Jetting?
05-16-2005 | 08:56 AM
#1
Guest
Posts: n/a
Jetting?
Hello everyone,
I am running a K &N, 2 Bros High mounts, with stock jetting and am getting a lot of carb back fires. Is this common for this bike and set up or does she need to be rejetted? I believe she has stock jetting. These pops and coughs happen at all rps and at all speeds and apper to come from under the seat and not the exhaust cans. They happen very occasionally and at no set time. Is there a stock jetting change I can make or do I need to rejet from the factory settings with a jet kit. If I need to rejet, Which kit is the best and easiest to install with the greatest results?
Thanks in advance for your time and comments on this subject.
Todd in WA
I am running a K &N, 2 Bros High mounts, with stock jetting and am getting a lot of carb back fires. Is this common for this bike and set up or does she need to be rejetted? I believe she has stock jetting. These pops and coughs happen at all rps and at all speeds and apper to come from under the seat and not the exhaust cans. They happen very occasionally and at no set time. Is there a stock jetting change I can make or do I need to rejet from the factory settings with a jet kit. If I need to rejet, Which kit is the best and easiest to install with the greatest results?
Thanks in advance for your time and comments on this subject.
Todd in WA
05-17-2005 | 12:44 PM
#2
Senior Member
Superstock
Joined: Jul 2004
Posts: 318
From: San Jose, CA
I have stock filter and de-baffled exhaust, and I am running stock jetting with no issues.
However, with K&N and pipes that you have, you DEFINITELY need to rejet, as you are running too lean. Running lean means running hot, and running hot damages the engine.
Do spend the time and money to rejet properly.
However, with K&N and pipes that you have, you DEFINITELY need to rejet, as you are running too lean. Running lean means running hot, and running hot damages the engine.
Do spend the time and money to rejet properly.
05-17-2005 | 06:02 PM
#3
Senior Member
Back Marker
Back Marker
Joined: Jun 2004
Posts: 208
From: East Tennessee
Re: Jetting?
I have 2Bros high mounts, K&N also. I have 45 stock pilots and 178/180 mains. TPS set at 510. It almost sounds like you might have a vacuum leak? I'm sure you've checked carefully. Also, mine has a rock steady idle if the carbs are sync'd exactly otherwise I get various problems. When sync'd it will rarely go out of adjustment but it always goes out of adjustment when I remove/replace the lower airbox.
PS: You live is a great town ! I know Poulsbo very well and visit often, I may even relocate there sometime!
PS: You live is a great town ! I know Poulsbo very well and visit often, I may even relocate there sometime!
05-18-2005 | 11:59 AM
#4
Senior Member
Superstock
Joined: May 2005
Posts: 312
Re: Jetting?
This is my first post and I would say it is appropriate that it is on the Tecnical Forum as I was a Honda mechanic years ago. Anyway your problem is a lean running condition (backfiring is a symptom of a lean mixture), the pipe will cause you to run lean in and of itself but a K&N will really add to the problem as intake mods tend to have a greater effect than exhaust mods. Yes you need to re-jet and Factory or Dyno Jet kits are good and I assume the make a kit for the Superhawk. JIM
BTW I have a '98 Superhawk, a '94 VFR 750, a 95 500 Interceptor, and two '70 CB500s.
BTW I have a '98 Superhawk, a '94 VFR 750, a 95 500 Interceptor, and two '70 CB500s.
05-18-2005 | 08:46 PM
#6
Moderator
MotoGP
Joined: Dec 2004
Posts: 2,553
From: South Texas
05-19-2005 | 06:42 AM
#7
Member
Squid
Joined: Jul 2004
Posts: 79
Re: Jetting?
superbling,
your 2-3rpm cough went away after raising the needle. what position are you on the needle.
My bike runs great from idle to redline when on the gas. I have a cough at 2-3 when i am at not on the gas. i have adjusted the mixture screws and it is almost gone... but still there stightly.
your 2-3rpm cough went away after raising the needle. what position are you on the needle.
My bike runs great from idle to redline when on the gas. I have a cough at 2-3 when i am at not on the gas. i have adjusted the mixture screws and it is almost gone... but still there stightly.
05-20-2005 | 06:21 AM
#12
Junior Member
Squid
Joined: Apr 2005
Posts: 14
Re: Jetting?
