Questions regarding backfiring issues, and fuel petcock.


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Hello everyone,

It's been awhile since I have posted anything and my build is currently at a stand still until I can get some money saved up to work on the bike. I have a few questions though relating to backfiring, both through the carbs and the exhaust, and with the fuel petcock. So, with the backfiring, I have tried tinkering with the screws that adjust whether there is more of a lean mixture or rich mixture running through the bike, and while the bike was running no matter where the screw was the left cylinder would backfire through the carbs. Sometimes after riding the bike and switching it off it would backfire through the exhaust and only on the left cylinder. I have done a carb rebuild, and cleaned the carbs (kind of a half ass clean), but no matter what I seem to do it always backfires. I have not synched the carbs yet, but when I took the carbs off it and pressed on the throttle plate they open up at the same time and same position. This is a noob question, but does that still mean it could need to be synchronized? Lastly, the hose to the vacuum petcock was way too loose and kept falling off so I cut the hose about a half an inch and couldn't manage to get it back on, but the bike seemed to be running fine without it, and didn't run out of gas or anything. Is this something that could cause an issue, and if so what issues could it cause, and what is the purpose of the vacuum line?

Thanks fellow XS'ers!
Well...the backfiring suggests a vacuum that vacuum line back on there and maybe it will solve the issue.
Do not half-ass a carb cleaning...those carbs need to be perfectly clean as they are very sensitive...
When you think you've cleaned them...clean once more...
When you take the carbs off check the carb boots for cracks and such as they would cause an air leak and thus backfiring
Well, I am back with both great news and bad news. I adjusted the carbs and reconnected the vacuum hose (no I did not clean the carbs) and got the bike running perfectly, and holy s**t these bikes are quick. It ran perfect for about a week, with minor issues such as my vacuum hose falling off. I tried zip-tieing the vacuum hose on but it seems to keep falling off, so if anyone has any good suggestions on how to keep it from falling off, I am all ears.

Now, the bad news.... Last night someone kicked down my apartment door, and stole my tail light off my bike and removed my seat. Living in a college town I knew these sort of things were bound to happened but I didn't think it would've happened this quick. There was no apparent damage/tinkering with the bike, but for some reason when I went out to ride this morning the bike completely changed. It felt like I was only riding on 1 cylinder. I immediately drove it home and checked out the bike and nothing looked out of the ordinary, but for some reason the right cylinder was backfiring, which it has never done before. I do not know whether it is just bad luck and my bike felt like acting up today and there is some issue that I have not addressed yet, or if there is possible tinkering that could have caused this. I am a newbie when it comes to this kind of stuff, but it seems odd that my bike would go from starting up within a half a second with no choke or priming and running perfectly, to not wanting to start and backfiring out the right carb and feeling extremely sluggish. Also I had to adjust the idle screw significantly to keep the bike running at idle. If anyone has any ideas what could cause these issues, or if they think it is due to tinkering, please let me know. I already filed a police report and would like to update it if there is more damage than expected.


P.S. a Manometer is on it's way
Do you have a filter on the fuel line? Something may have came loose in the line and clogged a port or something in one of the carbs. These bikes are finicky at times.

The manometer can be made cheaply also so no need to order one.
Vacuum line? Its for keeping a seal on the input boot. (ie Carb to head, so that there is no leak though that brass tube.
2, a original petcock, uses that vacuum to allow fuel to the carb.

security, My wife was always conscience that thieves want parts off of her bike, so she would use a huge tire lock, and supposedly the seat is suppose to be locked to the frame. I guess not on yours. Seems Ohio should have a bike bone yard. I would see if there is one close to you, and pick up missing parts. I hope they didn't jack up anything else as they stole you stuff. (I am not as conscience, but maybe I should be)

3. cut a portion of your current vacuum hose, and run to a local hardware store, and get a replacement hose from there. I am using vinyl tubing, That is good for about 2 years, if you get 10 feet of it, that will last you another 20 years. replacing a foot every 2 years ... There is silicon rescue tape, at those same stores that can protect from heat up to 500 degrees f. See hard ware store for their suggestions... those guys know alot, (unless you get that high school chick) if you don't have a cheap inferred thermometer, you might like to consider that, or you can use back of you hand on near the exhaust pipes, to see if there is any heat. (dont burn your self) (a spray gun with water seems to work too) that will tell you which carb needs more work.
4 cheap filter, will go so much further in protecting your carbs. I like paper due to my rusty tank was still getting past my paper carb, and my bike was still running. I suspect that the brass filter would have let bigger particles though. (note I have platicKoted my fuel tank, (or was it PUR15)
Manometer is everywhere, the cheapest one is the 2x4 with a vinyl hose and atf oil. the better alternatives are the ones with mason jars, (plural) and vinyl hoses. I like science and the 'B' option looks neat, but the option A is what i have in the garage, and it is durable. and if the engine drinks a sip of my ATF, not a big deal, it will just take a moment longer to clear it for back to normal attempt to start again. (I seem to remember if that was an issue having a "non-running car battery jumper'ed to my bike battery so I didn't have to worry about running out of charge.)

One other alternative to non running side is that the coil may not be getting voltage to the plug. Option a, trim .5 inches off of both ends of plug wire, recap, and try again. change plug, and cap for extra sure-ity. (don't think that is a word)