620 still slightly backfiring

[camatt29]

 just installed the power commander on my 02 620 monster I had issued with backfiring but they seem to be smoothing out i downloaded a generic map for a wyleco exaust and open airbox... i have the open airbox but a quat d x box and seem to be moving more air than the map suggests. the bike still backfires after full acceleration at about 5000 rpm sometimes... where in my fueling should get an adjustment to help with this issue low, mid, or top end?... also for any fuel experts out there im perplexed at the fact a lean condition causes backfiring? simpleton theory seems to point to more gas= exaust backfire

[duccarlos]

It's back pressure. Anyway, the proper way would be to put it on a dyno to figure out where to adjust it. In lack of that, you'll need to ride it around to identify at what RPM.

[camatt29]

i will be putting it on a dyno later this summer but im trying to make do now... i have mor parts on the way and dont want to dyno untill i have everything... im simply looking for an explanation of how to adjust the pc and why it would be  doing what its doing the fuel system as of now is a very confusing thing to me and i would like to be enlightened

[EEL]

I wouldnt chalk this up to backpressure right away. I had an exbox for a grand total of 15 days on my s2r800. It was a piece of $hit for fitment. I had a huge exhaust leak on the rear cylinder header because the pipe physically wasnt bent right. I was getting the same backfiring issue you were having  (approximately 5200 rpm for me).

I contacted the vendor and told him of how bad the installation was and ended up getting it exchanged for an arrow exhaust.

Suddenly the problem magically dissappeared (even though I had a full race system with pod filters)

Check for exhaust leaks at the header connections. The slip fit connections provided on a lot of aftermarket exhausts leak and result in this problem.

If you decide to dyno your bike anyways, check your valves, sync the throttle bodies and get everything up to spec before you do so. That way your fuel map is accurate.

[camatt29]

the previous owner had sent headers back to Italy two times before he got good fitment. its terrible they have so much trouble its such a good looking exaust... i rode today and had no problems whatsoever... aside from the clutch which may need changing very soon  . i made small fuling ajustments and put alot of miles on today didnt have one bang! ... still in the dark about the fuel system.. sigh

[Howie]

Are you hearing this through the intake or exhaust?

[EEL]

So you didnt answer the underlying question. Are YOU having fitment issues now? Any exhaust leaks?

Fixing fueling wont solve your exhaust leak issue. if the temp gets warmer or colder your bike will adjust fueling internally to compensate and you'll start having problems again. Thats what I was running into.

The power commander only adds or subtracts from the fueling map inside the ECU. It doesnt substitute a fuel map. Its more of an overlay than a replacement. Hence your fuel map changes based on environmental conditions (air pressure, temperature (in newer bikes (not yours) also o2 in the exhaust stream).

If you think you've solved your problem, go ride it in the hills and see what happens.

[OT]

If it backfires while engine braking, then I'd look for leaks.  You say it backfires AFTER full acceleration (which, in my mind, sounds like you've released the throttle -  like engine braking).

First place to look is the tightness of the header bolts -- make sure the headers are pulled all the way into the heads.  You can get to the rear-cylinder bolts by taking off the seat, sticking a few extensions onto a ratchet driver, and going straight in from above the tire.

[bikepilot]

I'd map it so it runs as well as possible and not worry about some burbles on engine braking. 

[camatt29]

sorry i havnt replied latley guys ive been away for a few days... yes it backfired under engine braking i put the dynojet in and the problem had... (i thought anyways gone away)... its not after long riding thebackfire comes back... through the exaust... it only seems to happen when everything is running very hot so im going to go over some of the header with some sealant and tighten the headers

[gfitzgi]

Not to horn in on someone else's advice, but I am having the same problem.

I have an '03 620 with 7k miles that has been dormant for a few years.  I have cleaned out the fuel pump to get the thing running, and checked my valves a few times (<----paranoid).  I always had issues with a few back fires at high altitude (9k+ft) when engine braking, but today I had long strings of them until I got the engine cooled down.

I will check the headers, but I think I even had my first intake backfire, very loud.

Since the bike has been sitting for so long and now I am packing on the miles, I am planning on going through my valves again in a few hundred more miles when i am changing the oil to see if anything has gone wacky.

Could my belts be too tight?  I seem to have a louder clicking noise coming from the belt area of my horizontal cylinder when the engine is warm, and a strange bird-like sound when I am above 230 degrees.

I figured I would post here since the problems are similar.  I will let you know if I have any breakthroughs.

Scott 3