1998 ZX-9R Low RPM Hesitation / Stumble - ZX Forums
 
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post #1 of 18 (permalink) Old 10-07-2012, 08:27 PM Thread Starter
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1998 ZX-9R Low RPM Hesitation / Stumble

Hi guys. First post here, and I just got a new to me 1998 ZX-9R. I've been reading and searching a lot, and there seems to be more information here than on other forums.

Please bear with me, because this will be long as I want to make sure that I cover everything that I've done so far.

I had a problem with it stumbling and hesitating off idle. This made it very hard to start off from from a stop. I had to slip the clutch and keep the RPMs high to keep it from dying. It required a slight amount of choke at all times. At RPMs above about 4k, it runs like crazy. Immediately, I suspected dirty pilot jets.

Here's what I've done so far:
Drained tank and filled with fresh gas
Ran Seafoam through this new tank (No change. Oh well, worth a try)

Removed tank and found engine breather hose completely disconnected.
Reconnected and ran. (slight help, will idle without choke now. Probably coincidence.)

Cleaned K&N air filter.
Removed and disassembled carbs. Relatively clean. Pilots were a little dirty. 3 of 4 diaphragms were pinched by the cap. When putting them back in, they seemed to be stretched and would not seat correctly. Completely cleaned and re-assembled as best as I could.
Verified that it has stock jets.
Reset AF screws to 2 turns out per service manual (were at 2.5 turns)
Pulled plugs. Looked like a rich condition. All of them were black. Replaced. Stick coils seem to not be seating as tightly as before being removed. They kind of wiggle a little in the hole.


After all of this, it definitely runs better. But, it still has the off-idle hesitation. And if you twist the throttle hard, it will bog and try to die.

So, here's my questions:

Could the diaphragms be causing my problem? The slides seem to work correctly.
Would the carbs being out of sync be the main cause (I haven't synced them yet)?
Side question, should the stick coils seat tightly in the plug hole? I've tried to push them down harder, but it seems like they're bottoming out and I definitely don't want to break them. They're definitely not as tight as before I removed them. The bike runs as is, but it just doesn't seem right.

Any and all help would be much appreciated. Thanks.

Last edited by nGoldenm; 10-07-2012 at 08:31 PM.
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post #2 of 18 (permalink) Old 10-08-2012, 08:52 AM
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Yes, absolutely. The diaphragms, not to mention, all the components have to be in ideal working order before your bike becomes a performance machine.

You've done a commendable job in giving us some history to work with. Given the diaphragms being pinched, you might want to consider buying a used set of carbs off eBay (~$75). That'll give you duplicates of parts so you don't have to pay three times as much for a few new parts.

Based on your operation description, I would have guessed spark plug fouling, incorrect float height and carbs that are out of sync. But start with getting the diaphragms straight first.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
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post #3 of 18 (permalink) Old 10-08-2012, 10:02 AM Thread Starter
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Thanks for the reply. That's what I figured. I'll have to pick up a set when I get a chance.

As for your guesses, I've replaced the spark plugs and I have verified the float height while cleaning the carbs (forgot to mention that).

Two more questions:

1) What about the stick coils not seating solidly. Is that normal or no on this bike?
2) For a carb sync, I know from prior threads where to hook up the hoses. However, my C1 does not have any vacuum fittings where they should be. I know that 2&3 are supposed to have blanking bolts installed, but all of mine have bolts installed. Would this cause any negative effects? The right size threads for these are 6mm, right?
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post #4 of 18 (permalink) Old 10-08-2012, 11:09 AM
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You have been doing your reading.

The spark plugs shouldn't have the metal screw on cap at the top, just exposed threads, I believe. The coil should zip down over the threads.

Intake blank bolts are okay, so long as all the vacuum plumbing that's dependent on them is properly routed or removed. 6mm should be correct on thread size. The brass nipples that were in those locations cost $15/ea. Too bad the PO discarded them. Carbtune Pro comes with a set of four, but they're plastic, so I don't advice leaving them in place after a synchronization.

Hope you got a good deal on your 9.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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post #5 of 18 (permalink) Old 10-08-2012, 03:07 PM Thread Starter
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e1_ZX-9r - Thanks for your replies. You've been very helpful. I appreciate it.

Quote:
The spark plugs shouldn't have the metal screw on cap at the top, just exposed threads, I believe. The coil should zip down over the threads.
Now, don't I feel stupid. Completely forgot to remove them. That would explain it! Completely apart the bike comes again! (Sixth time since Friday).

Quote:
Intake blank bolts are okay, so long as all the vacuum plumbing that's dependent on them is properly routed or removed.
Looks like it to me. All of the stuff has been removed and the hoses up near the head/spark plugs have been connected together.

Quote:
6mm should be correct on thread size. The brass nipples that were in those locations cost $15/ea. Too bad the PO discarded them. Carbtune Pro comes with a set of four, but they're plastic, so I don't advice leaving them in place after a synchronization.
Holy brass, Batman! $60 to do all four. Unless there's a cheaper alternative, I'll be purchasing that Carbtune Pro, and just swap them in as needed. They run about $80-90, right?

