High end adjustment on a Hobbit PA50

I'm trying to adjust my honda hobbit to rev higher and generally run faster - by adjusting the carb. However, there seems to only be an air mix adjustment screw and the idle adjustment - no apparent way to make it run smoother (and faster) at full throttle, that I can see.

Any ideas?

Rob K - Atlanta


Re: High end adjustment on a Hobbit PA50

ಠ_ಠ Jon Folks ಠ_ಠ /

Your going to have to raise or lower the main jet size in the carb by purchasing jets from some place like mopedwarehouse.com


Re: High end adjustment on a Hobbit PA50

Your Honda PA50 looks like it is the 20 mph version. You need a 30 mph Ramp plate on the variator (front pulley) to provide more top end speed.

I have a 30 mph ramp plate NOS Honda part for $25 plus shipping.

Re: High end adjustment on a Hobbit PA50

It's not as simple as just changing the plates, you need to do some modifications

Re: High end adjustment on a Hobbit PA50

If it's a Keihin 11.5 mm carb, it may already have a very large main jet.. a #78.

The PA50 II (yellow, 30mph model) has one.

That carb is a nice carb. There's no point in trying to get more speed by adjusting that air screw. It's an idle-mix air screw and has nothing to do with top speed.

To my suprise, while measuring things to bore out the carb, the carb actually has a 12 mm bore, not 11.5. Unfortunately, this bore is also a smooth taper and boring it out (to a possible 14mm) would have side effects that cannot be good for a good signal and for good highspeed air flow, imo.

Work on the exhaust and the variator. These two things will get you more top speed. On my PA50 II a performance exhaust alone gained me about 8 mph. The carb needs no changes.

Re: High end adjustment on a Hobbit PA50

Okay - thanks to all for the insights.

Two follow-up questions: What tools and how much work is involved in the variator switch out?

Second question - what specifically could I do to the exhaust? I guess I could "straight pipe" it, but that would likely be loud as hell? What other exhaust options are there?

Again - I appreciate the info sharing!

Rob K.

Re: High end adjustment on a Hobbit PA50

That front variator is held on only by that large thin nut. Prevent the clutch part from turning with something suitable and unscrew the large nut.. Once you manage to find a PA50 II ramp plate it's a piece of cake.

Anything but the stock muffler will be an improvement. That muffler is nice and heavy and quiet and is also the main restrictive element on these bikes. And yes, it will get really loud if you go in that direction, regardless of if it's a home-made straight pipe or a commercial expansion chamber. Go find some trash pipe from some bike and take out all the baffles and junk inside. Add some half-assed silencer on the end and thats about all you need.

I keep my daily riding bike stock simply because I like it quiet. I don't need to call cops or attract attention. 30 mph is ok for now. The variator helps get the thing up hills. Anyway, the suspension feels a bit squirly near 40 mph.. kinda reminds me of riding a skateboard down a hill.. but to each his own.

Re: High end adjustment on a Hobbit PA50

Yes, 30mph would be 10 more than I'm going now! If I wanted more speed than that - I'm likely on the wrong vehicle.

Anyway - One of the guys in this discussion indicated he had a variator for $25 plus shipping. I think I'll go that route.

If that will get me an x-tra 10 mph - I'll not bother with the exhaust. My yuppie neighbors already give me funny looks for riding mopeds....last thing I need is to have one of them start complaining about the noise too!

Re: High end adjustment on a Hobbit PA50

hey rob.. I was searching and found a few posts regarding differences between the PA50 I and Pa50 II. Since i don't have an 'I' i can't verify any of this.

One thing that will certainly restrict the RPM of your engine is a short exhaust-open timing. This is the period of time, or of chankshaft rotational degrees, that the export port is open.

The PA50 I seems to have a shorter exhaust-open time than the PA50 II. You could check it by removing the sparkplug and muffler, shining a flashlight into the exhaust port and observing through the spark plug hole. Turn the flywheel by hand, make marks on the flywheel and measure the total angle (before and after bottom dead center) that the port is open.

It's worth taking a look, imo, because you're spending money towards performance but may get little or no results in return.

The port on a PA50 II is open for a total of 130 degrees.

The port on a PA50 i is open for 115 degrees.

The fix would involve grinding away something near a millimeter or two at the top edge of the exhaust port so it is open for a longer period. I can't predict for sure that your bike will never see anything near 30 mph due to this porting difference but it may not.

This fix is cost-free, has been applied and tested on the PA50 II and will improve top end power on virtually any 2-stroke, within limits.

If the timing is as i stated, and you feel like getting into it, i can post some hints on how to go about it.

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