Backfiring/popping information

[mrbsyammy]

Re: backfire under deceleration

Originally posted by bikerphil
Sometimes richening the pilot screw adjustment will minimize this. Look at the color of the plugs and find the leanest one and start with that carb pilot screw. On my SF, all it took was 'bout 1/8 - 1/4 turn open to reduce backfire. HTH

I need to jump in the middle of this and get my quarters worth.. DO NOT LOOK AT YOUR PLUGS unless you have taken at least a 20-30 minute Hyway drive and that means sustained speed of at least 55MPH and when there is a safe place you can pull off the road hit your kill switch while you are going 55 MPH or better DO NOT SLOW DOWN TO A STOP this is very important because the minute you start slowing down your plugs will carbon up guaranteed. Pull your plugs out and then look at them this is the only true way you will see what is actually happening FACT NOT FICTION. Have you ever watched NASCAR racing? next time you see them running for the post you will notice that after their second lap they will shut their car off at full speed they do not slow down and then shut off because if they did they would get a false reading from their plugs..There thats a quarters worth and then some. GOOD LUCK..till then Mr Bill

[wapam]

Originally posted by TopCatGr58
Hey Wapam,

It's the Idle Mixture....Pilot Jet SCREWS, you can try turning them out 1/8 or 1/4 turns each and see how it behaves, sounds.

Of course, this is IF it's otherwise running strong in the upper RPM's. IF it's falling on its face under sustained hi throttle, then you may need to go up on the mains...follow the jetting guide in the tech tips for assistance there, depending on your mods, if any!
T.C.

Thanks TopCat. Please bear with me so I get all this clear in my head.

The Yamaha Service Manual says to not mess with the "idle mixture screw" settings. Now, is there an actual part called an "idle mixture screw" or are they referring to the "pilot screw"? IE, the idle mixture screw is just another name for a pilot screw.

If I turn these out 1/8 turn for instance and the bike runs worse, when I turn them back in 1/8 turn will I be right where I was when I started or have I just totally messed up the carbs?

Also, header pipes (right at the engine) have a goldish tint to them, and the bike stumbles right off idle (great top end). Could both of these conditions (along with my backfiring) be caused be a lean mixture?

Thanks again, I appreciate your (and everyone's) time.

[prometheus578]

pilot screw/idle moxture screw... same creature.
Lean mixtures heat up pipes. First gold, then blue, then black.
When it hits cherry red...
which is why we say.. if you're running the bike for any reason, doing checks and such, always place a fan to blow across the pipes and the engine colling fins.
Turning out a turn and then turning right back a turn does nothing but turn your wrist. No damage to bike. Idle mixture is adjusted with that screw

[wapam]

Originally posted by prometheus578
pilot screw/idle moxture screw... same creature.
Lean mixtures heat up pipes. First gold, then blue, then black.
When it hits cherry red...
which is why we say.. if you're running the bike for any reason, doing checks and such, always place a fan to blow across the pipes and the engine colling fins.
Turning out a turn and then turning right back a turn does nothing but turn your wrist. No damage to bike. Idle mixture is adjusted with that screw

By George, I think I've got it! Thank you.

[wapam]

I fixed the backfiring and the hesitation coming off idle. Cleaned the carbs and adjusted the pilot screws. Probably not perfect as I only adjusted by ear but a whole lot better then it was. Still a very, very slight hesitation (hardly even noticable) but for a 28 year old bike it runs darn well and good enough for me. Backfiring is gone.

Also found out that the bike won't run without the vacuum hose hooked up to the octopus. I couldn't figure out how you are supposed to adjust the pilots if the bike won't even run...oh well, at least I learned something.

THANKS to all for your help.

[DiverRay]

If you put the petcocks on "PRIME", it WILL run with the vacuum off. JAT