1974 Honda CB350F Bonneville Speed Record Holder – Rebuild Diary

1974 Honda CB350F Bonneville Speed Record Holder - Rebuild Diary
Nobody who contributed to building this bike 41 years ago would have anticipated this unlikely image—a not-particularly-built-for-speed CB350F with an AMA Land Speed National #1 plate.

On the Road Again — A year after setting a speed record the 1974 Honda CB350F lives again!

1974 Honda CB350F Bonneville Speed Record Holder - Rebuild Diary
Nobody who contributed to building this bike 41 years ago would have anticipated this unlikely image—a not-particularly-built-for-speed CB350F with an AMA Land Speed National #1 plate.

I’ll be the first to admit my mechanical skills are marginal at best. Even with the help of the best technical manuals, I can manage to find new and ever more creative ways to make what should be simple repairs monumental failures.

So, that is why every time I’ve had to repair or rebuild anything more complicated than a mouse trap, I do so with some trepidation and foreboding of what ill may befall the project at hand.

Rebuilding my 1974 Honda CB350F from the mandatory tear-down for tech inspection after setting a Production Classic division speed record at Bonneville is one of those projects. (See more about that story here: Bonneville Speed Trials - Diary for a New Record Holder).

In order to verify the displacement of a record-setting bike, the head must be pulled to allow direct measurement of bore and stroke. For air-cooled flat-head four-strokes and two-strokes, it’s a walk in the park. So simple, even I could do it with some degree of confidence I could reverse the process and have a runnable engine when I’m done.

An overhead cam—even a single overhead cam—engine like that of my Honda is another matter. There are parts—lots of parts—in that little four cylinder motor. Plus there is a lot of disassembly that must take place just to start tearing the engine apart. Off with the seat, gas tank, coils, headers and mufflers, carburetors, tach drive, side covers, battery, you name it, it’s gotta come off! All that must be done with an eye looking ahead to the day one must put it all back together.

1974 Honda CB350F Bonneville Speed Record Holder - Rebuild Diary at bonny
AMA technical inspector, Drew Gatewood handled inspection of the bore and stroke of the engine. Disassembly and packing of parts and subassemblies happened with a sense of urgency to allow us to get off the salt before bad weather closed in. Note that the engine is down to the barrels.

Now, to put it in perspective, I have done all this before, back in 2010 when I had initially established the record in the 350cc Production class. Having to leave before the week of competition was over, I did the tear-down, had the bike inspected and then had to leave to head back to Wisconsin.

It turned out that before we got home, my record fell to a much faster and newer Yamaha. Lacking the confidence to do that first reassembly, I took it to a Honda dealer to have them do the reassembly. But when I got the bike back, it missed, had terrible valve rattle and wouldn’t go over 45 mph, no matter what.

The mechanics at the shop said the carbs needed to be cleaned. I knew that wasn’t the case, so I took the thing apart myself and found the tappets had not been set, four of the tappet screws had even fallen out by that time, and the timing chain was set one tooth off on the sprocket. It was a miracle it ran at all, but perhaps even a greater miracle that I got those things sorted on my own. Yet, the job wasn’t done, so I turned the bike over to my friend, Bill Whisenant and the crew at his shop Motorcycle Performance in Madison, Wis. They got the thing straightened out in short order.

In 2011, when the Classic Production Class was created, that opened another opportunity to try again. In 2014, we went back to Bonneville and this time, the record speed of 80.102 mph stood.

So, with that tentative record speed recorded, it was to the impound area for inspection. But this time, the weather was a factor. We didn’t want a repeat of what had happened on a previous Bonneville trip.

When we took my 1984 Honda V30 Magna to Bonneville in 2010, bad weather moved in during the night after the first day’s competition and put enough water on the salt to shut down the competition the next day and we weren’t allowed to go out on the salt to even get the trailer off if we had to leave. As it happened we did have to leave by the next day, so at that event, I only got one timed warm-up run in. The next day, we were finally allowed out on the salt, but we had to clean things up, load up and head home.

Now, in 2014, with standing water already present in the impound area and the pits, I began the tear-down with a sense of urgency because more dark clouds were approaching from the southwest. We had to leave the next day, so we could not afford to have more rain once again keep us from being able to get our trailer off the salt. I would have to get the bike torn down, inspected and loaded on the trailer for the trip off the salt before the storm rolled in. As a result, there would be no attempt to reassemble anything on the salt.

Instead, we wrapped, taped and packed things in assemblies as they came off the bike and stowed them as best we could in the box of the pickup and trailer.

By about 3 p.m. with black clouds looming ever closer, I had the bike ready for inspection and Drew Gatewood of GEARS (Gatewood Engineering and Race Support of Chesterton, Indiana) did the honors.

