The Honda Aero 125 Thread

A bike we sold at the scooter store I turned wrenches at. The particular one I had a chance to ride, was kitted with a variator upgrade, bored and porting, and a tuned exhaust. Was a head snapper from standstill.

I don't think your fix will be an immediate problem, but safe to have the gasket bits, just in case. And you know how to work on carburetors, so it's an easy fix. One thing, if you find yourself disassembling Japanese carburetors with regularity, is to get a JIS, ( Japanese Industrial Standards..) set of screwdrivers, at least the #2 and #3's, as you've probably found that normal Phillips screwdrivers don't seem to work great on float bowl capscrews.

Yes I own one of his SuperCubs.. last year of the CA102 model the 1968. The blue ones are the fastest..

I replace all my Japanese carb screws with Allen screws. Most motorcycle CV carbs have 8 of them, 4 that hold the top cover on, 4 for the float bowl, and on many carbs, 2-3 more on the coasting enrichener cover. I have a couple of high quality JIS screwdrivers, and about a 100 of them that came in various Japanese bike tool kits.

The Rattler 110 was, I believe, the last 2 stroke vehicle over 50cc sold in the U.S. Made by PGO, sold by Genuine.

Wow, thanks for all the information; your Cub looks really great! Did you find that in Oregon? Is it hard to find parts for that or do you have to modify?

That beautiful Oregon countryside reminds me of growing up in Brookings, OR, up the Chetco River. Those country roads make for great trail riding without worrying about traffic except for the lumber trucks, raccoons and deer.

By bf replaced his screws on his 82 CX500 but I didn't have any trouble tearing apart my carb using an off-the-shelf screwdriver assortment package from a local Orchard Supply. Maybe I just got lucky, but getting nice tools is an ongoing process, for sure.

My real concern is my float bowl height. The problem the PO was experiencing with my 84 Aero was stalling out at idle. It couldn't even hold much of an idle before I cleaned the carb, but it seems to still have a bit of a stalling issue. I'm thinking that my float bowl height may need tweaking but I was reluctant to do so, it being somewhat brittle plastic without a replacement handy.

Maybe this is a good time to whip out my hair dryer?

At least with my new tire on the rear I can take her around the block at speed and see how it handles; that's what I'll be doing today.

Here I am riding down the street with a very serious expression , listening to the idle and wearing my concern on my sleeve. This girl wants to go! (The scooter, I mean). She's like a race horse out of the gate. She can go 0 to 60 in a second, but at a stop light every third stop she dies. I'm still investigating the cause. Hence the intense expression.



All you inmates please feel free to pipe in. For all you late-comers, I've cleaned the carbs and set the idle, but the float might need some adjusting which I didn't want to do to 40 year old plastic so I pretty much left it alone. Could this be the cause of the intermittent dying out at stop signs? Inquiring minds want to know.

So instead I focused on what I could do, which was lubricate my throttle assembly and cable, which was feeling tight and unresponsive. First step was to unscrew the three screws holding the lower dash panel.



Next, I put some gun oil on the throttle tube and let some drip down the cable where I hope it will do some good. Feels better already.



This is the other end where the throttle cable connects to the carb. This is the slide and the jet needle. I also added oil to the cable from this end which I'm hoping will work its was back toward the front. I also unscrewed it from the top of the carb in order to gain some slack at the handle grip. Sorry for the lousy focus.



This shot shows the throttle cable released from the grip. It hadn't been lubed in quite a while as far as I could tell.



Once I got everything back together, my bf suggested adjusting the cable tension. Here he's using two wrenches to take some slack out of my well-stretched cable (no nasty comments, please).



Any suggestions welcomed on how to keep her idling once she gets going. In the meantime, here's an image of unbridled youth.

I like to set the idle just a bit below clutch engagement, after the engine is fully warm and the bystarter has done its thing. If there is still an idle issue, and you can't adjust it out with the pilot jet screw, the next question would be the vacuum lines. I don't remember if you replaced them, but you should. If it's idling low, or the vacuum lines are even a little leaky, there might not be enough vacuum to open the fuel petcock reliably, assuming the scoot has a vacuum petcock like the ch150 and 250 have.

I just rode home through afternoon East Bay traffic, lane splitting the entire trip. Must have passed hundreds of cars, worth millions, on my 85 ch250, laughing all the way. Those people are crazy!

That is a REAL simple carburetor. But it can be a real pain to hold all those parts you have in you hand (cable, spring, needle, and slide) together while trying to screw the top on the carb. Everything will try to slip out through that keyhole slot on top of the slide. I've had a lot of moped carbs just like that, mostly Bing and Dellorto.

I would not mess with the float adjustment. If the float does not have a little metal tang on it where the needle goes, it is not adjustable. If it does, you don't have to bend it back and forth too many times before it will break off, and the float is ruined. One good thing, if you do break the float, a new one is still available, for $31.59 + shipping. Float level is almost never off unless somebody has messed with it. Adjusting the float level is not typically a part of cleaning/tuning a carburetor.

