Duster running rich
- Thread starter lenky1
- Start date
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remytherat
Well-Known Member
Post plugs?
Where? Idle, cruise, full throttle?
The jets have nothing to do with idle. Nothing, nada, zilch. In order for the jets to be involved, you must have enough airflow at the boosters to pull fuel through the jets. There is nowhere near enough airflow at idle, so changing the jets does nothing to clean up the idle. "What kind" of 750 is it?
Check the float level, it's the first thing to check off the list.
What's the list number? I'm just wondering if it has adjustable air bleeds and fuel restrictors. That will be the only way you can change the air fuel mixture at idle. If it's an older one, it's non adjustable.
Cam in the engine and where is the idle timing set?
IMO, a 340 with a stock cam should be somewhere around 14 btdc for idle timing.
IMO, a 340 with a stock cam should be somewhere around 14 btdc for idle timing.
Engine is 340 30 over. Zero decked. Kb pistons. 1.6 Harlan sharp rockers. Cam 292/508. No idea on install and timing as it was built 15 years ago by my uncle who is now deceased. Head have 202 160 valves. Holley electric fuel pump. Engine tuning is not my thing as I'm a body and paint guy. The information I'm giving is the from the stack of invoices he left in a folder. I really do appreciate the help. Thank you all
You don’t have a carb problem. You have a timing problem. With that cam at a MINIMUM you need to be 10.5:1 and 11 would be better.
You are going to need in the mid to high 20’s for initial timing, maybe more depending on your actual, measured compression ratio.
My best guess is the timing is all wrong. On top of that, to get the engine to idle you have the throttle blades open way too far and you are idling on the T slots or worse.
You are a serious candidate for using manifold vacuum on your vacuum advance (assuming you have a vacuum can on your distributor) to get enough timing at idle. If you ask nicely, @Bewy can post up his standard package of information on how to do it. Read it because most likely you’ll need to do it.
The other thing is you will most likely need to drill small holes in the butterflies to allow more air to the engine without screwing the curb idle screw in so far you are idling on the T slots.
Any idea on what your compression ratio is?
292/508 Have a grand time with that one getting a clean idle.
You have to know timing to get it set up. Setting it by the "book" will be an absolute disaster!
Its a 4 speed and the gears are 411. They compression was measured around 11 when built. I found the cam card and builder notes. Kb 30 over pistons. Cam is 292 508 108° centerline. Rear end is an 83/4 w 411 gears. Its a 4 speed w a McLeod clutch.
I forgot to add. Intake is an air gap. Also @Newbomb Turk i reread the notes. Looks like it just says engine was decked. It doesn't say how much
TT5.9mag
Two atmospheres are better than one
Idle mixture screws?
4 speed makes it easier to set up at idle. That isn't a DP carb... It's a vacuum secondary.
You have to get a timing light on it. Hillbilly timing tape the balancer if you need to.
If it cranks over easily now, turn the distributor a bit counter clockwise until it is hard to crank over. Then back it off some.
DO NOT drive it that way until you have a the timing sorted out. Only thing this does is give you an idea where the timing can go. Set the idle around 900 and try to get control of the idle mix screws. See if it cleans up.
I have a 292 cam in a 340 and it has 30+* of timing at idle, but is an auto car. I hate that engine... lol Didn't build it and no idea where the cam is installed, likely not where I would want it.
You have to get a timing light on it. Hillbilly timing tape the balancer if you need to.
If it cranks over easily now, turn the distributor a bit counter clockwise until it is hard to crank over. Then back it off some.
DO NOT drive it that way until you have a the timing sorted out. Only thing this does is give you an idea where the timing can go. Set the idle around 900 and try to get control of the idle mix screws. See if it cleans up.
I have a 292 cam in a 340 and it has 30+* of timing at idle, but is an auto car. I hate that engine... lol Didn't build it and no idea where the cam is installed, likely not where I would want it.
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Ok, that's the old model and is not adjustable on the idle circuit. You can make it such with lots of modification. If you can do it yourself, it'll save a lot of dough. If not, I would look at something different in a carburetor.
Try all this ^^^^^ before you replace anything. You might luck up and make a big improvement.
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