change in performance after adding header to 1500

[fuscavw]

I just added a 1 3/8 header/single muffler to a bone stock 1500 sp in my 67, now it's acceleration is rather flat in the top end, whereas before it had a little more in it at higher rpms. This engine remains bone stock, except for now the addition of the header. Any recommendations...carb adjustment maybe? Thanks!

[Miguel Arroyo]

If the engine can breathe better thru the use of a header and/or an intake you should allow more fuel to take advantage of the added air being moved into/out of the combustion chamber. In other words it may be runing lean, which can cause overheating.

[BirdLives]

I'm surprised to hear that it was your top-end that suffered, I would think it would hurt the low-end more.

Since you have a more efficient exhaust now, you need to get more fuel/air through the intake. You could get heads with bigger intake valves ($$$) or maybe try mixed ratio rockers like 1.25 or 1.4:1 on the intakes and keep the exhaust the same (less $).

The easiest thing to try would be to up the main jet as Miguel suggests.
If you're running the stock PICT carb, it's pretty easy (and cheap) to do. There are some good threads on here about rejetting.

[fuscavw]

Thanks for the comments, guys!