Bolserst,

Thanks for the excellent write up! Seeing someone take a methodical and educated approach at solving this annoyoance with the ZR-7s is inspiring. I've been reluctant to tear my carbs apart to exipriment with needles/jetting becuse I was afraid I'd just make the problem worse. I'm mechanically inclined, but not quite as skilled or patient at troubleshooting obscure carb problems like this as I'd like to be. Now that you've done all the hard work I'm ready to follow your lead.
Well, maybe when the weather warms up a bit it's only 10 degrees and windy here in New England tonight and the garage is neither heated nor insulated.

Anyhow, the question I have is proboably relativley basic for someone who's tinkerd with carbs before. How do you know what needles and jets to order? I understand that they are numbered but is that a universal numbering scheme that works for all bikes? Does that mean I can go to any place and order a #whatever jet and it will work - or do I need to provide other info too?

I'd really like to try an mimic your set up (Like you, I'm happy with stock intake/exhaust) but don't trust my machining skills. Also, if for whatever reason (say different tolerance stacking in my bike) the mod doesn't work for me I'd like to be able to go back to stock. So I'd like to get a set of needles to practice on. Can you offer some advice for the novice on what to order and where it can be found?

-ZxZr

Originally Posted by dr200se

When I purchased my ZR7S 4 years ago, it had the typical EPA lean mixture
and hesitation issues. I purchased a Dynojet kit and K&N filter and followed the instructions included with the kit to the letter. I adjusted the mixture screws and synch'd the carbs. The driveability and hesitation issues were soloved. I realize that buying the kit may be more expensive, but it certainly was a lot less hassle.

Hello dr200se,

That’s awesome that your hesitation and jetting issues were easily solved with an off the shelf jet kit. From reading this forum you know that not everybody has had the same positive experiences with jet kits for the ZR-7 whether they be from Dynojet, Factory Pro, or Ivans. Why some ZR7s respond well to the standard jet kits, and others don’t has been a bit of a mystery. There was also the concern that most of the jet kits reduced the mpg from 50ish to below 40. Had you checked what your mpg is now with the Dynojet kit?

As I posted back on nov-06-07, “…My real goal is to try and track down why my "new" 2001 bike is so different from my previous ZR-7S and fix it. This information would also be useful for others when trying to use available jet kits and getting frustratingly varying results…”

I wasn’t after a cheap fix, in fact with the dyno costs included I spent nearly $100. I wanted to try and track down why some ZR7s have hesitation and other don’t. Why some respond well to standard jet kits, and others don’t. I certainly didn’t consider it a hassle. In fact it was kind of fun taking a logical path to track down the problem.

What we learned was that the jetting variances that cause the off idle hesitation were:
1) NOT due to airbox or air filter leaks.
2) NOT due to pilot jet size or pilot screw setting
3) WAS due to lean mixture caused by tolerances in the needle-jet / jet-needle system system for the straight section of the needle.

As a bonus we confirmed the speculation that the stock #108 main jet was too rich for the stock exhaust and air-filter.
Changing to a #102 main jet produced a 3hp bump and improved fuel economy.

Originally Posted by zxzr

Bolserst,

Anyhow, the question I have is proboably relativley basic for someone who's tinkerd with carbs before. How do you know what needles and jets to order? I understand that they are numbered but is that a universal numbering scheme that works for all bikes? Does that mean I can go to any place and order a #whatever jet and it will work - or do I need to provide other info too?

I'd really like to try an mimic your set up (Like you, I'm happy with stock intake/exhaust) but don't trust my machining skills. Also, if for whatever reason (say different tolerance stacking in my bike) the mod doesn't work for me I'd like to be able to go back to stock. So I'd like to get a set of needles to practice on. Can you offer some advice for the novice on what to order and where it can be found?

-ZxZr

Don't let working on the carbs intimidate you. Just take some good pics as you dissasemble so you make sure it all goes back together the way it came apart with no extra pieces. Take your time and enjoy the process, learning what makes your bike tick. Don't be in a rush to throw it back together...poke around, move levers and slides, see how it all works.

When ordering needles and jets, you need to specify what carb make and series they are needed for. The ZR7 uses Keihen CVK carbs.
Sudco had online catalogs where you can look at what is available.

Main Jets: http://www.sudco.com/vol33/137.pdf
Pilot Jets : http://www.sudco.com/vol33/138.pdf
Jet Numbering schemes do not seem to be standardized for all makes and series of carbs.
For the Keihin carbs it is pretty simple. The Jet # is the jet hole diameter in 100s of millimeters.
So, a #35 pilot jet is 0.35 millimeter in diameter.
The #108 main jet is 1.08 millimeter in diameter.
Again, this is just for Keihin made jets. Other manufacturers use different numbering schemes.
Some companies consider their number scheme to be proprietary and won’t even share it with you…for whatever reason.


Jet Needles : http://www.sudco.com/vol33/135-136.pdf
These are a bit more complicated as each OEM manufacturer seems to get a custom made needle for each bike. In our case, actually 2 different custom needles. one for outer cylinders, one for inner cylinders.
The standard Keihin series N427-46 seems to be the best match to what comes stock in the ZR-7.
You’ll see that there are different combinations of diameter, length of straight section, and taper.

The closest match I found was needle # N427-46-HFG. It has the same straight section diameter that I wound up with (2.425 mm) and the taper starts at the same location(with clip in middle slot) but it tapers twice as fast(2.75 deg vs the stock 1.2 deg). This may cause things to be too rich in the 1/2 throttle range, or maybe not.
A set of 4 costs $18 + shipping from SUDCO. I think you may also need to buy clips if they don’t come with the needles.

