PA 50 II jet

Patrick Mattison /

What is the stock jet number for a 1981 Honda Pa 50?

Is there a preferred size?

Re: PA 50 II jet

it's a #78 .. and if the bike is in good tune this carb/jet combo works fine. And the main jet/butterfly carb will accurately flow a lot more mixture than the stock machine will ever demand.

It'll be adequate up to about 40mph, near 7,000 RPM, which should happen if you pump up the engine with an expansion chamber or other performance mods.

Beyond that point you might want to do something to avoid running a bit lean.

Re: PA 50 II jet

There are only two jets available from Honda, the #60 for the PA50I and the #78 for the PA50II.

Most jets for carbs like Mikuni are rated in fuel flow (like cc/min or some such) or bore size. The Honda jet numbers are related to the actual part number.

99101-124-0600 for #60

99101-124-0780 for #78

Certainly the #60 for the PA50I will be smaller than the #78 for the PA50II

Joew, have you ever run a #60 in a PA50II?

Re: PA 50 II jet

i was thinking that since the PA50I was discontinued starting 1980, the '81 bike's gotta have the #78 jet... unless some previous owner mix 'n matched some parts..

nope.. i never tried running a #60.. never needed (and have no desire) to mess with the stock carb at all.

I suspect a #60 may be too small to run a PA50II at it's normal 30mph top speed.. but since the #78 is capable of near 40MPH the swap might be an interesting experiment.

Re: PA 50 II jet

Jason Luther /

i bet they are the same. isnt the main difference (beside minor port differences) between the two, gearing?

Re: PA 50 II jet

not owning a PA50I. im not sure.. silverfoxhas the microfiches, but part numbers could be different for identical parts... but the jets have a ID number stamped on the screwdriver-slot ends..

i get the impression the rear wheel gear boxes have the same 12.4:1 ratio but variator ratios are certainly different.. And the carbs are different afaik, the PA50II having the 11.5mm Keihin where the PA50I has a 10mm. Someday i'll come across a PA50I and make a list.

Re: PA 50 II jet

from what I remember from messing with a I and a II, but not at the same time:

variator side of crankshaft


reed valve is one window on a I and 2 on a II, and there is a bump cast in the engine that makes swapping hard


I think the rear wheels and gearing are the same, but I'm not sure.

Try to find Fred (of Fred's guide)- he's still the expert he's always been, just crabbier.

Re: PA 50 II jet

Patrick Mattison /

thank y'all

Re: PA 50 II jet

For the '78 and '79 models the gerarsets in the rear gearbox are the same for the PA50I and PA50II according to the microfiche.

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