You know I wouldn't be replacing the carb screws with allen heads, for one, some of the smaller Honda screw threads aren't the same decimal mm pitch as hardware store bolts, and not every Bolts-R-Us has these screws. Best to use a tool made to take apart Japanese screws, which is what the JIS Screwdriver does. I've been really amazed at it's ability to remove even really corroded in small screws on old carburetors.

You're an Oregon girl, cool! Yeah, earlier this year I rode the Cub from CB/NB to the Ludlum House up the Winchuck for the annual ADV camp over in early April. I took an alternate route back home and did Rogue River/FS33 from Gold Beach to Powers-Coquille and got got nearly 100 mpg doing so. I also got to see an mama bear and her cub, at a little too close for comfort distance, while near the top of FS33's pass.

The Cub was from a friend in Washington, it's in pretty good shape but the engine in it presently is a 125 cc pitbike engine, and it's a bit Faster now. That day I was up the twisty Smith River road NE of Reedsport, OR.

Hey, you all. Glad the Brain Trust showed up on time. Time to lower the Cone of Silence and put our heads together.

Wentwest ~ Based on what you say my idle is set bit too high, because my rear wheel is rotating while on the stand. Of course, this is before it's warmed up, when it won't hold an idle, so I'm now leaning toward a funk-a-doo bystarter, which, I imagine, would account for making things over-rich as the engine heats up thus choking out the engine. Sound convincing?

My bf remembers faulty vacuum lines being a culprit back in his CX500 days but this usually showed itself as bogging down at high speed, not at idle. Blipping the throttle will keep her going, which makes me think that the vacuum isn't the issue but it's a great point and a cheap enough fix so it's off to the auto parts store I go. One less thing to worry about, anyway.

Anyone who commutes through East Bay traffic on two wheels deserves either a medal for bravery or a padded cell. Not sure which in your case.Love those big CH250's, though. Too much scoot for little old me, but a beautiful sight to behold. How about posting us a pic?

JerryH ~ Yeah, they are simple carbs, but the little things can still be vexing. There is no little metal tab on my float, but I guess I'm happy that I won't have to mess with it. I haven't checked but are they still available from Honda or are you quoting another source? Some friend of mine who is conversant in scooter said that sometimes the little rubber tip of the float needle can develop a ridge which can cause it to hang up in the jet, but mine looked OK. What do you think of the bystarter being the problem? I've seen new replacements available on the Ebay but for the Elite I believe it was — looks similar but maybe not similar enough. Seriously, I'd love to just have a manual choke in there and a knob on the dash. Has anyone done this mod that you know of?

YamaGeek ~ That sounds like a really great ride. Did you post it over in RR by any chance; I'd love see the view — and the bears! :eek1 I used to summer on my grandfather's ranch with my sisters growing up. There were bears
galore, and horses and cattle. It was a fun life with some mysterious happenings as well. Oregon's great.

What's your opinion on my bystarter being fritzy? That would make it bog as it heats up, no? I also haven't cleaned out the gas tank or the whatchamacallit where the gas comes out. The PO said that if the tank is less than half full, then the idling issue becomes a problem. This is like being a doctor trying to make sense of the patient's complaints. Only problem is, I've never been to med school.

Yes get 'em. I have stripped soooo many float bowl screws it is embarrassing. The two brands that I know of are Hozan and Vessel. Not many know about JIS screw drivers and not even Snap On makes them from what I can find.

This is the ones I got:
http://www.amazon.com/Hozan-JIS-5-J...id=1385568690&sr=8-2&keywords=jis+screwdriver
http://www.amazon.com/Hozan-D-69-St...id=1385568815&sr=8-5&keywords=jis+screwdriver
http://www.amazon.com/Vessel-125943...d=1385568998&sr=8-52&keywords=jis+screwdriver
http://www.amazon.com/Vessel-125942-P2x150-Impacta-Screwdriver/dp/B003BGZ9CO/ref=pd_bxgy_hi_text_y

Possible that your carb is not completely clean or got dirty again cause there was still crap in the lines/tank etc.

The only thing I can recommend is to go back through the carb and make doubly sure of all your work, fuel systems should always be worked on from the fuel tank down. Have you set the idle speed screw high enough? Are you sure the pilot jet is really clean? (They have really tiny orifices that can clog with the least amount of debris.) Was the O-ring in the face of the carb flange that mates with the manifold intact, flexible, clean, and most important, not cracked or worn. Always use an inline fuel filter, and whenever you take the carburetor apart, *always* check the float bowl for any sediments that you might have not seen earlier. Cleanliness and thoroughness.

DaBinChe ~ Those tools look really nice. Thanks for the visual on them. Can the home mechanic ever really have enough? Good thing Christmas is right around the corner. Honda's are funny. Built to outlast all of our lives yet on certain parts — small screws, for instance — they can appear to be made out of some form of hardened cheese. Weird combination.

So one vote for an incompletely cleaned carb.

