[bolserst]

I’ll get the apology out of the way first. I owned a 2002 ZR-7 for several years. This bike ran great right out of the box, no hesitation issues. Factory pilot screw settings were 1 1/4 turn out on all 4 carbs. I bumped them up to 1 3/4 turns as per the service manual and noticed the bike being much more eager off the line. Having read all the discussion about jetting on this forum I figured you guys were either nuts, or just needed something to complain about.

My sincere apologies…I now understand.

I picked up a 2001 ZR-7 as my replacement bike. This bike has HUGE amounts of hesitation at anything below 1/4 throttle position and an erratic floating idle. Also I noticed lean surging at cruise with throttle settings below 1/4. I removed the carbs and spent a day cleaning and checking them. Everything was stock and spotless, except one of the pilot jets was partially plugged, but I got it cleared out. The pilot screws were set at 0, 1/2, 0, 1/2 . I also noticed that when completely closed, the #2 pilot screw protruded nearly 1mm further in to the carb throat than the other 3. I set them all to 2 turns out. Idle was now solid, but the hesitation and lean surging persisted. I also noticed that the header pipes are blue where as my 2002 pipes had a nice straw color. I used the carb spray test to check for any airleaks around the airbox, carb boots, etc. None found. Once throttle gets past 1/4 things are pretty much as I remember on my other ZR-7, a nice smooth pull to 7k, and then a slower climb from there.

HOW CAN 2 “identical” unmodified completely stock bikes run SOOOO differently? Has any root cause been identified for this variance in jetting requirements for the ZR-7?

What I have done:
I used tape on the throttle grip to mark off 0 thru 100% throttle positions so I could identify the areas where hesitation occurred. As I mentioned above, all hesitation occurs at less than ¼ throttle. Most prominent at 1/8. As suggested elsewhere, I plugged up 1/3 of the intake and the bike ran great at low throttle settings but bogged down above 1/4 throttle. Based on these observations I ordered #38 pilot jets to richen up the pilot circuit. The bike is running better at idle and pulls a little better off the line(don’t have to rev and slip the clutch to get moving) but still hesitates at 1/8 throttle and some lean surging at cruise persists. The pilot screws are at 2 turns out except #2 is at 2 1/2. I set this based on pulling plug wires at idle and looking for equal RPM drop for each cylinder. With #2 set to 2 turns like the rest, the RPM didn’t drop at all when #2 plug wire was pulled. Smoothed out the idle a bit. Oh, and of course a careful carb sync has been down.

What I will be doing:
1) Tonight I will be trying 2 1/2 turns out on all carbs(maybe 3 on #2). This will probably be too rich at idle as blipping the throttle already results in RPM dropping slightly below idle momentarily and then recovering.
2) I have an dyno appointment for tomorrow to get some fuel/air mixture reading information. I will post my findings.

Questions:
1) Has anybody ever needed to use a pilot jet larger than #38 to cure hesitation?
2) I am beginning to think that the larger pilot jet is just helping out the real problem of a too lean setting for the straight section of the stock jet needle. Is it possible that there is a variance in stock needle diameter? I will measure mine next time I have them out.
3) Has anybody tried to modify the straight section of the stock needle to richen up the mixture for low throttle settings? I have done this before on a jetski carb that had problems with lean running. Of course it only had 1 carb.


Thanks for listening,
Steve Bolser
Saginaw, TX

 

[JonF]

The center carbs and outer carbs have different needles. Didn't mix them did you? You could play with float level hieghts for some fine tuning but what a pain on the butt that is. A shim on the needles may help you. I wouldn't go too much on the mixture screws. Mine is happiest at 2 turns out with the #38 pilot jets but I have them set at 1 3/4 turns out.

 

[bolserst]

Hello Jon,

Yes, I did carefully check that the correct emulsion tubes and needles were in each of the carbs as per the service manual. With longer needles on cylinders #2 & #3 make me think these cylinders would be getting a leaner mixture relative to #1 & #4 which seems like exactly the opposite that one would want, if trying to cool off the inner hotter running cylinders. Maybe the extra holes in the emulsion tube help out with this????

Oh yeah, float height....I didn't mention that. The float height spec is 17mm (+/-2mm). These were all set to 18.5mm...so lower fuel level, but still within spec. I set them all to 16.5mm to raise the fuel level. I really thought I was on to something when I found this, but alas, didn't notice much difference as far as helping at with the hesitation.