If you are only experiencing minor hesitation, going to a #38 pilot jet may be all that is required.
Feel free to send me a personal message and we can talk over your specific situation.

Thanks Bolerst,

That's great info. I'll spend some time looking over the sites you've linked and thinking about the problem again.

I fooled around with the screw settings last year but didn't really take the methodical approach you did with observing the changes. I was able to make some improvement but never really got rid of the hesitation.
After reading through this thread and now understang a little more about what proboably causes the hesitation, I think I need to start over making simple adjustemnts and observations first. As you did, I'll note the results and progress form there with adjustments before I go tearing into the carbs.

I'll send you a PM a little later with the details - I've got to go clear 7" of fresh snow out of the driveway right now...

I have been so busy I hadn't looked at this thread since November, and just read through it. This is a fabulous post!...Thanks!!

If/when I get the time to tinker with the ZR jetting, I think I will give this a try.

I realize I'm really late on this, but Dennis Kirk has the Emgo air filters at $7.99

moved: http://www.riderforums.com/showthrea...939#post438939

Hi Bolserst,

This is an outstanding post. Thank you very much for all the valuable info.

So I know this is reviving an old thread, but I figured since no one else has tried it yet I ordered a set of the needles (needle # N427-46-HFG) Bolserst was talking about so ill be the guinea pig for this one and let you all know how it goes.

Originally Posted by Ryan65r

So I know this is reviving an old thread, but I figured since no one else has tried it yet I ordered a set of the needles (needle # N427-46-HFG) Bolserst was talking about so ill be the guinea pig for this one and let you all know how it goes.

You might shoot brianzr7s a personal message. I believe he had ordered some needles to measure and try, but I can't remember exactly which ones he got.

I do remember he confirmed the diameter of the straight section would fix the hesitation, but I think the taper was too quick for optimal fuel efficiency like the stock needles.

thanks for the info. I sent him a pm and we'll see what he has to say. meanwhile ill have fun tinkering. I also got some #38 pilot jets to try out.

So i installed the new needles this morning fully expecting the bike to not even start up because their profile is so different. But i get them in without taking the carbs off and figure ill at least start it up and see because the weather is so crappy here that i didnt really want to go out for a proper test ride. I start it up at about 1/2 choke and within about 90 sec I had it off the choke and purring fine (normally i have to run it on 3/4 choke for like 5 min). Anyway, i give it a few revs and quickly realise that it has no more hesitation off closed throttle and it doesnt stumble anywhere allong the power band (of course that is under no load) but initial results seem promising so ill have to let you know how it is after I can get in a proper test ride. Just the difference in the sound of it revving makes me all tingly and excited though it sounds like a freakin superbike now! no more pause when you crank the throttle. yay!!!!!!

Well.... something is definitly not quite right...... Im not really sure what it is but having to push my bike nearly a mile to get it home tells me that something is up. It may just take some tweaking but im not quite sure where to start. Maybe the mixture. It seems like it does ok (maybe a bit rich) untill it warms up and then it just died. my battery was low too that might have had something to do with not being able to restart it but I tried every once in a while on the long "walk of shame" home. On the plus side there were no shortage of people stopping to offer me assistance (maybe theres hope for the world yet )

Any suggestions would help me. I may just have to go back to the stock needles and go to #38 jets. Thanks for the help.

Originally Posted by Ryan65r

... It seems like it does ok (maybe a bit rich) untill it warms up and then it just died.

Mixture does richen up as the engine warms up, so that makes sense.
A coupla questions...

1) Did it die at idle? or when you were twisting in more throttle.
1a)If at idle, was it after idling for a while? or after a bit of wide open throttle and then returning to idle.

If it died at idle due to too rich a mixture, you might check what you had your pilot screws set at. With thinner(richer) needle, you won't need as many turns out on the pilot screws to get a rich enough idle mixture. You might try the factory recommend 1 1/4 turns, if you aren't there already.

You might try the "blip" test to get an idea on your idle mixture
throttle lag

2) Before the engine was completely warmed up, did it accelerate well? or kinda feel like it was bogging down as you got past 1/2 throttle twist.

If bogging down at higher throttle settings, this is most likely from the quick taper on the needles. You might be able to offset this with smaller main jets.

3) Do you still have OEM air-filter and exhaust? or aftermarket.


Steve

Setup: no airbox mods. Freshly cleaned K&N. Two bros racing exaust. Stock jets as far as I know.

1) Not sure really. I had just gunned it for about a block, then slowed down to take a corner and when I was accelerating out of the corner it started to sound like it was missing real bad (like running on 2 cylinders almost) and no throttle response. I held in the clutch and coasted for a bit trying to rev it with no response and then it died. I coasted into a parking lot and waited for a bit then tried to start it. It tried and fired once then wouldnt. I figured it was flooded so i let it sit for a few min and tried again.... nothing. So i started pushing because I wasnt going to leave it there. I tried to start it every time I took a break from pushing it the mile or so home but no luck.

I should re-set my mixture screws I guess . they are at 2 turns.....

2)Yes it did feel a little boggy at 1/2 throttle. Felt good from closed to 1/2, and then after it got past the bog it felt fine and pulled like mad.

Any recomendation on the size of main jets?

Also is this worth persuing or should I just do stock needles and the #38 primary jets?

Thanks for the help!