Do anything to a stock VTR's intake or exhuast...first thing is to disable PAIR. In my book, this isnt an option... its a must. If it means reverseing the reed plate, clamping the two hoses, or pluging the nipple above the reed plate cover (they all cut off air flow), whatever... they all work.
Still have backfires and odd pops...then rejet.
Still have backfires and odd pops...then rejet.
05-20-2005 | 07:47 AM
#13
Moderator
MotoGP
Joined: Dec 2004
Posts: 2,553
From: South Texas
Re: Jetting?
05-20-2005 | 11:34 AM
#15
Senior Member
SuperSport
Joined: Mar 2005
Posts: 758
From: Laurel, MD
Re: Jetting?
Do anything to a stock VTR's intake or exhuast...first thing is to disable PAIR. In my book, this isnt an option... its a must. If it means reverseing the reed plate, clamping the two hoses, or pluging the nipple above the reed plate cover (they all cut off air flow), whatever... they all work.
Still have backfires and odd pops...then rejet.
Still have backfires and odd pops...then rejet.
05-20-2005 | 12:08 PM
#16
Senior Member
SuperSport
Joined: Dec 2004
Posts: 764
From: Nananimo, B.C.
Re: Jetting?
I just did the Dynojet install last night. The kit recommends that if you are using a K&N filter then you need to put the needle clip on the 5th position and go up 2 jet sizes (180 -> 185 etc). If you don't use the K&N then its the 4th position. Maybe they changed their instructions but thats what it says now.
05-21-2005 | 08:42 AM
#17
Member
Squid
Joined: Mar 2005
Posts: 43
From: Portland ORegon
Re: Jetting?
When I got my '98 it had just been serviced and it had been concluded that the jetting was 'excellent'. On the dyno things looked great, above 4k rpm of course. But it wasn't rideable in the city due to a misfire at 3k rpm. It has Erion pipes and stock air filter and supposedly had been rejetted. I moved the needles up one clip supspecting a lean mid-range, yanked the PAIR system to silence the exhaust popping, adjusted the TPS (I don't recommend this BTW). Recently I found that the springs and needles had been replaced up top, but that it is running all stock jet sizes. I guess it's a partial rejetting. I think it runs OK and I'm a bit tired playing with it at the moment, my only complaint is excessive vibration above 5k rpm even though the carbs are synched. I think it may be fuel starved when I whack open the throttle due to the stock jets (any thoughts on this?). My long winded recommendation is to listen to the group here and also follow the stetup from Greg Nemish's website:
K&N filter
Hindle round slip-ons
Sea level
Slow jet: stock #45
Mains: 185f/188r
Needles: clips in 2nd from bottom
Mixture screws: ~2.25 turns out
Good luck
K&N filter
Hindle round slip-ons
Sea level
Slow jet: stock #45
Mains: 185f/188r
Needles: clips in 2nd from bottom
Mixture screws: ~2.25 turns out
Good luck
05-23-2005 | 03:23 PM
#20
Senior Member
MotoGP
Joined: Apr 2005
Posts: 5,631
From: Montreal
Re: Jetting?
re:TPS mod
here is another area which yields conflincting opinions. I have spoken to three reputable tuners and all have said the mod is a waste of time. It seems to me that if the bike was designed to run at 500 ohms, then ideally it should be run at that for optimum performance. Who knows.
It seems to evoke opinions much as the K&N filter does.
cheers
here is another area which yields conflincting opinions. I have spoken to three reputable tuners and all have said the mod is a waste of time. It seems to me that if the bike was designed to run at 500 ohms, then ideally it should be run at that for optimum performance. Who knows.
It seems to evoke opinions much as the K&N filter does.
cheers
05-23-2005 | 06:02 PM
#21
Member
Squid
Joined: Mar 2005
Posts: 43
From: Portland ORegon
Re: Jetting?
I think it needs to be considered before done. The manual indicates it should be set to 500 ohms but it's not in the routine maintenance, only if you're replacing one. There seems to be a wide range of what people encounter for initial settings, as well has how the resistance can be controlled. I found the mod easy to do, but I couldn't even set the TPS at 500 ohms, mine won't go below 615 ohms. I didn't like where that left me and didn't want to start drilling wider holes or bending stuff. My TPS reads just below 500 ohms when it's off the bike with no tension on the spring. Also I did it when I was doing other carb work which is a bad idea because if it's out of tune you don't know what you did to mess it up. I just think it's better left alone, my two cents anyway.
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