Question about Chevrolet 2500

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1973 chevy truck vacuum diagram 350 crate engine, 650 edelbrock carb, turbo 400 trans, 4x4, 3/4 ton truck. need all the info i can get please. electrical diagrams, vacuum lines, etc. please and thank you. it is having issues when accelerating or going up hill it bogs down like air cut off. or run out of gas, but has gas. neutral, or park it will run but takes a min to catch back up after it falls down, but it wont stay when put back in gear. ok well any input would be greatly appreciated. thank you

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  • Joanna Raye Lee Aug 01, 2010

    It has HEI, the gates require vacuum in order to change the floor to defrost vent, and of course the distributor. The timing is set at 8. I hope this is enough information. Its almost like it is pinched just enough or got a partial clog somewhere, If you happen to know where to get a schematic or diagram on wiring and the vacuum system, let me know.
    Thank You for your time.

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  • Chevrolet Master
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Pretty sure I have the diagrams etc but they are buried away and would take a week to find.
BUT: The setup on that engine for that year is fairly uncomplicated and you could pretty much do away with all the emission controls etc and get the engine running really well. (just block off all vacuum ports on the manifold and carb except for the one to the transmission and power brake booster) I'm not really familiar with the edelbrock carb (looks like they are based on the old carter AFB carb though. I am partial to holley carbs, and the old quadrajet carbs)
What you need to check first though is your fuel pressure and delivery. You should be seeing 5-7 psi at the carb. With the fuel line disconnected, and attached to a rubber hose diverted into a container, you should see at least a gallon of fuel pumped at idle before the carb runs out of fuel. Make sure you don't have any leaks in the fuel line coming from the tank...with a pull type pump (mechanical pump on the engine) a leak often will not drip, but will allow air to be drawn into the line while running. Make sure that if your carb has a filter in the fuel inlet, it is clean. Make sure that the fuel line filter (sock) in the tank is also clean.
It's likely you have an egr valve on the manifold, If so, you can temporarily block it off with a small piece of metal from a soda can installed between the valve and the manifold. That will prevent it from working and if it has any leaks, blocking it off will eliminate it from the system. If that helps, replace the valve.
Your ignition system is fairly simple. a single 12 volt lead goes to the battery side of the distributor. You can block off the vacuum advance temporarily and just set the initial timing at about 8 degrees advanced. (depending upon fuel quality, you can go as high as 12) . The ignition module is not "testable" usually though they either work or they don't )
You do need to check the wires that attach to the pickup under the mount plate to make sure they are not partially broken and grounding when the advance moves the plate.
Back to your carburetor... If you are test driving without the air cleaner housing in place, it is possible that if there is a heat pad mounted to the underside of the hood, it can get drawn down against the carb inlet and cause problems. If the air cleaner housing is in place, make sure that the inlet door in the snorkel is opening or, disconnect the vacuum hose going to it as default on those is wide open. If you have tried everything I've outlined, you may have to go inside the carb and make sure that the power valve isn't frozen or that the float level isn't set too low.
Once you get it running right, you can begin to look for the diagrams etc you are looking for, but at least it will be running and usable.
The only other item that could give you a problem like the one you have is if the cam timing was set incorrectly at the factory (doubtful but it can happen) but I really would not worry about that just yet.
Hope something here helps!!! Good luck!

Posted on Aug 01, 2010

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  • Richard Scordino Aug 01, 2010

    I noticed that you mentioned "the gates" in your comment....Assuming you mean for the heater control, you can use any port on the manifold or carb for that, providing it has full time vacuum (some on carb only have vacuum when throttle is open) I'd leave that line disconnected and blocked at the port 'till you get the engine running right (don't need heat if engine isn't running) Timing is good at 8 providing the vacuum advance on the distributor is disconnected when you set it. Advance can be connected either to full time source or one that only has vacuum with throttle open on the carb base. Your engine will tell you which it prefers if you try both. Personally, I'd prefer a 750 cfm carb on a 350 engine but yours should work better than what you are seeing. Also if the flow rate on the fuel line from the tank is low, most times you can clear it with compressed air blowing through the line at the tank side of the pump with the fill cap removed from the tank. If the "sock" is obstructed it may blow right off the end of the pickup but if you have a decent in-line filter I would not worry about it!

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