86 Aero gas out Carb vent constantly

[the496rocket]

Have an 86 Aero 50 with a Polini BBK I put on 20 years ago, After riding, I am having an issue with fuel coming out of the carb vent/breather at the front of the carb, it’s not a steady stream, just some drips on the ground after sitting for a bit after riding, usually after I shut it off. Like a heat soak i suppose. It does not come out the overflow at the rear, just the breather. I have ran a longer hose out to the bottom because it was constantly running gas down the clutch cover ruining my fresh paint constantly. It seems almost as if the fuel in the bowl is boiling after a heat soak, because ALSO, if I stop after a long run, it will restart immediately after shutting it off, however, if I let it sit for 5 minutes the try, it struggles to start like it’s flooded. Have cleaned the carb several times, petcock and float/valve are working normally, float level is perfect. Also, sometimes when hitting large bumps it will die for a couple seconds then come right back. Also dies when dropping the back when idling. Bystarter is working properly, passageways in bowl are clean.

Only mods are the BBK, jet, and some holes in the stock airbox. Running the stock engine cover, and also even tried to put some heat tape around the carb. Extremely frustrating as usually I can figure this stuff out but this one has me stumped bike runs excellent, and tops out at 47mph gps.

About to run the breather up instead of down with a filter to trap any fuel so it can drain back as I’m out of ideas and frustrated. Embarrassing when you run into a gas station and come back out and the thing cranks for 10 seconds before it fires. Pretty sure it’s flooding as it sits, or the fuel is boiling out of the carb and takes a bit to fill again especially since the bystarter is warmed up. HELP!!

[bonesv]

It could be that your float needle is very slightly worn and allowing a small amount of fuel to enter the bowl when it should not be doing that? Or, I suspect, the seat is corrupted in some way (pitted or dirty?) and to remedy this, you could try using some baking soda and water solution with a Q-tip and swirl that seat area smooth again? Or, perhaps the float needle is incorrect for this carburetor? Is there a chance that the carb has been replaced by an aftermarket version? Then, concerning your other issue, I suspect the hard start is because the bystarter is cooling off after a few minutes and the carburetor "thinks" your motor is cold thereby allowing too much fuel to enter and as you stated, "struggles to start as if it's flooded." The secondary cover may be missing which covers the bystarter (like a heat shield) and holds the warmth around it for a bit longer time, either that or your fuel/air adjustment is not adjusted correctly, or, you may have a cracked or damaged reed valve? Have you installed a temperature gauge yet? What is your method of tuning the jet size? That size may be inaccurate also.
Lookup in the service manual http://www.hondaspree.net/other/Aero50_SM_85.pdf then also check in our pages in the help section of this forum under Board Index. Good luck with this issue(s) and let us know if you are still having difficulty and some other members might swing by with a suggestion or two. Cheers!

[the496rocket]

Appreciate the reply. I’ve tried it with and without the bystarter cover, polished the needle seat yesterday, I can keep vacuum on the Petcock for 5 min and no leaks so it’s working good, I don’t have a temp gauge but am getting today. Plug is a bit darker than cardboard. There’s a lot going on here I don’t understand, I installed this polini BBK when I was 16 and not very savvy with mechanical stuff like I am now. I didn’t do a proper break in or anything, no premix with stock oil pump (deleted with 32:1 now), stupid but I didn’t know better then. Right now, the compression is 90 at WOT, which is definitely low and the I can see the cylinder walls are scored a bit, so that could be the problem also, but it definitely acts as if it’s flooding, as holding the throttle wide open shortens the time to restart after a 3-5 min heat soak I discovered. Everything else on this bike is stock except for the exhaust, original rotted out. This one is from some other aero, unrestricted. Also, I have my mixture screw at 3 turns open, and less and it tens to load up. basically have the air maxxed out for the small carb.

THIS is what baffles me, and is kind of separate, I see people installing the Malossi BBKs and springs and variators, and happy to be hitting 45. This bike has 8200 miles on it, everything is original save for the BBK, I remember “boring” out the intake a bit in front of the carb (just the part above the reeds, probably did nothing), and I have 5 half inch holes in the airbox lid otherwise it won’t rev out. Belt, rollers, everything else has 8200 miles. (dad bought bike new) so I’m sure it’s all pretty well worn, BUT, the thing takes off very quick, and will hit 47 on flat ground verified by GPS multiple times. I was going to get a malossi BBK so I have a fresh cylinder but maybe they don’t have the performance the Polini did? Wish I could save this cylinder. A Polini variator kit and new malossi belt will be here today, interested to see what that does for it. But that speed really has me scratching my head with the low compression and super high miles on original clutching, but not complaining!

[the496rocket]

I cannot remember if I installed reeds or not with the polini kit. I put the polini Variator on today and I actually lost 2mph top end, and taking off was very sluggish, so I put the stock back on. I honestly believe the gas in the carb is boiling a bit or something. I can shut it off and itll fire off immediately. but the longer I leave it off, the harder it starts. and holding the throttle wide open helps. cold starts arent too bad. It also dies for a second or 2 when I hit large bumps, and comes right back, so I believe that to be flooding the cylinder out when that happens. Verified float bowl level again, 12.2mm on the nose. Debating an aftermarket carb cause that would probably remedy all this weird stuff, unless the gas is indeed boiling which these issues point too it seems. I ran a longer hose out the vent and up into a loop and back down behind the case by the other carb hoses and that stopped the leakage, so at least thats one issue remedied. Its very rideable as is, and runs great, but I just want to figure this crap out since I am just like that lol. I am also leaning towards the compression being an issue as well possibly. but it still gets up and goes up to 47.

