HELP *** Why is motor popping back thru exhaust when cold?

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rockracer
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HELP *** Why is motor popping back thru exhaust when cold?

Post by rockracer »

Here is what we have.

It is a fresh built BBC with roller cam, solid roller lifters gapped at .016.
We are running pop up piston's and 34 degree's timing.

When we start the motor and during warm up, it pop's back thru the exhaust and appears to have a miss. (It ran fine while breaking in the cam).

However, once the engine get's to operating temperature (above 175 degrees), the miss goes away and no more popping, it pulls strong up to 5700 RPM.

The headers are up-draft and brand new, no noticeable leak's.

Can anyone help explain this to me?

Should I be worried?

Thanks for your help.

Doug
ADR
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Post by ADR »

After you broke in that roller cam did you re-gap your valves again :D
Dale
rockracer
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Post by rockracer »

Yes, That was my first thought.
All the gaps where w/in .002 of each other (set @ .016)

Thanks for the input.
PLEASE any more idea's.
shawn
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Post by shawn »

What type of fuel do you run? Are these aluminum heads? Some more info. about the combo may help.
shawn
bill jones
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Post by bill jones »

-it sounds like it needs a choke or a way to richen it up when it is cold, sounds like it is too lean when cold, assuming that the engine doesn't have a variety of other issues.
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