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Discussion Starter · #1 ·
I just want to make certain that im clear on this...

when Im pulling hard WOT, and I let off the throttle completley, if I hear the backfire, afterburn, popping etc... thats a lean condition correct ?

now, what if Im pretty well all the way out on the A/F ?

I just put in the DJ #150 and the stock pilot (just monkeying around with jetting)

I have the A/F out about 3.5 turns 'ish... and it backfires, so I need to go to the next size up in pilot correct ? a bigger jet will give me more volume of fuel, so I should be able to richen it up a little more... correct ?

can someone clarify that the backfireing is in fact a lean condition ?
 

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Ive been told it's a lean condition, but I'm no mechanic to say for sure. Can't you just go by your sparkplug?
 

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Discussion Starter · #3 ·
pulling out the sparkplug is both not practical and not worth the bother... the fuel where I live is so full of detergents and additives, my plug doesnt foul till I have it so rich its belching black smoke...
 

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Yes from what I have seen it is lean, if you can't get it to stop with the A/F screw I would try a larger pilot jet.
 

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The Pilot Jet is the low speed jet. If it is doing it at WOT, it wouldn't be related to the pilot jet.
 

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Discussion Starter · #6 ·
Duramax, its happening when I let off from WOT... not at or on WOT

so after pinning it to some top end speed, and letting off WOT, as the engine compression slows me down, thats where im hearing the afterburn pops...so, with no throttle pressed, this is the pilot circuit no ?
 

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Mud, you are correct, it is lean and I would try a larger pilot. I was messing with mine last weekend and removed the stock spark arrestor from the stock pipe to see if I was up to the increase noise level. With no (reduced) restriction or back pressure, I got plenty of backfire when slamming the throttle shut from WOT. This shows that there is plenty of restriction in the stock exhaust. Did this condition develop after the addition of the new pipe? Perhaps you just now noticed it? Like you said, going up on the main has NO effect at the lower throttle positions. I guess the answer is to either add restriction to the exhaust (kinda defeats the aftermarket pipe) or go fat on the low speed jet. The farther you go on jetting though, the smaller the margin of error and the less forgiving the engine will be in all riding conditions. I make the comparison between a tractor and a dragster, both are great at what they are designed for...we are really to get the best of both worlds, a haul'n ass tractor!!! LOL...

Paul...

PS I didn't like the dB increase, reinstalled the spark arrestor, and put the new pipe idea to bed.
 

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Check to see if you have an exhaust leak!
 

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I have the 2" exhaust, drilled out baffles, Uni filter, DJ needle and stock #152 main jet. I had the backfire problem too. I put in a smaller pilot jet #45, made no other changes and it stopped it. Don't know why it worked but it did, plus it really increased the initial burst of power. Now I can pop the front end up without much effort. With all the stuff I have on mine (including a front basket) that is no small feat. Seem like every Rincon likes a different combination.

Backfire when letting of from full throttle is not a lean condition in my opinion. Rather I feel it is caused by too much unburned fuel suddenly igniting.
The smaller pilot must reduce this slightly. Just a theory; your results may vary.
 

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if you still have your dyno jet instructions you will find that it states that opening the idle mix will correct the backfiring.(making it richer). are you just having some slight popping or real loud bangs?
 

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Discussion Starter · #11 ·
just some slight popping...


im realy just trying to fine tune to perfection now...

I didnt realy do any siginificant modifications till after I installed the HMF utility exhaust...

there were instructions with the dynojet kit ?? ;)

parkgt you decreased your pilot and got low end out of it ? I decreas mine and its like ultra dyno slug...

guess im having a hard time wraping my head around getting more power by putting in less fuel... perhaps you have your A/F mixture set optimum now ?? just a thought...

Pablo... you make a good point there about how less forgiving the engine will become as I get closer and closer to what I feel is "perfect" thinking that with that aproach I will leave my tractor like dragster as it is...

so todays jetting tally, #150 Main, and #52 Pilot and the e-clip is on the 3rd notch...
 

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PARKGT, You are right on about it being unburnt fuel in the tail pipe. Lean (lack of fuel) obviously won't make a back fire, BUT what I believe is happining is that after a very rich WOT condition followed by a lean FCT (fully closed throttle) the air to fuel mixture is at the perfect explosion ratio. When the fuel rich exhaust hits the hot tail pipe in the right ratio...BANG. The same thing happens when you have a hole in the pipe or a leaky flange. It sucks in air, bringing down the fuel rich exhaust to the explosion ratio, and BANG...

If you want to run a experiment, try pulling the choke out little by little and make a few hot laps. I bet it will eliminate the back fire by riching up the lower throttle position. Just a thought...

Paul...
 

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i would say some slight popping should be ok. when i put the 2 inch tip on, mine was like july 4.ok now though.
 
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