Ironhead S&S Carb Issue or intake?

[bikereff]

First time post. I have a 76 XLCH with the following stuff: S&S "E" shorty, Andrews PB+ exhaust cams, Dyna S single fire electronic ignition with 3 ohm coils and a custom 2 into 1 exhaust that is short. Starts right up, no hesitation on take off, steady climb to speed. You can see the new exhaust on my posted picture of the bike. Oh yea, the exhaust does have baffles installed where the 2 into one is mounted.

Everything fine until I changed from full length drag pipes to the new exhaust. Ran into the dreaded 50mph dead band. My carb is an older S&S so I drilled the main air bleed to .048 and dead band went away. (thanks to the forum's guidance.)

Now problem is a cough (hiccup?) at about 60mph. At a steady 60mph, it will do this randomly and keep doing it until below 55. Right now the carb has a
.0295 intermediate and I've tried from .068 to .072 without clearing that cough. Checked for air leaks on intake without finding any. Overall seems to be running slightly rich, but not bad. Checked some other things like pushrod adjustments (good), wiring (still good), gas flow to carb (sigh, good), and carb adjustments (per S&S instructions, good).

Could this be still a carb issue (butterfly shaft and such) or timing (checked and seems to still be on the money)? I'm really at a loss and looking at other carbs (which is gonna be expensive).

[JBGoode]

Air filter?

[Motorbreath]

Originally Posted by bikereff

a custom 2 into 1 exhaust that is short.

Oh yea, the exhaust does have baffles installed where the 2 into one is mounted.

Everything fine until I changed from full length drag pipes to the new exhaust.

that sounds like a back pressure issue to me

[bikereff]

On the backpressure, too much or not enough? Never have run into the issue before. Any ideas on how to fix?

[bikereff]

The pipes do have 3 inch long baffles installed in each pipe at the 2 into 1 junction.

[bikereff]

Well, I gave up on trying to match the S&S Shorty to the pipes I installed. Got a great deal on eBay for a Mikuni 40mm carb. Installed and WOW what a difference it made. Runs really good just bolted on. Got finished with adjusting the pilot system and now it idles very well and starts on the 1st or 2nd kick every time.

Now I'm just dealing with a small exhaust leak on the front cylinder.

[jharback]

Sounds to me like its your pipes. It's to be expected with short pipes like that. They're made for looks not performance. They're going to have some dead spots and some popping on decel.

[mikethebike61]

Originally Posted by jharback

Sounds to me like its your pipes. It's to be expected with short pipes like that. They're made for looks not performance. They're going to have some dead spots and some popping on decel.

The decel popping is caused by a lean fuel mix. Which is caused by the shorter pipes.

[bikereff]

Haven't had much popping and when it happened it was very light. I adjusted the carb to try to compensate for the increased flow and the plugs show medium brown right now.
The only problem (which is interesting, and looks cool) the the 2-3" blue flames that sometimes come out of the end of the exhaust when going above 50 mph. Pretty sure it is an exhaust leak at the clamp.

[johnnyjellybean]

Originally Posted by mikethebike61

The decel popping is caused by a lean fuel mix. Which is caused by the shorter pipes.

Or an air leak