Re-jet absolutely necessary?

[kng254]

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

[Dogma]

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.

[TheCafeKid]

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

[kng254]

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.

[GabrielGoes]

i had the same set up with 105 main jets i dont know how the needle height was but the main jets were spot on!

[salty_monk]

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

[TheCafeKid]

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

[Steve]

Actually, it's only necessary to re-jet if you plan on riding your bike.



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.

.

[kng254]

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?

[gearhead13]

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.

[Steve]

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?

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.

.

[BassCliff]

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?

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

[kng254]

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.

[gearhead13]

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.

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.

[kng254]

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.

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.