1986 Honda Aero NB50 strange Auto Bystarter stalling issues.

[ForestTheBoy]

Hey all! I just picked up a 1986 Honda NB50 and this is my first moped. Outside of some minor tinkering on a 73 Honda cb350 I have near no mechanical experience. I'm doing lots of research lol.

I figured out the Aero has a cheap Amazon carb, and the Auto Bystart was left unplugged. But it seemed to run fine by my standards minus some mid range jutteriness. It tops out at about 35 on flat and 40 downhill.

I decided to try tuning the carb after reconnecting the Auto Bystart and taking a 15 minute ride. I went through some steps from another post here to tune it.

Now I have the Bystarter connected, it starts fine, but until the bystart turns itself off the engine loses power and dies close to half throttle. Wider throttle is great, acceleration is pretty quick.

This issue goes away when unplugging the autobystart, which sounds wrong. From my understanding when unplugged the autobystart stays in the enriched "choke" state.

I have no idea about how the variator is supposed to feel when it shifts and rides, but I did pop off the cover and check everything out in there. The clutch pads dropped a lot of debris, but the pads looked smooth. I didn't have the right size to open up and look at the rollers to check for flat spots, that's on my todo list.

I'm hoping to address this issue and fix the speedometer, as well as gain some performance. I hear stock Aeros can get closer to 40 on flat if set up right.

Thanks for any info you guys have!

{Edit: corrected bypass to Bystarter for clarity}

[zz28zz]

I've been wrenching on my own motorcycles for over 40 years, however never ran across a "bystarter" which is what I believe you are referring to. The Bystarter is a device that allows additional air and fuel to enter the engine when it needs it (cold eng). It's similar to a choke with fast idle functionality. It works by using electricity generated from the engs generator. When eng starts, it gets up to 12V. When Bystarter receives power it heats up some wax inside and causes a pin to very slowly extend. The pin is connected to what appears to be a mini needle/slide assy. Once the wax expands the mini needle/slide assy seats deeper into the carb blocking the additional air and fuel inputs. It's supposed to be fully extended by the time the eng is warmed-up and no longer needs the additional fuel/air to idle.

Since yours has trouble running at low speed after the Bystarter is warmed-up, it indicates the normal fuel passages used for idle(and low speed) are clogged somewhere. Sounds like it needs a good carb cleaning and verify all the tiny fuel passages are clear. See link for additional info.
http://hondaspree.net/wiki/index.php/By ... at_It_Does

[ForestTheBoy]

Yes, Bystarter is the word I was looking for.

Sorry if I didn't explain clearly enough, the opposite is actually true where the moped runs better hot once the Bystarter wax melts or "disengages". The first few minutes of operation is when I have issue in the low rpm range.

When the Bystarter is disconnected I don't have any issues with the idle or low end stalling. I worry the mixture is too rich with it unplugged long term though?

[zz28zz]

I have zero experience with aftermarket moped carbs. There may be a design issue with it causing odd behavior??

When I re-assembled my bystarter, I noticed when the 2 halves of the housing are screwed together, there's no obvious point to stop. The further that the 2 halves are screwed together, the further the little needle/slide gizmo protrudes from the housing and into the carb. Seems like that would play a part in the transitional performance from cold to hot. That's something I'm thinking abt adjusting (if needed) once I get mine running. The link I posted does show a pic with measurements for the proper amount of needle/slide protrusion when cold. I'm not sure if those measurements apply to my carb, but will use it for a starting point.

With carb on bench and a 12v batt handy, I squirted carb cleaner into air port feeding bystarter and saw where it comes out hole on motor-side of main slide. Then connect 12v batt to bystarter and repeated squirting carb cleaner every 10 secs or so until it stopped coming out hole on motor side of main slide. It only took abt 60 secs but not sure if that's right.

Since the bystarter adds additional fuel and air, it's hard to say if the overall mixture would wind up being too rich or too lean once past the "prime" operation. The bystarter fuel comes from a "well". That well holds enough fuel for a prime to start eng but that same well has restricted rate of re-fill due to a pretty small feed hole connecting it to the main float bowl fuel.

IMHO, if the eng runs better with bystarter wiring disconnected, there something wrong with the carb and the bystarter is helping to cover-up the carb issue.