While taking one last look at everything in preparation for the dyno run tomorrow, I noticed something about the stock air filter I hadn't seen before. The plastic frame was bowed on the side that the foam gasket surface gets pushed up against the airbox. This would cause nearly 1/4 inch gap that the foam gasket would have no chance of sealing up. I got some thick adhesive foam at the local hardware store and have it sealed up nicely.

No riding at night for me, so will have to wait until tomorrow morning to test the results.

Steve

 

[pkovo]

Please keep posting your progress. I'm one of those with a ZR that has less then perfect jetting. For me the hesitation has been minimized, but it's still there right off idle, usually only noticeable if I close the throttle in a turn and come back on. It's really only noticeable from completely closed throttle to slightly open.

I have my screws at 3.5 out, stock pilots, and needles slightly shimmed(I forget how thick the washers were but they were about the thinnest I could find). I use emgo paper air filters. I don't think the flow is much different, but I didn't like the way the stock filter fit, and I just like paper filters.

This setup has been a big improvement over the way it was when I bought it, but it's not perfect. I bought 38 pilots a long time ago, but every time I decide to put them in, I find a reason not to.

 

[bolserst]

I use emgo paper air filters. I don't think the flow is much different, but I didn't like the way the stock filter fit, and I just like paper filters.

Thanks for the info on your air filter. I hadn't heard of these before...just the K&N which changes air flow from stock. I searched the forums and saw pictures you posted of the Emgo air filter. Looks much better built than cheezy stock filter with its bendy-flexy warped plastic frame. I checked cost at the dealer this morning....Holy [email protected]!!! $48.
The Emgo air filter M929 on line costs $5.94. Is this the same part you are using? http://www.funkmotorsports.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=FM&Product_Code=M929

I will keep posting my progress...and try to keep changing only one thing at a time so we know what is actually going on, rather than guessing.
Yes, I am an engineer

 

[WMU_BRONCO]

Based on Pkovo’s experience with EMGO air filters I tried one. The quality of this filter is far better than the stock filter, and my bike runs just fine.

 

[bolserst]

As promised, I am posting the results of my dyno testing.
I didn’t realize that I would be unable to get reliable air/fuel readings at low exhaust flow rates with the stock exhaust since it has a folded path and the sniffer tube couldn’t even get in a foot. However, we could get reliable readings for the typical full throttle dyno runs and the results show a very rich top end, roughly 11.5 to 1 Air to fuel. Peak power and torque seem right in line with other stock dyno runs I’ve seen (70hp, 43ft-lbs). This would indicate that a #102 main jet is in order. I think I have read others using #102 main jets so I guess this is in line with at least some ZR-7s.

The dyno operator was able to help trouble shoot the hesitation although we couldn’t get actual air/fuel readings. For a fixed throttle setting he had the computer fix the RPM by modulating the dyno brake. Then we could try leaning or enrichening the mixture by cracking the air-box, or adding some flow restricting foam in the inlet. We could so the power output change, and assuming peak power output at 13:1 air/fuel ratio we could get a gauge on whether mixture was lean or rich to begin with. Spent nearly 30 minutes trying 3 pilot screw settings for 3 throttle setting(roughly, 10%, 18%, 25%).

Basically, what we learned was that with the #38 pilot jets, you could get the 18% setting nearly rich enough with 3 turns out, but then idle was WAY rich. If you set the idle mixture correctly things were quite lean at 10%, 18% and 25%. This all leads me to believe that the #35 pilot jet is probably the correct one to use, and that the straight section of the jet needles is just too fat. I took all the needles out and all four have a 15mm long straight section that is 2.44mm in diameter.

Does anybody know what diameter needle is used in the Factory Pro jet kit?
I may try to get my stock needles machined down before springing for a jet kit.

 

[Jeff]

Does anybody know what diameter needle is used in the Factory Pro jet kit?
I may try to get my stock needles machined down before springing for a jet kit.

If no one here knows, I'm sure a call or e-mail to Factory Pro would answer the question.

See also a similar thread here from '03:
http://www.riderforums.com/archive/index.php/t-4253.html

 

[JonF]

If you visit Ivans web site his testing also indicates the ZR is rich at WOT and high rpms. He attributes this to the small/restrictive airbox.

If you start with the main jets, work your way backwards, and eventually find a way to fix the hesitation and achive good driveability and economy you will be the man.

