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Discussion Starter · #1 ·
So I put on a vance and hines exhaust system and im spitting some flames after a hard rev

Too rich? Too lean?

Ive been told I can adjust the carbs via a screw before having to completely tear them apart. Is this possible?
 

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You can adjust the pilot screws, but that only controls mostly the low end of the throttle range, not the top end.

Did you rejet?
 

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Discussion Starter · #3 ·
No I did not rejet. I dont have the ability to work with the carbs like that. Dont really have the money (college student) to have the shop do it for a few hundred dollars.

I was hoping that I could adjust the carbs with said the pilot screws you spoke about.

As for the range, it spits flames at the end of the high rev...on the way back down to normal idle from a heavy throttle dump it begins to spit
 

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I know lots of guys say you don't have to rejet if you don't change the air, but I'm a fan of doing "the big 3" (pipes, jets, air) all at once. Without seeing the bike, I'll offer a theory that you have changed the exhaust velocity with the new pipes, making the exhaust leave the engine slower an the heat from the header pipes causes the unspent fuel exhaust to ignite. (lots of guys mistakenly refer to this as "back pressure," but it is not.) The velocity is not changed much at idle, but the higher the revs, the more noticeable the change is. Opening up the air intake will help some, but then you need to rejet.

It is easy to underestimate the affect exhaust can have on tuning, but it is pretty big. Again, I could be wrong, and without seeing your bike, it's hard to tell.

http://blog.jpcycles.com/2011/01/when-it-comes-to-your-bikes-engine-its-all-about-the-air/

Think of it this way: you have a garden hose, and you turn the water on. You want to water your garden, so you just hold the hose over it. The water just kind of rolls out the end and goes in the place you point it, but not very far or fast. It will only move faster if you turn the water valve up higher. Now, you put a hose nozzle on it, which changes the diameter of the hose from 3/4" to a half inch or less. What happens? The water speed increases, it shoots out further, and covers a wider area. This is more or less what happens when you remove your more restrictive exhaust system. You've opened it up like a garden hose, but now the exhaust doesn't move as fast, but with the same stock restrictive air system , it can't really draw much more air to speed up the flow. Hope this makes sense.
 

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Whether stock or aftermarket from what I've read unburned fuel is igniting in the exhaust. The main difference is that the stock exhaust is designed to suppress the effects (mainly the loud pops when letting off the throttle).

So unburned fuel igniting is normal. Whether it should be visible at the tailpipe I have no idea but would be concerned enough to verify the mixture and proper ignition. At best it sounds like very poor design of the exhaust.
 

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Did you replace the gaskets at the heads with the new exhaust? Any kind of air leak into the exhaust can cause it to ignite any unburned fuel.Adjusting the A/F screw may lessen the flames, but doubt will eliminate them completely without going pretty rich at idle. Blocking or removing the air injection, marbling, can do wonders for getting rid of the popping and flames you are getting, if not already done.
 

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Discussion Starter · #8 ·
Did you replace the gaskets at the heads with the new exhaust? Any kind of air leak into the exhaust can cause it to ignite any unburned fuel.Adjusting the A/F screw may lessen the flames, but doubt will eliminate them completely without going pretty rich at idle. Blocking or removing the air injection, marbling, can do wonders for getting rid of the popping and flames you are getting, if not already done.

Yes I did replace those gaskets. I dont have any leaks anywhere...

Can you explain blocking/removing air injection? (marbling?)

And can you tell me how to adjust the A/F screw? An image of where it is located, maybe...

Thanks!
 

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Discussion Starter · #9 ·
I know lots of guys say you don't have to rejet if you don't change the air, but I'm a fan of doing "the big 3" (pipes, jets, air) all at once. Without seeing the bike, I'll offer a theory that you have changed the exhaust velocity with the new pipes, making the exhaust leave the engine slower an the heat from the header pipes causes the unspent fuel exhaust to ignite. (lots of guys mistakenly refer to this as "back pressure," but it is not.) The velocity is not changed much at idle, but the higher the revs, the more noticeable the change is. Opening up the air intake will help some, but then you need to rejet.

It is easy to underestimate the affect exhaust can have on tuning, but it is pretty big. Again, I could be wrong, and without seeing your bike, it's hard to tell.

http://blog.jpcycles.com/2011/01/when-it-comes-to-your-bikes-engine-its-all-about-the-air/

Think of it this way: you have a garden hose, and you turn the water on. You want to water your garden, so you just hold the hose over it. The water just kind of rolls out the end and goes in the place you point it, but not very far or fast. It will only move faster if you turn the water valve up higher. Now, you put a hose nozzle on it, which changes the diameter of the hose from 3/4" to a half inch or less. What happens? The water speed increases, it shoots out further, and covers a wider area. This is more or less what happens when you remove your more restrictive exhaust system. You've opened it up like a garden hose, but now the exhaust doesn't move as fast, but with the same stock restrictive air system , it can't really draw much more air to speed up the flow. Hope this makes sense.
Yes, this all makes perfect sense.
 

