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Message started by kylejang on 02/14/18 at 15:53:59

Title: About backfire issue.
Post by kylejang on 02/14/18 at 15:53:59

Hello. I have a question about backfire issue. I am from Toronto, Canada.
Today weather was warm 5C (41F) so I start up bike outside and found something strange. After bike was warm up, gear in neutral, when I revving little bit with half choke on there was no backfire but when choke is off with revving little bit bike start to backfire. With my little knowledge opening choke will allow more fuel to burn right? So more fuel means more chance to having backfire? I am confused or is something wrong with my carburetor but I recently cleaned up carburetor. If I am wrong please don't hesitate educate me. Thank you everyone who read and reply. Have a great day.

Title: Re: About backfire issue.
Post by eau de sauvage on 02/14/18 at 15:58:37

Is it actual backfire, or just popping from fuel in exhaust? How is it when you're riding normally.

Title: Re: About backfire issue.
Post by justin_o_guy2 on 02/14/18 at 16:47:59

I wouldn't worry too much about how it acts before it's been ridden long enough to get it up to operating temperature.
As long as it will fire up without drama, it's not too far away from good.
Don't idle it on the sidestand.
That starves the cam of oil.
Get it fired up and ride away gently.

Title: Re: About backfire issue.
Post by Dave on 02/14/18 at 17:16:27

The backfire when you close the throttle results because the closed butterfly and slide has closed all the fuel flow except for the idle circuit...however the high vacuum caused by the closed throttle and revving engine causes a lot of air.......which results in the fuel air mixture being too lean to burn in the cylinder - but it can be ignited in the exhaust. When the choke is "ON" it does richen the mixture a bit and there will be less backfire - however the mixture likely is too rich for good performance of the bike once warmed up.

The bike is primitive....it can backfire when you close the throttle. You can reduce that by being more gentle closing the throttle.....close it slower and if the bike backfires when decelerating - just add a tiny amount of throttle and the noise will stop.

Title: Re: About backfire issue.
Post by Serowbot on 02/14/18 at 17:31:59

Yup,.. what Dave said...

Title: Re: About backfire issue.
Post by kylejang on 02/14/18 at 19:37:13

Weather was nice but snow was everywhere so I haven't chance to ride. What is the difficult between popping sound from exhaust and backfire? When I heard the sound it doesn't sound like consistent for example I know consistent potato sound for Harley Davidson.
How about turn fuel mixture screw to more lean side it will help?
When I was cleaning carburetor I found out previous owner(I am 6th) already removed plug and set fuel mixture to rich position(I checked spark plug and found out tip and front side is all black so I replaced) as a now I think I set up mixture screw back to neutral position no hesitation but not high revving at neutral gear. Please let me know what you thinking. Thank you.

Title: Re: About backfire issue.
Post by batman on 02/14/18 at 20:59:28

I think you should read up on how to adjust the mix screw. and you adjust idle speed with the screw on the other side of the carb, the knurled one with the spring on in it.

Title: Re: About backfire issue.
Post by IslandRoad on 02/15/18 at 00:19:31

The carb is subject to atmospheric conditions. My bike will after-fire (pop from the muffler) on a cool morning before a hot day. The rest of the time it doesn't. Look for a good average setting when you tune it.

Title: Re: About backfire issue.
Post by piedmontbuckeye on 02/15/18 at 07:34:47

IMHO, the popping and backfiring is caused by too lean a situation when very cold due to not enough choking. The engine as explained above hasn't had time to fully warm up & on real cold days, that time is really extended!

I took mine out last week on around 30 Deg. morning, and a full choke wouldn't keep it running until the third start, then, the popping didn't stop for about 8 miles. I usually never have any problem like that when temp is around 45 Deg. or above!