 

[fastisgood]

maybe this is a stupid question but i was wondering if after market exhausts give you more hp bc of less constrictive air flow an less back pressure than if you took off your exhaust and eliminated back pressure wouldnt you get even better results than spending 1000 dollars on a full exhaust system jus to get a little better airflow????.......not to mention the wieght your taking off the bike from completely removing your pipe????

 

[bolserst]

I believe some amount of back pressure is desired, so free flowing exhausts result in the potential for more top end HP than with no exhaust at all.

I desire to keep the stock exhaust because it is the quietest option I know of, and the stock 70HP is more power than I need anyways. Others, with different goals make different exhaust and jetting choices.

I am not after more horsepower, just a nice smooth power delivery with no hesitation like I had with my completely stock, unmodified 2002 ZR-7S. 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 know when machines are designed tolerances are allowed for. One could assume that if all the tolerances stacked up in the lean direction you get a bike like my current one. If they all stacked up rich....you'd get a great running bike like my last one. I'm just trying to figure out what these variables are to demystify the variance in the jetting characteristics of the stock ZR-7S.

 

[bolserst]

My opinion is still that the ZR-7S stock jetting is pretty good for idle and anything above 1/4 throttle. Yes the top end is a bit rich, but this allows customers to add free flowing exhaust/air filter and get a power bump rather than a lean/overheating problem. The off idle to 1/4 throttle mixture is dominated by the diameter of the straight section of the needle. This is what Kawasaki had to set rediculously lean to pass emissions.

Calls & emails to Factory Pro and Ivans all yielded no information as to the diameter of the needles they supply in their jetting kits. I was told this was proprietary information.

So, based on the logic that fuel delievery thru the needle jet/jet needle opening is proportional to the open area I have decided to remove 1mil(.001") from the diameter of the straight section of all my stock needles. I've done similar things with 2-stroke needles before to fix lean spots, so hopefully doing it 4 times won't be that much more difficult.

Oh, I also stumbled on this article that seems to mirror my experience, but with the big V-twins. http://www.ridermagazine.com/output.cfm?id=217441

I'll post results of my efforts on Monday.

 

[Jeff]

My opinion is still that the ZR-7S stock jetting is pretty good for idle and anything above 1/4 throttle. Yes the top end is a bit rich, but this allows customers to add free flowing exhaust/air filter and get a power bump rather than a lean/overheating problem. The off idle to 1/4 throttle mixture is dominated by the diameter of the straight section of the needle. This is what Kawasaki had to set rediculously lean to pass emissions.

I agree completely with your conclusion, even if my road to discovery was significantly less tortuous than yours. When I got my '02 nearly 2 years ago, it also suffered from the off-idle hesitation phenomenon. I decided fairly early on to install the K&N air filter, and knew I'd have to at least turn some screws to get things right. Turned out things were so lean that I was amazed it ran at all. But in my case all it took was a little trial and error with screw settings to get things right as rain; perfect really. More recently I added a Jardine street can and was almost expecting that to upset things. Nope. Still no hesitation at any throttle position, no flat spots. Not sure why I run so well through the straight section of the stock needle, but in any case my experience seems to confirm your observation about the stock jetting in general. My '02 runs like your old one did out of the box, it just took me some turning of the screws to make it so; nothing I've done since then has upset the balance.

As for the Jardine, I wasn't after more hp, but rather hoped to get rid of the remaining vibes at around 5k (the bar ends didn't take care of it completely, mission now accomplished), and frankly to give the old-fashioned girl a little attitude.

 

[bolserst]

As for the Jardine, I wasn't after more hp, but rather hoped to get rid of the remaining vibes at around 5k (the bar ends didn't take care of it completely, mission now accomplished), and frankly to give the old-fashioned girl a little attitude.

So the Jardine exhaust completely got rid of the 5k vibration?
Interesting, guess the back pressure of the stock exhaust is the culprit?

On both my ZR-7s the 5k vibes seem to come and go. With careful carb sync things would be smooth as glass in that range for a month or two and then the vibes would slowly return.

I also noticed they seemed to be worse when the bike wasn't completely warmed up. On the highway if I was cruising in the vibe zone for longer than 30 seconds, they seemed to eventually work themselves out and then things would be smooth as long as I kept the revs up. If I stopped and then got back on the highway...same routined again, vibey for 30 seconds or so, and then slowly smoothing out. Very odd behavior, but so much less vibey than some other bikes it was easy for me to live with.

