HONDA EXPRESS - Stock jet size?

Hi all,

anyone know the stock main jet size for a 1981 Honda Express?

I'm looking to downsize my jets as I think I'm running rich...


Re: HONDA EXPRESS - Stock jet size?

If a stock bike is in tune it should run fine with the stock main jet.

At less than wide open throttle a carb relys on things other than main jet's size to control the fuel:air mixture ratio.

Carb cleanliness and adjustment might be called for.. Intake air restriction can have the same effects as too much fuel.. a partially closed choke or a dirty air filter.

Re: HONDA EXPRESS - Stock jet size?

Jonas Quimby /

What he said.

Make sure you have a new, clean air filter, that your carb is SPOTLESS inside, and that the needle on the end of the throttle is in the middle position. Especially this last part, as the needle controls mix.

If your bike is bogging down at high speeds, I'd suggest cleaning the muffler.

If it's bogging down when you give it any gas once it warms up, your idle mix is too rich.

Re: HONDA EXPRESS - Stock jet size?

Hi guys,

I had a feeling I would see you Jax,

Well I cleaned the carp so clean I would eat my soup from it, and the adjustments are good off the start. The problem is the bogging at high RPMs. I have a new air filter, clean as a whistle.

I cleaned the muffler with the draino technique, and it worked. I was able to see a distinctive difference when putting it back on, however, the bogging remained when at high RPMS.

Thats left me to believe, that either it's the main jet (or needle set) or as joew said, somethign to do with my auto choke.

I figured for the investment of a few bucks I could rule out the jets before buying a new choke box.

Do you guys know where I coudl find smaller then stock jets? I tried my local honda dealer , and he can only get stock size...

Re: HONDA EXPRESS - Stock jet size?

PS, Another pointer is that I just went out for lunch and forgot to open my fuel vent, and was putting along wondering why it was running so well... top speed 40 kmh (25 mph)

so when it's starved for fuel it works better...

again, either theres a restriction of air at high rpms, OR jets are too big...

Can I test the Autochoke by removing the hoses from the carb, effectivly giving it no choke? or would this give it too much air?

Re: HONDA EXPRESS - Stock jet size?

this is curious.. has the bike's engine been modified in some way or is it still stock? Did the problem occur along with a severe change in the weather?.. or with something else that might effect carburation, like moving a great distance into a different climate?

Did the bike every run correctly to your knowledge?

_Can I test the Autochoke by removing the hoses from the carb, effectivly giving it no choke? or would this give it too much air_

i'd encourage you to try disconnecting the auto-choke for testing purposes.. if disconnection makes a difference, it's malfunctioning you probably found the problem.

Re: HONDA EXPRESS - Stock jet size?

I was told that it ran well prior o me owning it, but I purchased it non-running. It did pass a goverment saftey nispection to get it "road worthy" by the previous owner..

everything is stock, there has been some climate change, but I've been experiencing this in all climates. (the moped was bought 5 miles from me) to the best of my knowledge it originated in my city in 1981

I think I'll try removing the auto choke on the way home tonight, I suppose I should wait till i warm up the engine... Or I suppose I could just cover the holes on the carb with my hand to get started...

I'll post my findings in the morning...

Re: HONDA EXPRESS - Stock jet size?

Jonas Quimby /

Just a quick note - If you disconnect the choke hose from the carb, be sure to cover the port over so the carb doesnt suck air in. Otherwise your mixture will lean way out and you'll have no idea what fixed the problem.

Ever find out what size jet you currently have?

Also, have you checked the needle position yet?

New jet will be a few bucks and a trip to the store, but the needle can be moved in 5 minutes.

Re: HONDA EXPRESS - Stock jet size?

Are you sure I would want to cover them? I would think that the auto choke funcionting properly would restrick air flow only at a cold start, once the engine is warmed up, it should open completly allowing filtered air in, unrestricted...

I can't read the size on the jet, any tips?

needle is in it's original middle seat, I've played with this before , and after taking your advice, I returned it to the middle. It should only effect middle range RPMS anyways right?

Re: HONDA EXPRESS - Stock jet size?

Jonas Quimby /

The auto choke does two things.

