• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

Re-jet absolutely necessary?

  • Thread starter Thread starter kng254
  • Start date Start date
K

kng254

Guest
I would like to install a V&H 4into1(street) and keep the stock airbox with a k&n air filter(not pods)and hopefully not have to re-jet my 80 gs1000g. I usually just do a search and get my answer, but I'm finding to many different senarios.Hope to get ideas to my situation thanks for any help
 
Yes, it would be necessary. Just the filter by itself should get a re-jet. Not sure what to get though. Call Dynojet and ask.
 
If you want it to run properly, absolutely necessary. These bikes were jetted on the lean side from the factory to begin with to pass EPA regulations. Adding the filter alone will allow for more airflow, which will require a change in jetting to compensate. The pipe will add even more flow, as well as a backpressure change. Failure to rejet will result in the bike having numerous flat spots in the rev range, if it doesn't fall flat on it's face in the midrange to begin with. Continued running with this overly lean, hot burning set up could result in burnt valves and other damage, none of which is cheap to repair. Do it right the first time, and you'll be very pleased. The dynojet stage one kit for your bike is the easiest, most painless way to go about it. Spend the little money now, or spend A LOT of money later. Choice is yours
 
now i'm wondering maybe i'm already jetted I bought the bike it already had a k&n in it,and it runs awesome pulls hard in all gears. is pulling the carbs the only way to find out if its already been jetted. Speaking to P.O. to ask isn't an option.
 
A lot of the time with just a pipe you can get away with going up 2.5 on the main jet size (maybe 5 depending on your elevation) & then opening up the pilot screws a turn or so as long as you keep the airbox. This was my experience on my 1000G & I have read of others success with the same on other bikes.

I ran a V&H 4:1 & a K&N Inbox. My 1000G was a 1980.

The way the needles work, (at least I believe) putting a fatter main jet in does serve to richen the mid range a little too (as that is where the needle is getting it's full from).
Easy enough to raise the needle a stage or half stage using some washers too.

From memory I went up to a 102.5 on the main jet, raised the needles one stage & ran the pilot screws at 2.5-3 turns out. No hesitation & ran fine through the range. I live at Sea Level. I shouldn't think running a 105 instead would harm anything, might even be a little better, I never tried those.

Cheers,

Dan :)
 
Last edited:
The needle serves to meter the fuel flow from around 1/4 to about 8/10 throttle (thereabouts). The fuel actually comes up throught the main jet, so with the CV type carbs, if you're going to attempt to rejet by hand vs a kit ( and in this case you may be able to accomplish just that, but with pods, forget it!) you need to assure your main is the correct size first, as this is what will be metered by the needle and needle jet. The problem with jetting for pods without a kit lies in the stock needle design. The taper of the needle is set up so that as the needle is lifted by the slide, more and more fuel is delivered because the needle taper gets smaller and smaller allowing more fuel to get around it. The stock mikuni needles have a very slow taper to them, and are relatively fat in comparison to a jet kit needle of just about any make. Therefore, with the amount of air introduced to the system with pods, it's simply too slow to deliver the necessary amount of fuel, and the end taper too blunt. The bike will have flat spots all over the rev range. You can somewhat compensate for this with a very large main, but then the bike chokes on fuel at WOT. ( incidentally the way I understand it, the pilot circuit is fed from the main on CV carbs as well, so running a big fat main jet will cause you problems all over too). But, since you're only looking for a small increase in fuel flow, you may find that a 2.5 main jump, and shimming the needle with some washers to raise it up in the needle jet so more fuel passes sooner, will work for you. That's alot of trial And error and plug chops to tune perfectly, Soooo, were it me, I'd spent the $100 on a DJ kit, follow the instructions and be done with it :)
 
Actually, it's only necessary to re-jet if you plan on riding your bike. :p



If you plan on riding your bike, yes, it will be necessary. How much will depend on your bike and your location (elevation).

My #2 son's 850 has a pipe of unknown origin (see pic in sig) and a K&N filter insert. The mains have been bumped from 115 to 120 and the idle mixture adjustment screws are out about 2 3/4 turns. Bike runs great. :dancing:

.
 
