Question:

[ARCHIVE_Eliminade]

Throttle flat spots/ZL 900

Has anyone else noticed flat spots in the throttle on their ZL900? I seem to have flat spots between 1-2k rpms and 4-5k rpms.
I made some aluminum air filter covers, and since then, I don't notice the 1-2k rpm flat spot so much, but the 4-5k rpm spot is still there. I think the aluminum covers actually restrict a lot of airflow, 'cause the bike takes forever to warm-up now. It used to take about 45 seconds, and now it takes 4-5 minutes.
I also have a D&D 4 into 1 (I think) exhaust that was on the bike when I got it, but the bike tends to make a lot of little popping noises when I decelerate leading me to believe the bike wasn't retuned after the new exhaust was fitted.
Anyway, if anybody has any experience with this, any advice would be appreciated.

-Josh

 

[ARCHIVE_allent]

my bike makes a lot of "popping" noise also. Exspecially when I decelarate.

My mechanic said it was normal. I am not sure. I don't know what to do about it. What do you mean "retune"? The bike starts and runs awsome. That is really my only complaint with the bike. Kinda nerve racking actually. I find myself looking at toher people to see if they notice it.

Any ideas?

 

[ARCHIVE_Rocket]

Throttle flat spots

Have you checked your two fuel enrichers? If yours has them fitted they'll be on the left side of two carbs with a small hose connecting these two valves to the other two carbs.

They have a diaphram in them and when they are perforated the bike runs rather rough, mine was particularly bad when cruising on steady throttle.

Good luck

 

[ARCHIVE_Eliminade]

Thanks for the tip, Rocket. I'll check on that diaphragm.

allent, I could be wrong, but from what I understand, popping when decelerating is backfiring and a sign that your fuel mixture is too lean or too rich. I think this happens when a less restrictive exhaust is installed and the fuel mixture isn't adjusted for it.

 

[ARCHIVE_Joker]

Has your bike had a rejet done on the carbs after the air filters and exhaust? I know mine ran like crap after adding the Holeshots and removal of the airbox till I got the jet kit in.
Joker

 

[ARCHIVE_Eliminade]

I got the bike at least 3rd hand, so I don't know if it was ever rejetted. Eliminutter, I know you live in Indiana. Do you know anyone you would recommend to do it, or a comprehensive how-to write-up?

-Josh

 

[ARCHIVE_TheELIMINUTTER]

Hey Josh, If you have a D&D Expect Poping when Downshifting, Flat Spots, Do you have Pod Filters?????, E Mail Me, [email protected] Rocky

 

[ARCHIVE_clif]

The weirdest thing: I took a longish trip (PA to VT, 1,200 m.) and everything worked well (except gas mileage) until a couple of days later when I took it out again. The cam chain was rattling like hell (new tensioner, I suppose) until thoroughly warm and then BACKFIRING AT FULL THROTTLE over 7,500 rpm! Am I too rich, ignition missing, or what?

 

[ARCHIVE_Rocket]

Throttle flat spots/ZL 900

Hey Clif,
Careful mate, after a noisy/loose chain incident, caused by sticky/broken tensioner or otherwise, and with associated symptoms (back-firing through the carbs, after-firing through the exhaust and poor economy) I'd be seriously looking at confirming your camshaft timing. If either gear has slipped a tooth on the chain this can be the result. What's more, you may also be risking valve overlap issues which could result in bent valves or worse, holed pistons.

I feel for you mate, we all do...

Rocket

 

[ARCHIVE_rammy1500]

I just got my bike back from the dealer since it was running poorly (see my Prime riding thread). I now have the same flat spots at 3K and 5K once in awhile. The service manager told me that its because the "sliders" in the carbs are slightly worn (6100 miles?). Of course for $488 for new "sliders" and another $240 to remove the carbs and repair, the flat spots will disappear. I'm still trying to figure out if by "sliders" he is talking about the jet needle and seats and not what you get at White Castle.

 

[ARCHIVE_Rocket]

rammy1500
I’ll assume there’s some seriousness in your question about the definition of sliders. While I’m not an expert on the subject, I’ll throw in my explanation anyway. If I write something out of place I’m sure others will be adequately motivated to correct me. I guess this is another reason why this site is so good, we can all learn.

The “Slider” is not the needle or the needle’s seat (jet) perse; it’s the alloy piston (in which the needle is mounted) that slides up and down the carburettor throat. This piston is controlled by the vacuum diaphragm on top and as the piston and bore wear the resultant gaps allow excess air to bypass and or start to bind/stick the piston against the carburettor body. During small throttle position changes the small vacuum variations to the diaphragm are supposed to make minute piston height changes accordingly (and therefore fuel/air mixture changes). Constant Velocity (CV) carburettors are great for maintaining the correct fuel air ratio however this function relies on the slider travelling in unison with the throttle butterfly.