YamaGeek ~ Second vote for the same thing. Got to admit I've been mostly working at the carb and then fighting my way upstream toward the tank. Completely backwards. I was able to locate these, which should help:

http://www.cmsnl.com/honda-nh125-1984-aero-125-usa_model1169/gasket-set_16010kg8305/#.UpY5KxD3OPw

So I guess now I'll drain the gas from the tank (straining it through a few coffee filters into an old V8 container without any irony), clean everything from there down and then see what that gets me. One thing's for sure: When this scooter runs, it doesn't fool around.

Thanks for all your help and as usual I'll post the results...

I am a professional auto/truck/equipment mechanic. Been one for 35 years. You can NEVER have enough tools, but make sure they are good ones. The cheap ones will not only break, but will also usually destroy the fastener you are trying to use them on. I have a lot of Harbor Freight power tools, even an engine crane, and have had good luck with them. But I will only use high quality hand tools, like screwdrivers, wrenches, and sockets. Snap-On is my favorite brand, But I also have tools from Mac, SK, Bonney, and a few others.

If there is no metal on the float, then it was not meant to be adjusted. New Honda oem floats are available from cheapcycleparts.com, along with several other oem parts.

As for replacing carb screws with Allen screws, I have done a lot of them that way. They are almost always M4x0.7 Allen screws are a lot higher quality than the pot metal ones that come stock, and almost impossible to strip out. Also, on some carbs, like my XT225, they allow you to remove the float bowl without removing the carb. Stripped stock screws can usually be removed by needle nose visegrips. They are so soft the visegrips bite right into them. But it is also possible to break the head off that way, and leave the threaded part stuck in the carb with nothing to get a hold of.


As for cleaning carb jets and small passages, I have found that the small E string from a guitar is just perfect for this. It is smaller than any jet, and is a precision made piece of stiff wire. I have never damaged anything doing this. Many instructions on cleaning carbs also recommend using compressed air. I have found that spray carb cleaner works better. Just make sure you protect your eyes when using it. Getting it in your eyes is NOT fun.

Honda provided a JIS screwdriver bit and handle in the tool kit that came with motorcycles and scooters, and I use that for the little carb screws. Haven't lost one yet.

The bystarter is one of the most screwy devices Honda ever devised. If it fails the scooter almost always starts easily when cold, but runs sort of crappy when warm, and is hard to restart, like at a gas station after filling up. It runs off electricity directly from the stator, so the engine has to be running to power it. It controls an entirely separate little intake circuit. When the engine just starts it's open, in the withdrawn position, as the engine runs and power goes to it, it heats up a blob of wax inside that pushes a cylinder and pin out, finally blocking the separate circuit and plugging the extra jet. If the wires aren't connected right it never extends. If the resistance isn't right it doesn't heat up properly and may not extend. In the service manual there's a way to test it, and you should try it.

I have completely removed it from one of my 250's and blocked off the passages, and the engine runs great. When cold it's a little tricky to start, but if I hold the throttle open some, crank the engine a bit, and then slam the throttle closed, it starts. In coastal California you don't need the cold start enrichment.

Search the discussion on the Yahoo CH250 forum, or look at www.CH250.net in the Tech Tips for more on the bystarter.

Run without gas cap as they can plug and not allow proper venting.

Just to test. Not advising to go capless.

Happy Thanksgiving, everyone!

Taking into consideration what everyone has posted, I decided to make a delicious pumpkin pie — it's simple, easy, and I know that the parts are still available.

My latest brainstorm is to take the bystarter off, plugging the hole, and then see if it runs any better after warming up. If so, then I know that the bystarter is at fault and then I can decide whether I want to take it out of the system all together.

This doesn't mean that I'm not going to give the entire fuel system a good cleaning and the carb another going over because it can only help, but it seems to me that the bystarter is the most likely cause of my bogging problem.

I'm putting the turkey in the oven and that gives me three and a half hours to focus on my Aero. After that, it's my turn to bog down in an easy chair and wonder if my bystarter will ever work again.

~ Tootles

You can just unplug the bystarter and hook it up to any 12 volt battery source including your scooter battery. Put a ruler underneath it and after a couple of minutes the plunger/needle should extend a few millimeters.

If you live with a mild winter climate you could probably seal the enrichment hole and do without. Another idea is to buy an automotive control cable and fashion a manual choke using your old bystarter and plunger/needle assembly. I used this trick on both two-stroke and four-stroke scooters. Two-stroke engines/carbs seem to be more cold blooded than their four-stroke brethren.

You say unplug the bystarter, but it looks to me like the two wires just go into a big black wire that goes under the floorboard, so there is no coupling to unplug as far as I can tell. My tech book shows these two little neat electrical couplers but I'm not seeing it.



I understand the test you're recommending; I just can't see a way to do it without actually cutting the wires which I haven't wanted to do.

Another question while you're here: What would you use to plug the hole? And are you talking about the hole where the needle goes or where the bystarter attaches to the carb, or both? Whoops, that's more than one question.

I find this bystarter a bit confusing as I believe it works opposite than most other choke systems — I could be wrong about that. The important thing to me is understanding that if it's not working, does that mean the mixture is too rich and would that make the idle die once it's warmed up, which is the exact problem I'm having.

Thanks for your help, as well as everyone else's. It's great having so many experienced scootbots to bounce off of.