Last word, final word on Jetting, please

[Seaking]

My 06 Venture has K7N Air filters and RoadKing Screaming Eagle slipons which sounds great, add a noticeable oomph of power boost (albeit small but noticeable over stock).. When I inquired about doing this, I had been told that "re-jetting" was NOT required..

 

I now have a new set of slip ons someone sent me as a return of favour (free!) and I'd love to try them on.. they fit a Roadking.. These are turn downs with beautiful chrome. When I look down either end, I can see light glowing in.. and the burner louvres (dunno what to call them..) I wonder how LOUD these will be.. I'm willing to give them a try, because as they say: Nothing Venture'd Nothing Gained.. =)

 

But something got me a puzzlin though.. My buddy wants my Screamin Eagles to try on his bike but says that everyone he's talked to and everywhere he's read (other than here) claim and state that no matter what anyone else says, he needs to re-jet after installing any after market slipons.. My Venture runs GREAT as is, no rejetting or anything..

 

I remember this being more of an issue with VTwins like my VStar etc.. but huh?

 

So what's the story here? With these new pipes I have, which seem more open than previous slipons, is re-jetting in my future?

 

What say the learned guru-riders of the forum?

 

Cheers, thanks in advance.

[Tom]

While I am not a guru on this I have been around MANY Ventures and NONE have needed rejetting.Its actually laughable in my opinion to do so. Bottom line is..You will use more fuel,NO MORE ZIP AT ALL. My friend rejetted his and has NEVER gotten it right since,but he gets 25 MPG! Oh Yea..we stay neck to neck in all gears.The only way to get it to run better in my opinion is IF you could get more air to it then rejetting MAY help.V7Goose can answer more eloquently than I.

[raceman62race]

I am not an expert in this area but I will throw in my 2 cents worth. I have been running stock road king pipes for a little over 6 months with stock carb steeting and I have had absolutely no problems. In my own mind, I have a hard time understanding why the re jeting would be necessary as long as you don't tinker with the air filter box. I use to have a Suzuki VL 1500 and a popular mod was to remove the air horn from the air filter box and that unrestricted the air flow and that required re jetting. On the Suzuki, (and I would assume the Yamaha is the same) it relyed on the negative pressure created from the design of the filter box to help pull fuel out of the carbs. If you took the filter box off and tried to rev up the engine, it would start stumbling. Put on the breather box and she runs fine. It's still going to have the same negative pressure in the filter box reguardless of the slip ons. I would like for someone to explain the theory for re jetting with a exhaust change.

[BuddyRich]

The color of your plugs will tell the tale. I am running RK's drilled all the way out and K&N's. My plugs are showing they are burning normal. I have known 2 people who rejetted their RSV's and both wish they had not cause their mileage dropped to the mid 20's with no powergains. Your breather tubes (channel) are only going to let in a certain amount of air.

[Seaking]

While I am not a guru on this I have been around MANY Ventures and NONE have needed rejetting.Its actually laughable in my opinion to do so. Bottom line is..You will use more fuel,NO MORE ZIP AT ALL. My friend rejetted his and has NEVER gotten it right since,but he gets 25 MPG! Oh Yea..we stay neck to neck in all gears.The only way to get it to run better in my opinion is IF you could get more air to it then rejetting MAY help.V7Goose can answer more eloquently than I.

 

Thanks to all for your responses.. my ride buddy's RSV is stock and I've ridden his bike and can tell you that mine has a bit more kick to it..

 

I went to change the pipes over to the downturn pipes and busted the clamp collar where the tightening bolt goes through.. weird.. So tomorrow morning, off to purchase two new ones (so they match) and try it again.. everything fits and hangs well.. Just waiting to hear what it sounds like hehe..

[Tom]

Thanks to all for your responses.. my ride buddy's RSV is stock and I've ridden his bike and can tell you that mine has a bit more kick to it..

 

I went to change the pipes over to the downturn pipes and busted the clamp collar where the tightening bolt goes through.. weird.. So tomorrow morning, off to purchase two new ones (so they match) and try it again.. everything fits and hangs well.. Just waiting to hear what it sounds like hehe..

 

You ever get down this way and we will set the floats on it and sync those carbs and We will watch you ride off into the sunset with a big grin on your face!

[V7Goose]

I don't think you are going to get the final word on this, certainly not from me, but I'll give you some thoughts.

 

Internal combustion engines are very particular in how they breath, and there are MANY things that affect it, including the size, shape and length of the intake tract, the size, shape and length of the exhaust, the cam lift and valve overlap, the shape of the intake port, placement and size of the valves, the shape of the combustion chamber, and probably several other things I have not mentioned. To get the best charge packed in the combustion chamber, the engine relies on the speed of the air rushing through the intake tract (not just the volume), a period of time when BOTH intake and exhaust valves are open at the same time to create a full flow, and some back pressure in the exhaust to control this flow-through until the exhaust valve closes.