Consider this; the fuel flow is controlled by the Needles position above its Seat/Jet and the venturi effect of the airflow across it. As the needle rises it increases the jets opening to allow more fuel and likewise when the needle raises so does the slider which increases airflow. This fuel/air mixture change is happening in unison because the needle (fuel) and slider (air) are connected together, i.e. as the controlled airflow across the jet changes so must the fuel flow because the needle and slider are physically joined. This partnership should ensure the correct fuel/air mixture is maintained at all throttle positions. Now when you twist on the throttle the butterfly opens downstream but this doesn’t provide more air and fuel for the engine. The first thing that happens at throttle-up is the increased vacuum is now applied to the top of the sliders diaphragm which begins to pull it up the bore against spring pressure (remember the slider is still relatively closed and the butterfly is opening so the vacuum increases markedly until the slider moves to balance the pressures on either side of the diaphragm). So you see, unlike conventional carburettors where the butterfly controls the go gear, the CV carburettor supplies the go gear via the slider.

This is the reason bike CV carburettors don’t have accelerator pumps for rapid throttle openings. Ordinarily when the throttle is suddenly opened there’s a great rush of air down the throat but the mixture is lean because fuel is heavier than air and its inertia prevents its delivery at the same rate. So while the fuel is trying to catch up the accelerator pump puts in a little extra. In a CV carburettor there’s no need to compensate for the fuels inertia because that sudden rush of (butterfly) air has to wait for the sliders combined fuel/air mixture to meet the demand together.

Now if your slider is worn we can assume that at times when it is stuck (not moving perfectly in tune with vacuum demands) the greater throttle/butterfly demand will draw the airflow across the needle’s jet at greater speeds because the slider doesn’t move up as expected. This higher velocity airflow increases the venturi effect so one would think more fuel will still be delivered. Well this is so but it’s inadequate because the needle is not moving and the resultant mixture is not as it should be. This is why Constant Velocity carburettors are susceptible to slider wear and the resulting effect on performance.

Right Wrist Twist…

 

[ARCHIVE_knightkadosh]

Hey rammy1500,

For whatever it’s worth, especially considering the amount of money we are talking about here, I had a similar problem earlier this year, after pulling them out, my vacuum slides appeared to be galled and were beginning to show signs of spalling, so I polished them to a high luster, they now slide effortlessly. Make no mistake about this; the wear marks are still there, although they are now reduced from my polishing off the rougher angles, edges, and ridges. This may, if nothing else, help to reduce your flat spots, although this may not be a perfect solution entirely, it certainly made a noticeable improvement for me. I should have also spent an appropriate amount of time polishing up the carburetor throats, although at the time I was in a bit of a hurry, this would of course additionally improve you slider action, as both pieces would now be polished to a high luster and the sharp angles, edges, and ridges of both pieces are significantly reduced. I’ll be going in the carburetor throats with a dremel tool for some polishing during my winter tear down. Again, this is not a perfect solution, but certainly worth the extra effort considering the amount of money the other option requires, or at least in my humble opinion it does.

Brian

 

[ARCHIVE_rammy1500]

Thanks for the reply, I wasn't sure how they work since I also have an '84 Camaro for which I've had problems with the carb on it as well. Of course, I've tried to understand how the CVs work using the knowledge gained from the Rochester and couldn't put 2 and 2 together.

Is the slider and diaphram displayed in the parts diagram on the KAW website? Would it be the same as the vaccum valve # 16126?

 

[ARCHIVE_Elimiboss]

Rammy, the part you are talking about on the website is indeed the slider. That is the "vacuum valve" that slides up and down in the bore of the carb.

So you were working on a carb off of a camaro eh??? Wouldn't happen to be one of the computer controlled Q-jets would it? I just recently got done rebuilding one on my 86 firebird and let me tell you they have not one thing in common. I can tear down a MC carb in my sleep but those damn Qjets are a pain. Nothing in common at all!

Ethan

 

[ARCHIVE_rammy1500]

I have a book on the rochester carb but it isn't even close to the MC carbs in principle so much for lucking out there. Do I have to remove the carbs from the bike to polish the sliders? or can I remove them from the top of the carbs? Not real interested in spending that much money for one more month of good riding here in Ohio.

 

[Rick_in_WA]

Ok guys,...... lets say you have a zl that you could part out <possibly help resurect a couple more~....or just take about a year to totaly re-do.... in the interim, spend a few bucks...<found money< . buy another ZL or buy a ZRX1100 as a viable summer mile buster..............A concourse could be found for about 1/2 the cost of the ZRX, as well as 1/2 the cost of the other ZL..< local Seattle purchace..... both ZL and ZRX are the same money, both have the same miles on them, the ZRX is not a stocker has aftermarket pipe and jet kit and corbin seat

 

[monkeyhanger]

:good luck: THIS MIGHT NOT BE A POPULAR THOUGHT BUT I DO LIKE THE ZRX.I HAVE JUST HAD TO SELL MY BLACKBIRD TO FINANCE THE TRIKE FINAL PUSH, HARD DECISION TO MAKE MATE. GOOD LUCK

 

[Rick_in_WA]

of all of us ZL owners the ZRX is a popular choice, and WE HAVE TO ADMIT, the ZRX just has the "Classic" Kawasaki look as well as the raw grunt of the inline 4

 

[zl900_moab]

ZL, what site are you on???
moab...

 

[zlMark]

thats easy,, be the "Tough guy that doesn't dance" The concours is nice so is the zrx. Is what i like about them the most is i can use some of the parts on my 85' ZL900 Eliminator<<getting rare and no longer depreciating. Now take a chance at never being a zl owner ever again and part it out. Trust me I know this(82 KZ1000J)