Carb Flame Up With Good Timing???

[off2wildblue]

I have a rebuilt 289 with the stock rebuilt 2bbl carb and stock manifold. The engine is bored at .60 over and a mild cam with a stock exhaust manifold.

The car ran perfectly for a few months and during start it flamed up. The air breather had flames coming out of it and burned up. This was after it was driven for awhile and happened out of the blue. Took it to the mechanic that built it and he said the timing was dead on. It worked fine and thought that it was maybe some trash in the carb that messed with the float but it should be fine. I installed two new filters. One before the fuel pump and one after the pump. This is in addition, to the stock one screwed into the carb.

I drove it daily and two months later it happened again. Again right after I drove it all day. I heard a pop this time and then it flamed up. I couldn't get the fire out so I tried to start it again so the carb would suck the flames back into the carb. My mechanic said it would work...it didn't. It was worse. I managed to get it out and let it cool, took off the air breather and it started fine and got it home.

Any ideas?

I would get a new carb or rebuild it but I am afraid it will still do it. Can it be something in the rebuild that needs adjusted, such as rods or valves? What about choke adjustment?

I am freaking out. Can someone give me something to check or consider?

Vince

 

[horseballz]

Symptoms sound to me like one or more intake valves not closing/seating completely or one or more exhaust valves not opening properly. Either of these issues COULD be caused by a need for valve adjustment, however the exhaust valve(s) not opening might also be caused by a cam going south. Flat tappet cams HATE the new oils and their lack of zinc (ZDDP) additives. Couple this with our current, crappy fuel blends that percolate (boil out the float bowl into the manifold from heat soak) at a lower temperature that older, regular gasoline, and you have a recipe for your particular situation! You're likely going to need to pull your valve covers, check valve adjustment (if they are adjustable) and/or measure the lift/duration of each valve. It IS possible that if the rockers are not adjustable, the pushrods may be a tad too long, giving you a little too much lifter pre-load. Please let us know what you find out.
HTH,
Gene

 

[rbohm]

it sounds like an intake hanging open, and excessive fuel in the intake system.