SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Xthaspot on April 25, 2014, 09:31:20 AM
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Ok here is the deal. I have been trying to get my boat to idle and this thing is kicking my a$$... I have an olds 455 with edelbrock aluminum heads and a dual quad offy tunnel ram. Running two edelbrock 600 carbs. Am I under carburated? This engine is running about 9.5-1 compression.
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Couple of things here, (1) what's your cam profile, (2) are the carbs new, old, rebuilt, etc, (3) tuning a dual quad setup is tricky at best, (4) how many hours on the engine and is it freshly tuned up, i.e.- cap, rotor, wires etc. You'll need a balance chamber to link between the two carbs to ensure they're both drawing equally. So you know what the jetting is on the carbs?
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The carbs have been rebuilt recently. The distributer and wires were brand new last summer along with the rest of the engine. I'm running the JM 25-28 shown in the picture. The carbs are going to be stock jetting except for
The metering rods I went one step smaller.
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Ok here is the deal. I have been trying to get my boat to idle and this thing is kicking my a$$... I have an olds 455 with edelbrock aluminum heads and a dual quad offy tunnel ram. Running two edelbrock 600 carbs. Am I under carburated? This engine is running about 9.5-1 compression.
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How does it run? anything wrong? if not leave it alone. 1200cfm for a 455 is fine i would think.
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Can u sync two carbs without a Manometer (balance chamber)
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I have two vacuum gauges I'm using to sync them. I can get them to sync the same. I think I might be experiencing a little bit of timing issues and adjustment. On the carbs. With that cam I believe I may have to run at 1200 rpm at idle.
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If the manifold has a common plenum you don't need anything .While it's running put your hand over one carb at a time and see if it smooths out if it smooth a out that's where your vacuum leak is also what's your total timing? Your going to want to be around 38 degree total
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At what RPM are you trying to get it to idle? You should be shooting for about 1100 in the water which should equate to about 1250 or so on the trailer.
How much base timing do you have? In theory, you should only have 12 or so degrees built into the mechanical advance, so with a max timing of say 36* BTDC it would stand to reason you will have approximately 20-24* idle timing. Much lower than about 15 degrees and you will have a heck of a time getting it to play nice at idle.
If your TR has a common "box", trying getting it to idle on just one carburetor, turn the idle screw all the way closed on one carb and concentrate on the other, this can sometimes take the volatility out of it.
Also, since you say you were using vacuum gauges, what idle vacuum numbers are you seeing?
GT