1987 GMC Pickup Hesitates on Throttle

GMC
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LYNN6271967
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I have a 1987 GMC p/u with a 1998 Chevy 350 vortec engine they pull the fuel injection off and put 650cfm carb.now can you pull the vortec heads off and replace with normal 350 or high performance heads?
Mar 8, 2006 at 10:57 AM
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NOS
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why not leave the same heads on it. what is reason you want to change heads? they have the large 2.2in intake valves not sure why you wanted to carb an injected motor anyway they preform better than a carb motor. if you intakmanifold fit ok with no problems. thoes heads shoould be ok. but i think you will run into a problem with your distributor not working right because of the computer and all you may have to wire in an hei distributor and do away the computer stuff all together also how you feeding your cardb most of thoes motors don't have a place to put in a mechanical pump unless yours has a block of plate injected fuel pumps have a higher pressure rating than a regluar on. good luck on your project hope somw of this helps ya out. NOS
Mar 8, 2006 at 2:01 PM
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LYNN6271967
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I just bought the truck with carb on it and it has a hei ignition.When you step on the gas it chokes for a second.it has a electric fuel pump in the tank,it also has a fuel pressure gauge under the hood.a friend told me to change out the heads it would make it run better!
Mar 8, 2006 at 2:28 PM
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NOS
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how much pressuer is that pump putting out a car only needs 51/2 to 71/2 psi to run any more than that and it is flooding i'am not real sure changing heads is the answer a fuel injected engine runs on a ratio of 14.7to1 ratio that is at a pressure of 60 psi this is too much pressure for a car try puting a pressuer regulator in the line to the carb and turn it down till you reach a 71/2 pis reading on your pressure guage and see what that does for ya (NOS)
Mar 8, 2006 at 4:26 PM

Suggested Repair

Do not replace the Vortec heads as the first step if the intake fits. The brief choke when accelerating is more likely flooding from the in-tank electric pump. Install an inline fuel-pressure regulator and set carburetor pressure to about 5.5–7.5 psi, then recheck the under-hood gauge.

Conversation Summary

The owner has a 1987 GMC pickup with a 1998 Chevy 350 Vortec converted from fuel injection to a 650 cfm carburetor and HEI ignition. It chokes briefly when the throttle is opened, and a friend suggested changing the heads. The expert said the Vortec heads should be fine if the intake fits and advised regulating the high-pressure electric pump down to about 5.5–7.5 psi so the carburetor does not flood.

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