OK Dean, here is what I remember from that fun chain saw episode. It was quite amazing as you say.

Hallum’s powerful 2-stroke motor successes were notice fairly soon in the latter 1960’s by a rather unique couple of serious woodsmen who were very active loggers in the Pacific Northwest. They were attending regularly scheduled logging competition-festivals in those many Northwest towns whose primary economics was based on felled trees and reducing them to manageable sizes. There was much included in these festivals including the traditional log rolling, axe work, and those quite effective two-(person) long cross cut saws.

I wandered into Losfar’s Boathouse one afternoon and Hallum was still feeling amused by the earlier events. Jim took me outside where a test log about 15 inches in diameter and the professional size Stihl long bar chain saw was sitting. Saw chips were everywhere. The saw owners had earlier left for home in Mt. Vernon. The Stihl was left behind because it required a new starting cord handle that would not fracture and blow apart if the saw motor kicked back when starting because of fixed ignition timing with high compression. This was a very serious problem; a little hard for outboard racers to know even with a few snatched-back starter ropes.

Jim told of two loggers arriving one day from Mt. Vernon, (half way to British Columbia from Seattle), some months earlier and telling him about these chain saw competitions which they regularly entered and how really serious (maybe only bragging rights, yearly total points, and a trophy) the events were. They showed Jim their "Pro Logger" Stihl chain saw which was very nicely loop scavenged but very “over square” (bore/stroke) compared to all of the racing motors Jim normally dealt with.

The loggers asked Jim if he could make their Stihl saw into a “racing chain saw” like his other excellent motors they knew about from reading and local talk. Jim liked the idea of finally having a motor to “hot rod” that was really over-square and an excellent design otherwise. The other important factor was that cutting logs was best done at a stable rpm, not yet exactly known. It was a motor power load where the chain produced the most chips, kept its momentum, but was not necessarily peak rpm. Somewhere above max. torque.

Pipes could be tuned for maximum effect exactly at this power range for max. applied torque at a stable cutting rpm. A few test cuts with the upgraded motor showed the best rpm band.

Jim could only tell me of his modifying work on this Stihl. The raised cyl. porting, reed valves behind multiple pumper carbs, high compression & combustion chamber reconfiguration, and a pipe that was set for best torque at cutting rpm.

The only failure was the starter rope handle which would blow up in those strong logger’s hands if the motor kicked back. First fix was a water ski double-hand-hold handle with the starter rope wound around it. That was good for cutting tests but was not going to be any good flopping around in contests. Jim made something work but I do not know what it was except that it did not use the familiar traditional handle with a center knotted starter cord in a through hole.

After that the real fun began and Jim was really chuckling as he told about the amazing success the loggers told him they were having with their new saw. (A side note I vaguely recall is that they were eventually restricted from competition by rule changes).

The Stihl saw was a very new brand in USA Logging at that time. I think that all former dominant Pro saws were American cross flow designs. Sometimes big heavy beasts because of large motor size for the power required. The Mt. Vernon loggers who brought the Stihl to Jim were already suspicious characters “packin’ thet ‘ferren’ equipment”.

The chain saw cutting competitions were what you might imagine except for one where a standard size long log was cantilevered out at 20 or 30 degrees above horizontal. The logger ran out from the base, whacked off a marked width slab, and ran back to set a time. They also did a standing cut on a large standard diameter horizontal log and another event which was a vertical pole climb, cut, and max. rapid descent to trip the clock. These loggers were very tough, agile characters,... no surprise on that.

The bottom line on this was almost magic viewing for those attending these logging competitions. The Hot Rod Stihl cut all diameter logs in times thought impossible before then. The angled log had the hot-rod-piped Stihl back at the base before the competitors were half way through their cut. The same for the vertical climb topping cut and even shorter for the standard horizontal log. It was an almost impossible situation for the competitors. My guess is that all Pro chain saws out working in the forests were soon lighter, more powerful, and more efficient for the loggers.

As with the 100 mph Anzani, needed change was suddenly obvious. Another ‘Bravo’ for a serious NW logger, Jim Hallum engine mod’s, and the “MukPipeCo.” tuned pipe. A proven practical precision tool regardless of whatever may have been happening internally.

An additional thought. I am pretty sure that there was not a valved twin pipe in the final configuration here but at first an open megaphone may have been part of the tests. I used to know that detail, .. it is a short blip in memory, now gone.

R.R.