Quote:
Hope you got a good deal on your 9.
Not a smoking deal, but not bad either. Paid $2,400 with 25k miles. It is very clean cosmetically. Came with a K&N filter, full Micron exhaust, and brand new Pilot Power tires. I'm not good at fixing cosmetic problems myself, but non-major mechanical I can usually do. So, I thought that this would be a great bike with a little bit of work.

So, I fixed my spark plug uh-oh. And this thing runs MUCH better now. It had weak spark since the stick coils weren't making good contact. It is very rideable now. It still has a very slight hesitation off idle and is rough in the very low RPMs. I think that after a carb sync, 95% of the problems should be fixed.

Next on my list, after the carb sync, is to fix the diaphragms and do a valve clearance check when money and time allows. And then sync the carbs again.
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post #6 of 18 (permalink) Old 10-08-2012, 03:15 PM
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maybe i'm just spoiled, but the synch kit i've got has its own screw-in brass nipples...plastic ones work too.
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post #7 of 18 (permalink) Old 10-08-2012, 03:16 PM Thread Starter
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Quote:
Originally Posted by zxn9ne View Post
maybe i'm just spoiled, but the synch kit i've got has its own screw-in brass nipples...plastic ones work too.
What kit is it?
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post #8 of 18 (permalink) Old 10-08-2012, 04:17 PM
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I've got the carbtune kit and love it. The price varies because its a UK item. They deal with US customers constantly so it's no biggie to buy directly from them.

There are other companies that make carb balance tools or you can make your own. Just look around at different parts suppliers. Bikebandit, kneedraggers, or some of the site sponsors on the left should have something.

Trey

Red 98 ZX9R for sale. I can delivery to an extent.

https://www.zxforums.com/forums/buy-s...tml#post800204
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post #9 of 18 (permalink) Old 10-08-2012, 07:32 PM
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When I got mine it had a hesitation problem also.. It just happened to be a disconnected air intake hose under the headlight..

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post #10 of 18 (permalink) Old 10-10-2012, 05:49 PM Thread Starter
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So, I went by the local Kawasaki dealer to see if they could cut me a deal on the vacuum fittings, and they just so happened to have a wrecked ZX-9R in the back. If I pulled them myself, I could have them for free. So, I pulled the tank, removed the fittings, and put it back together in 7 minutes flat. I guess practice makes perfect.

I synced the carbs tonight with my homemade tool, and they were almost perfectly in sync. Only had to make a slight adjustment between left bank and right bank. So, that's not the problem.

I checked all of the air intake connections, and everything is nice and tight. Not the problem.

I took a video off my phone of the carb slides in action. Just want to make sure the diaphragms aren't working properly before buying a set of carbs just to swap them out. To be honest, I'm not sure how they should look in operation, so could you guys take a look and tell me if they are operating normally or not? Thanks.

EDIT: Are the diaphragms/slides interchangeable between a C and an E model carbs? I could probably get the diaphragms from that wrecked 2000 pretty cheaply if needed.


Last edited by nGoldenm; 10-10-2012 at 05:57 PM.
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post #11 of 18 (permalink) Old 10-10-2012, 07:26 PM
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Interchangeable, no. E model 9s use Keihin CVRD 40mm carbs. The slide is differently shaped and the carb is shorter on top and in depth from the B, C, & F model CVKD 40mm. Being that as it is, you may be able to swap CVRD to a bike using a CVKD, but not the other way around.

Can't tell what's wrong with yours by the sound of it, but it's definitely not peppy. Compression or bad fueling in the pilot circuit would be my guess.

Here's a video of my bike idling and another at WOT, so you can get an idea of what you're striving for, if I may be so bold.


GoPro sound quality isn't great, but...

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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post #12 of 18 (permalink) Old 10-10-2012, 11:00 PM
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Upon watching your video a second time, what are the cylinder compression PSI numbers warm? It may not be compression, but then it may be. It runs as though the timing chain is a couple teeth off, which would cause it to run like complete crap and if a piston bumps into the valves, will get worse. Low PSI numbers, something below 130 would be your key.

Any idea if the PO perhaps adjusted them sometime before selling it to you? Did the bike always run this way?

The carb slides appear to be functioning correctly.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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post #13 of 18 (permalink) Old 10-11-2012, 07:24 AM Thread Starter
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Quote:
Originally Posted by e1_ZX-9r View Post
Upon watching your video a second time, what are the cylinder compression PSI numbers warm? It may not be compression, but then it may be. It runs as though the timing chain is a couple teeth off, which would cause it to run like complete crap and if a piston bumps into the valves, will get worse. Low PSI numbers, something below 130 would be your key.

Any idea if the PO perhaps adjusted them sometime before selling it to you? Did the bike always run this way?

The carb slides appear to be functioning correctly.
The bike has ran this way (actually worse, before the carb cleaning and new spark plugs) since I bought it a week or so ago. I have no idea if the PO adjusted it or not.

