Straight exhaust, no muffler, cause Lean running?

[schrocketeer]

My new to me '86 K100 RT has a straight pipe, just a few inches past the 4 to 1 collector (see photo). Would just that change, compared to the OEM muffler, cause the bike to run Lean?

What I mean by Lean:
It has great acceleration from 4k-7k RPM.
However at steady throttle (highway at 70mph) it will pop and surge.
Also from cold start it doesn't run smoothly for several moments. Rev up and clutch slip to launch. Fast idle switch doesn't change anything.
Hot start takes a full throttle while holding the Starter button for a few seconds.

Fresh fuel filter, fresh 93 octane Ethanol-free fuel, checked and cleaned Throttle Position Sensor and Coolant Temp Sensor.
56k miles.

[The Mighty Gryphon]

A certain amount of back pressure is necessary for proper combustion and intake/exhaust flow. 

The factory has an army of engineers with computers, dynos, tests stands, etc along with access to large data bases of performance testing every variable that can affect the power output, torque curves, component reliability, fuel efficiency and emissions.  The final result is a balance of all the above arrived at after literally thousands of hours of research, testing and design. 

That somebody with a hacksaw and maybe a file is going to improve the product of all that effort is beyond ridiculous. 

[schrocketeer]

With the spare parts that came with this bike, there's an OEM muffler. After some unsuccessful effort to knock off this straight pipe collector (installed by a P.O.), I'm pondering dropping the whole exhaust system so I can knock the aftermarket collector off, and reinstall the OEM. I don't want to put too much stress on the exhaust manifold studs.

Either that or find a muffler that will bolt on to the 2" Outside Diameter angled pipe. There's a Remus TYP 125 on eBay, that says it came off a K100 RS / RS for $80.

[sooprvylyn]

Your alternate, if you still have the aftermarket muffler, is to install a baffle/spark arrestor in it to help add a little backpressure.

[Kaos]

Your alternate, if you still have the aftermarket muffler, is to install a baffle/spark arrestor in it to help add a little backpressure.

Soopr's right. A baffle will help a load.
In my other k Ive used a db killer and that impacts the startup of the bike.