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Post by studioj on Jul 14, 2023 14:08:08 GMT -5
I have a 2006 Yamaha Minarelli with 2500 miles on it. Never abused and always garaged. The motor has a 70cc Polini big bore kit and 20mm carb on it that have been on it since it was < 1 year old. No mods to the variator. Never had the left side cover off. After having sat (inside) for about a year, the motor started as usual but quickly died and I have not been able to start it again. There's no vacuum. I've had the entire top end and right side of the engine apart, but nothing seems to be "wrong". The cylinder has 180# compression after turning it over with the starter for about 3 seconds. If I squirt ether into the intake I can not get any life out of it. If I take out the plug and squirt ether into the spark plug hole and replace, I can get it to turn over briefly. I replaced the reed cage. No difference. I'm down to the crank seals but before I tear the motor down (It's still installed on the scooter) just thought I would check with the powers that be to see if I am missing something obvious.
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Post by Lucass2T on Jul 14, 2023 15:32:25 GMT -5
In 1 sentence, whats the problem?
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Post by geoffh on Jul 14, 2023 15:36:06 GMT -5
Welcome to the forum,I ran a Yamaha for years,change the gas,test the petcock by sucking on the tube,it should flow freely,change the plug,check the "hidden " filter in the gas tank.keep asking till your sorted.
Geoff
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pili
Scoot Enthusiast
Posts: 279
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Post by pili on Jul 14, 2023 23:02:37 GMT -5
If you have good compression it should create vacuum. Apply vacuum to the petcock and see if it runs. If so there has to be blockage in the vacuum port on the carb or the hose is leaking.
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Post by studioj on Jul 15, 2023 5:57:16 GMT -5
In 1 sentence, whats the problem? The engine will not start or run. No fuel to combustion chamber. Carb is not the problem. |
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Post by studioj on Jul 15, 2023 6:03:34 GMT -5
If you have good compression it should create vacuum. Apply vacuum to the petcock and see if it runs. If so there has to be blockage in the vacuum port on the carb or the hose is leaking. I've already done all that... actually replaced the petcock etc thinking that was the issue. It's not. I've completely removed the carb from the engine at this point. No vacuum can be felt while cranking with my hand over the intake boot (the rubber boot that connects the carb to the reed cage). So while I have no vacuum, I still get compression.... that tells me that air is entering the system from somewhere that it should not. The only place I can think that can happen is the crank seals but I have never had a 2 stroke where the crank seals just failed. Usually they leak over time. I was hoping someone more familiar with the Minarelli than I could offer some advice... or perhaps confirm my suspicions before I rip the motor down. |
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Post by Lucass2T on Jul 15, 2023 6:31:41 GMT -5
In 1 sentence, whats the problem? The engine will not start or run. No fuel to combustion chamber. Carb is not the problem. Reeds could be broken. Crank seals could be worn. Both are things you can fairly easy check without having to disassemble the engine. |
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Post by Zino on Jul 15, 2023 7:31:19 GMT -5
no fuel to combustion chamber
check flow of fuel from tank to carb
check petcock function
remove both hoses from carb
suck on the vaccuum hose the fuel hose should pee out fuel real fast.
a broken reed will show alot of compression but is hard to start
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Post by snaker on Jul 15, 2023 9:11:42 GMT -5
Also check for a plugged exhaust.
No air can get in if air isn't getting out.
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Post by classacted on Jul 15, 2023 9:18:56 GMT -5
make an effort to check the exhaust port of the cylinder. I've seen them almost completely filled with carbon.
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Post by studioj on Jul 15, 2023 11:13:20 GMT -5
Reeds could be broken. Crank seals could be worn. Both are things you can fairly easy check without having to disassemble the engine. Reeds were replaced as part of my initial troubleshooting. Reeds are not the problem. I suspect crank seals. Have had the stator side apart and it does not appear to be that seal. Have not yet disassembled the variator side. I am at that point which is why I was asking for other's opinions/experiences before I pulled it apart. The reason I don't suspect the seals is because the problem was very sudden... it ran fine and then it died and would not restart. My experience with dirt bikes etc is that seals don't tend to fail catastrophically. They tend to fail gradually... that's why I question whether it may be the seals... but I am sort of down to them as the last possible reason. |
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Post by studioj on Jul 15, 2023 11:19:00 GMT -5
make an effort to check the exhaust port of the cylinder. I've seen them almost completely filled with carbon. I removed the pipe when I was inspecting the top end. I had the same problem with the pipe on and with the pipe off. Here's the one thing about the exhaust port that has me scratching my head... with my compression tester in the spark plug hole and the carb off but reed cage and intake on, and the pipe off, I get 180# of pressure in about 3s of cranking. If I put my hand over the intake, no vacuum and still get 180# of pressure.... that's what lead me to think I have a vacuum leak (seals). But then I put my hand over the exhaust port and crank... I could feel "chug chug"... it felt like vacuum... which there should not be... ever. Still got pressure in the cylinder which made me again think crank seals. Just seems like the seals are failing very prematurely... I have engines that are 50 years old and still going strong on the original seals... |
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Post by studioj on Jul 15, 2023 11:20:09 GMT -5
Also check for a plugged exhaust. No air can get in if air isn't getting out. Good point, but had the cylinder off... everything looked clean. |
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Post by oldgeek on Jul 15, 2023 13:03:55 GMT -5
........... If I take out the plug and squirt ether into the spark plug hole and replace, I can get it to turn over briefly. That alone tells me there is a carb or fuel delivery problem. |
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Post by classacted on Jul 15, 2023 14:13:46 GMT -5
that's a real mystery how you don't have vacuum at the intake manifold when the carb is removed. you have great compression.
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