Question? Is it timing or Fuel???

chevy 350 with HEI dis. two barrel carb.
There is a mid range fluster ?? The engine runs fine but when you get into the half way point in the throttle it back fires through carb then when you hit about 2500rpm it comes on . It will cherp second gear shift .
I have tryed another carb and it does the same thing
I replaced the mechanical advance and tryed diffrenet springs I ve checked the vacuum advance it works.
On these HEI distributors when the coil is bad will it do this???? I thought that when a coil went out it will not work at all. Help please if anyone has had this problem .

 

I'd say mostly timing. Backfires probably took out the power valve in the carb tho. How long since it was rebuilt? Could be the timing gears/ stretched chain if it's an old engine.

 

My big block did that because of a flat cam. Not all the time though. Dean

 

what kind of carb,rochester 2 bbl.? backfire through the carb means it's too lean,sounds to me like you should check the fuel delivery,pump,pump pushrod length,lines,filter (inline AND the one at the carb inlet) etc.etc. you don't need that much fuel for idle speed or steady cruising,but get on the gas and it's probably starving out.throw a can or two of B-12 chemtool in the tank while you're at it,that'll clean out the sock filter on the pickup tube.

 

make sure your running enough voltage to the hei,and the right gauge wire

 

Me and SamIam went through both carbs . The accelerator pump works fine . Its weird its like timing but can get a
handle of what its doing.

 

This engine came with the truck and its gota have alot of miles on her. The engine looked like they just put it in there to see where to line everything up .
Its a 48 ford truck with a camero clip. It didn't have anything on it like carb ,Distrib, Alt. exhaust. I figured I would try to get it running got the HEI from junkyard
carb from my dad ( and rebuilt it) Its got headers and flowmasters . With exhaust like that would I have to up the main jets????? more air needs more fuel right. I was thinking maybe it was undercarbed but it doesn't run like undercarbed when a engine is undercarbed if you back off the throttle and pump it the accelerator pump takes up the lean problem and you can feather the throttle right.
I think smokin joe is right the engine is wasted

 

put a timing light on there,if the timing mark jumps around a lot the timing chain is probably shot.

 

I am going to do that this morning thanks.
And thank you guys for all the replys I will let you know what I find out .

 

Does this thing have an EGR valve? If it does and it's stuck open...

 

put a vac gauge on it and the movement of the needle and where it sits will tell you what the problem is.....Marq

 

SamIam and I figured it out it was the pick up module we
swapt out the dist. with a new one and Sam layed a black mark down his street . So the next thing we tryed was dist. cap worked fine then we chaged the module and that was it.
I am still going to buy a distributor because the engine ran like it was brand new with the good distributor.
Thanks for all the help.

 

and people ask me why i still run points glad you got it figured out-george