[bonesv]

I have seen Keihin carburetors on eBay from Italy for about $100 or so shipped. Real, Keihin, not fake ones. I have a few myself and they work well with a 70cc BBK if you set it up properly and don't have to ride wide open ALL the time. I can show you where to acquire a correct intake for it as well but these are oem style PB carbs so you can source jets easily. I prefer to use a stock-style air box with mine which keeps it from being difficult to tune. Also, the Malossi BBK is just about the same as the Polini kit is for the Aero or you could get a set of rings and hone that Polini cylinder to try to save money. My choice would be the new Malossi kit I hope my suggestions help

[the496rocket]

I like the looks of that first one, unless they’re both the same, I haven’t don’t a TON of research on carbs, but it would be nice to have one with better “tune-ability” I wouldn’t mine. A few more mph, I’d like to be able to go 55 to keep up with traffic but with the stock 11:1 the engine would probably be screaming. I am happy with it now except for the carb boiling/evaporation issue. It’s very hard to start after sitting overnight, by starter is new and passage in bowl is clean. I can tell the bowl in the carb is basically empty after running it and sitting. No leaks anywhere now that I ran the vent higher, just think it’s evaporating from heat or something. Driving me crazy.

Is that first one and /or both plug and play? Everything looks pretty similar. Maybe except the airbox I’m not sure.

[the496rocket]

Also, I see the opening at the engine side of the stock carb is about 17mm, but the inner diameter of the stock carb is smaller, are these ones on ebay larger? Appreciate the education, not much documentation for learning on my own out there!

[bonesv]

The one from Italy is the better choice. You will need the intake manifold from the same 100 cc scooter and the appropriate air box which will have to be carefully fit into your smaller scooter dimensions. I can help you but you better get that carb asap before it is gone for good! There are no more anywhere of this quality. I will get you an intake and air box but grab that carb NOW! if you are going to do this. Then send me a PM with your text # and I will send you some pics to show you what to do and where to get the rest of the stuff you must have for a successful conversion. Cheers!

[bonesv]

I'm getting back to your recent problems after re-reading the last few posts of yours. It sounds to me like the main jet is a little bit big for the current setup. You said 3 turns out and you have 5- half inch holes in the air box? Is that correct? And it's still running rich? If you acquire one of these carbs which I suggested, please purchase some jets to have in order to tune. Here are the ones you would need for either one of those carbs.
https://jetsrus.com/a_jet_kit_scooter/h ... 0_SK50.htm
You would need jets # 88 - 90 - 92 - 95 - and maybe 98. Also, purchase a new screw driver if you can. Be aware that the Philips head screws on most Japan made bikes are a special type called JIS or japan industrial spec and I made the purchase of this screwdriver to save the trouble of replacing screws which became stripped out by my American standard Philips tips. You should consider owning one especially if you change out jets often or work on anything made in Japan. Here is a #2 JIS tipped Philips head from Amazon: https://www.amazon.com/Vessel-Megadora- ... r=8-6&th=1

[the496rocket]

first, I appreciate you taking the time bones. seems like the links disappeared, or got deleted I managed to fine what was one of them I believe, but its the one located in Florida, ill link it below. as far as jetting, my temps never reach 300 and my plug is chocolate milk every time I check it, I did an experiment, when I shut the bike down after a run, the temp climbs as it normally would when heat soaking, so I aimed my blower fan right into the cooling intake duct and let it sit, 10 minutes later, it fired off immediately. something about the heat soaking is causing the issue and evaporating the fuel It seems. at least I no longer get gas leaking tho.

I have 2 options, I dont necessarily trust this cylinder anymore with the scoring and the sub-90 compression, even though it seems to run okay, besides these annoying issues, but the performance is dropping, when I put it in, I slammed it together and ran it without break in or chamfering anything, didnt know any better, she's scarred for sure. and it makes odd noises when running, I think its time for a rebuild, but I am wondering how much I am going to have into it, by the time I buy a new malossi kit, the carburetor, intake, and manifold, and porbably new seals and what not, maybe bearings, and possibly have the same performance, (45 seems pretty good as is wounded), or 2: get an AF16. Guy 2 hours from me will sell me a complete one minus the large shroud for $600, which obviously is more than rebuilding what I have but it would be nice to have options to get it to go 55 to keep up with traffic. Guess it depends what the manifold and airbox will cost.

heres the link to the one i DID find although it says its for an aero 50..??: https://www.ebay.com/itm/186722197560?_ ... ondition=3

[bonesv]

No that's great news about you buying the Elite with AF16 motor! The Aero's motor is not the best platform besides the wore out bore-it's shorter stroke crankshaft, and hard to find gears and limited range. An AF16 stock-stroke with a 72cc BBK and the 9:1 gears is really the best all around setup unless you are drag racing (or want to impress your friends hahaha and spend too much money) in my opinion. The drive belt/pulley/clutch/springs/variator is the key with the right exhaust and matching carburetor setup. This is not overly expensive and lots of guys here are using this mid-high performance equation. I can send you another private message with carb and intake links, and exhaust sources for you to compare and search out the best price for yourself. The air box you can purchase from me as these are harder to find if you want to keep it stock-looking and not be approached by the police but it may not be a concern. It depends-where are you located? Check your private messages tomorrow-the link is at the top of any page ^^^