I don't have a compression tester, so I'll have to get one or rent one. As soon as I can get that done, I'll post back. Thanks for all of the help.
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post #14 of 18 (permalink) Old 10-11-2012, 07:53 AM
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You'll need one with special 10mm threads. If you've never done one before this is the procedure I would recommend:

1) Warm the engine up, important to get the oil and metal warm/hot. Results will accurately show compression numbers
2) Pull all the spark plugs and for ease, take the carb bank and move to the side of the intake boots (out of the intake boots, of course). Clear anything that might get sucked into the intakes as you proceed with the next step
3) With the tester screwed into a spark plug hole, crank the motor with the electric starter. Crank for for about eight seconds or until the PSI does not improve. Record cylinder number & PSI.
4) Repeat on remaining cylinders.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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post #15 of 18 (permalink) Old 10-15-2012, 05:23 PM Thread Starter
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Just a quick update. Sorry e, but I haven't gotten around to the compression test yet. I'm going to do it eventually, I promise!

But I did pull the carbs to clean them once again. I noticed something this time though.

The needles aren't stock. From looking at pictures, I think it's a Factory Pro setup. The E-clip was on the third notch with two washers on top. I also thought that it had stock jets earlier, since I looked at carb 1 which has a 155. According to my manual all carbs should have a 155. But 2 and 3 have a 158. Also, the diaphragms look pretty good after reseating them properly last time. They're still a little stretched, but there aren't any holes from the pinched places. You can just see where the rubber was marred. Looks like I got lucky for once.

Following Factory Pro's carb tuning guide, I increased the float height to 15 mm and set the AF screws to 2 1/2 turns as they were originally (before I knew about the jet kit and dropped them to 2).

After buttoning everything back up, it fired immediately, and the idle was rock solid. Still a VERY slight hesitation when cracking the throttle, but nowhere near what it was. It will not die when blipping it full throttle. Just takes around a second for RPM to catch up. Took it around the block, and everything is 100% better above about 2500 RPMs. It still seems a little off under that when starting from a stop though.

As soon as I get around to the compression test and valve check, I'll post back with the results. Just got to get a full day I can devote to it.
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post #16 of 18 (permalink) Old 10-15-2012, 06:00 PM
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Interesting. I would have thought 15mm would make for more throttle hesitation. It does on my 00 and 02. The 02 is right on the fine edge at 14mm, but still very close to the ideal 13mm throttle response.

When you pulled the jets, how did you verify they where Keihin? If they didn't have the K Keihin stamp then they're not Keihin. 150's may come with Factory Pro kits , but they're also standard stage 1 jets on Dynojet. FP are said to be the same inlet diameter of Keihin, but DJ have larger IDs at the same # size as Keihin.

The fact its a little off < 2,500 RPM would almost exclusively be the pilot fuel circuit...given a sound engine (compression test > 150 PSI) and a proper tune. However, if you did the FP CV carb tuning procedure incorrectly and didn't start by selecting the main jets that pulled the hardest, then all your fuel circuits and settings may be fubar; and won't not be fubar until you do the procedure correctly.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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post #17 of 18 (permalink) Old 10-15-2012, 07:04 PM Thread Starter
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Quote:
When you pulled the jets, how did you verify they where Keihin? If they didn't have the K Keihin stamp then they're not Keihin. 150's may come with Factory Pro kits , but they're also standard stage 1 jets on Dynojet. FP are said to be the same inlet diameter of Keihin, but DJ have larger IDs at the same # size as Keihin.
I didn't see a K stamp, but I wasn't looking for it either. It may be a Dynojet kit then.

Quote:
The fact its a little off < 2,500 RPM would almost exclusively be the pilot fuel circuit...given a sound engine (compression test > 150 PSI) and a proper tune. However, if you did the FP CV carb tuning procedure incorrectly and didn't start by selecting the main jets that pulled the hardest, then all your fuel circuits and settings may be fubar; and won't not be fubar until you do the procedure correctly.
I don't have any other mains to try. But it does seem to pull extremely hard up top. So, I moved forward assuming it was correct.

Same goes for the needle. Seemed correct as their procedure states.

I raised the float as the bike seemed to be rougher in the below 4k range when warm. Was 14mm before.

Left the AF screws at 2.5 turns for now. Almost seems like their description of a rich pilot with the slight hesitation (not quite a bog, but could be just slightly too rich), so I might try to turn it in a 1/4 turn or so and see what happens.

I'm trying to do this right as i understand it and with what I have at my disposal. If I'm not doing this correctly, please tell me. You know much more about these bikes than I. However, I can't argue with the progress. It's like a different bike from how I got it.
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post #18 of 18 (permalink) Old 10-15-2012, 07:09 PM
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Sounds like you're on the right course and I agree with your methodology.

Alright! Trading bikes for a while was fun.I'm ready for mine back. No, seriously, get off my bike. Ahh, what a privilege it is to have such a sweet ride.
At the track she's said to be outclassed, but on the street, she reigns unmatched. She's the only big-bore canyon carving hypermiler I know of. -- Picture gallery, K&N air filter, SuperTrapp Aluminum Racing Series exhaust (Made in USA), ZG touring shield, & otherwise stock.
Science & OODA literate. ACA covered.
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