Hey guys I have this 78 f-150 that I rebuilt back in 97, I went through the whole thing. Here is what I did and had done to it, The problem is I have alot of backfireing happening and is really running like crap. This is a four wheeler and when I got it all put back together this thing would get-her I mean side ways when I hit second gear with 33's on it. Ok Here it is new everything, upgraded the cam, all new bearings 600 holley dual feed, performer 400 intake, headers,
new pistons & rings heads were all gone through and shaved had to put guide plates and hardend pushrods in it I also due to the over sized cam, put roller rockers in. I also had the crank turned and balanced and fitted with new bearings new distributer that is an accell with an accell coil. Now here is what happened maybe you can tell me what the problem is. I am thinking that it is that holley carb and maybe some timing issues. One day I had it out and I took off as I always do full throttle and just after I hit second comming sideways it backfired through the carb and it hasent been rite since all these parts where purchase new in 97 so they really arent to old and the motor only has about 7k on it. any info and tech tips that you can give me would be well apprietiated. Oh one other thing is that I have messed with the curve adjustment on the distributer and am not to sure where or how to get it back to where it needs to be.

 

Look for a bent valve. Backfiring through the carb means that exploding mixture is getting into the manifold. Could also be that the timing chain jumped a link. At any rate, an intake valve is open when it shouldn't be.

'97 is 7 years ago, and the kind of miles you put on your truck, 7k is probably equal to 77k.

 

You may have said the majic word!! Holle, and back fire... When a holley burps from the carb, chances are you blew the power valve. Pull it apart and check it I bet you find that it is bad

 

agate I have never pulled a holley apart so I really dont know what I would be looking for can you give me the run down and discription of how to.

 

Check lifter preload / rocker arm geometry. Did you measure pushrod length ? or just buy stock length. It' doubtful the stock length will work with all your modifications. I agree that the power valve is probably blown if it doesn't have the protector. But the question is why is it backfireing.

 

as scroob said check for bent valve or pushrod off.only takes a minute to take off rocker covers.roll the engine over and watch the valve train to see if everything ok.

 

thanks for the reply mark, Guys out their that are giving me tips and info on this motor let me go into allitle more detail for you. This motor ran extremly well for quite some time. I had it over to my cousins he is a mechanic by trade and he set the float bowl fuel hight for me and this backfire through the carb happened on test ride hasent be nearly the same since. I drove the truck from michigan to goerga shortly after. it ran ok but I just dont have the power I did and it was all the sudden the motor still runs well but not nearly like it did. the heads were completely redone by car quest and after I got the motor all put back together I took the whole motor to carquest and had them tear it down and make sure that everything was proper. They had fit the crank and cam with new bearings the first time it was their, they also put the heads all together for me and said that everything looks very good. This is all info during rebuild. and like I said this motor ran very very well untill that backfire through the carb.
It may be possible that I have messed up the timing alittle trying to get it to run right
I even messed with the valves alittle and they could be out of wack alittle creating it to back fire more. will a power valve create your motor to run this way also. and one other thing this holley carb is 1997 600 dual feed is it new enough to have a protector for the power valve? I have never delt with power valves before so I really dont know were to even start. I hope this help you all in trying to help me solve this problem
thanks fellas

 

Forgot about the power valve - check that first. Just pull the float bowl and you'll see it screwed into the metering block. It's round with a rubber center and a serrated edge. Make sure you have a rag under the carb to catch all the gas when you remove the float bowl. Obviously, don't do this with a hot engine.