backfireing and popping...

[Dr89]

i was reading up on some things while in the process of jetting yet another quad....and i found this from the official Mikuni American Corporation website....and i quote

"it is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid to high rpm. in fact, one should expect a well tuned high performance engine to 'pop' and 'crackle' when the throttle is closed at high rpm."

im sure some of you already knew this but everything i've ever heard or or read has taught me that when im finished there should be no backfiring what so ever, so i just found that kinda surprising.

[GPracer2500]

Originally posted by Dr89
i was reading up on some things while in the process of jetting yet another quad....and i found this from the official Mikuni American Corporation website....and i quote

"it is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid to high rpm. in fact, one should expect a well tuned high performance engine to 'pop' and 'crackle' when the throttle is closed at high rpm."

im sure some of you already knew this but everything i've ever heard or or read has taught me that when im finished there should be no backfiring what so ever, so i just found that kinda surprising.

I love it! A very nice observation.

Keihin and Mikuni offer some of the best info out there on carburetion. I mean, come on--if they don't know everything there is to know about motorcycle/ATV carburetion than who does? :D

I pilot circuit that is jetted correctly WILL usually exibit a slight pop on decel--especially at higher RPM. It's when that pop becomes excessive that a lean pilot circuit likely to blame.

What you've stumbled onto is one of the more minor points about jetting. For basic jetting it's generally OK to back off on the pilot curcuit just until any noticable popping stops. That's why we've all heard that a popping exhaust means a lean pilot curcuit. But there are much better methods for tuning a pilot curcuit and if you do it right, you'll probably get a little popping under some conditions.

In my experience, most people who do their own jetting tend to jet fatter then they really need to. Or I should say, fatter than what is best for optimal combustion. To an extent, that's fine because it's a little safer to be rich. If you make a mistake going rich than your not going to hurt anything. Go too lean and you might hurt something. So, the idea that a perfectly jetted pilot curcuit should be silent just gets re-inforced.

[Dr89]

yea...who'd of thought

[ohsobad_chevy]

Originally posted by GPracer2500
I love it! A very nice observation.

Keihin and Mikuni offer some of the best info out there on carburetion. I mean, come on--if they don't know everything there is to know about motorcycle/ATV carburetion than who does? :D

I pilot circuit that is jetted correctly WILL usually exibit a slight pop on decel--especially at higher RPM. It's when that pop becomes excessive that a lean pilot circuit likely to blame.

What you've stumbled onto is one of the more minor points about jetting. For basic jetting it's generally OK to back off on the pilot curcuit just until any noticable popping stops. That's why we've all heard that a popping exhaust means a lean pilot curcuit. But there are much better methods for tuning a pilot curcuit and if you do it right, you'll probably get a little popping under some conditions.

In my experience, most people who do their own jetting tend to jet fatter then they really need to. Or I should say, fatter than what is best for optimal combustion. To an extent, that's fine because it's a little safer to be rich. If you make a mistake going rich than your not going to hurt anything. Go too lean and you might hurt something. So, the idea that a perfectly jetted pilot curcuit should be silent just gets re-inforced. '

GP, you are my idle, bro!! Great asset to our forums!!!! Well appriciated. :)