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Yes I did replace those gaskets. I dont have any leaks anywhere...

Can you explain blocking/removing air injection? (marbling?)

And can you tell me how to adjust the A/F screw? An image of where it is located, maybe...

Thanks!
once you alter the carb settings, youre on a slippery slope to an expensive visit to an expert. i cant recommend you touching the carbs if youre not even sure where the setting screw is. Does the bike ride ok? If so, leave it alone.

Running the engine wide open while its standing is a VERY BAD thing. You shouldnt do it, and you certainly shouldnt adjust anything because of what happens when doing it.
 

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once you alter the carb settings, youre on a slippery slope to an expensive visit to an expert. I cant recommend you touching the carbs if youre not even sure where the setting screw is. Does the bike ride ok? If so, leave it alone.

Running the engine wide open while its standing is a very bad thing. You shouldnt do it, and you certainly shouldnt adjust anything because of what happens when doing it.
^^^^^^^^^^
this!
 

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Discussion Starter · #12 ·
I have not ridden it yet, so I cant say if it rides okay or not.

I do know how a bike is supposed to run, and i am confident i have the ability to adjust the air mixture screw. Turn it all the way in, record how many turns so i know where my starting point was, and go from there. I used to race motocross for years so i have a decent amount of mechanical knowledge, but a cruiser is new to me.

If any of you are willing to give me a few pics of where this adjustment screw is that would be greatly appreciated!
 

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Discussion Starter · #14 ·
Ugh. Okay I will just leave it as is. hopefully it runs okay, otherwise it will have to go to a shop. Thanks for the help!
 

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Ugh. Okay I will just leave it as is. hopefully it runs okay, otherwise it will have to go to a shop. Thanks for the help!
Repeat after me

IF IT AINT BROKE DONT FIX IT.

just changing the pipes is very unlikely to affect the running of the bike. NEVER make adjustments without a very good reason, and you will enjoy your riding.
 

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Repeat after me

IF IT AINT BROKE DONT FIX IT.

just changing the pipes is very unlikely to affect the running of the bike. NEVER make adjustments without a very good reason, and you will enjoy your riding.
Disagree, going from factory with baffles an the plenum to straight pipes will always cause adjustments to be required. More air out requires more air / fuel in. Cobra slip ons are one of the few that did not require changes. That is exactly why I chose them.
 

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Discussion Starter · #17 ·
JTucker -- They arent straight pipes if that makes any difference to your post. There are mufflers for sure, just not sure how "packed" they are.
 

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Disagree, going from factory with baffles an the plenum to straight pipes will always cause adjustments to be required. More air out requires more air / fuel in. Cobra slip ons are one of the few that did not require changes. That is exactly why I chose them.
if you want more power, then yes, you have to have more air in and more air out.
But you have it kinda backwards. the engine sucks the air in and pushes it out the pipes. if you just change the exhaust, the inlet is still sucking the same amount of air that it always did. if no more air is getting in, then the engine cant push more air out, so the pipes cant let more air out because there isnt any more air.
What does (can) happen is that as the same air volume is now in a bigger pipe, the engine back pressure drops and its possible to get a louder exhaust but lose some performance, which can be cured simply by welding a big washer inside the header pipe to give the restriction back to the engine, but overall, changing the pipes does not require an air or fuel change.
 

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if you want more power, then yes, you have to have more air in and more air out.
But you have it kinda backwards. the engine sucks the air in and pushes it out the pipes. if you just change the exhaust, the inlet is still sucking the same amount of air that it always did. if no more air is getting in, then the engine cant push more air out, so the pipes cant let more air out because there isnt any more air.
What does (can) happen is that as the same air volume is now in a bigger pipe, the engine back pressure drops and its possible to get a louder exhaust but lose some performance, which can be cured simply by welding a big washer inside the header pipe to give the restriction back to the engine, but overall, changing the pipes does not require an air or fuel change.
We are saying the same thing in different ways. lack of back pressure requires more air for same performance. If you add more air, but no more fuel, then you go lean which will cause more popping, this is why straight pipes often require jets. Since yours have baffles, you should be able to tune it our. For mine, about 2-3/4 turns out made it very strong and idle perfect.
 
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