1983 aero 50 died and can't get to start

[mbilderb]

My son was riding his 1983 Aero 50 that we restored. We have about 300 miles on it since the restore. Yesterday it died on him. The way he describes it, it sounds like it ran out of gas. He said it started revving without any power the bogged down and died. The problem is it had 1/2 tank.

The bike has spark, but the spark plug is dry.

I checked the petcock. It is clean and performs properly when hooked to the vacuum. I checked the carb. It is a chinese aftermarket, but appears to work as well. The bystarter may not be working anymore, but I am dubious about that item to begin with. When I place my hand behind the carb and crank it, making a seal, gas is pulled back onto my hand.

I took the manifold off and removed the reeds, they were wet, and there appears there may be some leakage around the seal. Notwithstanding, I still get a decent suction from the manifold when I crank the motor.

What I don't understand then is where the breakdown may be in getting the fuel to the spark plug. What is likely to have failed, and prevent fuel getting to the spark plug?

[Bear45-70]

My son was riding his 1983 Aero 50 that we restored. We have about 300 miles on it since the restore. Yesterday it died on him. The way he describes it, it sounds like it ran out of gas. He said it started revving without any power the bogged down and died. The problem is it had 1/2 tank. Compression check before you screw around with anything else.

The bike has spark, but the spark plug is dry. No fuel, carb is dirty.

I checked the petcock. It is clean and performs properly when hooked to the vacuum. I checked the carb. It is a chinese aftermarket, but appears to work as well. The bystarter may not be working anymore, but I am dubious about that item to begin with. When I place my hand behind the carb and crank it, making a seal, gas is pulled back onto my hand. Bystarter only works when the engine is cold. All it is is a choke system without a butterfly valve. Have you tried priming the engine?

I took the manifold off and removed the reeds, they were wet, and there appears there may be some leakage around the seal. Notwithstanding, I still get a decent suction from the manifold when I crank the motor.

What I don't understand then is where the breakdown may be in getting the fuel to the spark plug. What is likely to have failed, and prevent fuel getting to the spark plug?

[martynkim]

I have a good oem carb for that bike.

[mbilderb]

Compression is 30 - 45 psi. I think we found the problem.

Since I wasn't riding it when it failed, can anyone give me a likely scenario? I saw a post earlier mentioning a soft seizure, could that have been the cause? If it is, what is the effect and what can be done about it?

When we rebult, the rings were sticking but once we took them off and cleaned out the grooves, they were well within tolerance, and compression was fine too. I think it was 160 or 165. I am going to pull the jug tomorrow. Any suggestions on preventative measures?

[mbilderb]

I have a good oem carb for that bike.

Thanks, I think the carb is OK. I wish I would have been in contact with you 9 months ago, before I cut down the throttle cable to accept the Chinese carb.

[mbilderb]

Compression is 30 - 45 psi. I think we found the problem.

Since I wasn't riding it when it failed, can anyone give me a likely scenario? I saw a post earlier mentioning a soft seizure, could that have been the cause? If it is, what is the effect and what can be done about it?

When we rebult, the rings were sticking but once we took them off and cleaned out the grooves, they were well within tolerance, and compression was fine too. I think it was 160 or 165. I am going to pull the jug tomorrow. Any suggestions on preventative measures?

As a preventative, I think I am going to start running premix.

[Bear45-70]

If the carb is not jetted properly (This is likely with a Chinese carb) it probably melted the piston from being too lean. Pull the head and cylinder and see.

[mbilderb]

I took off the jug. The carb wasn't the problem -- it was the reused wristpin clip.

closeup damage.jpg (81.7 KiB) Viewed 7755 times

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zoom out damage.jpg (81.87 KiB) Viewed 7755 times

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cylinder damage.jpg (49.63 KiB) Viewed 7755 times

So, now I have to decide whether to junk and get something else, or rebuild. Any suggestions? Anybody have a good jug and piston for an 83 Aero 50? Any suggestions for an economical upgrade?

[mbilderb]

I have a good oem carb for that bike.

Do you have or know where I can get a replacement piston and/or jug?

[martynkim]

I have a good oem carb for that bike.

Do you have or know where I can get a replacement piston and/or jug?

I have that too. Pm for more info...

[mbilderb]

I took the jug to the local Yamaha shop (they do all the borings for all other motorcycle shops in the area) and they think that a .20 over boring will fix the jug. The question is whether I can get an oversize piston, or will it be more economical to buy a used piston and jug, or replace with an alternative motor. Any suggestions? Know of anyplace to get an oversize piston and rings for this model?

[Bear45-70]

I took the jug to the local Yamaha shop (they do all the borings for all other motorcycle shops in the area) and they think that a .20 over boring will fix the jug. The question is whether I can get an oversize piston, or will it be more economical to buy a used piston and jug, or replace with an alternative motor. Any suggestions? Know of anyplace to get an oversize piston and rings for this model?

Used pistons,rings and jugs are a major crap shoot. For these items I either go new or I don't go at all.

[martynkim]

I took the jug to the local Yamaha shop (they do all the borings for all other motorcycle shops in the area) and they think that a .20 over boring will fix the jug. The question is whether I can get an oversize piston, or will it be more economical to buy a used piston and jug, or replace with an alternative motor. Any suggestions? Know of anyplace to get an oversize piston and rings for this model?

Used pistons,rings and jugs are a major crap shoot. For these items I either go new or I don't go at all.

Well the entire engine is available unmolested. That is up to the buyer though.

[mbilderb]

OK I took Bear's advice to heart. I went to the yamaha shop and we ordered an over bore piston (40 bore base - I believe used for the razz) bored the cylinder .20 over. We need to put it together, then we'll post the results.

Yamaha Piston.jpg (66.69 KiB) Viewed 7694 times

[mbilderb]

Runs like a charm. So far, most of the things I needed for the 83-84 Aero I have gotten from Yamaha.