1974 Honda CB350F Bonneville Speed Record Holder - Rebuild Diary tear down
Once the tappets were set, the carbs reattached and pipes back on, the engine phase was done and completion of the reassembly was only hours away.

As soon as inspection was complete, the bike, now nothing more than a rolling chassis with half an engine, rolled up the ramp, got tied down and off the salt we went. The next morning, I checked the load found everything secure and we headed east toward Wisconsin on I-80. Little did I realize that the trip home would cause the only damage ever suffered by either of the bikes I’ve competed on at Bonneville.

Despite checking the load every morning and evening at our overnight stops on the way east, I never noticed that the carburetors, which I had secured back against the frame away from the engine with loops of wire had gradually worked loose and moved downward just enough for the left end carburetor to come to rest on the wiring harness where it drops down into the engine case.

When I unloaded the bike at home and lifted the carbs, I found that the carb had ground through all the wires! This was particularly distressing news because I tend to have extraordinarily bad outcomes with wiring. The other thing that turned up was a small mystery spring lying on the floor of the trailer. Where it came from, I hadn’t a clue, but it looked like something that had to have been an external component—of something.

Like it or not, reassembly of the bike would not simply begin by reversing the tear-down process; it would have to start with wiring repairs on wires that have very little room to work on to begin with. That became the first step of the rebuild and I managed to get it done in September 2014.

I buffed the piston crowns and head clean of carbon about the same time—all a confidence building exercise as well as part of the rebuild process. By October, I had worked up the gumption to fit the new head gasket and fit the head atop the cylinders. It went pretty well and another major milestone was completed—but winter was closing in and my unheated garage isn’t a great place to work, the rest of the rebuild would have to wait till 2015.

Spring came, and, well, so did riding time. During the summer, I only managed to fit the cam cover and breather cover back into place, which resulted in the rest of the rebuild getting pushed back to August. When I realized August would mark a year since the bike last ran and it was still incomplete, I decided one day to lock myself in the garage and not come out until the Honda was once again a completely assembled motorcycle; hopefully also able to start and run normally.

So, on the morning of the last Saturday in August, exactly one year and two days since that record-setting run in Utah, I went back at it. Much to my amazement, by the end of the day, the job was done.

Setting the tappets was the first order of business, then tappet hole covers went back on, followed by refitting the coils, spinning in new spark plugs, reattaching the carburetors, air box, air filter, then the header pipe/muffler units, passenger foot pegs, fuel tank, seat, battery, fresh oil change and finally after a final once-over, putting the key in the ignition and turning it to the “on” position.

Much to my relief, the neutral and oil pressure lights came on! I turned the key off and kicked the engine over about ten times to pump some oil up into the top end, turned on the fuel, set the choke and turned the key on again for real. I hit the starter button and after a brief hesitation the starter spun the engine and after only about three seconds, the little four fired up and with a few blips of the throttle revved with the same smooth, throaty note it had before.

1974 Honda CB350F Bonneville Speed Record Holder - Rebuilt
The CB350F was built for leisurely day-trips and light touring and that’s what it’s doing now, shown here in the Lower Wisconsin Riverway at Avoca, WI.

At first a couple of the carbs leaked gas, but it had done that before when I first got the bike after it had sat unused for a long time—once the floats and carb internals get moving lubed by the fuel itself, overflow stops and the bike sat, able to run well, but not able to sustain an idle.

When I went to adjust the idle speed, the mystery of that small orphan spring I had found on the floor of the trailer when we got home from Bonneville was solved—that spring was the tensioner for the idle speed adjustment dial—the dial that was now missing from the carburetor bank. As I knelt next to the bike pondering what size screw might work as a replacement, I spotted something that looked out of place down on the back side of the engine. It was the idle speed adjuster! This was my lucky day—I was able to fit the adjuster back in and by the end of that Saturday, I was able to throw a small set of day-trip saddle bags over the Honda and take it for a cruise down the Lower Wisconsin Riverway.

I left much of the equipment and decals required for Bonneville competition in place, but this CB350F is retired from racing. It is now going to be devoted to what its designers had in mind: relaxed touring in the back country and short hops to the pop shop.

My other Bonneville bike, the 1984 Honda VF500C Magna sits in the garage along with the 350. It also still has the required competition equipment still in place, even as I ride it regularly as one of my favorite street bikes.

Who knows, maybe it will make one more run at a record at Bonneville sometime. That liquid-cooled, double overhead cam, V4 500cc engine is a rocket—but it would be a nightmare to reassemble!

1974 Honda CB350F Bonneville Record Holder - Photo Gallery


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.