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I just picked up a '74 Honda XL250, and it had been sitting for about 8 years. As the story always goes, (I know the person that I bought it from, and they've no reason to bullcrap about it) it was running when it was parked. The only reason she stopped riding it, is the clutch cable snapped.

Anyhow, I got it home, and started tearing into the fuel system. Even the fuel shutoff valve was packed solid with DRIED varnish. Don't even get me started on the tank itself. Long story short, I got everything flowing good, but it still wasn't getting fuel to the bowl. So, I pulled the carb apart, and cleaned it up. I made sure that all the circuits I could find (entirely possible I missed one, I'm used to working on carbs that are way bigger, like on a classic land yacht) were cleared out, and the float and valve was working real good.

I got it all back together, and on the bike, and it's not getting fuel into the cylinder (judging by smell in the exhaust pipe, which is accurate in my experience). I realized that I hadn't seen any vacuum lines, or ports on the carb when I had it off. Does this bike have a vacuum line on it? If it's not a lack of this, then what the Hades else could it be? Granted that I used all the original carb parts, so that may be fouling me up, but I couldn't wait for my rebuild kit that's supposed to show up this week.

Anyhow, any and all help you folks can give would be most appreciated. Have a good 'n.
 

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The quickest way to tell if there is a vacuum-operated petcock is to read the valve positions.

If it says "PRIME", "RES", and "ON". There should be a vacuum line. If it says "OFF", "RUN", and RES", it does not have a vacuum-operated petcock.

I'd make sure you have fuel flowing to the carb itself as a first step by testing the fuel line. It could be that the float is not adjusted to allow fuel to flow past the valve as well. Check the adjustment and make sure fuel is filling the bowl.
 

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Just remember that the varnish can be anywhere in route from the tank to the carbs. The varnish will dissolve completely if placed in lacquer thinner. However,the lacquer thinner is not exactly friendly to the rubber parts it encounters in the fuel system. Think about replacing even the fuel line with new and also placing an inline fuel filter in the line.
I have heard plenty of cases where old gas is drained out and then the system plugs up when fresh fuel is added. What occurs is the new fuel softens the varnish into goo,and it plugs things up again.
Seafoam also contains [i think the main ingredient is] lacquer thinner. A gallon of LT is about 15 bucks at a paint store,and Seafoam is much higher than that.
If I encounter severe tank varnish,I pour in a quart of the LT and swish it around occasionally, then dump it out after an hour and save it in a glass jar until it clarifies,then strain it out for the next use. It will eventually lose its powers after a few uses. Then I take the rest of the gallon and do the same, and keep the two batches separate to be used over again.
If you see rust in the tank,your further rust treatments will work much better after the varnish is gone.
 
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