Wont start! Backfires violently!

fcarlos085 · Posted: March 1, 2009, 3:22 pm Post subject: Wont start! Backfires violently!

hello everyone!

Im new here!,and i just purchased a 77 bobber project with xs650 engine.
At the current moment the bike has not started in over a year. So i changed the oil and also the oil filters.I just finished wireing up the electrical of the bike which includes the ignition also and new spark plugs. Checked both cylinders for spark and they both fire nicely. New battery installed and on a battery tender too. Now the carbs i did not touch. Dont really know much about them. So this week i got the oppertunity to finaly try and start the thing with no luck! I put fresh 93 octaine in tank opened petcock looked at my fuel filter for flow it was good. ignition on,choke on then i started kicking it. i must have kicked it over 10 or 15 times! and i got NOTHING? so i checked the carbs and seen that the barrels had a lite film of fuel inside. so then i decided on starting fluid. sprayed the carbs with a light mist, then i proceded to kick it over again. at the second kick it poped out the exhaust then the third kick there was a HUGE! flame that shot out the exhaust with a LOUD BANG! got scared so i put down the can of starter fluid and continued to kick it over, but i got nothing but backfires! and flames shooting out the exhaust! What could the problem be??? i have spark! so is it the carb?? why would it backfire with starting fluid?? im Stumped!!

xsjohn

Timing sounds wacked.......are the wires crossed or something ...........

xsjohn

fcarlos085

i dont think so, but if they were what wires are you refering to?

jayel

dirty pilot jets/choke circuit and yes does sound like the timing could be off ..... right side cylinder (top set of points) shoud fire at "F" mark turn the engine over until those points are open (may have to turn engine to get on right stroke) make sure those top points fire that plug or timing could be 180 out or wires crossed

jayel · Last edited by jayel on March 1, 2009, 4:12 pm; edited 1 time in total

wires from points to condensers to coils

Romer

LOUD BANG absolutly bad fuel. I had the same problem. clean tank, replace filter, clean carbs. If straight pipes you may need to baffle.

fcarlos085

thank you! i am going to try what you said i will bring back an update when i can.

kingwj

could be the plug wires are reversed. You can switch the leads from the points.

pumps

fcarlos do you have a manual? If not get one.

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Good spark and correct timing are the absolute FIRST things to check. You'll feel like a chump if you get those carbs all torn apart and put them back together and find you've got the same problem you had when you started. Check ignition timing takes ten minutes tops. Carb overhaul can take DAYS.

Think about it.

Romer

Carbs will take 2 hours tops after soaking in cleaner. If they have been sitting for awhile, wouldn't hurt anyway.

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Right, Romer:

Romer wrote:

Carbs will take 2 hours tops after soaking in cleaner. If they have been sitting for awhile, wouldn't hurt anyway.

. Carbs will take 2 hours for a guy like you, who knows exactly what he's doing and doesn't make any mistakes. But a newbie tearing into his first set of carbs ain't gonna get it done that fast and probably won't get it done right the first time -- or the second -- or the third -- and that's why I say it CAN take days.

eanwhile, he doesn't know if the ignition is OK, which means that when he puts the carbs back together and he's still got the same problem, he won't know if it's the ignition or if he f***ed up the carb job.

I don't dispute the idea that the carbs will need doing anyway. I just argue that the ignition is basic to everything else, and he should be certain the spark is doing what it's supposed to do WHEN it's supposed to do it before he runs off into the sunset chasing carburetor problems that might -- or might not -- be present.

kingwj

do one at a time, then you can look at the complete carb if you have a 'moment'. And the backfire tells me that jimmythetrucker is on the right track, your ignition is not set correctly. Now if you were in Newark, DE and not Newark, NJ I'd give you a hand.

Romer

I agree with switching the wires first to check fire. Thats a given. My carb rebuild was the first on a motorcycle. They really are straight forward and simple. Just lay each piece out as you go. kingwj is right. take a moment look at the finished one. Move on Smile

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