Author Topic: Is this carb OK?  (Read 4096 times)

Offline Chevygold

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Is this carb OK?
« on: July 02, 2022, 02:09:01 PM »
When I got my truck the fuel system was quite dirty, guess it had been sitting a while, the carb which was on it was an
Edelbrock, not sure what model, but it ended up choked with crud from the tanks. Anyway after giving the tanks a good clean out I needed another carb, I had one I'd rebuilt for my Corvette but due to a mismatch with the manifold it wasn't suitable so I fitted a Brawler 670 and now it's happy.
The carb I had from the Corvette was a Holley List 6619-1 which is a 600cfm with electric choke, this has worked OK on my truck but can't help wondering if it might be a bit small?
The truck came to me with a 383 stroker but I have no other info about the motor other than a sticker from Crane Cams saying the cam is CARB compliant with an EO No. D225-21 but don't know if this identifies the cam or not?
Truck is a 76 C10 longbed with a TH400 tranny, it seems to run OK and seems OK on fuel although I've never tried to get a consumption figure.
Googling the cam sticker seems it covers various cams and valve gear so no help there!
Any ideas?
Thanks
Graham

Offline Shifty

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Re: Is this carb OK?
« Reply #1 on: July 02, 2022, 03:21:27 PM »
600cfm would be a bit small for a 383....just about right for a mild 350.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Chevygold

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Re: Is this carb OK?
« Reply #2 on: July 02, 2022, 05:05:58 PM »
That's what I thought although I have to say the truck runs well, wish I knew what was in the motor but I'm not about to pull it down just to find out! Might have to get another Brawler, have been very pleased with the one I put on my Corvette, setting up was very straightforward but will have to wait for the exchange rate to improve as it's not good for me just now and with petrol around 2 pounds a litre I'm restricting my driving and spending my time working on making improvements.
Thanks
Graham

Offline JohnnyPopper

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Re: Is this carb OK?
« Reply #3 on: July 10, 2022, 11:19:21 AM »
So Shifty, would a 750 cfm be too big for a mild/crate 350? Looking to improve gas mileage for obvious reasons!
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Shifty

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Re: Is this carb OK?
« Reply #4 on: July 11, 2022, 09:26:44 AM »
Still a little big.  You could pull it off with a vacuum secondary Holley with a heavy spring on the vacuum chamber, but I'd stick around 650, possibly even a 600 with a little tuning.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Chevygold

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Re: Is this carb OK?
« Reply #5 on: July 11, 2022, 01:32:16 PM »
The Brawler I have on my 'vette runs sweet, it's a 670 vacuum secondaries and electric choke, seperate idle adjustment in each choke, again I don't know the build of the 350 motor but suspect it has been breathed on a bit before it came to me, car was originally a 350/350 and still has the original heads on a truck block to get the 4 bolt mains, performer inlet, beyond that I'm only guessing.
Graham

Offline Shifty

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Re: Is this carb OK?
« Reply #6 on: July 12, 2022, 09:05:22 AM »
The Brawler would indeed be a decent choice, but because of the weight of the truck, the secondaries would want to open very early, hence the heavier spring mod, delay it a bit.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline Chevygold

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Re: Is this carb OK?
« Reply #7 on: July 17, 2022, 04:45:46 PM »
The Brawler would indeed be a decent choice, but because of the weight of the truck, the secondaries would want to open very early, hence the heavier spring mod, delay it a bit.
Thanks Shifty if things improve on the currency front I'll get one on order.
Graham

Offline Chevygold

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Re: Is this carb OK?
« Reply #8 on: January 23, 2023, 02:41:15 PM »
Latest update, I managed to find a Street Avenger 670cfm over here at a good price, did a rebuild with all new gaskets etc. and fitted it on the truck yesterday, all standard jets, idle screws 1 1/2 turns out, floats set to middle of the float bowl and she started up first turn of the key, good idle on the auto choke and after warm up.
Didn't have time to put the vacuum gauge on it so that's the next step, a quick snap of throttle results in clean accelleration in neutral but if I open the throttle slowly I get a stumble at about 1/2 throttle  which feels like weakness, will need to get my gas tester up the exhaust to be sure.
Will let you know how I get on tomorrow, float bowls have the windows to see the fuel level but finding it very difficult to see the level, first attempt at setting the secondary level resulted in fuel pouring into the chokes as too high!
Any suggestions welcome.
Thanks
Graham

Offline ehjorten

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Re: Is this carb OK?
« Reply #9 on: January 24, 2023, 09:16:37 AM »
Your 383 in high performance trim has a volumetric efficiency of around 85%, so a 600 CFM carburetor properly tuned and matched to the other engine components is going to be good to about 6,000 RPM. A heavy truck with an automatic transmission, depending on your stall speed is going to like a smaller carb and will accelerate quicker, even though your top end power may drop off a bit. I would say your choice of a 670 CFM Carb isn't bad though, but it might not be as snappy as with the 600.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline Chevygold

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Re: Is this carb OK?
« Reply #10 on: January 28, 2023, 02:04:29 PM »
OK had a bit of time today to spend on my truck while the wife was looking the other way! Put the vacuum gauge on it and got the idle set 20" vacuum at 900 rpm, smooth acceleration up to about 15" vacuum then a slight stumble which quickly cleared, could be the power valve opening? will get it out on the road and see what it feels like. I have a selection of springs to try in the secondary diaphragm and see how I get on it has the plain spring in there just now but I have the brown and black to try to hold the secondaries back.
Thanks
Graham

Offline Chevygold

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Re: Is this carb OK?
« Reply #11 on: May 24, 2023, 02:21:09 PM »
OK finally got time to give it a road test and it coughed and spluttered badly when trying to get moving so guessed it was going weak.
Next step I moved the secondary jets to the primaries and put a pair of 83's in the secondaries and now its worse than before!
Spent today fitting an AFR gauge and now I can see what's going on.
Starts easy, one pump on the gas to set the choke twist the key and immediate start followed by a smooth idle, off choke get an AFR of about 12.6 so my initial tuning was pretty good!
As soon as I try to give it any gas it goes really weak and won't rev at all, it's almost as if it's worse with the bigger jets in the primaries, how can this be?
Thanks
Graham

Offline Shifty

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Re: Is this carb OK?
« Reply #12 on: May 24, 2023, 03:38:02 PM »
How is your fuel pressure?
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

98 C2500 ext cab longbed

Offline JohnnyPopper

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Re: Is this carb OK?
« Reply #13 on: May 24, 2023, 08:46:20 PM »
Also fuel filter?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Chevygold

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Re: Is this carb OK?
« Reply #14 on: May 25, 2023, 04:02:21 AM »
Don't have a gauge on the fuel inlet but it was fine on the previous carb, filter on the inlet clean also filters on each carb inlet clean.
I'll try raising the fuel level and see what that does, windows not very clear so difficult to see the level, any suggestions for cleaning them?
Thanks
Graham