Hobbit Jets??

I am confused (what's new?) about the jet sizes in the Hobbits. My parts fiche says that the '78 PA50I uses a #80 and that the '78 PA50II uses a #78. This is backwards to my thinking. Ususally jets are rated in something like ml/min flow rate. This would mean that the slower I model has larger jets than the faster II model.

Can anyone confirm this?

Re: Hobbit Jets??

The jet may also be rated on a wire gauge style size- lower number is bigger?

Re: Hobbit Jets??

Hmmm. That's possible but I would not think that the Janese would stoop so low as to use wire size gauge as a means to size the jets.

Re: Hobbit Jets??

does your fiche also show the compression ratio? According to Joew the compression ratio is also higher on the I, if I remember correctly.

Re: Hobbit Jets??

true .. stock compression ratio is higher on the slower bike. High compression improves low-end torque and since the bike (in stock trim) is never gonna reach high speed there's no danger of high compression ratio causing cylinder-head heat problems.

Butterfly carbs are a lot different than slide carbs. There is no slide to adjust venturi size and no jet needle to meter part-throttle fuel delivery. The butterfly carb's part-throttle metering completely depends on the (what would be the "needle") jet size in the center of the venturi and on the air bleed circuit and emuslification tube under it.

One good thing about the butterfly carb is that it can, size for size and all other things being equal, pass a lot more air and fuel than can a slide carb.

A slide carb has a slide that travels up and down in a wide groove cut into the walls of the throat. The sides of the groove often have sharp corners which causes turbulence. The slide itself obstructs air flow. So, air flow past and under the slide causes lots of air resistance.

But a butterfly carb has a smooth, unobstructed throat from one end to the other and flows much better. (This superior flow along with the huge #78 jet is probably the reason that, in my experience, adding a performance exhaust and gaining over a thousand RPM didn't require a change in main jets.)

My guess as to why the slower bike would have a larger mainjet is that it's carb is tuned strictly for lower speeds. A richer mixture is needed at lower speeds since air flow is slower and fuel atomization is poor. Larger drops of fuel don't burn. If fuel doesn't burn it may as well not even be there. And when fuel "isn't there" the mixture that does burn is burning lean. A larger mainjet probably helps correct this condition.

Re: Hobbit Jets??

Check your diagram again, I'm pretty sure a pa50I uses something like a 60, the 78 sounds right but I replaced my stock jet with a 78 because I was running too lean, now it's too rich. Basically as I put it Honda provides you with two jet options: Too lean, or Too rich. Check 50cc.nl they have a malossi carb available for the Camino (pa50II) I've been thinking about ordering one.

Re: Hobbit Jets??

I got out my microfiche and my mega magnifyier to check the jet# out. The page # on the mf is 1B5. The jet # for the PA50I is not clear and it is possible that it is a #60 in stead of #80. To confirm this I checked in the front of the mf and on page A5 (specifications page) it also shows that the jet # for the I is #60 and #78 for the II. My error. This would make more sense. The shop manual shows that he compression ratio is the same at 6.5:1 for both models for years 78-79-80. It is interesting to note that for the '81 PA50II (no I model that year) the compression raio was shown at 6.5:1

Thanks for the info guys.

Re: Hobbit Jets??

Damn.. i was thinkin and hoping that a #80 jet was available and could be stolen off a PA50I. .. oh well.

As far as the differences between the two bikes, information i've been able to track down is all over the place.

Like the '83 manual specs pages states that there are two models.

Compression ratio:

6.7:1 (40-45km/h)

7.0:1 (NL-25km/h) NL is the Netherlands?

So, evidently, a slower bike did have a higher compression ratio, which makes sense.

But popular wisdom says that by '83 they had long ago dropped the slower PA50I model..

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