013 Z06 White, 1953 Chevy 3100

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stevel98

Awww... join the CCCUK!

Sat 02 Dec 17 19:10

Re: SBC engine


Black smoke usually means its very rich, either too much fuel or not enough air. If so, I wouldn't expect it to spit back as it doesn't sound like its leaning out.

Plugs ok? Correct heat range?

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Dellb

Club Member

Sat 02 Dec 17 20:14

Re: SBC engine


Plugs and timing are new and fine. Air filter is off for testing. I have onerhauled the carb, and fitted new joints and needle valves etc. The carb is modified to replace the secondary metering plate with a metering block. Primary jets are 72, and secondary jets are 79. The engine is a 400 with a very serious cam. The engine ran fine when I bought the car albeit with a bent crank. There was no smoke, and the idle was lumpy due to the cam.


--------------------
Derek L G

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roscobbc

Committee Member

Sat 02 Dec 17 23:52

Re: SBC engine


What hg are power valves (4.5hg?) Big cam means low vacumn - low vacumn means stock power valves will flood engine with too rich mixture at low rpm. Use 1.5hg. (Might be other way around - it's getting late!)


--------------------
CCCUK Chairman & Editor, Vette News
'68 coupe - 4 speed - 3.08 - 489 cu in - 570 bhp @ 5850 rpm - 606 ft/lbs torque (821 Newton Metres) @ 3850 rpm
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aaroncorvette

Club Member

Tue 05 Dec 17 07:48


Could be the choke? Manual or auto choke?


--------------------
'71 vette convertible + the odd mod.
I thought we won the war?

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roppa440

Club Member

Tue 05 Dec 17 09:50

Re: SBC engine


Same old story.

You need a lot of initial advance with a big cam.

Once you have that and the idle speed right you can measure the manifold vacuum and fit a power valve rated 2-inches of vacuum below that.

With the correct timing the engine will be only running on the idle mixture circuits. Currently the throttle blades will be open too far for the idle circuit to work. You are trying to idle on the main jets and probably a stock 6.5" power valve fluttering away.

To get the high initial advance (probably around 20-25 degrees) without increasing the total (mechanical only) advance (36 degrees) you either need to connect the distributor vacuum can to manifold vacuum instead of ported OR, if you don't have vacuum advance on the dizzy or enough vacuum, modify the distributor to limit the amount of mechanical advance it gives to about 10 degrees.

You will thank me for it.

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stevel98

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Tue 05 Dec 17 11:11

Re: SBC engine


Excellent solution as usual, Dave.. Thumbs up

We've all been waiting for this, ..what kept you? Very Happy

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roppa440

Club Member

Tue 05 Dec 17 11:20

Re: SBC engine


stevel98 wrote (View Post):Excellent solution as usual, Dave.. Thumbs up

We've all been waiting for this, ..what kept you? Very Happy


Mainly a few worrying hospital appointments. Rolling Eyes
But it looks like I am not going anywhere in a hurry.

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stevel98

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Tue 05 Dec 17 12:28

Re: SBC engine


Not good.. Sad

Hope your going to be ok and not have to swap your C5 for an SUV. Rolling Eyes

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