I recently changed the exhaust on my '72 FLH from the stock headpipe/dual mufflers to 1 3/4", 36" long slash cut drag pipes. I tuned the S&S Super E myself and got close, and my dad's mechanic friend (who has owned a shovelhead for years) got it just right, at least up to 60mph (ended up with a .295 intermediate and .72 main jet). Low end I haven't noticed much of a power loss, mid range has a bit of a flat spot (which I expected), but I've lost quite a bit of top end power, which I have never heard of with open pipes. With the stock exhaust I could run it at 75-80mph all day. Now I can't even get it to do over 70mph. I tried a fatter main jet, and it seemed to make it even worse... should a .72 main jet be too rich for a nearly-stock shovel with drags? I will be checking for an intake leak later today. Could improper ignition timing be a possibility? It has a Daytona TwinTec electronic ignition I installed last year and it ran great... any ideas? Thank you! -Danny (sorry, I didn't intend to write a book).

 

The s&s manual calls for .066-.072 for a 74" stocker. Since it was worse with a bigger jet I'd try a smaller one.

 

I'll try it. But it still confuses me since it didn't have this problem with the mufflers, even with the same jets.

 

Jetting needs can be different because you changed air flow through the engine. If it's pulling air harder on the intake sometimes it's pulling more fuel too. You just have to test and adjust. You might want to search for the lollipop mod on the pipes. I used to just use a stack of nuts instead of a washer.

 

I had a flat spot in my acceleration on my ironhead (with drags). I cured it by putting high temp silocone sealant around the exhaust right at the cylinders and letting it cure for a couple of days before I started it. It accelerated so well after that it darn near ripped my arms out when I hit the gas.


carl