 

All of that stuff is obviously interrelated, so once you begin messing with any part of it, it is hard to know what the results are going to be. Factory designs spend a lot of time getting it all right for normal driveability and economy, and it doesn't often pay to start messing with it. In fact, the average shade tree mechanic that thinks somehow he can do better is sadly mistaken.

 

Now for just the pipes - the big question is how much different the air flow is compared to stock and if the intake tract can provide more air to blow through. Changing just the pipe to a more open design will probably do nothing but drop your fuel mileage, since more unburned gas will blow through during the valve overlap. That can be controlled a bit with jet changes, but probably at the expense of power. If you want more power out of the bike, you must get more air and fuel into the engine - that usually means changing the intake tract. Even if the existing intake can handle the needed increase in air that an open pipe can use, larger jets MUST hurt fuel mileage. IMHO, the RSV has such a convoluted and nasty intake design, nothing you could do short of putting filters right on top of the carbs would improve it, and even that might not produce good results, since you would not have a tuned port to affect the air speed. Do a little reading on the theory behind Yamaha's YICS system to lean more.

 

Bottom line is that if you change pipes to something with similar flow, all will be fine, but if you go to a very open pipe, something MUST suffer. The good news is that our engine is so de-tuned to start, it tolerates these changes pretty well.

 

I am sure I have made a number of misstatements in all of that, so any carb and engine experts should feel free to correct any of it they like - won't hurt me none. But this is a complicated subject, and any short post is unlikely to treat it with complete accuracy.

Goose

[Seaking]

You ever get down this way and we will set the floats on it and sync those carbs and We will watch you ride off into the sunset with a big grin on your face!

 

You have a date lol.. take about a week to get there from Nova Scotia but hey, what the heck =) If you guys can do a lot to train me to do my own maintenance it will be well worth the while!

 

I couldn't get the proper clamps today so I put the OEM pipes back on..

 

I've been out for a ride with them on (first time since last year) and Hmmmm after this weekend's riding I'll have a strange report for you if all holds true to what I experienced today about the diffs of aftermarket vs OEM pipes..

[Seaking]

I don't think you are going to get the final word on this, certainly not from me, but I'll give you some thoughts.

 

Internal combustion engines are very particular in how they breath, and there are MANY things that affect it, including the size, shape and length of the intake tract, the size, shape and length of the exhaust, the cam lift and valve overlap, the shape of the intake port, placement and size of the valves, the shape of the combustion chamber, and probably several other things I have not mentioned. To get the best charge packed in the combustion chamber, the engine relies on the speed of the air rushing through the intake tract (not just the volume), a period of time when BOTH intake and exhaust valves are open at the same time to create a full flow, and some back pressure in the exhaust to control this flow-through until the exhaust valve closes.

 

All of that stuff is obviously interrelated, so once you begin messing with any part of it, it is hard to know what the results are going to be. Factory designs spend a lot of time getting it all right for normal driveability and economy, and it doesn't often pay to start messing with it. In fact, the average shade tree mechanic that thinks somehow he can do better is sadly mistaken.

 

Now for just the pipes - the big question is how much different the air flow is compared to stock and if the intake tract can provide more air to blow through. Changing just the pipe to a more open design will probably do nothing but drop your fuel mileage, since more unburned gas will blow through during the valve overlap. That can be controlled a bit with jet changes, but probably at the expense of power. If you want more power out of the bike, you must get more air and fuel into the engine - that usually means changing the intake tract. Even if the existing intake can handle the needed increase in air that an open pipe can use, larger jets MUST hurt fuel mileage. IMHO, the RSV has such a convoluted and nasty intake design, nothing you could do short of putting filters right on top of the carbs would improve it, and even that might not produce good results, since you would not have a tuned port to affect the air speed. Do a little reading on the theory behind Yamaha's YICS system to lean more.

 

Bottom line is that if you change pipes to something with similar flow, all will be fine, but if you go to a very open pipe, something MUST suffer. The good news is that our engine is so de-tuned to start, it tolerates these changes pretty well.

 

I am sure I have made a number of misstatements in all of that, so any carb and engine experts should feel free to correct any of it they like - won't hurt me none. But this is a complicated subject, and any short post is unlikely to treat it with complete accuracy.

Goose

 

As always, Goose, you come across with words of wisdom and leeway, good info, thanks. My VStar is highly modded with the air in and out that I'm fairly familiar with the general concepts though not to your level.. I wasn't too sure what a V4 would do with those turn down pipes.. I'll have to wait until I get the clamps to try them on.. But that might have to wait until I do more riding with the OEMs on the bike.. I noticed something different with them this time that I found very different than the last time I had them on.. could be the K&N filters, I'm not sure,,.

 

But more on that later..

 

Thanks again M8