Backfire thru carb & lil' tapping...
Thread Starter
Drifting
Joined: Sep 2001
Posts: 1,427
Likes: 1
From: Boxford Mass
Backfire thru carb & lil' tapping...
For the record.. I'm paranoid. All the time.
When I start the car and its warming up, there's an occasional backfire thru the carb. It only happens when the car is warming up. I also hear a slight tap thats there all the time. Sounds like a valve, that familiar "tick" sound.
Remember, I'm paranoid. Could they be related? Here are some facts...
- Rebuilt engine has about 250 miles on it.
- Hyd roller cam in it
- Engine currently as a 670 Holley Street Avenger which is a little small, but that shouldn't have a negatve impact.
Any help appreciated...
Did I mention I'm paranoid? I'm getting ready to drive the car from NJ to Massachusetts in a week or so. I really want to get there...
--Jack
When I start the car and its warming up, there's an occasional backfire thru the carb. It only happens when the car is warming up. I also hear a slight tap thats there all the time. Sounds like a valve, that familiar "tick" sound.
Remember, I'm paranoid. Could they be related? Here are some facts...
- Rebuilt engine has about 250 miles on it.
- Hyd roller cam in it
- Engine currently as a 670 Holley Street Avenger which is a little small, but that shouldn't have a negatve impact.
Any help appreciated...
Did I mention I'm paranoid? I'm getting ready to drive the car from NJ to Massachusetts in a week or so. I really want to get there...
--Jack
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Re: Backfire thru carb & lil' tapping... (Fevre)
If the pistons are forged you could have a little piston slap due to the clearance. Once it warms up it should go away. Mine is a bear to keep running when cold and makes a lot of racket with the solid lifters and forged pistons. If it goes away when warm you should be OK
Thread Starter
Drifting
Joined: Sep 2001
Posts: 1,427
Likes: 1
From: Boxford Mass
Re: Backfire thru carb & lil' tapping... (Gordonm)
Exhaust is tight, no leaks. The engine is all forged, but the cam doesn't have a tremendous amount of lift... like .509 plus 1.6 rockers.
Senior Member since 1492
Joined: Aug 2000
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Re: Backfire thru carb & lil' tapping... (Jack71)
I had that anoying tick-tick sound on 3 GM SB's. Once was a blown header gasket one was a stripped exhaust manifold bolt and the third was simply a loose exhaust manifold.
Safety Car
Joined: Aug 2000
Posts: 3,734
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From: Southeastern PA
Re: Backfire thru carb & lil' tapping... (Jack71)
I had a similar problem and found that I had adjusted the valves too tight. Caused the engine to rock back and forth and it was spitting.
Loosened the valves to zero lash and re-tightened.
Loosened the valves to zero lash and re-tightened.
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Joined: Aug 2000
Posts: 3,711
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From: San Antonio TX
Re: Backfire thru carb & lil' tapping...
I had a problem like that in another engine. Turned out the valve guide was too tight. Eventually, the valve seized in the guide and got acquainted with Mr. Piston. Normally this is a hot engine issue since the valve expands more than the head and closes up the clearance. You wouldn't tend to notice it when cold. When it occurs and how long the tapping lasts would be good to know. It could be something as inert as a lifter bleeding down needing a couple of seconds to pump up.
That you have a backfire through the carb indicates that your mixture may be lean(carb mixture or vacuum leak), that your timing is off, or that you have a valvetrain issue. Me, I'd look for a vacuum leak first but you'd have to provide more detail under what circumstances the backfire occurs. Otherwise we're all just guessing in very broad areas.
That you have a backfire through the carb indicates that your mixture may be lean(carb mixture or vacuum leak), that your timing is off, or that you have a valvetrain issue. Me, I'd look for a vacuum leak first but you'd have to provide more detail under what circumstances the backfire occurs. Otherwise we're all just guessing in very broad areas.
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Joined: Oct 1999
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From: NorCal
Re: Backfire thru carb & lil' tapping... (Jack71)
With the low miles, I'd suspect slightly retarded timing (probably timing chain stretch - they do it within a few miles) on the cold start pop, and slightly loose rocker. Re-adjust it all and then see how it works.
Hans
Hans
