I have a 91 RS with a 305 TBI that I have been rebuilding. I went to start it for the first ime last night but couldn't get it to run.

The symptom:
Car will start but backfires through the intake or wont start at all

What I have tried:
If I retard the timing the car wont start
If I advance the timing to where the car will run, it backfires through the intake (it will run but with moderate backfiring)
I backed off the valve lash thinking that the valve may not be closing and allowing the combustion to come back past the valve, but this only calmed it down. The rockers are bordering on being too loose in my opinion but it seems to be helping to back them off.


I have put on 416 heads and installed an LT1 cam in the engine. I dont know could this be causing my problems? I thought the pushrods would still be the correct length and I seem to have plenty of adjustment range for the rocker arms... I am not sure off the top of my head but isnt the cam base circle the same? Why does it seem like the valves are not closing?

I can use any and all the help I can get right now. I really want to get this thing running.

 

when you changed the heads you changed the length of the pushrod.
Get that corrected and go from there.
is your dampner mark, and timing tab zero mark, or point in aligment with the #1 piston compression stroke TDC? Did you verify this before, or after installing the heads, fi so by what method?
Don't take this stuff for granted verify it.

 

so I checked timing position and it is correct. Checked pushrod length and it is correct. I made sure the umbrellas werent hitting the bottom of the rocker.

I plan on checking the valve lift with a dial indicator on the valve spring umbrella to make sure all the valves seem to be closing. I am not sure how well this will repeat knowing the hydraulic lifters could bleed off some of the lift??? I am also going to do a compression test to see if one of the valves is sticking open.

Any other thoughts or ideas???