 

[Jeff]

Right, the vibes are nearly completely gone now, and it's been 6 months since I balanced the carbs, though you're right of course - unbalanced carbs are always the cause of MUCH vibration. I suspect though that nearly everything I've done has contributed to the improvement, even including the sprocket replacements. That didn't just bump up the ground speed at which the vibration began, it actually ameliorated it somewhat. Probably something to do with the mass of the respective sprockets, sympathetic vibration, actual gearing ratio, etc. But yes, the most dramatic effect has come from reducing the back-pressure through the exhaust.

 

[bolserst]

Reducing the diameter of the straight section of the stock needles by 1 mil (.001”) has completely removed all hesitation and lean surging issues my bike had. Period. I’m actually pretty stunned at how dramatic the results were. This is also with the stock #35 pilot jets installed and set at 2 turns out. It was kind of odd at first, especially when I would slow for a turn and then get back on the throttle. I had never noticed how much I tensed up my shoulders and arms waiting for the inevitable herky-jerky hesitation as I tried to every so slowly roll back on the throttle. Now, power just smoothly feeds back in as I roll it on.

Here are a few pictures and details of what I did. I used a drill press and a 3/4” wide strip of 400 grit paper backed sandpaper to removed .001” from the diameter of the straight section of the 4 stock jet needles. I pressed the sharp tip of the needles in to a block of wood to help stabilize the needle while I worked. It took about 15 minutes per needle. Sand for a bit, measure 5 to 6 places down the length of the needle to make sure things were reducing uniformly. Holding the sandpaper strip in the middle worked pretty well at uniform removal with just a touch more in the middle. I would then pull from the top edges, or bottom edges to even things out. So, sand, measure, sand, measure, etc until you’re there.

Then, polish things up with some steel wool. Finished…well except for the other 3 needles.
When I had finished the first needle and was comparing it to the other 3, I was thinking “there is no way this is gonna make a lick of difference”
So, looked over my calculations one more time before doing the other 3.

To give you an idea of how much I removed, typical Xerox paper is 3.5 mil thick. So, I removed about a third the thickness of a piece of paper. The gap between the ID of the needle jet and the outside diamter of the jet needle was about 6 mil, and I increased it to 7 mil.
It really amazes me how small the opening is and how tight the tolerances of all these carb parts have to be. Here is a picture of the needle sitting in the jet.

I have orderd one of the Emgo paper element air filters(thanks to Pkovo and WMU Bronco) and a set of #102 main jets. I plan to set up another dyno appointment to check out my final setup. I will try to get runs with stock and Emgo filters so we can see how they compare. All information I’ve seen concerning the Emgo is that it is very similar to stock.

One question that still remains is what effect this change had on gas mileage. I should be able to determine that this coming weekend.

 

[Jeff]

Really great contribution. I'll be printing out this series of posts for my ZR-7S hardcopy folder. Thanks. :ithank:

 

[bolserst]

Your welcome Jeff.
If anybody else is interested in undertaking a similar needle mod, feel free to contact me with any questions.

One other thing I forgot to mention, was that I had been looking at the available aftermarket Keihin needles to see if there was something close that could be purchased to affect the same change. The closest 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 may just have to give them a try, just to see. That's the dern curious engineer part of me taking over again.

Several people asked me why I didn't try other needles or jet kits first before "butchering" my stock needles. Well, I wanted to just change one thing at a time to pointpoint exactly the cause/effect that produced the improvements. A whole new needle set would not have given us this insite. So I put my money where my mouth was, so to speak, to prove that my theory that the straight section needle diameter is the root cause of the ZR-7 hesitation. My curiosity is now satisfied.

 

[JonF]

Very good info. I'll make this a sticky.

 

[dkawa]

Emgo M929 air filter

Going back to the side conversation about Emgo air filters. My stock filter was damaged when I was working on the bike. It was out on the floor on a newspaper and some little kid stepped on it. My Nephew to be exact. I ordered a new one from the dealer and it looked worse then the old one. Like you said, " bendy, flexy, and bowed". I had an 86 GPZ 550 a long time ago and that was the filter that was in my bike when I bought it (used of course). I believe the Kawa code was ZX 550A GPZ. I sent Bike Bandit and email, as I couldn't seem to get a match from the web site on the exact m929part number. They replied back "The particular emgo filter you are looking for is not offered by BikeBandit.com at this time. We will forward your email to a product manager so that they may consider including that item in our product offering. Please visit us often to view our new products."
Some dealers sell after market like Emgo or the best price right now seems to be http://www.funkmotorsports.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=FM&Product_Code=M929
:alcy: