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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: muleystruck on June 02, 2016, 10:15:04 am
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Hello, all. I have an 86 Scottsdale with a 4.3 v6 and the my6 trans. The po had replaced the original carb, Im assuming a qjet. with an Edelbrock. I'm not impressed with the carb as fuel mileage is bad. I know these trucks aren't the best for mpg but only 10 mpg isn't cutting it. I don't drive the truck hard as I'm trying to get the best mpg I can. I will admit I'm not very experienced adjusting carbs. I didn't get anything with the new edelbrock (info,manual,) so I borrowed a book from my bro. He has a v8 Vega with the Edelbrock. What carb was actually on this truck from the factory? I know it has 3 73 ratio rear gear. This truck is very clean, only 2 small rust spots(cab corners).Appears it was well taken care of by the original owner. After he passed on other members of his family used the truck and didn't respect it. I appreciate any info from yall. Thanks Muley
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what size carb?
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It should have a Rochester M4MED quadrajet. The best I was ever able to wring out of a 4.3 in an 86 was 13mpg. The 305 in my 85 got 15mpg. The 4.3 doesn't have enough grunt to take advantage of the overdrive in the MY6.
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i think the key to all this ( i have a 4.3 too) is to find out what size the idle tubes, main jets and metering rods were that originally came with the carb on this engine. i am going to try to get the bottom of it after i get the engine in.
So, i don't think the problem is quadrajet or even edlebrock. The main issue i think, is calibration.
The cfm for this application may have even been 800cfm (pretty sure, not 100% positive though). This particular carb for an 86 4.3 had the dual capacity accelerator pump and unless the truck was originally a california truck, the carb should be otherwise non-computerized. i'm pretty sure that if you leave the dual pump unplugged, the carb will just act like a normal single accel pump.
Right now, i am using a jeg's reman quadrajet # 15805. This has .073 main jets and -50M metering rods. The best mpg i could get was 16.59, but the engine was hosed from the beginning.
Every now and then i see NOS GM 4.3 carbs on ebay.
i am not familiar with the MY6 trans. What is the top ratio?
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MY6 is the OD trans with .73 as high
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Wouldn't an 800 cfm carb be about twice as much as would be needed for a 262 cu in 6 ? I'm running a 750 on a 454....???????
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Wouldn't an 800 cfm carb be about twice as much as would be needed for a 262 cu in 6 ? I'm running a 750 on a 454....???????
You would think so, but i think all 85-86 trucks got the 800cfm version irregardless of engine size-----maybe to save money?