The heat contolled choke (the bystarter)

[bear4570]

Well, I've been thru the shop manual from cover to cover and all they talk is cleaning the air filter for it and removing and replacing it. Nothing about how it works and not even a good picture of hose routing. The one on my Aero 80 is acting up. Starts and runs fine when cold as soon as it warms up the motor dies from being to rich (wet plug). So where do I get info on it?

[bear4570]

This thing is not electrical and has half a dozen hoses running all over the place on the carb. Sort of like an old heat driven choke on old carbs but this thing does it with vacuum off the manifold, run thru a heat controlled valve bolted to the head and then back to the carb on a couple of hoses. See the gang of hoses behind the carb, those are only four of the six hoses this thing has.

This thing is not electrical and has half a dozen hoses running all over the place on the carb. Sort of like an old heat driven choke on old carbs but this thing does it with vacuum off the manifold, run thru a heat controlled valve bolted to the head and then back to the carb on a couple of hoses. See the gang of hoses behind the carb, those are only four of the six hoses this thing has.

[bear4570]

I think I have this apparition figured out as to how this works but I may not care. I ordered a spare carb for my Aero 125 the other day. It arrived to day. It appears to be identical to the 80 carb except that it has different low and main jets and has an ELECTRIC bystarter on it. The venture is the same size as is the throttle bore. Maybe this explains the lackluster performance from the Aero 125, Not enough carb! So swap the jets, mount the carb, wire in the bystarter and I should be good to go.

[bear4570]

To my great dismay, the 125 carb has a longer throttle stroke than the stock 80 carb, so it will not work. However since I figured out how this insane vacuum and heat operated choke works, that is suppose to work, I just made it into a manual choke by running a line from the carb to a valve and from the valve to the intake manifold. Mounted the valve in the left side of the center cover under the seat and I'm golden. Works great and I put 20 miles on the scooter testing everything out.

[bear4570]

Here is my fix for the vacuum/heater bystarter.

Read all the instructions first and then start working.

Get a good valve that seals well (I got a small ball valve) with 1/4" hose barbs and about 3 feet of 1/4" fuel resistant tubing and 8" of 3/16" tubing.

The vertical nipple on the front of the carb goes to the plastic inlet filter with the 3/16" tubing. You must plug the second nipple.

Then from the 1/4" nipple at the rear of the carb run to the valve, it faces toward the back of the carb (the front of the scooter).

I mounted my valve in the left side of the center cover down near the carb level. Drilled a hole for the handle portion of the valve to stick thru to the outside and then secured the valve in place.

Run the other side of the valve to the 1/4" nipple on the manifold. I used tie straps on all connections.

Valve open is like the bystarter when cold. Once engine warms up, close the valve and ride. My wife has no problems with operating this system. Oh yeah, make sure you do NOT kink the hoses, otherwise the system will NOT work (experiences speaking here).





If you look carefully at the top hose off the valve in the bottom picture you will see it has a bit of a kink in it, but it is better than the first piece I had there which kinked completely closed. Made me a bit crazy as to why it didn't work at first.

[bear4570]

Well, it has been several weeks since I modded the vacuum/heat contolled bystarter to a straight manual system. Starts every time, warms up quickly and when I shut off the valve the engine settles down and idles properly. So I now declare this mod a success.

[bear4570]

Kiss drawing of the manual bystarter valve.

[peterdorrington]

Thanks Bear
Looks like a great mod. I have been doing my nut trying to find out how the choke system works. I know it increases fuel and not choking the air as a normal carb.What is the function of the pipe ? Does it draw extra fuel through into the intake manifold from the float bowl?
Peter , Cape Town

[bear4570]

This is an enrichment system, that does the same job as a choke without putting any obstruction in the air inlet of the carb. Two strokes are very sensitive to these disruptions to air flow, so this solves two problems. Enrichment of the fuel mixture for cold starts and improved performance. Yes, it uses manifold vacuum to suck extra fuel into the intake via the bystarter bowl with it's own fuel pickup in the float bowl. The control box on the head, as the head heats up closes a valve and cuts off the vacuum supply, there by shutting the enrichment system off.

[peterdorrington]

Thanks Bear. The scooter has been standing for 15 yrs and runs great. The cold start is however a problem. I have made the mod as set out. On cranking the engine I can see fuel / vapor coming up from the carb to the inserted valve / then going down into the intake manifold.
When cold OAT 5 to 13 deg celsius : On cranking it now fires up and runs for about 2 - 3 seconds then dies. If I crank it again it repeats the process. If warm it starts 1st time and runs fine.
The air screw is turned out 1.5 turns. and idles fine when hot. When riding and you close the throttle it tends to keep the rpm and not drop as fast as I would expect. Could there be a jetting issue on the idle / main jet that influences the cold start procedure but runs OK when warm ?
Can the plug be fouling in the start up when cold? Sorry about all the questions but am starting to obsess a bit with the excitement of getting a 27 yr old scooter running.
Cheers Peter Dorrington

[bear4570]

Yes, it could be an idle mixture problem. It might idle fine but unless you adjust the idle mixture screw for the highest RPM possible you have not adjusted the idle mixture properly. Then adjust the idle speed screw until the rear tire just does not turn.

[peterdorrington]

thank bear.
I downloaded the manual and it also gives a description on the idle setup thanks
free download (120MB) at www.hondaspree.net/Aero80_NH80_Manual.pdf
cheers
Peterd

[aerofly]

Bear, thanks for this great info, I think I may have to give this a try. My Aero 80 does not want to start after sitting for week to 10 days. Once started it runs great, and if used every day, no problems. In the past resorted to a start fluid shot to get it running.

After running it runs great, and starts fine as long as I don't let it sit. What did you do with the hoses from the heat valve? Do you think your mod will help?

Aerofly

[bear4570]

Starting fluid is a major NO-NO with 2 strokes motors. It not only washes the oil off the moving parts allowing metal to metal contact but it is explosive and has been known to explode in the crankcase, which will destroy your reeds making a for sure non-running engine. This choke system works well and even my wife has no trouble with it, but I suspect you may have a leaking float bowl drain valve causing you issue. Or a bad petcock leaking fuel into the intake system.

[aerofly]

Thanks for the reply! In the leaking float bowl scenario, wouldn't I see fuel on the ground? I have opened the drain and immediately I get fuel, so I'm thinking it's full.

As for the bad petcock, I have checked the plug when trying to start after sitting, and it does not appear to be wet.

It seems like a fuel starvation or leak down because it starts/runs great if used everyday. At least it's helping me to pull out what hair I have left. (old fart)

I still like your conversion but am still confused what to do to the hoses from the vacuum/heater when this conversion is made. Do I just plug the remaining hoses?

Thanks again for the info... I love this scooter!

Aerofly