Backfiring and stumbling

[KDH123]

  I installed my pcIII and Dynatek ignition with Dl's curves, running on curve 3.  The map I downloaded is the GYTR map off of Krandalls site as suggested. With the quad running in neutral, at about 1/4 throttle, maybe a little less, the motor stumbles, between there and half it clears up, but then starts backfiring a little with more stumble. If I just hit the throttle, it revs just fine, but backfires like crazy on decel. I richened up the low rpm setting as far as it would let me, and the idle smoothed out and it seemed to help some.  I added more fuel to the mid and high range as well, but could never get the backfiring and stumble to go completely away. Should I try a new map? This is my first experience with a pcIII so I really don't know much about them.  Plug color when I pulled it the other day was a very light tan.

06 700r
HMF full exhaust
prodesign intake(that I bored out, rounded off the edges and polished)
k&n w/protec lid
Dynatek programable
HC stage 2
PCIII

[Homesteadraptor700]

I belive the back fire on decel is a sign your ritch. I would try a different map. Try HMF by DL700 map it is leaner than the GYTR map you put in. see how that works. You said in your sig you bored out your intake? How and why? just curriuos.

[Krandall]

the only bad thinga bout the HMF one is the cam.. that's what makes his build so unique.

[tonyrt44]

I belive the back fire on decel is a sign your ritch. I would try a different map. Try HMF by DL700 map it is leaner than the GYTR map you put in. see how that works. You said in your sig you bored out your intake? How and why? just curriuos.

on the contrary

backfire on decell, stumble on accell are result of LEAN conditions

[1badazz_700r]

  on the lean condition. when your letting off the throttle it is automatically full closed indicating more fuel is needed if you have a back fire. also check your intake tube and make sure it is totally sealed at all connections and no holes. cause if you added all the fuel it would let you and its still acting up i would say something isnt right

[KDH123]

Homesteadraptor700, It was more of a honing than boring.  I didn't like it, it had squared off edges and a small gouge on the inside. I rounded off the edges and cleaned up the inside then polished it up.
I found a place here called Motiva.  They build race cars and have a dyno.  Dave that runs the place is pretty cool.  He told me to bring my quad down and he would try it out on his dyno, if it would fit. We made it, barely. A stock width quad would not make it for sure.  He played with it for awhile, came up with a map that had a real nice curve to it.  I rode it the other day and it ran great, but I still had the backfire on decel. No stumbling anymore.  I pulled the plug and it is really clean, too clean for my comfort.  I will check all the boots, etc for leaks today when I can.  What's the best way to do that?  Use starting fluid and spray around the boots?

[Homesteadraptor700]

KDH123: , It was more of a honing than boring.  I didn't like it, it had squared off edges and a small gouge on the inside. I rounded off the edges and cleaned up the inside then polished it up.

Ok, just tweaking to perfection.  Have you compared your new map to the original map and see where the changes are made. I'm curious if the higher end RPM range are leaner now than your earler map was. Does or did your motor run at a high RPM at idle and not a smooth idle before your new map? Then drops down very easy when you start to engage the clutch to were it would want to stall? It's possible you may have a vacuumm leak but if you did not remove the throttle body I would kinda think not. If the boot that connects the throttle body to the air box/filter were to leak it would be minimal unless you have a really restricted filter. I think you may need to tweak your map some more you may have ben lean on the low RPM and ritch and the high RPM. Hope the best for you.

[KDH123]

I don't have my sheet in here with me, but we were able to squeeze almost 12hp more out of it in the 6-7000 rpm range from when we started.  Yes, it used to run at a higher rpm at idle than it does now.  Actually sounds like it has a cam in it now. A while back, I pulled the pipe air box, etc.  I did not remove the throttle body, but I did tighten up the boots and I think that may have done something.  The tip of the the plug has a whitish residue on it. I am sure I have a leak somewhere. The fuel I use may be leaving a residue also, I hope anyway.  I think it is lean. When we had it on the dyno, we started by adding as much fuel as we could, then started cutting it in half.  We made several runs with it and the map we have now made the most hp and tq.  The problem we were having was getting a good a/f reading from his machine, since he is set up for race cars, not single cylinder engines. We pretty much gave up on that because no matter what we did, it showed a reading of almost 18.

[1badazz_700r]

I would not use starting fluid at all,use carb/choke cleaner and spray around everythingwhile its running you can also get a popping/backfire sound on decel if your exhaust is not sealed.