Help! Flaming backfire!

[Bizzy13]

I adjusted my valves yesterday and cleaned my carbs. I put everything back together w/ new fuel lines and fired it up. Runs a lil rough but no longer has the slow throttle down on deceleration. New problem is that upon decelerating I'm getting backfiring and flames out of both pipes. I know these pod filters don't fit right and they block off the air jets, but it wasn't doing this before. Is this a mixture problem, a valve problem or something else?

 

[Scorpio1963]

Have you synced your carbs?If not this is what your problem is,also if the valve lash gap isnt set correctly you will also expereince the symtoms you mentioned like back firing.

 

[willem]

it's most likely a jetting problem. Pod filters increase air flow, which makes your bike run lean. That's causing the backfires and flames. Better get it fixed soon, before you blow up your pipes and valves. Look around the forum for jetting advice, I read that going up 2 sizes is usually a good start. Other than that, it's mostly guesswork and trial and error.

Good luck

 

[Pork Chop]

I thought flames out the exhaust was unburnt fuel igniting in the exhaust.

 

[Bizzy13]

The carbs were jetted and set up by a cycle shop, but Im not sure what stock is on this bike. The mains are 137.5, someone on here told me that's stock jetting on these bikes?!! I might have to rejet if that's the case. As far as pods causing this, it wasn't doing this before I set the lash and cleaned the carbs. I did a bench/wire sync, I will do that over again as well. I set me lash at .010 & .018, that's correct right?

 

[willem]

I thought flames out the exhaust was unburnt fuel igniting in the exhaust.

yes, that happens when your bike is running too lean or too rich. Running too rich causes the mixture to not burn completely (too little oxygen) which makes your exhaust fumes combustible. Running too lean will make some strokes not ignite, which also causes fuel to end up in your exhaust. When the next stroke does fire, it'll ignite the fumes in the exhaust as well.

 

[Bizzy13]

Makes sense because it sounds like its missing

 

[Pork Chop]

Hey Willem thanks for the explanation.

 

[Scorpio1963]

I know on another thread you were talking about your mains being 137.5 .My bike is an 81 which had the same jet size.Also if I remember correctly the pilot is 42.5 stock.If you want to know if your bike is running lean or rich take out the plugs and look at what they are telling you.If they grayish tan color thats good.Black and sooty is too rich.No color to whitish is too lean.

Now Im running pods and baiscaly open exhaust without the crossover inbetween.I experimented with jet sizes going up 2 to start with.Then I bumped it one more size up and I also changed the pilot up 1 size.3 and 1/4 turns on the mixture screws and my plugs are telling me that fuel mix is where it should be.YOu have said that when your bike is running you have flames and backfiring,did you run he bike for a while after you noticed this or just shut the bike down?I ask this because after all the jetting and modds I made when I 1st started my bike it did the the same thing but after a couple minutes it stopped and hasnt done it since.

 

[Bizzy13]

Stock mains are 135 on these. I didn't check the plugs last night cuz it was dark, but it ran for probably 20 mins and still kept up the backfire. I dunno what my pilots are.

 

[HoughMade]

What are your idle mixture screws set at now?

 

[Bizzy13]

I was dickin around w/ them last night after dark so I'm not sure. Tonight Im going to readjust vakve lash & resync and start at 3 turns.

 

[Bizzy13]

I assume you mean mixture screws...

 

[HoughMade]

Yes- for the fun of it, start at 3.5 and see what it's like. If I get too much popping on deceleration, I just need to richen the idle mixture a bit. However, I have a fully stock intake ans exhaust, so yours may not have enough range- try it anyway.

 

[Bizzy13]

Will do man. Thanks. I'm running pods and open headers but Im up 2 1/2 jet sizes so I should be able to straighten it out w/ the mixture. Hopefully.

 

[xschris]

Hough where did you find a stock 79 exhaust for you bike. The 79 stock pipes are hard to find, did you find them on ebay or another on line site?

 

[HoughMade]

Hough where did you find a stock 79 exhaust for you bike. The 79 stock pipes are hard to find, did you find them on ebay or another on line site?

When I say "stock" I mean stock restriction. I have mufflers with about the same backpressure as stuck even though they are aftermarket.

 

[Bizzy13]

Okay I readjusted valves and we're running much better. Im at 3 turns out mixture wise. 3 1/2 was showing black plugs. But there's still a flaming back fire on high revs. ?? Still maybe try resyncing carbs. I'm running out of ideas.

 

[xschris]

Hough I don't think the mufflers you have there are ever close to stock back pressure. The stock ones are 31" long and less than a inch hole at the end. Yours looks to have a 2"+ outlet. They look to be off a much larger displacement bike. I say this because you would never get a popping back like that from a stock set of pipes. Unless there are big holes in them Bizz unless you put some more restrictive mufflers you will still get the fire out the back With my 80 that has a free flow 2-1 on it when I let off the gas fast it will give a rumble/pop sound. My stock 79 you can barely hear it running

 

[Bizzy13]

It didn't do this before I cleaned the carbs and adjusted valves. My old 82 KZ didn't do it either and it had way short pipes. I got the popping yea, but not flames. Maybe these bikes are different though, idk