The Hobbit Tillotson

The traditional view in the vintage moped scene is that pumper carbs are an intriguing novelty, but whatever advantages they offer are outshined by the performance of conventional float / venturi carbs. AND YET - they are the standard carburetor of basically every snowmobile, jetski, gokart & ultralight aircraft from the 70's & 80's. With that kind of pedigree its understandable why many have tried, even if only a few shall succeed. (RIP myself)

For the Puddle Cutters Anniversary raffle bike, I wanted a larger carburetor. The dimensions of the Hobbit subframe meant either using a manifold that placed the carb outside the subframe, or embrace the hellish tedium of removing the subframe & carb for every carburetor adjustment. I prefer the look of the enclosed carb & was concerned that an external carb might interfere with pedal operation, especially if its next owner was a noob. These factors encouraged me to take another chance on a pumper carb. A bet that cost me exactly $19. The device was a clone of a Tillotson Hl-324A carb. Approximately 20mm bore, if it worked this could've been the cheap and possibly easy solution to many a Hobbit owners woe. ALAS! My 11th hour panic to locate an airleak had me eject the tillotson, So I'll never really know what might've been.

If you have no idea what Im on about, a Tillotson / pumper carb does not use physical jets to regulate stoichiometry: "jetting". In a traditional PHBG, SHA or Bing type carb, you swap out jets and needles and slides until you arrive at the preferred combination of parts. And off you go. A pumper uses the collapsing atmospheric pressure from the engine cranking over to pull a spring-loaded diaphragm that squirts / pumps fuel into the venturi. A pumper has no jets, but two screws to control the amount of fuel getting pumped. One screw for low speed, one for high. The procedure for balancing the two is pretty straight forward. If the crankcase pressure is too little or great, the spring can be swapped or modified. Easy Peasey, right?

Sorta not really. On the plus side, the HL-324 drops RIGHT IN. The studs on the stock manifold are within a millimeter of the mount. You'd need to drill holes to access the adjustment screws, but the location of these holes doesn't interfere with the case, wiring, variator, etc.. The overhead clearance between carb & frame isn't enough to prevent damage, so the carb must be flipped diaphragm side down. This is where it gets kinda tricky, because it requires a custom bracket to reorient the angle the throttle & choke cable. The choke is also complicated by needing to be held open through a spring. (wack)

Meanwhile... The Manifold and reed also need some prep. First, the stock manifold was bored out to fit the larger venturi diameter. I used a stepper bit, followed by a forstner bit to open the manifold. The stock reeds were upgraded to a boyensen set. I was unclear as to how the reed valve might interfere with the pulse line the carb needs so I located a usable spot on the reed valve and drilled out the reeds with an acrylic bit. I then drilled a hole in the manifold isolated from the carb venturi. The hole then aligns with a channel on the spacer plate between the manifold & carb. Finally the channel aligns with another hole facing the pulse hole.

To reiterate, I pulled this carb off the bike literally hours before a raffle in my desperation to resolve an airleak. That airleak was ultimately due to a bad seal, so it's a reasonable assumption this set up would've worked as expected. Unfortunately, I'll likely never know. I posted all this in the event that another hobbit builder wants to give it a shot. If that's you, Godspeed & happy hunting!

Puddle Cutters 17th Anniversary Raffle Hobbit

Stacks on Stack on Stacks -was the battlecry. Almost a year ago, The Puddle Cutters were planning the next rally and trying to develop an operational budget. With some, but not much in the bank we were scoping the rally to fit our budget. (weak) I said that I could double the gang's budget if they backed me up on building a raffle bike. And that they did, Gang gang. The plan was to raffle off a bike during our anniversary ride (mid-march) and use the funds we made to pump up said jamz. Barney very generously donated a non-running roller PA50II Hobbit to the cause. The bike was a ridden-hard & put away wet ex-Uphill Battle bike. It obviously was the source of much joy & gaiety for its previous owner. I do love bikes with personality & it truly wouldn't have taken much to bring it back to operational status. But y'know what sells raffle tickets? Sex Appeal. So I said f**k it & my maximalist tendencies took over. Full frame up rebuild, here we go.

So for starters, here's what we had... The hobbit was missing most of its plastics, had no spark, likely engine rebuild candidate, the gas tank had holes in it and it had been crashed enough to prevent the pedals from working. #mopeds On the plus side- the rims, tires, forks, frame & subframe were in good shape and it had a complete wiring harness and most major parts, including a circuit pipe.

So I took the bike apart as far as I needed to validate every system & redo the paint. I washed the hell out of everything, before stripping the paint down to the metal. I made a few choices: I really like bikes that look complete & making everything work correctly was a key goal. The engine would get rebuilt with every upgrade that still allowed for a mostly-stock appearance. I went for the Metrakit, a stuffy crank, JBot/Treats variator, stock ignition, boyensen reeds & a 20mm Tillotson carb (for extra razzle dazzle).

Every Hobbit in the world is yellow, or red if you're unlucky. I wanted a color that that would make the raffle hobbit unique, but felt appropriate to 1978. I settled on Oldsmobile Bronze engine enamel. -bc 1. Gas resistant & 2. Sparkles. After welding up the gas tank I primered and sprayed everything. At this point, Travis, Kyle & Kristin from the club had all donated body panels & a rare AF OEM pedal crank to the cause.

If you've worked with the metrakit, that exhaust port is no joke. Even though the studs were a match, it seemed silly to restrict the new engine to the dimensions of the stock header. So I cobbled together a new header from pieces I had laying around. Getting everything to fit correctly in the closer quarters of a circuit pipe was a real challenge. But hey, at least it looked nice when it was done.

At this point in the process, I had blown up our planned timeline and missed the Anniversary ride deadline. Kyle / everyone was super cool about it. We had another opportunity a few weeks later at The One Moto Show's kick-off night. At this point I was assembling the bike, including the persnickety wiring. I really wanted everything to work, including the stock ignition switch. I was able to rebuild the old switch using a new lock column off treats.

At this point I had everything to finish the build of the bike & the One Show deadline was approaching quickly. I assembled the bike enough for photos, but the engine had a persistent air leak that wouldn't allow the bike to run for more than a few seconds. We were already selling raffle tickets and I was indeed panicking. As it was the only unorthodox component, I swapped the 20mm Tillotson back for the stock carburetor (which had been bored to 13mm). The air leak persisted even then. I was sweating bullets as the raffle was within 36hrs. I pulled the motor to look for broken gaskets, etc. The flywheel side seal was brand new from the rebuild kit, but did not feel snug. I replaced it with another seal I had laying around. After reinstalling the engine, by the power of Greyskull, the hobbit started and ran. (deep breaths) The jetting was all over the place, but had enough power to get me to the One Show event. The raffle Hobbit was the Belle of the Ball that night and we sold out of tickets (limited to 250). The Puddle Cutters did the raffle live on Instagram and a lucky fella from Washington state won:)

I got lucky again in that the winner of the Hobbit was not physically present at the event. This gave me precious *precious* time to correct the jetting. After a few rounds I had the Hobbit ripping hard and lifting the front wheel. 'Launching' is a good word for it, I see why so many guys dig these built hobbits. I put a huge amount of elbow grease into the project, but it takes a village or whatever. So many people contributed to donate parts, or worked to coordinate the raffle itself, or promoted online. In the end, the raffle bike was a tremendous success, doubling our raffle budget and allowing our small club to go hard on the rally. My heartfelt thanks to everyone who contributed to the project & everyone who bought tickets! Before:

After: