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Old 07-08-2016, 08:09 AM
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85 Silverado 305

I need help. I have read on some sites that the 1985 Silverado with the 305 is a gas guzzler. Why is this? Some comment "that is why they have two gas tanks" why is this considered considered to be such a dog?
Thanks advance. Harv33

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Old 07-08-2016, 09:07 AM
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Originally Posted by Harv33 View Post
I need help. I have read on some sites that the 1985 Silverado with the 305 is a gas guzzler. Why is this? Some comment "that is why they have two gas tanks" why is this considered considered to be such a dog?
Thanks advance. Harv33
which fuel system... do you have a california emission truck with the full feedback carb system

or do you have the 49 state version with the non feedback system..

or some version of either..

the feedback carb system can get excellent fuel economy if it works perfect..

i know the system inside out and backwards..

you will need with a feedback system at least a dwell meter.. digital or analog.. (needle gauge type) and this is not to work on the ignition system.. this is to monitor the duty cycle the computer is sending to the carb..

with feedback systems.. you will find a green wire with a green connector but its not connected to anything. its up near the passenger side front of the carb. set the dwell meter to 6 cylinder scale.. yes.. i know you have an 8.. set it to 6 anyway.. hook up to the green wire and ground the other test lead.. if the system is working properly.. you will have a reading at warmed up idle.. between 28 and 35 degrees of dwell in 6 cylinder mode.. very slowly increase the engine speed to around 2500 RPMs.. you should have 25 to 45 degrees of dwell.

please .. don't start turning screws.. yet..

in impalas or caprices.. a 5.7 with a feed back carb can easily knock down 21MPG.. a 5.0 can get 23MPG and the 4.3 can knock down 26MPG on the freeway. trucks get less fuel economy because of many issues.

please verify that your choke pull offs are properly working and hooked up..
the primary choke pull off on the passenger side front of the carb only pulls the choke blade open about 3/16 of an inch.. this is to prevent flooding during a cold start..

the secondary choke pull off mounted to the passenger side rear of the carb does more. it pulls the fast idle cam when the vacuum is applied.. but its hooked to the 3 or 4 nipple thermal vacuum switch mounted to the outside of the air cleaner housing. if the vacuum hose order is screwed up.. the engine will be stuck at fast idle.. sometimes it will hold the choke blade closed. causing fuel economy to suck..

pictures from various angles with the air cleaner on.. and with the air cleaner off..

you can also pull codes from the computer on feedback systems by jumping the A and B terminals on the connector under the dashboard. turning the key on and counting the check engine light flashes.
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