Backfiring

Hi

I have recently bought a KZ550 Spectre, but it has a 4 into 1 stainless steel Motad exhaust fitted. This is very load and I really want to reduce the noise level.

I am getting a lot of backfiring when decelerating and could do with a few poiners as to how to resolve this.

Also, what should be bike idle at in terms of RPM's?

thanks

sounds like an air leak?

Hi, a couple things maybe. . .

I find that 1000 rpm at idle is about where my particular motor seems balanced between response when pulling off from a light (no accelerator pump) and idle pulses which sometimes occur. You might give some more information about the age of the bike (miles) and where your idle mixture screws are set at. It can make a difference if there is some varnish in the carbs, especially where you are concered, regarding what is happening when you decelerate. What is happening is when you back off the throttle, the mixture goes lean, causing the unburned fuel to ignite as it is traveling down the exhaust manifold. Once the throttle is closed, only the idle circuit is active, so maybe richening it up can help. The other thing to check is maybe for a stuck advancer. Timing can cause issues.

Hi

Thanks - it's a 1983 Kz 550 F1 Spectre with 13000 miles on the clock, but don't think that they can be believed.

I have no idea where the idle mixture screws are set.

I have only just got the bike and know very about em!!

I have bought an old Service Manual and will take a look.

I suspect that the carbs will need cleaniong and that the exhaust has a leak!!!

I currently idles at around 1500 rpm, which sounds fast.

Here's some information that might be helpful with your new purchase. . .

www.totalmotorcycle.com/buyersguide/Kawa...550-GPZ-ZX550GPZ.htm

I wouldn't suspect the odometer reading until you've verified that it doesn't work. You might have bought a low mileage bike. I got my KZ from the original owner in 2000 or so. . .22 years after he purchased it brand new. . .with only 12,600 on the odometer. Sometimes people buy a motorcycle, ride it a little, and discover parachuting is safer, because of the reserve chute. In my case, Jeff had gotten tired of rolling the bike into (and out of) his mom's basement in the hopes of riding, but long storage would discharge the battery, make the bike hard to start, etc. . . so him with a baby on the way, and me with money in hand, I bought his pristine KZ650 for $500 bucks, about a dollar a pound.

As it turned out, Jeff thought his extra fifty or so pounds of weight due to aging changes was the cause of the bike running sluggish, but I found the timing advancer stuck retarded was more likely the cause.

If you have a factory service manual (as versus aftermarket) verify your engine serial number, as sometimes (as in my case) there is a suppliment which can make a difference in service options.

Just a reminder.. you cant have an explosion i.e. backfire with out oxygen..
I'vefound that about 90% or better of the noiseswe call decel backfire is a combo of an air leak in the exaust tube some where and a bit of a rich mix. The rich mix could be from older worn slides hangin up for a split second or dirty carbs .. easy to fix the dirty part if its running ok inthe pulling part just an ounce or so of something like seafoam in the tank to clean the carbs..

You can also have something in your combustion chanber that is preigniting. I always use gumout carb and valve cleaner to clear such carbon,and if you use it be ready to reset your valve clearances

Issue seams to have died down a little since I re-fitted the exhaust. Was leaking badly at the manifold - still blowing now.

The Engine seems to be running well, so I don't really want to mess with it, as I can live with the exhaust popping.

I think I'll concentrate on getting the exhaust sound and take it from there.

Thanks for the help.

Post edited by: screwfox, at: 2007/01/23 15:41