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Discussion Starter · #1 ·
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Hello,

I have a 1997 yamaha virago 750. My dad parked it 2 years ago when he hurt his back. The bike ran great when parked. It has sat for the last 2 years. I had the carbs cleaned and rebuilt at a yamaha shop. The bike starts and will idle. The front cylinder does not warm up, the back does. I can feel exhaust from both pipes. I did a compression test and the cylinders were within 10%. I did change the spark plugs, there is a spark from both wires. I noticed the petcock is leaking fuel and is not the original. Any ideas or suggestions on what to check?

Thank you,
Chad
 

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Since you have spark in both cylinders and compression in both it sounds like fuel issues.
Were the carbs bench synchronized so they are at least close enough to run? Once it's running on both cylinders then you can do an accurate synch.
When you pulled the plug from the dead cylinder do you smell gas on it? Maybe one of the carbs has a stuck float, open the drains on both and see if they have fuel in each. If not then just knocking on the bowl might unstick a float, if not then you might have to take that carb bowl off.
The leaking petcok needs to get fixed but that wouldn't stop one cylinder from firing
 

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When you say there is spark, is that from the spark plug electrode or did you just check the plug wire with a pen tester?

Is the front plug wet from gas? It should be if it is getting gas and not firing. If not, gas is not getting to the cylinder.

Try swapping spark plugs and see what happens. Just a matter of narrowing down the usual suspects, spark, gas and compression.

These are the easiest things to try first. Let us know.

R. S.
 

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Carbs cleaned and rebuilt once upon a time, means almost nothing once it sits parked with old fuel in it for a few months. If you own a motorcycle with carburetors, you better know how to service carburetors or consider buying a motorcycle that is equipped with fuel injection. That's a reality of modern fuel.


... just a wild guess, the original fuel petcock was vacuum operated so you could not forget to turn it off, likely that feature has been obsoleted and now you just have a leaking fuel tap.
 

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Discussion Starter · #7 ·
Since you have spark in both cylinders and compression in both it sounds like fuel issues.
Were the carbs bench synchronized so they are at least close enough to run? Once it's running on both cylinders then you can do an accurate synch.
When you pulled the plug from the dead cylinder do you smell gas on it? Maybe one of the carbs has a stuck float, open the drains on both and see if they have fuel in each. If not then just knocking on the bowl might unstick a float, if not then you might have to take that carb bowl off.
The leaking petcok needs to get fixed but that wouldn't stop one cylinder from firing
I would think the yamaha shop would of synced the carbs. I was unimpressed with the shop, it took them 3 weeks to rebuild the carbs and put 2 tires on. I will check the bowels, thank you. I will check the plugs. Before it was at the shop, the bowels were not filling with fuel. I was hoping have them rebuilt would of solved any carb issues or the float sticking.
 

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Discussion Starter · #8 ·
When you say there is spark, is that from the spark plug electrode or did you just check the plug wire with a pen tester?

Is the front plug wet from gas? It should be if it is getting gas and not firing. If not, gas is not getting to the cylinder.

Try swapping spark plugs and see what happens. Just a matter of narrowing down the usual suspects, spark, gas and compression.

These are the easiest things to try first. Let us know.

R. S.
I checked it with a pen. I did change the spark plugs 3 days ago, hoping that would help. I will pull them and look to see if wet from the gas, thank you!
 

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Just checked the parts manual and it sure looks like the carburetors are identical twins, you could start moving parts that are common to both cylinders from one to the other and see if the problem moves to the opposite cylinder, same goes with plugs and coils.
 

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Discussion Starter · #11 ·
I did have a sparkplug fail before. May just try another one to check or if you swap them then the other cylinder would not fire.
I checked the the spark plugs. The bad cylender did not smell like gas. It did not appear to be worn like the other cylinder. The float bowl was not filling like the other one. I tapped on the bowl and it ran and did get warm like the other cylender. I found a hose that is not connected. It branched to a 3 way line. 2 of the lines branched to the carbs, the other side did not connect to anything. Would that go to anything? I will try to upload a picture of it. Thank you
 

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Discussion Starter · #12 ·
Just checked the parts manual and it sure looks like the carburetors are identical twins, you could start moving parts that are common to both cylinders from one to the other and see if the problem moves to the opposite cylinder, same goes with plugs and coils.
Thats a good idea! That would be a good way to check the wires and coil.
 

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I found a hose that is not connected. It branched to a 3 way line. 2 of the lines branched to the carbs, the other side did not connect to anything. Would that go to anything? I will try to upload a picture of it. Thank you
Can't really make it out from the pic but it sounds like it could be just a vent hose.

S F
 

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If it is a crankcase vent, it would go to the air box where it can expel hot gases and oil mist into the air box and draw in clean air. Follow it back and see what it is attached to.

... crankcase on a 4-stroke needs to operate close to atmospheric pressure at all times, Piston internal combustion engines all have some blow-by and that is completely normal. Crankcase vent hose is usually a little larger diameter then fuel or vacuum lines.
 

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Discussion Starter · #16 ·
Then they did it wrong. Period.

Why are you on the internet asking when you should have the bike at the shop?
I wouldn't take it back to that shop. I feel like they didn't do something right and trying to narrow down some ideas. They told me that the valve were bad on that cylinder and it failed the compression test. I had it tested again and they were within 10%. Trying to find ideas, that way I don't have to keep throwing money at it.
 

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I wouldn't take it back to that shop. I feel like they didn't do something right and trying to narrow down some ideas. They told me that the valve were bad on that cylinder and it failed the compression test. I had it tested again and they were within 10%. Trying to find ideas, that way I don't have to keep throwing money at it.
Ok I understand.

Well its the carbs. You need to take them off and open them up.
 

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Guys.

We need to stop worrying about telling people to disassemble carburetors. If you cant clean and rebuild a carb then set it to spec in a half hour or so you shouldnt even own a motorcycle. There are 12 year olds that can do it blindfolded.
 

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Most things are dead simple if you have somebody show you how the first time.
Like adjusting valve clearances. Or servicing carbs, clutches, brakes, suspension, fuel injection, electrics and bearings.

If you have 2 identical motorcycles almost anyone can troubleshoot a problem, just start switching out assemblies until the problem goes to the other bike. Too easy.
 

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It branched to a 3 way line. 2 of the lines branched to the carbs,
If it is a crankcase vent, it would go to the air box where it can expel hot gases and oil mist into the air box and draw in clean air.
Doesn't sound like a crankcase vent. Re-read post # 11, Trials.
Seems more like a carburetor vent but can't really tell much from the one pic.

S F
 
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