popping and backfiring

[hotrodbanshee]

What would cause my shee to miss and pop at wide open throttle (Rich or Lean) condition? I am at sea level and running 300 mains. It runs great idle to 3/4 throttle. My mods are below. Please help fast.

[scotts96fast]

Any kind of back firing I would say it's lean.

Did you make any changes to the machine?

Edited February 20, 2005 by scotts96fast

[hotrodbanshee]

I just rebuilt my topend with new weisco prolites. It had stock pistons before with 135 psi compression. Now it has 185 psi compression. I was running 400 mains with the stock pistons. A friend of mine told me that the motor is more efficent now and does not need as big of jets. He said to try 280 mains. I also changed my oil/fuel ratio from 32:1 to 40:1(castor 927).

Edited February 22, 2005 by hotrodbanshee

[scotts96fast]

with 185lbs are you running race gas?

[hotrodbanshee]

I am mixing c12 with 93 octane 50/50.

with 185lbs are you running race gas?

326645[/snapback]

[hotrodbanshee]

Well I dropped the needles one notch and put in 280 mains. Mid range was great but topend was really lean,(plugs were white) and it sputtered and backfired really bad at WOT like a fourstroke hitting it's rev limiter. So I put in 330 mains and the plugs got a little darker, still not dark tan and it still sputtered and backfired @ WOT. I think I am going to try 350 mains next. Could something else be causeing it to run bad at WOT or just a lean condition? I did put in new plugs.

[scotts96fast]

I wouldn't worry about anything else until you get some color on the plug!!Do your plug chops...Some people read the smoke ring on a brand new plug.2 -4 mm I belive is good to go.....

[jaysea1]

At sea level with those pipes you should be at 320 mains...+ or - a size, I would start at 320 and do the plug check.

[hotrodbanshee]

I just got finished installing 350 mains. Ran a whole lot better. Did not miss and backfire this time. Pulled the plugs and they were darker. Still on the light side though. I am going to put 370 mains in tomorrow and run her.

[Banchetta]

Your answering your own questions and doing a great job, jetting is trial and error. Just keep reading your plugs and you'll be fine. DON"T listen to your friend.

[Yamaholic in va.]

[Dont go above 32:1, unless you like rebuilding crank assemblies.

[64xracer]

when my shee had your combo I run 380 mains at 1600ft in 50-60 degree weather

[Ducman]

Your symtoms sound lean, but I can't see needing mains larger than 340 for your setup unless you have port work or something we don't know. I have had a bad plug act almost like a lean condition pop or misfire on the top end but you said you already changed the plugs. Is the plug boots making a good conection with the plug electrode?

 

How long does it take to get color on the porcelin (SP?) part of your plug. My shees dialed perfectly, backed up by the dyno sniffer, and it takes 20 minutes of hard riding to make the porcelin turn light tan and it doesn't get much more than a medium brown after hours and hours of riding. However when I do a WOT plug chop with a new plug it makes the 2mm dark band at the top of the porcelin. I have seen slightly too rich and slightly too lean to get a perfect 2mm ring. Do a WOT plug check with new plugs, cut out a section of the threads, and look for the 2mm band. If its real dark and more than 2mm your too rich, if its not quite 2mm then lean. It's accurate, i.e. if its 1.5mm then your lean, 2.5mm then your rich. I like this method. It gives you something you can measure and takes the guess work out of looking at shades of brown. Pluss I'm slightly color blind. I think the color on the porcelin throws a lot of people off. Or do a WOT check with old plugs and look at the color on the strap and the bottom ring (flat metal edge) of the plug.

[scotts96fast]

This has nothing to do with jetting,but in a way you were trouble shooting.One good thing to do is pressure test your motor for air leaks.Alot of people think they have a jetting problem when they have a air leak.I made my prussure tester for a few bucks and use my air compressor.i will check it once a year if I don't tear the motor apart...Also check it after rebuild.

[race-a-holic]

This has nothing to do with jetting,but in a way you were trouble shooting.One good thing to do is pressure test your motor for air leaks.Alot of people think they have a jetting problem when they have a air leak.I made my prussure tester for a few bucks and use my air compressor.i will check it once a year if I don't tear the motor apart...Also check it after rebuild.

331877[/snapback]

I believe it is the jetting.A friend of mine had a Banshee with pro-circuit pipes and K&N filters.Once it hit it's top end, it would pop like a 22-rifle went off.Sounded awful.He put bigger jets in it,and the popping stopped.It ran a lot faster too.He ended up putting 400 jets in it.It's run good ever since.No problem with fouled plug either.