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1970 Duster 340 - Carb Leak, No Choke Plate, Dirty Carbon Air Filter
Hey Y’all,
Just took my car out from literally years of storage and I have a few questions.
This thing was built (not by me) for the drag strip, but that was two owners ago in 2005.
In order to get this thing to idle - you have to fire it up and rev the engine at roughly 2000rpms for approximately 5 minutes until the temp gauge reads 160 degrees. After this it idles and drives fine.
If you stop for a quick visit somewhere the car becomes a pain in the *** to start again because it’s been cooling down for 30-60 minutes. Sometimes it ends up flooding if you’re feathering the gas pedal too much.
The carb (4 barrel Holley 750 double pumper) does not have a choke plate.
I assume it didn’t have one because it was a racer - but I’d like this thing to be a leisure weekend driver with my wife.
Am I able to get a choke installed? Would it be worth it? Would there be a lot of playing around to get it to work properly?
I also noticed my air filter is extremely black and has a ton of carbon around it. Your hand instantly becomes black when you touch it.
Any hints for this?
I also fired up my fuel pump today (about 5 seconds to test) and noticed that the carb is dripping fuel around the base plate. I’m assuming this would be a bad gasket?
Any help/tips would be appreciated.
Pics included with descriptions.
Driver Side View Passenger Side View Dirty Air Filter Yellow squiggles is where fuel was sitting on top of the base plate. Yellow arrow is where there was a constant fuel drip (even after the fuel pump was shut off). Yellow squiggles are where fuel was sitting on top of the base plate. Top view of carb. Why is there a black tube there?
Hard to say anything without knowing what went into the engine, drive train, etc.
Also don't know how much you want to put into it.
First, "real" race cars generally aren't happy on the street. They are built for wide open throttle and don't like running at part throttle. That explains why it's running rich.
The carb is going to need a rebuild, and you should be able to find a choke butterfly and shaft for it. You can use a manual choke if necessary.
750 cfm, btw is pretty big for a small block, unless there's a good sized cam in there, a high stall converter and steep gearing.
Cam specs would help a lot in figuring out what's going on. Without that, we're just using band-aids.
Hard to say anything without knowing what went into the engine, drive train, etc.
Also don't know how much you want to put into it.
First, "real" race cars generally aren't happy on the street. They are built for wide open throttle and don't like running at part throttle. That explains why it's running rich.
The carb is going to need a rebuild, and you should be able to find a choke butterfly and shaft for it. You can use a manual choke if necessary.
750 cfm, btw is pretty big for a small block, unless there's a good sized cam in there, a high stall converter and steep gearing.
Cam specs would help a lot in figuring out what's going on. Without that, we're just using band-aids.
Archer
The previous owner didn’t know much - but this is what I know.
-12:1 Keith Black Pistons (roughly 185 psi in each cyl)
-Hi Lift Solid Lifter Crane Cam
-Engine & Drive train rebuilt in 2005 (2,800rpm stall converter & shift kit put in)
-727 torqueflite automatic tranny with B&M slap shift installed
-Mini tubbed
-8 3/4 rear end with 4.10 gears
-Dyno was apparently 400 HP
Is there a way to figure out cam specs?
Id say I know my way around a car, but I’m not very versed when it comes to engine work/tear down jobs.
Actually, there are ways of figuring out cam lift and duration and converter stall, but before going too nuts, if it were my car, I'd do a carb rebuild first - and loose the heat shield (metal plate under the carb).
12:1 pistons, aren't going to be too happy on pump gas either. Even with additives, you'll probably have to retard the timing to keep it from pinging. That might be adding to the problem. Also ways around that, like water injection but again, is it really worth it?
Since I don't get to a track any more, I've toned down my engine a bit, and to be honest, it's a heck of a lot more driveable (read "fun") on the street.
Actually, there are ways of figuring out cam lift and duration and converter stall, but before going too nuts, if it were my car, I'd do a carb rebuild first - and loose the heat shield (metal plate under the carb).
12:1 pistons, aren't going to be too happy on pump gas either. Even with additives, you'll probably have to retard the timing to keep it from pinging. That might be adding to the problem. Also ways around that, like water injection but again, is it really worth it?
Since I don't get to a track any more, I've toned down my engine a bit, and to be honest, it's a heck of a lot more driveable (read "fun") on the street.
Archer
Honestly I wouldn’t mind putting some money into making it more street worthy. The thing is extremely loud, inconvenient to start, and expensive on fuel/additive.
The #1 cylinder needs work anyway (judging by a compression test, the rings need to be replaced in that cyclinder)
That being said, I wouldn’t mind downsizing the pistons and rods to get a lower compression when the time comes to get the engine done.
I imagine swapping out cams would be ideal in that situation too - but I have a feeling that requires a lot of adjustments to timing, etc
Also found some old paperwork that states the car has a 2800RPM stall converter.
Theres also a note in regard to the solid lifters about adjusting the lash every 5,000 miles
That all sounds about right - for a pretty cool race car.
Since you're in the market for a rebuild, I think you're on the right track.
Random thoughts:
There are plenty of good hydrolic cams from Comp Cams nd others, just keep the lift under 500 and the duration under 300.
Here's one example, it's a little over stock, but not crazy: https://www.summitracing.com/parts/c...yABEgLdpvD_BwE
Keep the compression around 10:1, and while a 600 cfm carb would be optimal, you might get the 750 to work with a lot of tweaking.
While I'm partial to Holley's, some of the Edelbrock carb/manifold kits are a nice upgrade to what you have. Ther Eddy Performer RPM would be a great choice for a manifold. https://www.edelbrock.com/performer-...fold-7176.html
The converter stall and gears get into a greyer area. While lower (numerically) on both would give you better overall drivability, what you're expecting the car to do have to factor in.
Since I'm sure the heads you have were worked to some degree, aluminum heads, while cool looking won't buy much in the seat of your pants area.
07-26-2020, 04:40 PM
