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Discussion Starter #1
I recently bought a 1984 Honda VT500FT Ascot (my first ever motorcycle) as a starter bike. I rode it for 2 weeks (200 miles) and it ran great. I should mention that I have no prior riding experience or experience with working on motorcycles. Also, I made the mistake of filling up with old gasoline (1-2 months old).

The other day, I went to start it and it was difficult to start. I can only keep it running if the throttle is open. If I let off the throttle and let it idle, the rpms slowly drop down until it reaches ~500rpms and stalls out. While running, it smells like gasoline. It also backfires sometimes when trying to start it. I have been led to believe the carbs need cleaned.

This past weekend I:
drained the oil and noticed it was very thin and had gasoline in it
removed the gas tank and drained the gas
removed the petcock and noticed the petcock screen was mostly non-existent

I want to try to clean the carbs without taking them apart (sea foam). Is this worth a try?

What should I do next? Any tips are greatly appreciated. I don't have experience working on motorcycles but I should be able to figure most things out using my engineering background and the internet.
 

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Gas in oil, smell of gas while running, no filter; I'd say you have something blocking the float valve, keeping it from closing. That lets the carburetor overflow, and much of that goes directly into the cylinder and into the oil. Can you remove the float bowls (bottom of the carb) without much difficulty? If so, put some fresh gas in the tank (it doesn't take much) and close the petcock. With the float bowl off, and something to catch the gas, open the petcock and lift the float until the fuel stops flowing - don't be rough with it. Maybe let it open a close a few times, to wash any junk out of it.

Before you try to start it again, change the oil, or engine damage will occur. You may not have done much damage, so far, but don't push your luck.

Since this came on suddenly, and the screen in the petcock is compromised, I'd guess that junk in the tank is just going directly into the fuel lines. If that is the case, it will just happen again, so you may want to get a small, in-line fuel filter for the line from the petcock. Seafoam will clean your fuel system pretty well meaning it will loosen more junk in the tank, so get that filter before using it.
 

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Discussion Starter #3
WintrSol, thanks for the information.

Last night, before I got your post, I did the following:

put new oil and oil filter in
re-assembled airbox, petcock and gas tank
drained the float bowls using the drain screws (two carbs)
Tightened the drain screws
dumped 1/3 can of seafoam with ~equal amount of gas into the gas tank
started the bike. It started great on the first try and ran smooth for about 15 seconds before stalling. I wasn't expecting it to start, just wanted to get seafoam in the carbs.
I added a bit more gas and tried to start it again but it would not fire.

I'm assuming the seafoam is now in the carbs and I wanted to let it sit for 24 hours. Tonight I plan on draining the carbs again. dumping more gas in and seeing if it will start. I have a new petcock screen on order and will install that when it arrives. I will also try what you suggested, removing the float bowls.

I have some questions about the petcock. I believe it is a vacuum assisted petcock but am unsure how it works. It has three lines coming off of it. one to the rear cylinder, one to the bottom of each carb and one to the top of each carb. Why are there two lines to the carb? Do they both deliver fuel?
 

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A vacuum controlled petcock will not allow fuel to flow when in the normal ON position, unless the engine is running, which creates the vacuum that opens the valve via a diaphragm. Such a petcock also will have a PRIME position, which is there to fill the carbs before starting the engine. If you drain the carbs, and they refill with the petcock in the normal ON position, the petcock is defective.
 

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Discussion Starter #5
My petcock doesn't have a prime position, only on off and reserve. However, it does have a line going directly to the rear cylinder which I thought was the vacuum line. With the key off, petcock in the on position and the carb drains open, gas flows freely from one of the carbs, the other it just drips slowly. Which is correct? or should it not be coming out at all if the bike isn't running?
 

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From what I can find, the stock petcock IS vacuum operated, so should not let fuel flow in the ON position, so I would guess the diaphragm is stuck.

As far as fuel flow rates, does the fuel line directly connect to the carb that drains, and another line goes from that one to the other? Or, does the fuel line split in two, going to both carbs? If the former, then that would be normal, as the first in the chain would have to fill before letting fuel reach the second.
 
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