1984 Aero 80 shuts down once warmed up

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MogyDad
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1984 Aero 80 shuts down once warmed up

Post by MogyDad » Mon Dec 31, 2018 11:00 am

I pulled an Aero 80 out of long term storage. Drained fuel and flushed tank. Stuck petcock diaphragm released and tested to work. Oil tank drained and new oil added. Air cleaner washed and element oiled.
With new battery, engine started up and ran very well until warmed up. Once returned to idle, the only way to keep it running was to work the throttle. Otherwise it bogs down until it shuts off. Pulled and cleaned carb. No improvement.
Assuming a vacuum problem, I pulled the line and applied a continuous vacuum with a syringe. This time the engine ran at high rpm until warmed to idle then stalled out.
The scooter only has 1500 miles on it and was running fine when parked. Any ideas?

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vintagegarage
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Re: 1984 Aero 80 shuts down once warmed up

Post by vintagegarage » Mon Dec 31, 2018 12:43 pm

MogyDad wrote:
Mon Dec 31, 2018 11:00 am
Assuming a vacuum problem, I pulled the line and applied a continuous vacuum with a syringe. This time the engine ran at high rpm until warmed to idle then stalled out.
I know you think that sentence is clear, but it is ambiguous. What line? The vacuum line to the fuel valve? Did you plug the tube that the line normally connects to on the intake manifold, so air wasn't sucked into the manifold during your syringe test?

Just a guess, but despite cleaning the carb, the carb idle circuit is still plugged up. Does your air bleed screw still have the limiter cap on it, or are you able to get to the air bleed screw to turn it? If you can turn it, does it do anything when you do? How did you clean the slow jet, and are you positive that it is open?

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Re: 1984 Aero 80 shuts down once warmed up

Post by MogyDad » Mon Dec 31, 2018 6:19 pm

Sorry. Trying to be concise and clear sometimes conflict.
I pulled the line from the manifold and used a syringe to create a vacuum. I did not block off the manifold.

The limiter cap is still on the air bleed screw so rotation is restricted.

I dismantled the carb as best as I knew how, and cleaned the jets, and interior with carb spray.

This is certainly not my area of expertise and appreciate any specific advice you could share.

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Re: 1984 Aero 80 shuts down once warmed up

Post by vintagegarage » Mon Dec 31, 2018 6:40 pm

I think the slow jet is removable in that carb. Look at the workshop manual at:
http://www.motorscooterguide.net/Manual ... Manual.pdf

Look at section 4-6 on page 40.

Once you have the slow jet in your hand, you should be able to see light through it. The jet hole is very tiny, and if you need to clean it out, you need a piece of very fine wire, such as a "High E" guitar string. Blowing through it rarely clears it out. When it is clear, you should be able to suck air through it. That jet has perhaps the smallest hole anywhere in the carb, and is usually the first thing to clog up when a scooter sits for many years. If you can suck air through it by mouth without first cleaning it with a wire, then your problem is probably not a clogged slow jet. If you can't suck air through it, then it definitely needs cleaning.

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Re: 1984 Aero 80 shuts down once warmed up

Post by MogyDad » Mon Dec 31, 2018 8:06 pm

There are two removable jets in that carb. The main and the slow. Had them both out, viewed daylight through every hole I could find, and blew air as well. I’ll try again tomorrow.

Meanwhile, I’ll try that fuel valve syringe bypass again. This time with the manifold nipple plugged.

What strikes me as odd is how well the engine runs when cold, but won’t hold consistent rpms when warm without constant revving. To me it acts like fuel starvation, but quickly recovers with throttle manipulation.

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Re: 1984 Aero 80 shuts down once warmed up

Post by vintagegarage » Mon Dec 31, 2018 8:19 pm

Can you suck air by mouth through the slow jet, yes or no? The hole that should be clear is at the very top end of the slow jet and it points straight up. If that hole is clean, then I am out of ideas and will drop out of this topic.

Once the float bowl is full of gasoline, the scooter should idle for at least a minute before running out of fuel, even if the fuel valve remains fully closed. When you open the throttle, the main jet comes into play and since it runs fine on the main jet, you have enough fuel in the carb.

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Re: 1984 Aero 80 shuts down once warmed up

Post by MogyDad » Mon Dec 31, 2018 8:45 pm

I’m going to pull the carb tomorrow and will advice what I find.
Actually, it doesn’t run real well on the throttle advance once warmed up. It bogs down and cuts out until I rev the throttle. If I release the throttle to idle, it eventually stalls.

Will see what a more thorough carb cleaning brings, meanwhile thanks for your help and suggestions!

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Re: 1984 Aero 80 shuts down once warmed up

Post by MogyDad » Tue Jan 01, 2019 2:53 pm

As an update I pulled the carb and cleaned it more thoroughly. The slow jet was not obviously clogged, but as I rotated some fine wire in the wider portion of the jet, I dislodged some powdery residue. That may have been the culprit.

After reassembly, I broke off the air screw restrictor and reset the air screw to 1-1/2 turns.

Scooter started easily and continued to run after warm up. Also not bogging down or cutting out as before. Not sure what resolved the problem, but we’re back in business.

Thanks for your expertise and assistance. Happy New Year!

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