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Message started by Keith55 on 07/07/08 at 14:22:44

Title: backfire
Post by Keith55 on 07/07/08 at 14:22:44

I've tried all of the things I could find about the backfire of these bike but can't stop it. I got it running really well but when I stop the engine after about 2 sec. its a very loud backfire . I stop and get about 3 steps away and there she goes. Blammm! Is there a way to stop this?
I'm scaring the children.

Title: Re: backfire
Post by skrapiron on 07/07/08 at 14:31:34

It's just the bike's way of saying 'Honey, I'm home!'

The only way I found to eliminate it is to pull the choke out one notch before shutting down. It momentarily creates a super-rich a/f mix and eliminates the backfire.

The shutdown pop is half the fun of owning a big single!

Title: Re: backfire
Post by Keith55 on 07/07/08 at 14:35:58

Sorry But this ain't no ,Pop, it sounds like a 12 ga going off.
But thanks I will try the choke thingy see if that helps....

Title: Re: backfire
Post by verslagen1 on 07/07/08 at 14:38:25

One guy pulls the choke out and as he kills it lets out the clutch.

The problem is some fresh air is mixing with your exhaust gases which contain some unburnt fuel. Once it hits something hot enough, kapow!

So, 3 ways to stop it. eliminate the fuel or eliminate the air. A very small air leak in your exhaust is enough to get a kapow. It can be several places, head and header (check the gasket and retorque the bolts) header and muff (check the clamp and seal with a candle) and all over the muff in case there is a rust thru.

3rd way, get a supertrapp. I never get anything but a poof and I've leaned out the idle alot so that I get mild pops on shift. 8-)

Title: Re: backfire
Post by Keith55 on 07/07/08 at 14:48:22

Yes It won't do it when cold. I mean if I just crank it and kill the engine after just running it for 5 or ten mins it don't do it. But if I ride fore 20 or 30 mins. then she Booms! It is a 1987. it only had 582 miles on it whan I got it. looks like it was alway kept up. no rust any where but I'll check the muff.

Title: Re: backfire
Post by verslagen1 on 07/07/08 at 14:57:23

The header is dual wall and so is the muff.

check the holes on the bottom, leaks will show up here. This knowledge is brought to you by our fellow members. ;D

Title: Re: backfire
Post by Keith55 on 07/07/08 at 15:00:39

Will do thanks

Title: Re: backfire
Post by oksavage on 07/07/08 at 18:01:21

I am also experiencing the "hit the deck,drive by" style backfire. I've adjusted the mix screw a little and I can't tell any difference in the bike. What should be happening. I have an 86 with 18K and a Jardine slash cut. The bike was a California model but a previous owner removed all the extra stuff. Consequently I have lots of tubes under the seat that go nowhere. The idle/mix screw cover was already off so someone previously adjusted it. The other day i was riding and began to experience these weird hiccups/jerking as I took of. It only clears up if I go at about 1/4 throttle or better. Which way should my next adjustment go?

Title: Re: backfire
Post by Sandy Koocanusa on 07/07/08 at 19:17:25

When I hear "hiccups/jerking" I immediately think petcock. That's what mine did when the petcock went T.U.

Title: Re: backfire
Post by oksavage on 07/07/08 at 20:29:44

what was wrong with the petcock?

Title: Re: backfire
Post by Sandy Koocanusa on 07/07/08 at 20:37:37

The truth is, I don't know. That was back when just changing it was a test of my nerves. I just put in a new one and all my troubles vanished. I have the old one laying on my desk now, in about a dozen little pieces. The diaphragm was kind of leathery, and I suspect it just wasn't holding vacuum properly.

When I get back around to it, I'll finish modifying it to the "on/off" type. That will probably happen some evening this winter, though.

When I decided to change it was when the fine folks here suggested that I run it on prime. That seemed to clear things up, so I just swapped it out.

Title: Re: backfire
Post by Sandy Koocanusa on 07/07/08 at 20:45:47

Regarding tuning the air/fuel mix:

Check out the article in the Tech section titled "Lancer's Straight and Simple Carb Tuning." I read that thing over and over, and could never hear the engine changing speed. Using the information he provides, though, I was able to get rid of my backfires. Just do it the way he says to.

When I finally WAS able to hear the engine change pace, I had just changed my pilot jet for a larger one. Then it all made sense. Just based on what I experienced, if you can't hear the thing changing, turn the screw out about three turns and run it for awhile. If that won't fix the backfires, you either need a bigger jet, or the cause of the racket is something else, like an exhaust leak.

Title: Re: backfire
Post by BurnPgh on 07/07/08 at 21:31:28

i tried tuning the carb by lancers method several times and couldnt notice any difference in engine speed until i turned the idle down quite low. With a low idle i adjusted it, turned the idle back up and now USUALLY its just a poof on shutdown. If it's just rained i get a small bang but not 12 gauge style like i used to. I like the poof. The bang, not so much.

Title: Re: backfire
Post by LANCER on 07/08/08 at 01:32:22

Sounds like ya'll are learning to "hear" the engine as you go through the tuning process. It is easier to do if you have a tach on the engine, then you can watch the rpm change as you turn the pilot air adjusting screw. As in the tuning instructions, you are looking for the highest rpm you can get. If the pilot jet is the correct size, you should be able to find a "rpm high spot", and turning either left or right from that spot will decrease rpm. If you find that as you turn the screw OUT (richening the mixture) the engine just continues to slowly increase in rpm until you get to 3 turns out, then you need to go to a bigger jet; start over and look for the "rpm high spot". Whenever replacing a jet with the next larger size, it is usually easier to begin the process with the screw set at 1.5 turns out.
Then, with the pilot air adjusting screw set at the spot that your engine likes best, readjust the idle screw for proper idle rpm of about 1000-1200 rpm.

Title: Re: backfire
Post by Brad_THMP3R on 07/08/08 at 09:12:57

how about a video of this 12ga goin off? Mine did a little fart once. I started it up the other day at work, revved it a little, snapped the throttle shut in an effort to get it to backfire. Bang!! and one of my co-workers with a kawasaki 800 pissed his pants and said, what the h3ll was that!! ;D

Title: Re: backfire
Post by Keith55 on 07/08/08 at 13:46:17

Wow! pulling the choke out before stopping the engine did the trick. I mean it don't do nothing at all ,nothing, thank you very much Skrapiron.... If anyone else is having the trouble with backfire <<Try it

Title: Re: backfire
Post by skrapiron on 07/08/08 at 17:51:28

You're welcome, Keith. :)