Rejetting necessary after third party exhaust?

[zombie]

Listen to EVERY high performance engine built. They ALL pop when closing the throttle.
It's in the nature of the exhaust. Being more "free flow" in design it can not "muffle" this pop.

What is happening is there is always unburnt fuel in the pipe. (that's what cats are for). this fuel does ignite every time the exhaust opens. With an open pipe design you can here this fuel burning. A closed pipe masks the sound. That's all there is to it.

Old school chopper guys purposely run rich to amplify the effect.
You can minimize the pop by getting your combustion as close to perfect as possible but you will have to balance your jetting/needle height or injector duration/pulse width to gain perfect combustion across the rpm/load range.

Only experimenting will yeild results, and they will change with weather conditions, road conditions, and even to some degree the brand, and state of your engine oil.

Embrace the pop! Become one with your engine! I am your father Luke! 

[guile]

Listen to EVERY high performance engine built. They ALL pop when closing the throttle.
It's in the nature of the exhaust. Being more "free flow" in design it can not "muffle" this pop.

What is happening is there is always unburnt fuel in the pipe. (that's what cats are for). this fuel does ignite every time the exhaust opens. With an open pipe design you can here this fuel burning. A closed pipe masks the sound. That's all there is to it.

Old school chopper guys purposely run rich to amplify the effect.
You can minimize the pop by getting your combustion as close to perfect as possible but you will have to balance your jetting/needle height or injector duration/pulse width to gain perfect combustion across the rpm/load range.

Only experimenting will yeild results, and they will change with weather conditions, road conditions, and even to some degree the brand, and state of your engine oil.

Embrace the pop! Become one with your engine! I am your father Luke! 

Haha, I like your style Zombie. May the force be with you ..

I notice a little stalling at the end of the throttle. Could this be coming from the size #130 main jet (size #118 is stock)?

[zombie]

It could be loading up w/ fuel. How does it run from 1/2 throttle up? How about idle, and slow acceleration?

If the low end is good (not going above 1/2 throttle) then the main might be too rich.
If you have any stumble  at low rpm then the pilot may be too lean.
Sometimes you can compensate by adjusting the fuel mix screw to richen up the low end.
Changing the pipe effects both jets, and you might have to go up a jet or two on the pilot.

Jetting is a pain in the you know what. But when you get it right it is it's own reward.

[guile]

It could be loading up w/ fuel. How does it run from 1/2 throttle up? How about idle, and slow acceleration?

If the low end is good (not going above 1/2 throttle) then the main might be too rich.
If you have any stumble  at low rpm then the pilot may be too lean.
Sometimes you can compensate by adjusting the fuel mix screw to richen up the low end.
Changing the pipe effects both jets, and you might have to go up a jet or two on the pilot.

Jetting is a pain in the you know what. But when you get it right it is it's own reward.

The low end is good, good pick up. It only stalls at high rpm; at the end of the trottle.
This means that I should lower the main jet in size then?

[zombie]

That's a 50 /50 call.  I'd get a set of jets ranging from 125-145. (steps of 5). Your slide needle should be adjustable as well.
The way to figure if you need more or less jet is to raise the needle (lower the clip), and see if it improves. If it does then you need more jet. If it is worse then lower the needle (raise the clip) to verify.
Even if one of these positions works GREAT, you still need to jet accordingly, and return the needle to the center clip position. Reason is you want to have a margin for adjustment either way to fine tune. You never want to be at the end of an adjustment. (especially if there are mobsters involved)

You're real close.

[guile]

Thanks zombie!

[zombie]

Welcome you are...

[guile]

The Diaphragm has swollen and won't fit properly; it won't seat well. Any suggestions?

[zombie]

That's from Ethanol
Let it sit in front of a blow drier (no heat) for 1/2 hr. It will shrink back as the Eth evaporates.

[guile]

Thanks zombie; worked great.
I settled with raising the needle and installing a main jet size #125. I notice a fairly big improvement in mid throttle.
The pops are still there, but the cows have to get used to them.

[zombie]

I worked on a dairy farm as a kid. That should qualify my saying, f*** a bunch of cows!

Glad it's working out. You might find you will need a colder plug in the winter due to the thinner air. Depending on how close your jetting is to perfect, you might even want to try one hotter, and one colder now to dial it in further. Higher numbers are colder.
You have to love jetting. It sucks.
I really am happy for you. This makes my day, and it's only 8am

[guile]

We're lucky to have you on the forum 

[zombie]

It keeps me off your mom!

Sorry.

[guile]

It keeps me off your mom!

Sorry.

don't be

[zombie]

Oh my god... I'm crying here.
You started my day w/ a smile, and ended it w/ tears... What a day!