I was looking over my carbs today trying to figure out if its been jetted.I noticed that the fuel mix screws were visable. That means the top was drilled right? so does that mean its been jetted?:?:
 
My new V&h 4-1 came with a sheet of paper with jetting recommendations to use with the pipe. It says for an 80-81 1000 to go to a 125 main and a 42.5 pilot.:cool:
 
kng254 said:
I was looking over my carbs today trying to figure out if its been jetted.I noticed that the fuel mix screws were visable. That means the top was drilled right? so does that mean its been jetted?:?:
Click to expand...
No, that only means that somebody got tired of the bike being so "cold-blooded" and adjusted it to where it would run better.
They might have also done the main jet, but there is no guarantee until you open up the carbs and look for yourself.

That adjustment only affects idle and very low throttle openings. At those openings, your bike isn't working hard enough to cause damage due to incorrect fuel mixture. The jetting that you need to worry about is the MAIN jet that is in the bottom of the carb. If you have free-flowing pods and a very free-flowing exhaust system you might have to increase the pilot fuel jet by one size, but you can usually get what you need by using the stock pilot jet.

Depending on what pods and pipe you use, you might require anything from 2 to 8 sizes larger on the main jet.

.
 
kng254 said:
I was looking over my carbs today trying to figure out if its been jetted.I noticed that the fuel mix screws were visable. That means the top was drilled right? so does that mean its been jetted?:?:
Click to expand...

Hi,

Not necessarily. The caps were taken off the idle mixture screws some time in the past so that the idle mixture could be adjusted. Due to EPA mandates, these bikes were adjusted lean when they left the factory to satisfy emission requirements.

If the bike runs good, it may have already been re-jetted. But the only way to know for sure what sizes are in there is to have a look at the jets. You can get an idea of how close the jetting is by performing plug chops and reading the plugs. Your bike will run great when it's very lean, but it will also run much hotter and start burning things like valves and pistons. You need to have enough fuel in the mix to ensure proper operating temperatures. Keep us informed.


Thank you for your indulgence,

BassCliff
 
OK so I've decided to go with the DJ kit stage 1,but the more I read the more I think I'm going to have it installed by mechanic instead of doing it myself. I just hope I'm not going to have make 50 trips to the mech since these carbs sound so finicky.
 
kng254 said:
OK so I've decided to go with the DJ kit stage 1,but the more I read the more I think I'm going to have it installed by mechanic instead of doing it myself. I just hope I'm not going to have make 50 trips to the mech since these carbs sound so finicky.
Click to expand...
I wouldn't get a dynojet kit for just a pipe, besides I have heard and read about people having problems with stage 1 setups. Just increase your main jet and pilot jet. Maybe raise the needle by a washer or two. Without the bigger pilot jet you would probably get popping under deceleration.
 
gearhead13 said:
I wouldn't get a dynojet kit for just a pipe, besides I have heard and read about people having problems with stage 1 setups. Just increase your main jet and pilot jet. Maybe raise the needle by a washer or two. Without the bigger pilot jet you would probably get popping under deceleration.
Click to expand...

It came w/ K&N filter in stock air box which is why I thought it might have already been re-jetted. What sizes should I go up and who should I order them from.
 
With just a stock style K&N replacement filter you could more than likely get away with out a rejetting. However, when you mess with the exhaust then you MUST re-jet. A better flowing exhaust system will allow the engine to take in more air, doesn't matter if you have the stock intake setup with a stock filter or pod filters.
 
kng254 said:
It came w/ K&N filter in stock air box which is why I thought it might have already been re-jetted. What sizes should I go up and who should I order them from.
Click to expand...

Hi,

Mr. salty_monk mentioned that with his bike, a K&N filter in a stock airbox with 4n1 pipes, he went up 2.5 (one size) on his main jet and turned the idle mixture screw out another whole turn. But you might have to go up two sizes on your mains. To be sure, you have to perform plug chops and read the plugs at each throttle setting to be sure you have the right mixture for each carb circuit. There are notes about plug chops on my website and guides for carb tuning, such as:

For CV Carb jetting, see the very informative article at Factory Pro. Also see the carb jetting tips at Motorcyclecarbs.com, Inc.

Mikuni Motorcycle Carburetor Theory 101 - from Ian Williams Tuning

See the vendor list in the READ ME file for carb parts vendors.

Thank you for your indulgence,

BsssCliff
 
gearhead13 said:
My new V&h 4-1 came with a sheet of paper with jetting recommendations to use with the pipe. It says for an 80-81 1000 to go to a 125 main and a 42.5 pilot.:cool:
Click to expand...
You left off the important part about removing the stock air box lid. If you skip this part your bike will run too rich.
 
You must log in or register to reply here.
Back
Top