Thread: New topend rebuild but can't get rid of the backfire

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Mike----you have something basic going on and are dancing around the problem-----------You just worked on the engine rebuilding the top end--------you have a poor valve job, incorrectly set lifters, vacume leak somewhere(intake ports, vaccume hoses, carb base gasket, crossed plug wires------

A new distributor is the last thing you need------

Put new wires, cap,rotor and insure that they are proper order---It is very common for a couple wires getting put on in the wrong place at the cap--if you have 7/2 mixed up 7 will fire 2 90* early-------

And another question----why did you do the rebuild????????????what was the previous symphomes??????????

The truck is a show truck / nice day cruiser. Its my brothers truck and everytime we would go to shows he lacked that muscle car sound. Knowing that sound isnt just from throwing in a lopy cam and be done with it, he went ahead a purchased a complete topend kit , including mild cam, complete heads , intake, roller rockers, flat hyd lifters, pushrods , double row timing chain etc... its a learning project for both of us but we also bought books and did research on the rebuild along with talking to many on this site. Knowing everyone here has alot of experience when working with cars i know i've come to the right place. Im going to be readjusting those valves today following the link on page one.

When, in your original post, you said you tightened the rocker arm until you "felt a slight drag on the pushrod" did you mean that you were ROTATING the push rod to feel the drag OR were you checking the push rod play by the up/down clearance?

I was rotating the pushrod

new flat tappet cam!!!!!!!!!!!!!!! you maybe have a flat lobe or two--is there any noticeable clicking when running?????????

did you prime (fill) the lifters

The engine sounds smooth with no clicking noises of such. I did not prime the lifters , i lubed them for the initial break in along with priming the engine with that special tool

Did you have oil coming out all lifters while priming?? I rotate the engine by hand when priming to get oil into all lifters but I prime them before install.

Yes we double checked every lifter and all had oil

Originally Posted by jerry clayton

new flat tappet cam!!!!!!!!!!!!!!! you maybe have a flat lobe or two--is there any noticeable clicking when running?????????

Wait a minute! Somewhere I had it in my head that you had a roller lifters, not just roller rockers. What steps did you take on initial startup with the new parts to break in your cam? Did you use a high zinc oil or high zinc additive to prevent galling? What was your break in process? How many miles on the new cam at this point, and did you have the backfire problem on initial startup with the new parts?

Mike---------how come your profile doesn't have your birthday or any other info??????????

We did add the zinc additive into the oil prior to intial startup. We put a little fuel in the carb for immediate startup. Once started quickly brought up to around 2300 rpm for 25 minutes. After that we shut it down changed the oil once again and added the zinc again. We did the total timing and took it down the road. At that point the edelbrock was too lean. Changed the metering rods and moved the linkage on the accel pump and it was running great. He took it out on a couple rides probaly 150-200 miles in all. Then as we felt comfortable we began giving it wot. Thats when we discovered the backfiring

Originally Posted by jerry clayton

Mike---------how come your profile doesn't have your birthday or any other info??????????

It should, i remember filling it out. What would u like to know ???????

Well, I'd like to know if your old enough to remember when Bob Hoover flew at the Reading Airshow---------

No, just kidding, but these days a persons age will put into perspective what range of vehicle technology(or lack of tech) he is familiar with----carbs, contact type points distributors, oil filters,air cleaners, alternators or generators

What brand, wt, and type of oil did you use and how much of what zinc additive did you add?????

Originally Posted by jerry clayton

Well, I'd like to know if your old enough to remember when Bob Hoover flew at the Reading Airshow---------

No, just kidding, but these days a persons age will put into perspective what range of vehicle technology(or lack of tech) he is familiar with----carbs, contact type points distributors, oil filters,air cleaners, alternators or generators

What brand, wt, and type of oil did you use and how much of what zinc additive did you add?????

post #3 i said lifter going away ..........it better be no detergent oil when you add the wizz bang zinc cam and salad dressing oil . still remember my dad holding up a iron 392 block girdle under the T and asked me for the bolts that i could not find... so i ran and hid in my room till he cooled off that was 40 years ago