When cold it delivers raw gas into the engine. As it starts to work up it puts in a mix of air and gas. Once it heats fully it closes.

Hence you want to cap off the connector.

As for the jet, got a magnifying glass?

The needle position effects the mix at all speeds to a degree or another.

Re: HONDA EXPRESS - Stock jet size?

magnifying glass, I like that! :)

After heating up, I stuck a piece of duct tape over the hole, noticed a little difference, but I stalled at stop signs?

Another clue for the autochoke...

About a month ago I adjusted my carb after heating up properly. But I found that from a cold start I wasn't getting enough fuel and it wouldn't start, or would lean out and stall. I had to richen the mixture at idle, causing my to bog and have poor acceleration from a stop (when I'm fully heated up)

Jax from what you have said, if my choke was working properly, when I adjust the carb heated, it should't cause problems fromt he cold start..

tonight I will pull the jet and take a peek...

Re: HONDA EXPRESS - Stock jet size?

Jonas Quimby /

I imagine that if you really did have the wrong jet that you would run into problems a bit like what you describe.

It's rather annoying that in 1981 Honda stuck on a better carb that requires less farting around with only to strap a failure prone auto choke box to it.

To top it off it's just differant enough that it wouldnt be very easy to rig up a manual choke again.

You might have luck with spraying a cleaner into the choke's fittings though.

Re: HONDA EXPRESS - Stock jet size?

2-stroke engine will run rich after overheated or worn piston skirt. Crank case vacuum increase due to leaky down-stroke to cause rich mixture. You’re right to reduce air/fuel better but noisy piston slap and possible broken rings.

What cause overheat.....usually remove expansion chamber while running (driving) to run lean intake to overheat piston skirt....and score cylinder wall. Or poor lube flow to oil engine’s piston as well bearings.

Very common problem after experiment with expansion chamber modification or remove.

To adjust main jet is to move needle lower (lean) or higher (rich) setting in relationship to throttle valve opening. Look for small ring-groove on needle. If more then one grooves…use the one closer to end to lower needle into jet’s hole (reduce fuel flow).

I believe you are going to need new piston/rings and re-bore cylinder and gasket set.

Caution to all 2-stroke/expansion/chamber (look-light muffler) owner…NEVER drive without expansion/chamber! Or you will run rich and noisy piston slap equal overhaul.


Sojourn for Christ, Jerry

Re: HONDA EXPRESS - Stock jet size?

Hi guy's

okay, I took apart and cleaned my carb AGAIN...

I seem to have the stock jet #75, I did notice come junk in my idle jets, cleaned it all well.

put it back together, first little while it stalled at stops, and had a very hard time starting. I filled up the gas, and that seemed to stop (probably dirty fuel line?) BUT the bogging started again....

did you read jerry's response about piston rings etc?

Re: HONDA EXPRESS - Stock jet size?

you've already cleaned the carb a couple times and yet keep finding dirt.. makes ya wonder if something is supplying fresh dirt..

Is the fuel system upstream of the carb clean? screens /filters in place and functioning?

btw.. use new spark plugs.. no kidding.. i just had some serious idle and 4-stroking problems and a new plug cured everything in the time it took to switch plugs.


As far as what jerry says, it's kinda hard to understand.. and leads into topics that i see as having no relationship to your troubles.. and he also seems to contradict himself..

_What cause overheat…..usually remove expansion chamber while running (driving) to run lean intake to overheat piston skirt_

and yet:

_NEVER drive without expansion/chamber! Or you will run rich_

Re: HONDA EXPRESS - Stock jet size?

i know this topic is 5 yrs old, but i just had to comment(especially since there was never a definite resolution posted). first, let me try to understand completely... so your ped runs fine until high speed and then it bogs down at a certain speed? youre unable to go any faster after that?

i had this problem with my 80 NA50. turns out stock air filters are restrictive. i removed mine and just ordered a K&N replacement. ive yet to try it, but am predicting it will solve all my problems considering it runs great without any air filter. the part # is 62-1511 in case youd like to look into a replacement. it does require removing the stock air box though, but the filter i just mentioned comes with a spiffy chrome guard that covers half the filter that should protect you from rain. hope this helps.

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