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small miss

792 views 11 replies 7 participants last post by  81scottsdale400 
#1 ·
hey fellas im back again hopefully to fix my problems this time ok by now some of you guys know my truck if not its a 1981 chevyrolet scottsdale half ton with a 79 400 sb chevy in it i just got the top end put back together and the exhaust on it but now ive noticed that when the truck is cold and u take off in it it tends to backfire and miss when u shift into second gear and if your cruising at 30 mphs and u step on it it spits and sputters and shakes really bad but it gets a little better when the truck hits running temperature but every now and then when u take off from a stop light it will cut out and sputter idk whats going on and im close to giving up but yet i dont wanna get rid of a rebuilt motor thats only a year old please help anything will help
 
#2 ·
sounds like the timing is too advanced when cold and not enough choke , they do sell thermostatic controls that limit the timing on the motor when cold , it was part of the OEM package for emmisions controls , everyone takes them off andpitches them , but sometimes its best to leave them on .
 
#6 ·
ok here we go lol no i havent changed the fuel filters ive only owned the truck for a year and have been driving it for 2 months and the choke is also acting weird it keeps idleing around 1500 after u hit the clutch and doesnt move till u hit the throttle then it comes down to where i adjusted my idle which is around 700 and idk how to properlly adjust the carb srry im kinda new to the whole engine guessing game thing and the carb came with the truck so im not sure what cfm it is and im not sure about my cap and rotor i didnt pay much attention to it its and HEI system i thought it could be the valves too is that possible? hopes this all makes sense get back at me thanks
 
#8 ·
81scottsdale400 said:
ok here we go lol no i havent changed the fuel filters ive only owned the truck for a year and have been driving it for 2 months and the choke is also acting weird it keeps idleing around 1500 after u hit the clutch and doesnt move till u hit the throttle then it comes down to where i adjusted my idle which is around 700 and idk how to properlly adjust the carb srry im kinda new to the whole engine guessing game thing and the carb came with the truck so im not sure what cfm it is and im not sure about my cap and rotor i didnt pay much attention to it its and HEI system i thought it could be the valves too is that possible? hopes this all makes sense get back at me thanks
You have to start somewhere, so how's about at the beginning?

Tune it up first. Plugs, wires cap rotor, filters (air, oil and fuel) oil change, PCV valve, check/fix all the vacuum leaks, replace vacuum hoses as needed.

Get a timing light and vacuum gage.

When (if) you get to this stage, get back and we'll get you going. Or at least find out what's the deal.

But until you do the basics, you're just shooting in the dark.

BTW, you're encouraged to make complete "sentences". These sentences can also be divided into "paragraphs". :mwink:
 
#9 ·
ok the plugs are new, plug wires are new cap and rotor are decent shape oil change is fresh only 2 weeks on it air filter is brand new oil filter is new fuel filters arent new. runs worse with the pcv valve and new vaccumn hoses and vaccumn leaks are plugged off where not needed since the intake is of a 90s 350 sb chevy.
 
#10 ·
replace the fuel filter as you might have water in it or alot of dirt and they are cheap and you wouldn't believe how many service calls I get for dieing /rough engines in the winter atributed to a old filter doing its job keeping the gunk out of the carby . one of my older trucks ( c-60 series w a 27 ) has a problem of running rough when the fuel filter starts seeing water and plugging up. tell the new guys to change it and they argue with me about it s something else , filter changed it runs like a top .
 
#11 ·
81scottsdale400 said:
ok the plugs are new, plug wires are new cap and rotor are decent shape oil change is fresh only 2 weeks on it air filter is brand new oil filter is new fuel filters arent new. runs worse with the pcv valve and new vaccumn hoses and vaccumn leaks are plugged off where not needed since the intake is of a 90s 350 sb chevy.
Did you just change the plugs, cap, and wires in the last day?
 
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