# Question for Lars ...



## BobG (Dec 20, 2006)

I have a 70 Goat, 400, Holley 650, aftermarket air cleaner, 3 speed auto ... 

I have a problem when the goat kicks down ... as it winds up, it seems to backfire at around 4800 - 4900 rpm. This only happens when I kick it down to second and accelerate- like getting on the highway or passing. I haven't noticed it from a dead stop, and it hasn't happened when the motor reaches 5K on a 1-2 shift, even under HARD acceleration. 

What I'd like to know is ... is this a timing issue (points not set right / timing advance not right) ... a tuning issue (carb set too rich/lean) ... or something serious (cam worn or other problem). 

I know that GM had a problem with some soft camshafts with the '70 model year, but I thought that was limited to the buick and olds 350's ...

any help would be greatly appreciated.


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## lars (Sep 28, 2004)

You're leaning out. Check your carb setup (float levels), bump jet size up 2 sizes, and verify that your fuel pressure is staying above 3 psi under the backfire condition. You can "T" a fuel pressure rubber hose into your fuel line and tape the pressure gauge to the outside of your windshield during a test drive. It's very common for GTOs to suffer fuel starvation at the top end of 2nd gear (high fuel flow requirement).

Of course, before you play with the carb, make sure your total timing is set at 36 degrees.


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## BobG (Dec 20, 2006)

Thanks very much, I'll check those things


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